LTE BIBLE

LTE BIBLE

Farhatullah Mohammed

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Definitions and Benefits

PING PONG HANDOVER: - Ping-pong handovers occur when the MS is handed over from one cell to another but is quickly handed back to the original cell. This causes unnecessary signalling and can give an indication of incorrect handover parameter settings or a dominance problem in the area. TDD 20MHz BANDWIDTH: - Channel Bandwidth is supported for LTETDD with maximum Resource blocks of 100. Frame Structure Type 2: Frame structure type 2 is used for LTE-TDD. Radio frame structure is same as frame structure type 1, but subframes are timely multiplexed with a specific DL/UL ratio in a radio frame. eNB supports uplink-downlink configuration. Special Subframe: The special subframes defined for DL/UL switching in frame structure type 2 consist of the three fields DwPTS (Downlink Pilot Timeslot), GP (Guard Period), and UpPTS (Uplink Pilot Timeslot). eNB supports special subframe configuration #7 of DwPTS: GP:UpPTS = 10:2:2 for TD-LTE. Normal Cyclic Prefix: Addition of redundant bits to avoid data loss. Normal CP (cyclic prefix) of 4.7us is appended to each transmitted OFDM symbols. Benefits: Operator can provide LTE service without being affected by inter-symbol interference In normal cell coverage environment. End User Benefits: End-user can receive LTE service without being affected by intersymbol interference In normal cell coverage environment.

Downlink QPSK, 16QAM and 64QAM Support: UE can be configured to report CQI (Channel Quality Indicator) to assist the eNodeB in selecting an appropriate MCS to use for the downlink transmissions. Support QPSK,16QAM and 64QAM modulation in DL. eNB selects among QPSK, 16-QAM and 64-QAM schemes in response to the CQI feedback from UE. Benefits: Operator can dynamically change modulation order according to the downlink channel environment. Uplink QPSK, 16QAM and 64QAM Support For UL transmissions, the link adaptation process is similar to that for DL, with the selection of modulation and coding schemes also being under the control of the eNB. eNB estimates the supportable uplink data rate by channel sounding and selects appropriate modulation for the result of estimated UL channel quality. Support QPSK and 16QAM modulation in UL. Benefits: Operator can dynamically change modulation order according to the downlink channel environment. Cell Specific Reference Signals: Cell-specific reference signal (CRS) is transmitted in all DL subframes in a cell supporting PDSCH transmission. CRS is transmitted on one or several of antenna ports 0 to 3. It is used for both demodulation and channel estimation purpose in DL. This CRS is also used for LTE-Advanced UEs to detect PCFICH, PHICH, PDCCH, PBCH, and PDSCH. Operator Benefits: Operator can provide multiple antenna transmission.

LTE Bible End User Benefits: LTE user can estimate downlink channel and demodulate control and traffic channel data. Positioning Reference Signal: Positioning reference signals shall only be transmitted in resource blocks in downlink subframes configured for positioning reference signal transmission. Positioning reference signals for OTDOA, which is one of UE Positioning methods. Operator Benefits: Operator can provide an OTDOA based location service to LTE user using positioning reference signal. Synchronization Signal: Synchronization signal is composed of primary and secondary synchronization signals. The synchronization signals always occupy the 72 sub-carrier (6RBs) of the channel, which make a same cell search procedure regardless of channel bandwidth. Primary Synchronization Signal (PSS) detection to obtain the physical layer cell ID (within a group of three) and slot synchronization. Secondary Synchronization Signal (SSS) detection to obtain the Cyclic Prefix (CP) length, the physical layer cell group ID and the frame synchronization.

spans the same bandwidth as the allocated uplink data. Operator Benefits: eNB can demodulate uplink data and control information by the channel estimate from this signal. Sounding Reference Signal: Sounding reference signal provides uplink channel quality information as a basis for scheduling decisions in the base station. The UE sends a sounding reference signal in different parts of the bandwidths where no uplink data transmission is available. The sounding reference signal is transmitted in the last symbol of the subframe. The configuration of the sounding signal, e.g. bandwidth, duration and periodicity, are given by higher layers. Operator Benefits: eNB can estimate uplink channel response from receiving this signal. •The channel estimate is utilized in next uplink scheduling. Random Access Procedure Types: Random Access Procedure are of two types; contention-based and non-contention operation.

Benefits: Operator can make a time synchronization with LTE UE by using synchronization signal.

Operator Benefits: eNB support contention based and contention free operation of random access procedures. And also, Helps in minimizing the chance of collision.

End User Benefits: UE can find out a physical cell ID of serving cell by resolving synchronization signal.

End user Benefits: Contention-free random access procedure helps UE minimize the chance of collision.

•UE can find out frame and slot starting time by resolving synchronization signal.

Variable Number of OFDM Symbols:

Demodulation Reference Signal: Demodulation reference signal is used for channel estimation in the eNodeB receiver in order to demodulate control and data channels. It is located on the 4th symbol in each slot (for normal cyclic prefix) and © Farhatullah Mohammed

The number of resources (OFDM symbols) used in each sub frame for PDCCH shall be dynamic based on the requirement of the CCE (control channel element) by the load of control signaling. There shall be dynamically varying CFI (control format indicator) within the range specified in the standards for different bandwidths. 3

LTE Bible Operator Benefits: Cell capacity is increased in cases where not all available PDCCH resource are needed. End User Benefits: Subscribers may experience higher throughput in downlink in typical scenarios with low load on PDCCH and high utilization of PDSCH CCE Aggregation for PDCCH: Each PDCCH is transmitted using one or more so-called Control Channel Elements (CCEs), where each CCE corresponds to nine sets of four physical resource elements known as Resource Element Groups (REGs). The number of CCEs used for transmission of a particular PDCCH is determined by the eNB according to the channel conditions.CCE aggregation for PDCCH: 1, 2, 4, and 8 CCEs. Operator Benefits: Cell capacity is increased in cases where not all available PDCCH resource are needed. End User Benefits: Subscribers may experience higher throughput in downlink in typical scenarios with low load on PDCCH and high utilization of PDSCH. Basic DCI Formats In order to minimize the signalling overhead it is therefore desirable that several different message formats are available, each containing the minimum payload required for a particular scenario. For this motivation, several DCI (Downlink Control Information) formats are defined in standard. DCI formats 0 (PUSCH grants), 1 (PDSCH assignments with a single codeword), 1A (PDSCH assignments using a compact format), 2 (PDSCH assignments for closed-loop MIMO operation), 2A (PDSCH assignments for open-loop MIMO operation). Operator Benefits: In order to minimize the signalling overhead it is desirable that several different message formats are available, each containing the minimum © Farhatullah Mohammed

payload required for a particular scenario. For this motivation, several DCI (Downlink Control Information) formats are defined in standard. PDSCH Resource Allocation: PDSCH resource allocation types 0, 1 and 2 Operator Benefits: Enable to enhance a flexibility in spreading the resources across the frequency domain to exploit frequency diversity. PUCCH Format The PUCCH supports different formats depending on the information to be signalled. The mapping between the PUCCH format and the Uplink Control Information (UCI) supported in LTE. PUCCH format 1,1A, 1B, 2, 2A, 2B. Operator Benefits: minimize the resources needed for transmission of control signaling. HARQ in DL and UL: MAC Layer Hybrid ARQ uses Incremental redundancy technique to discard erroneously received packets and request retransmission providing robustness against transmission errors. Operator Benefits: Achieve reliable data transmission by sending a message of ACK/NACK. Basic Link Adaption MCS adaptation based upon channel information and error statistics. Operator Benefits: Match the transmission parameter such as modulation and coding scheme (MCS) as well as MIMO transmission rank and precoding to the channel condition on resource allocated by the scheduler. •Serve the best resource allocation under the restriction of limited resource pool CQI Correction 4

LTE Bible CQI correction performs CQI adaptation in order to compensate possible non-idealities of the link adaptation in LTE. e.g. CQI estimation error of the UE, CQI quantization error. Operator Benefits: Enable the better link adaptation from facilitating this feature •Enable downlink radio resource scheduling to serve the best resource allocation Scheduling with QoS Support: Based on the QoS profile of the user, the MAC scheduler will be aware of the priority GBR and AMBR requirements of the users. Accordingly, the scheduler can prioritize the users, ensure guaranteed bit rate and also control the Maximum Aggregate Bit rate allowed for the user. Operator Benefits: Operator can differentiate traffic data according to the QoS class of LTE user. End User Benefits: LTE users can be served the better QoS with their priority in the system.

Frequency Selective Scheduling Frequency selective Scheduling allows eNB to select the best subband for resource allocation on downlink based on the subband CQI feedback from UE. Similarly the best subband selection can be done based on the SRS information. Operator Benefits: Exploiting available channel knowledge to schedule a UE to transmit using specific Resource Blocks (RBs) in the frequency domain where the channel response is good. •Maximizing radio resource utilization Power Control

© Farhatullah Mohammed

In uplink, eNB supports closed loop power control by providing TPC, Transmit Power Commands to UE. eNB also provides open loop power control parameters for the UE to perform open loop power control based on the RSRP measurements Operator Benefits: It can provide the improvement of performance or the expansion of coverage according to the operation environment through Close-loop power control. End User Benefits: It can prevent the unnecessary power consumption of UE and provide the stablization of reception performance. DL Power Allocation Relative PDSCH power for reference symbols defined by two different parameters: ρA and ρB. End-User Benefits: Optimized downlink power allocation will have an impact on the performance of an LTE UE. Paging DRX: Paging DRX refers to the discontinuous operation of the UE in idle mode, where in UE periodically wakes up from sleep mode to monitor the control channels for Paging operation. End User Benefits: Enabling this feature results in longer battery life times. Active DRX: When Active DRX mode is used, even in RRC Connected state, UE sleeps during inactive periods and monitors PDCCH only during certain wake periods. This functionality improves battery life while UE is in connected state. This feature includes both Short DRX and Long DRX. End User Benefits: Enabling this feature results in longer battery life time 5

LTE Bible IRC – Interference Rejection Combining: Receiver supports interference rejection combining based on MMSE criterion. Operator Benefits: Achieve the better quality of signal and improve system performance by cancelling the interference at eNB receiver. DL SU 2x2 MIMO DL single user 2x2 MIMO supported in TM3 and TM4. Operator Benefits: Provide improvement in cell capacity and throughput as UEs with good channel conditions can benefit from the multiple streams transmission. End User Benefits: Served the improved throughput or reliable communication due to the multiple streams transmission. 2Rx Diversity:

End User Benefits: Users can perform PLMN selection and cell selection, then access to a cell within E-UTRAN. Also they can perform intra-frequency cell reselection. SIB Broadcast(SIB5) eNB broadcasts SIB type 5 for Inter-frequency cell reselection. End User Benefits: Users can perform interfrequency cell reselection SIB Broadcast(SIB6) eNB broadcasts SIB type 6 for cell reselection to UTRAN End User Benefits: Users can perform cell reselection from E-UTRAN to UTRAN. SIB Broadcast(SIB7) eNB broadcasts SIB type 7 for cell reselection to GERAN

Rx diversity with 2 antenna

End User Benefits: Users can perform cell reselection from E-UTRAN to GERAN.

Operator Benefits: Enable to facilitate receiving diversity to select one better qualified path or combine two paths.

RRC Connection Management

•Enable to communicate the more reliable transmission condition. 4Rx Diversity: Rx diversity with 4 antenna Operator Benefits: Enable to facilitate receiving diversity to select one better qualified path or combine two paths. •Enable to communicate the more reliable transmission condition. MIB & SIB Broadcast(SIB1~4) eNB broadcasts MIB and SIB type 1, type 2, type 3 and type 4 for PLMN selection, cell selection and intra-frequency cell reselection.


eNB performs RRC connections management procedures such as RRC Connection Establishment, RRC Connection Reconfiguration, RRC Connection Reestablishment and RRC Connection Release. Operator Benefits: Operator can provide radio connectivity to its subscribers within LTE network. End User Benefits: LTE users can have a radio connection with an eNB for LTE service. UE Context Management: eNB maintains UE contexts while the UEs are in RRC_CONNECTED state, and supports Initial Context Setup, UE Context Release and Modification according to requests from MME.

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LTE Bible Operator Benefits: Operator can maintain UE context for its subscribers in RRC_CONNECTED state. E-RAB Setup and Release eNB supports handling of E-RAB allocation, configuration, maintenance and release. Operator Benefits: Operator can provide EPS bearer service to its subscribers and manage E-RAB resources for user data transport. End User Benefits: Users can obtain EPS bearer service within E-UTRAN. E-RAB Modification eNB supports handling of E-RAB modification. This is used for QoS modification of one or serveral E-RABs. Operator Benefits: Operator can modify ERAB QoS of ongoing session. S1 Interface Management S1 interface management procedure is to manage the signaling associations between eNBs, surveying S1 interface and recovering from errors, i.e. Error indication and Reset procedures. Operator Benefits: manage the signaling associations between eNBs, surveying S1 interface and recovering from errors. NAS Signaling Transport eNB supports transfer of NAS signaling messages between MME and UE. Operator Benefits: This feature allows eNB to transfer NAS signaling messages between MME and UE. MME Overload Control eNB cooperates with MME to handle the overload situation of the MME. S1 overload control procedure is used as defined in the 3GPP standard. Overloaded MME sends S1 © Farhatullah Mohammed

Overload Start message to eNB with ‘Overload Action’ IE, then eNB restricts RRC connection requests towards the overloaded MME. Operator Benefits: Signaling load reduction toward overloaded MME. MME Selection and Load Balancing When eNB receives a RRC connection request message from a UE, eNB searches and selects a MME that has served the UE before. The selection is based on S-TMSI information in the message. Otherwise, eNB performs load-based MME selection function for a new call that has no S-TMSI information in the message. Operator Benefits: UE can keep the same MME while it moves around even in idle mode, so that the UE can use the same IP address. •Load is distributed over multiple MMEs. Operator can control relative load of a specific MME by adjusting Relative MME Capacity at each MME. eNB Configuration Update X2 eNB Configuration Update procedure is to update application level configuration data needed for two eNBs to interoperate correctly over the X2 interface. Operator Benefits: Update application level configuration data needed for two eNBs to interoperate correctly over the X2 interface. RIM Procedure: RAN Information Management(RIM) procedures exchange the arbitrary RAN information (e.g., SIB) between RAN nodes belonging to different RATs. The RAN information is transparently transferred via core network nodes (MME and SGSN). End User Benefits: eNB can provide 3G system information for UEs so that they can attach to 3G network quickly. This will help 7

LTE Bible UEs reduce connection setup time during CSFB or handover X2 Interface Management: X2 interface management procedure is to manage the signalling associations between eNBs, surveying X2 interface and recovering from errors, i.e. Error indication and Reset procedures. Operator Benefits: This feature enables operatoir to manage the signalling associations between eNBs, surveying X2 interface and recovering from errors. •Efficient usage of the radio resources with the help of X2 interface management. Paging:

the same eNB. UEs can move between the cells without any message exchange with MME. Operator Benefits: Operator can provide connected mobility to its subscribers between cells in same eNB. End User Benefits: Users in connected state can be moving within E-UTRAN, with change of serving cell. S1 Handover: S1 handover is mobility control functionality between two adjacent eNBs using the S1 interface with MME. S1 handover is used when there is no available direct interface with target eNB, or target eNB belongs to other MME group.

When eNB receives a paging message from MME, the eNB transmits the paging message to the UE in RRC_IDLE state based on the idle mode DRX configuration cycle.

Operator Benefits: Operator can provide connected mobility to its subscribers between cells in different eNBs.

Operator Benefits: Operator can provide mobile terminating service to its subscribers.

End User Benefits: Users in connected state can be moving within E-UTRAN, with change of serving cell.

End User Benefits: LTE users can receive a notification for mobile terminating call in RRC_IDLE state. •Save on battery power and signaling Idle Mobility Support: To support UE's idle mobility in E-UTRAN, eNB broadcasts relevant cell reselection information in SIB messages so that the UE can perform intra-LTE cell reselection when needed. Operator Benefits: Operator can provide idle mobility to its subscribers within E-UTRAN. End User Benefits: LTE users in idle state can be moving within E-UTRAN. Intra-eNB Handover: Intra-eNB handover is mobility control functionality between cells that belong to © Farhatullah Mohammed

X2 Handover X2 handover is mobility control functionality between adjacent eNBs. X2 based handover is used when there is an available direct interface with target eNB and target eNB belongs to same MME group. Operator Benefits: Operator can provide connected mobility to its subscribers between cells in different eNBs. End User Benefits: Users in connected state can be moving within E-UTRAN, with change of serving cell. Data Forwarding: During handover, source eNB forwards PDCP SDUs in sequence to target eNB. Direct data forwarding is used when a direct path between source eNB and target eNB is available. Otherwise indirect data 8

LTE Bible forwarding is used, where PDCP packets are delivered to target eNB through S-GW. End User Benefits: Users can obtain session continuity during handover within E-UTRAN, with almost no interruption. Inter-Frequency Handover: Inter-frequency handover is mobility control functionality between cells that use different frequency band. eNB provides UEs with measurement gap information in order for the UEs to perform inter frequency search. Measurement Gap avoids scheduling of data for the UE during inter frequency scan periods Operator Benefits: Operator can provide connected mobility to its subscribers between cells which have a different center frequency. End User Benefits: Users in connected state can be moving within E-UTRAN, with change of serving cell. Handover to CSG/Hybrid Cells: To support inbound mobility toward CSG/Hybrid cell, macro eNB performs CSG/Hybrid cell specific measurement control and handover signaling. Operator Benefits: Operator can provide connected mobility to its subscribers from macro cells to CSG/Hybrid cells. End User Benefits: LTE users in connected state can be moving from macro cells to its own CSG cells or Hybrid cells. Multi-target Preparation: Multi Target preparation allows eNB to trigger handover procedure to more than one target eNodeB for improving user experiences. Handover preparation message is sent to multiple candidate target eNBs based on the measurement report received from the UE. Only one target is chosen for the UE to handover. If the UE © Farhatullah Mohammed

fails handover to the above target, the UE can re-establish the connection successfully with the source eNB or other target eNBs that already have the UE context. If the handover is successful, then the source eNB cancels the handover preparation with the other candidate target eNBs. End User Benefits: Users can obtain session continuity with fast recovery of ongoing sessions though handover failure has been experienced during handover. Intra-LTE Redirection: This is intra-LTE mobility functionality towards different LTE carriers from serving carrier. Operator Benefits: Operator can provide connected mobility to its subscribers between LTE carriers, though not interfrequency handover. Idle Mobility to CDMA Network (HRPD/1xRTT). To support UE's idle mobility to CDMA network (HRPD or 1xRTT), eNB broadcasts relevant cell reselection information in SIB8 message so that the UE can perform cell reselection towards CDMA network when needed. Operator Benefits: Operator can provide idle mobility to its subscribers to CDMA network. End User Benefits: Users in idle state can move to CDMA network. Optimized Handover to HRPD Optimized PS handover to CDMA2000 eHRPD is outbound mobility control functionality to eHRPD network, in case of the UE has preregistered to the target eHRPD network and optimized handover can be possible. When mobility event to eHRPD is occurred, eNB initiates optimized handover by sending a request message for handover preparation to the UE. After handover preparation 9

LTE Bible between the UE and HRPD network, the UE handovers towards eHRPD network. Operator Benefits: Operator can provide connected mobility to its subscribers from E-UTRAN to CDMA2000 HRPD. End User Benefits: Users in connected state can move from E-UTRAN to CDMA2000 HRPD, remaining the connected state. CSFB to CDMA2000 1xRTT CS fallback to CDMA2000 1xRTT enables the delivery of CS-domain services when a UE is being served by the E-UTRAN. When eNB receives CSFB indicator from MME, then performs a procedure of redirection to CDMA2000 1xRTT. Operator Benefits: Operator can provide CS service to its subscribers from E-UTRAN to CDMA2000 1xRTT. End User Benefits: Users can do a CS call while staying in E-UTRAN, by transition to legacy CS network (1xRTT). Idle Mobility to UTRAN To support UE’s idle mobility to UTRAN, eNB broadcasts relevant cell reselection information in SIB6 message so that the UE perform cell reselection towards UTRAN when needed. Operator Benefits: •Operator can provide idle mobility to its subscribers to UTRAN. End User Benefits: •Users in idle state can move to UTRAN.

•Operator can provide connected mobility to its subscribers from E-UTRAN to UTRAN. End User Benefits: •Users in connected state can move from EUTRAN to UTRAN, remaining in the connected state. PS Handover from UTRAN UTRAN PS handover is mobility control functionality between E-UTRAN and UTRAN PS domain. Operator Benefits: •Operator can provide connected mobility to its subscribers from UTRAN to E-UTRAN. End User Benefits: •Users in connected state can move from UTRAN to E-UTRAN, remaining in the connected state. Redirection to UTRAN without SI This is outbound mobility control functionality to UTRAN. When mobility event to UTRAN is occurred, eNB redirects the UE towards UTRAN. Operator Benefits: •Operator can provide connected mobility to its subscribers from E-UTRAN to UTRAN. End User Benefits: •Users in connected state can move from EUTRAN to UTRAN. Redirection to UTRAN with SI

UTRAN PS handover is mobility control functionality between E-UTRAN and UTRAN PS domain.

This is outbound mobility control functionality to UTRAN. When mobility event to UTRAN is occurred, eNB redirects the UE towards UTRAN and transfers system information of neighboring UTRAN cells.

Operator Benefits:

Operator Benefits:

PS Handover to UTRAN


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LTE Bible •Operator can provide connected mobility to its subscribers from E-UTRAN to UTRAN. End User Benefits: •Users in connected state can move from EUTRAN to UTRAN. CSFB to UTRAN with Redirection without SI CS fallback to UTRAN enables the delivery of CS domain services when a UE is being served by the E-UTRAN. When eNB receives CSFB indicator from MME, then performs a procedure of redirection without system information. Operator Benefits: •Operator can provide CS service to its subscribers by using legacy CS network (UTRAN) End User Benefits: •Users can do a CS call while staying in EUTRAN, by transition to legacy CS network (UTRAN) CSFB to UTRAN with Redirection with SI CS fallback to UTRAN enables the delivery of CS domain services when a UE is being served by the E-UTRAN. When eNB receives CSFB indicator from MME, then performs a procedure of redirection with system information. Operator Benefits: •Operator can provide CS service to its subscribers by using legacy CS network (UTRAN) End User Benefits: •Users can do a CS call while staying in EUTRAN, by transition to legacy CS network (UTRAN) CSFB to UTRAN with PS Handover

CS fallback to UTRAN enables the delivery of CS domain services when a UE is being served by the E-UTRAN. When eNB receives CSFB indicator from MME, then performs a procedure of PS handover to WCDMA. Operator Benefits: •Operator can provide CS service to its subscribers by using legacy CS network (UTRAN) End User Benefits: •Users can do a CS call while staying in EUTRAN, by transition to legacy CS network (UTRAN) Capacity based Call Admission Control Capacity-based CAC determines whether to admit or reject the establishment requests (e.g. idle to active transition, handover, additional E-RAB establishment) for new radio bearers, based on maximum number of calls and bearers supported by eNodeB/Sector. New calls are allowed only if the pre-configured maximum number of calls and bearers allowed for that sector and for that eNB are not exceeded. In case of no resources, emergency calls are allowed by preempting existing calls. Operator Benefits: •By limiting the maximum number UEs or bearers per cell and per eNB, considering radio and backhaul bandwidth, operator can control the minimum QoS level provided for UEs. •Operator can protect the system from being shutdown due to overload or congestion QoS based Call Admission Control QoS-based CAC determines whether the eNB accepts a new bearer based on the current resource utilization and the QoS requirements of the new bearer. Operator Benefits:


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LTE Bible •Operator can provide QoS guaranteed service to UEs. •Operator can configure how much resources(PRB, backhaul bandwidth, number of GBR bearers) can be used for GBR services. Preemption In case of no resource available, eNB admits a new bearer by preempting existing bearers. The decision is based on ARP (Allocation and Retention Priority) information of new bearer(s) and existing bearer(s). Operator Benefits: •Operator can provide UEs with differentiated service based on service or based on UE class.

Operator Benefits: •Operator can reduce the amount of incoming calls per call type. AM, UM and TM Data Transfer at RLC Layer: eNB supports three different data transfer modes at RLC layer; Acknowledged Mode(AM), Unacknowledged Mode(UM) and Transparent Mode(TM). TM is used to transfer RRC signaling messages without RLC overhead. AM, which allows retransmission, is used for reliable data transfer and UM is used for delay sensitive data transfer. Operator can configure a transfer mode AM or UM per QCI. •RLC AM provides a reliable data transfer between eNB and UE.

•Operator can design a high-priority service which is always available even in network congestion.

•RLC UM allows a simple data transfer for delay sensitive packets.

Cell Barring

•RLC TM removes RLC overhead to save radio resources.

When eNB is overloaded or a cell is used for testing, operator can configure eNB to transmit cell barring message via BCCH(SIB type1). Accordingly, UEs will not camp on the cell but test UEs can access. Operator Benefits: •Operator can prohibit UEs from camping on a specific cell, which enables operator to test the cell for the commissioning of base stations without any interference of commercial UEs. Access Class Barring In order to limit UE's access to a cell, operator can manually configure the access class barring information via LSM. eNB broadcast this information in SIB type 2 message. Operator can control how many UEs to be allowed and how long time period it is valid and which type of UE behaviors are restricted. © Farhatullah Mohammed

Header Compression ROHCv1(RTP, UDP, IP) eNB and UE compress the IP header part of user data packets for transmission over the air. The compression algorithm is RoHCv1(Robust Header Compression) defined in IETF RFC3095 and other related RFCs. RoHC Profiles 0,1,2 and 4 are supported. Operator Benefits: •eNB increases user data throughput by applying RoHC to user data transmitted over the radio link. •When this feature is enabled for VoLTE, eNB can accommodate more VoLTE users at the same time. End User Benefits: •UE can enhance throughput. Integrity Protection: Null/SNOW3G/AES 12

LTE Bible Control plane data integrity protection using security algorithms between eNB and UE.

•Operator can provide different user classes for different quality of services.

•Per compliance of the data integrity discipline of communication, eNB shall ensure the data is not modified during the transmission.

End User Benefits:

•Integrity protection, and replay protection, shall be provided to RRC-signalling.

Operator Specific QCIs Support

Ciphering: Null/SNOW3G/AES eNB supports SNOW 3G/AES as an encryption algorithm to protect user plane data and control plane data transferred between eNB and UE. Operator Benefits:

•Users can use a premium service that provides better quality even in congestion.

eNB supports extended QCIs that are defined by operator. Operator Benefits: •Operator can define a customized QCI for a specific service, where QoS characteristics of the extended QCIs may be different from those of standard QCIs in terms of priority, resource type, packet delay budget.

•Confidentiality of software transfer towards the eNB shall be ensured

End User Benefits:

•Sensitive parts of the boot-up process shall be executed with the help of the secure environment.

•UE can receive a customized network service that is suitable to a specific application.

•Prevent UE tracking based on cell level measurement reports

QCI to DSCP Mapping

End User Benefits: •Support privacy protection for user information Standard QCI Support eNB supports standardized QCI(QoS Class Identifier) as defined in 3GPP TS 23.203, which is characterized by priority, packet delay budget and packet error loss rate. eNB handles scheduling of the bearer based on its QCI information. Operator Benefits: •This feature enables operator to plan a variety of premium services; end-to-end QoS differentiated services in 9 different levels as per defined in 3GPP standard. •Operator can provide high-quality VoLTE service by using guaranteed bit rate bearers. © Farhatullah Mohammed

eNB marks uplink packets with a DSCP value so that intermediate nodes can support QoS for packets heading to EPC. DSCP value is determined depending on QCI. For this, operator can configure QCI to DSCP mapping table according to its service and QoS policy. Operator Benefits: •Operator can manage traffic from eNB to SGW for end-to-end QoS service. •In addition to bearer traffic, operator can setup appropriate DSCP values to signaling traffic and OAM traffic for system optimization. For example, setting a high priority on signaling message will reduce call setup time while a DSCP value for regularly generated OAM ftp traffic needs to set not to affect user traffic. GBR and MBR Support 13

LTE Bible eNB reserves radio resource to support GBR(Guaranteed Bit Rate), and eNB limits the throughput not to exceed MBR(Maximum Bit Rate). For this, QoS based call admission control and QoS aware scheduling algorithm are used. GBR and MBR are bearer associated parameters and MME sends eNB these parameters during ERAB setup or modification procedure. Operator Benefits: •Operator can provide high-quality QoS services by using GBR bearers. End User Benefits:

•Operator can provide a UE with 8 different kind of services at the same time, where each service has different QoS characteristics such as QCI or ARP. End User Benefits: •A UE may have maximum 8 different kind of bearers at the same time. Each bearer has different QoS characteristics such as QCI or ARP. This ensures better user experience and fair allocation of radio resources to UE QCI-based Throughput Differentiation for Non-GBR Bearers

•By configuring MBR, operator can prevent GBR UEs from overusing data and monopolizing radio resources.

Operator can configure "weight factor" for each different Non-GBR QCIs. Then, NonGBR bearers can achieve throughput in proportion to the ratio of weight factor between them. This takes effect only in case of resource limitation. When there are enough resources, each bearers are able to transmit all of its own data.

•Efficient usage of the radio resources

Operator Benefits:

UE-AMBR Support

• Operator can support differentiated throughput for non-GBR OCI. Thus ithis feature enable an operator to implement various accounting plan according to QoS (even for the same service).

•UEs that connect a GBR bearer can achieve at least the guaranteed bit rate that system allows even in cass of congestion.

eNB limits the total bit rate(UE-AMBR) that a UE can achieve through its non-GBR bearers. MME sends eNB UE-AMBR parameter during UE Context Setup or Modification procedure Operator Benefits: •By controlling UE-AMBR, operator can prevent a UE from overusing data over NonGBR bearers and monopolizing radio resources. •Operator can differentiate subscribers by setting UE-AMBR differently per user classes. Max 8 Bearers per UE eNB supports up to 8 data bearers for a UE, including default and dedicated bearers regardless of their resource types

(For example, normal download vs. high speed download, normal video streaming vs. HD video streaming) End User Benefits: • User can enjoy premium service with fast speed in network congestion state Load Balancing between Carriers In the LTE network with multiple carriers, the load balancing algorithm selects UEs from a high-loaded carrier and hands them over to a co-located and low-loaded carrier. The UE selection algorithm is designed to guarantee QoS after handover to another carrier.

Operator Benefits: © Farhatullah Mohammed

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LTE Bible Operator Benefits: •This feature distributes the amount of traffic on multiple carriers and provide even QoS on each carrier. End User Benefits: •The bad QoE due to overload will be reduced Load Balancing between Sectors (Mobility Load Balancing) Load balancing within an intra-carrier occurs between cells of intra-eNB or inter-eNB. UEs in the boarder area are selected and handed over to the low-loaded neighbor cells. The load balancing algorithm considers serving/target cells' signal strength at UE. The algorithm is designed to balance the average per-UE non-GBR resources among cells. Operator Benefits: •This feature relieves the overload state of a cell. End User Benefits: •The bad QoE due to overload will be reduced. Idle UE Distribution In multi-carrier network, Idle UE distribution algorithm makes idle UEs distributed over carriers by giving a different priority of frequency to each UE via IdleModeMobilityControlInfo in the RRCConnectionRelease message. Idle-toactive transition UEs will be distributed over multiple carriers when they camp on. For this feature, Operator should configure the parameters, which control the idle UE ratio among carriers. Operator Benefits:


•This feature distributes the amount of traffic on multiple carriers and provide even QoS on each carrier. SPID based Dedicted Priority SPID based Dedicted Priority SPID based Dedicted Priority eNB supports dedicated signaling with cell reselection priorities based on SPID 254, 255 and 256. Operator Benefits: •Operator can control idle mode camping RAT and carriers of a UE based on absolute priorities determined by subscription information. Load Distribution over Backhaul Links When eNB has two backhaul Ethernet links alive, eNB distribute load between two links. Operator Benefits: •By monitoring one backhaul link, operator can monitor all the traffic of a specific UE. DL Flow Control between SGW and eNB When downlink radio link of a cell is congested due to the limited bandwidth, eNB sends XOFF message to SGW so that it stop sending packets in downlink. eNB sends XON message to resume data transmission at SGW. This flow control scheme works per UE or bearer or QCI. Operator Benefits •This feature enables for SGW to count packets that are actually delivered to UEs, which prevents overbilling for packets overflowed and dropped at eNB due to air congestion. •This flow control feature reduces the number of packets dropped due to air congestion because both eNB and SGW can buffer packets. 15

LTE Bible eNB Overload control(Adaptive Access Barring) eNB periodically monitors the load status of CPU processor. When CPU overload is detected, eNB performs automatically adjustment of the access barring control parameters based on CPU overload level(Minor/Major/Critical). Operator Benefits:

•In MOCN, operator can highly utilize radio resources between different PLMNs by configuring som portion of radio resources shared between them. shared between operators. Inter-PLMN Handover Inter-PLMN handover is mobility control functionality between cells that served PLMN is different from each other.

•Operator can reduce the number of call attempts to an overloaded eNB, which can prevent the eNB from shutting down due to overload.

Operator Benefits:

End User Benefits:

End User Benefits:

•LTE users can avoid access to an eNB under congestion

•LTE users can obtain EPS bearer service in other network operators’ area which is not the subscribed network operator.

Multi-PLMN Support In a shared cell, eNB periodically broadcasts a SIB1 message which includes supporting PLMN id list up to 6. According to the selected PLMN id included in RRC Connection Setup Complete message, eNB routes the control message to an appropriated MME to make a connection to the network. Operator Benefits: •Operator can reduce CAPEX. Flexible Configuration for Radio Resource Sharing eNB allocates the radio resources(PRB, active UE capacity, bearer capacity) to each PLMN id according to the radio sharing ratio configured by operator. Operator can configure some portion of the resources dedicated to each operator and remaining resources to be commonly Operator Benefits: •Operator can wholesale a portion of spectrum by configuring some portion of radio resources dedicated to a specific PLMN id.

•Operator can provide connected mobility to its subscribers within a shared network.

Load Balancing between Multi-operator Frequencies To support traffic management for the network with both carriers only for a specific operator and shared carriers for multiple operators, eNB provides the concept of carrier-group. Load balancing using the carrier-group concept has two operations: load equalization within the same carrier-group and offloading the overloaded traffic between carrier-gro Operator Benefits: •Operators can distribute the amount of traffic on shared multiple carriers. End User Benefits: •The bad QoE due to overload will be reduced. ups. Usage Report per PLMN eNB provides usage data per PLMN to LSM. PRB usage, user data usage, number of UEs, number of bearers, and signaling messages will be counted per PLMN. Operator Benefits:


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LTE Bible •Host operator can figure out how much data is consumed by each partner operator. •The usage data can be utilized for the purpose of settlement among partner operators

•LTE users can do an emergency call while staying in E-UTRAN, by transition to legacy CS network (UTRAN). CMAS (Commercial Mobile Alert Service)

To support IMS emergency call, eNB performs emergency call specific admission control, security handling and mobility control.

CMAS is a public warning system developed for the delivery of warning notifications. The CMAS warning notifications are short text messages (CMAS alerts). The CMAS warning notifications are broadcasted via SIB messages.

Operator Benefits:

Operator Benefits:

•Operator can provide Emergency service to its subscribers while they are staying in EUTRAN.

•Operator can provide public warning notifications to its subscribers while they are staying in E-UTRAN.

End User Benefits:

End User Benefits:

•LTE users can do an emergency call while staying in E-UTRAN, as well as in legacy CS network.

•Users can be notified for public warning messages from network, and then they can avoid some disasters or accidents.

Emergency Call via CSFB to CDMA2000

ETWS (Earthquake and Tsunami Warning System)

IMS based Emergency Call Support

This is CSFB to CDMA2000 1xRTT functionality for emergency call Operator Benefits: •Operator can provide Emergency service to its subscribers by using legacy CS network (CDMA2000 1xRTT). End User Benefits: •LTE users can do an emergency call while staying in E-UTRAN, by transition to legacy CS network (CDMA2000 1xRTT). Emergency Call via CSFB to UTRAN This is CSFB to UTRAN functionality for emergency call Operator Benefits: •Operator can provide Emergency service to its subscribers by using legacy CS network (UTRAN).

ETWS is a public warning system for warning notifications related to earthquake and/or tsunami events. ETWS warning notifications can be either a primary notification (short notifications delivered within 4 seconds) or secondary notification (providing detailed information). The ETWS primary and secondary notifications are broadcasted via SIB messages. Operator Benefits: •Operator can provide public warning notifications to its subscribers while they are staying in E-UTRAN. End User Benefits: •Users can be notified for public warning messages from network, and then they can avoid some disasters or accidents. Enhanced Cell ID

End User Benefits: © Farhatullah Mohammed

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LTE Bible In the Cell ID (CID) positioning method, the position of an UE is estimated with the knowledge of its serving eNodeB and cell. The information about the serving eNodeB and cell may be obtained by paging, tracking area update, or other methods. Enhanced Cell ID (E CID) positioning refers to techniques which use additional UE and/or E UTRAN radio resource such as TA (Timing Alignment), UE measurement reports to improve the UE location estimate. Operator Benefits: •additional UE and/or E UTRAN radio measurement reports to improve the UE location estimate. OTDOA The downlink (OTDOA) positioning method makes use of the measured timing of downlink signals received from multiple eNode Bs at the UE. The UE measures the timing of the received signals using assistance data received from the positioning server, and the resulting measurements are used to locate the UE in relation to the neighboring eNodeBs. Operator Benefits:. • to improve UE location estimate using by both UE's received signals from several eNBs and assistance information from eNB. Intra-LTE ANR ANR allows automatic discovery and setup of neighbor relations when a UE moves from a serving eNB to target eNB. ANR also automatically sets up the LTE unique X2 interface between eNBs, primary used for handover. Operator Benefits: •ANR minimize the manual handling of neighbor relations when establishing new eNBs and when optimizing neighbor lists.

•This will increase the number of successful handovers and lead to less dropped connections due to missing neighbor relations. RACH optimization During self-configuration phase, EMS supports RSI(root sequence index) autoconfiguration using location information. Subsequently, during the operational phase, each eNodeB collects the information pertaining to any RSI conflicts and informs EMS about conflict information for reconfiguring. For RACH optimization, eNB collects the statistics of the dedicated preamble allocation attempt/success and optimizes the number of dedicated preambles. eNB also collects the statistics of the preamble transmission during RA and optimizes the PRACH Configuration Index, Preamble Initial Received Target Power, Power Ramping Step. Operator Benefits: •In the SON framework, as soon as the eNodeB is powered up during the autoconfiguration phase, it is allocated to a RSI(Root Sequence Index). Such a RSI is determined using a RSI auto-configuration algorithm that uses the location information with neighbors. Thus, SON ensures that each eNodeB has a RSI value at the time of installation without requiring explicit human intervention. •In operation phase, SON ensures that each eNB and LSM supports RSI collision/confusion detection and RSI reconfiguration without human intervention. In addition, RACH optimization will reduce the amount of manual processes involved in the RACH related optimizations like the number of dedicated preambles, PRACH configuration index, preamble initial received target power and power ramping step. PA Bias Control


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LTE Bible eNB supports power amplifier bias control by adjusting PA bias for low RF load without a specified carrier shutdown. Two types of PA bias control mechanisms are supported: Predefined Time schedule based and Traffic load based. Operator Benefits: •PA bias control provides high power efficiency with low RF load. •PA bias control saves about 6.7% of consumed DC power in 800MHz. Test of VSWR The functionality of VSWR(Voltage Standing Wave Ratio) test is used to measure return loss in transmitting antenna of power amp unit. Operator Benefits: •This feature provides an efficient method for measuring return loss in transmitting antenna of power amp unit. Packet Loss Detection over S1 eNB counts and provide statistics about lost packets and out-of sequence packets occurred during delivery from SGW to eNB. This feature can be enabled only when eNB interworks with EPC. Operator Benefits: •Operator can decide the quality of backhaul network. Difference between CCO – Cell change Order and Redirection: CCO from LTE (only possible towards GSM) differs from the LTE->GSM redirection mainly such that with CCO if the UE can't successfully camp and access the given target GSM cell, it has to return to LTE, whereas the redirection can have multiple target cells/frequencies and the UE can attempt to find service in any of them.


With Rel-9 redirection also the system information messages for the target GSM cell (or, in fact, up to maximum of 32 GSM cells) the performance can be equal (or even better in case the single target cell with CCO cannot be found or access fails) that the CCO with NACC (network assisted cell change, which means the system information for the target GSM cell is provided with the CCO). In practise the above means that redirection typically would perform equally well and in many cases (esp. if the redirection or CCO is made blindly, i.e. without UE reporting GSM cells) better than CCO, and therefore it is typically used with CS fallback. Cell reselection Cell reselection is the process of changing the mobile's serving cell (either in idle mode or while actively transmitting data). Cell reselections can be initiated by the mobile or network. When the network initiates a cell reselection, it sends a Packet Cell Change Order (GPRS/EGPRS) or a Cell Change Order (W-CDMA/HSPA), which provides the parameters necessary for the mobile to find and synchronize to the destination cell. If the mobile was actively transferring data at the time of the cell reselection, any subsequent allocation of traffic channel resources to continue the packet data transfer are handled by signaling between the mobile and destination cell, and does not involve the origination cell. Handover Handover refers to a cell transition that occurs when a circuit-switched (CS) connection is in place (such as CS voice, CS data, or Dual Transfer Mode). Handovers can only be initiated by the network. During a handover, the network sends the mobile a Handover command, which provides information about the destination cell, including the traffic channel configuration. The procedure for mobility from LTE to another RAT supports both handover and Cell Change Order (CCO).The CCO procedure is applicable only for mobility to GERAN. In case of handover (as opposed to CCO), the source eNodeB requests the target RAN node to prepare for the handover. As part of the ‘handover preparation request’ the source eNodeB 19

LTE Bible provides information about the applicable inter-RAT UE capabilities as well as information about the currently-established bearers. In response, the target RAN generates the ‘handover command’ and returns this to the source eNodeB.


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2. -

Introduction

LTE is abbreviated as Long term Evolution. LTE is successor of not only UMTS but also CDMA 2000. LTE is introduced to get higher data rates of 300Mbps peak downlink and 75Mbps peak uplink in 20MHz Carrier for FDD. LTE is an ideal technology to support higher data rates for the services VoIP, streaming media, video conferencing. LTE uses both Time Division Duplexing (TDD) and Frequency Division Duplexing (FDD). In FDD, both uplink and downlink uses different frequencies. Uplink and downlink uses same

frequency in TDD.

LTE – FDD -

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LTE – TDD

LTE supports bandwidths from 1.4MHz, 5MHz, 10MHz and 20MHz. LTE devices have to support MIMO, for the base station to transmit several data streams over the same carrier simultaneously. The entire interfaces between the nodes are IP based including the backhaul, connection to the base stations. Quality of service mechanism have been standardized on all the interfaces to ensure the requirement of voice calls for constant delay and bandwidth Advantages of LTE: High Throughput: High downlink and uplink throughput can be achieved. Low Latency: Time required to connect to the network in the range of few hundreds milli seconds. FDD and TDD in the same platform: Frequency Division Duplex – FDD and Time Division Duplex –TDD. Superior End user Experience: Optimized signaling for connection establishment and other air interface and mobility management procedures have further improved user experience. Seamless Connection: LTE supports seamless connection to the existing networks such as GSM, CDMA and WCDMA. Simple Architecture: Low operating expenditure because of simple architecture.

LTE Bible -

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LTE uses OFDM transmission schemes., it uses OFDMA in Downlink and SC-FDMA in uplink. A Resource block is a basic entity in the LTE terminology which when modulated using OFDM sub-carriers becomes Resource Elements – which is the smallest unit of the LTE spectrum. A Physical Resource Block (PRB) is defined as smallest unit used by the scheduling algorithm. TTI : Transmission Time Interval is the duration of the transmission on the radio link. TTI is related to the size of the data blocks passed from the higher network layer to the radio link layer. Link Adaptation or Adaptive Modulation Coding: It is the ability to adapt the modulation scheme and the coding rate of the error correction according to the radio link. If the condition of the radio link are good, a high level efficient modulation scheme and a small amount of error correction is used.


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3.

Resource Blocks in LTE

Resource Element: RE is the smallest unit of transmission resources in LTE, in uplink and downlink. RE consists of 1 subcarrier in the frequency domain for duration of 1 symbol (OFDM in the downlink and SC-FDMA in the uplink). -

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Subcarrier Spacing: It is the space between the individual carriers, in LTE 15KHz. There is no guard band between these subcarrier frequencies , rather Guard period is called as Cyclic prefix is used in the time domain to help prevent multipath Inter Symbol Interference (ISI) between subcarriers. Cyclic Prefix: A set of samples which are duplicated from the end of transmitted symbol and appended cyclically in the beginning of the symbol. This can form a type guard interval to absorb Inter symbol interference (ISI). Time Slot: 0.5ms time period of the LTE frame corresponding to 7 OFDM symbols (7CPs) when normal CP=5usec used. And 6 symbols(CP=6) when Extended CP = 17usec is used.

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- Resource Block Resource Block: A unit of transmission resource consisting of 12 subcarriers in the frequency domain and 1 time slot (0.5ms) in the time domain. 1 RB = 12(Subcarriers) x 7 (Symbols ) = 84 Resource Elements. (For Normal CP :- 7 symbols) 1 RB = 12(Subcarriers) x 6 (Symbols ) = 72 Resource Elements (For Extended CP:- 6 symbols) LTE Subframe or TTI = two slots i.e.. 1ms in time LTE frame – 10ms or 10 subframes or 20 slots. Bandwidths directly affects the throughput. Different Bandwidths have different number of RB. 10% of the total bandwidth is used for the Guard band. This is not valid of 1.4MHz bandwidth. For 20MHz Bandwidth, 10% of 20MHz = 2MHz is used for Guard band and 18MHz is effective bandwidth. Number of subcarriers = 18MHz/15KHz = 1200 Number of Resource blocks = 18MHz/180KHz = 100RB

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Resource Blocks in Frequency Bands.

Resource Blocks (RB): - Basic unit of resource for the LTE air-interface. - eNodeB scheduler allocates RBs to UE to allow data transfer. - Defined in both time and frequency domains. In Time Domain: - Occupies 0.5 ms slot in time domain. - Consists of 7 OFDMA symbols when using Normal Cyclic Prefix. - Consists of 6 OFDMA symbols when using Extended Cyclic Prefix. In Frequency Domain: - Consists of 12 subcarriers. - Each subcarrier is of 15 KHZ. - Each RB occupy 12*15 = 180 KHZ in frequency domain.

- The GRID generated by One Sub-Carrier in the Frequency Domain and One Symbol in the Time Domain defines a RESOURCE ELEMENT (RE). - RB consists of 84 (12*7) REs when using Normal Cyclic Prefix. © Farhatullah Mohammed

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LTE Bible - RB consists of 72 (12*6) REs when using Extended Cyclic Prefix. - A single RE can carry a Single Modulation Symbol (2 bits when using QPSK, 4 bits when using 16QAM, and 6 bits when using 64QAM).


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4. Resource Allocation & Management Unit Reading various LTE specification, you will see many terms which seems to be related to resource allocation but looks very confusing. At least you have to clearly understand the following units. i) Resource Element(RE) : The smallest unit made up of 1 symbol x 1 subcarrier. ii) Resource Element Group (REG) : a group of 4 consecutive resource elements. (resource elements for reference signal is not included in REG) iii) Control Channel Element (CCE) : a group of 9 consective REG iv) Aggregation Level - a group of 'L' CCEs. (L can be 1,2,4,8) v) RB (Resource Block) : I think everybody would know what this is. This is a unit of 72 resource elements which is 12 subcarrier by 6 symbols. vi) RBG (Resource Block Group) : This is a unit comprised of multiple RBs. How many RBs within one RBG differs depending on the system bandwidth. (Refer to RB Size allocation for each System Bandwidth for the details) We use these units in hierachical manner depending on whether it is for control channel or data channel.

For PDCCH, the hierachy would be : RE --> REG --> CCE --> Aggregation Level ==> I think a couple of example would give you more practical understanding. Example 1 > a PDCCH transmission © Farhatullah Mohammed

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LTE Bible i) The CCE index for a certain subframe = 4 ii) Aggregation Level is 2 iii) The subframe is sending DCI1 only Resource Allocation : Network would allocate the DCI 1 spreaded over CCE4, CCE5.

Example 2 > a PDCCH transmission i) The CCE index for a certain subframe = 4 ii) Aggregation Level is 2 iii) The subframe is sending DCI1, DCI 0 Resource Allocation : Network would allocate the DCI 1 spreaded over CCE4, CCE5 and allocate the DCI 0 spreaded over CCE6, CCE7.

Example 3 > a PDCCH transmission i) The CCE index for a certain subframe = 4 ii) Aggregation Level is 2 iii) The subframe is sending DCI1, DCI 0 and DCI 3 (power control) Resource Allocation : Network would allocate the DCI 1 spreaded over CCE4, CCE5 and allocate the DCI 0 spreaded over CCE6, CCE7 and allocate two CCE for DCI 3 but DCI 3 would be allocated to a common search space (not to a user specific search space).

For PDSCH, the heirachy would be RE --> RB --> RBG


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5. -

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LTE Throughput Calculation

Throughput calculation for LTE – TDD For any system, throughput is calculated as symbols per second. For 20MHz Bandwidth, there are 100 Resource Blocks and each resource block have 12 x 7 x 2 = 168 symbols per ms in case of normal CP. 168 symbols per ms = 168000 symbols per second = 16.8Msymbols/sec For 64QAM, there are 6 bits per symbols. The Throughput will be 6bits per symbol x 16.8 M symbols per sec = 100.3 Mbps For LTE MIMO ( 4Tx and 4Rx) the throughput will be calculated as 403.2Mbps Many simulations indicate that 25% overhead is used for signaling and controlling. The effective throughput is 300Mbps. 300Mbps is valid for downlink and is not valid for uplink. In uplink there is single antenna on UE, so with 20MHz we get maximum of 100Mbps, after considering 25% overhead, 75Mbps throughput is achieved in uplink. Throughput Calculation for LTE – FDD FDD is a paired spectrum has the same bandwidth for the downlink and the uplink. 20MHz FDD system has 20MHz for downlink and 20MHz for Uplink. For Throughput Calculation: Bandwidth – 20MHz UE Category 3 For Cat 3, TBS index 26 for (75376 for 100RB) and 21 for (UL 51024 for 100RB). Throughput = Number of chains x TB size DL Throughput = 2 x 75376 = 150.752Mbps UL Throughput = 1 x 51024 = 51.024Mbps

PEAK CAPACITY -

To consider the peak capacity, let us consider 2x5Mhz system The number of resource elements in one subframe of 1ms = 12subcarriers x 7OFDM symbols x 25 Resource blocks x 2 slots = 4200 Resource elements. Calculating the data rate assuming 64 QAM with no coding (64QAM is highest modulation used in downlink LTE) 6 bits per 64QAM symbol x 4200 RE/1ms = 25.2Mbps MIMO data rate for 2 x 2 MIMO = 2 x 25.2 = 50.4Mbps Subtracting the overhead related to control signaling such as PDCH and PBCH, reference and synchronization signals and coding which are estimated as follows PDCCH can take 1 to 3 symbols out of 14 in a sub-frame. Assuming that on average 2.5 symbols amount of overhead due to PDCCH becomes 2.5/14 = 17.86%. Downlink RS uses 4 symbols in every third subcarrier resulting in 16/336 = 4.76% overhead for 2 x 2 MIMO configuration. Other channels (PSS, SSS, PBCH, PCFICH, PHICH) added together upto 2.6% overhead. The total approximate overhead for the 5 MHz channel is 17.86% + 4.76% + 2.6% = 25.22%. The peak data rate is then 0.75 x 50.4 Mbps = 37.8 Mbps. Note that the uplink would have lower throughput because the modulation scheme for most device classes is 16QAM in SISO mode only.


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There is another technique to calculate the peak capacity which I include here as well for a 2×20 MHz LTE system with 4×4 MIMO configuration and 64QAM code rate 1: Downlink data rate: Pilot overhead (4 Tx antennas) = 14.29% Common channel overhead (adequate to serve 1 UE/subframe) = 10% CP overhead = 6.66% Guard band overhead = 10% Downlink data rate = 4 x 6 bps/Hz x 20 MHz x (1-14.29%) x (1-10%) x (1-6.66%) x (1-10%) = 298 Mbps. Uplink data rate: 1 Tx antenna (no MIMO), 64 QAM code rate 1 (Note that typical UEs can support only 16QAM) Pilot overhead = 14.3% Random access overhead = 0.625% CP overhead = 6.66% Guard band overhead = 10% Uplink data rate = 1 * 6 bps/Hz x 20 MHz x (1-14.29%) x (1-0.625%) x (1-6.66%) x (1-10%) = 82 Mbps.

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LTE Bible

6.

Frequency Bands

Frequency Bands of LTE:


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LTE Bible

7.

LTE Frame Structure

DOWNLINK FRAME STRUCTURE: -

Frame structure type 1 1 Frame = 10 ms = 10 subframes (1ms subframe each) 1 Frame = 10ms i.e.. 1 subframe = 1ms Applicable to FDD and half duplex FDD.

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Frame structure

The duration of one LTE radio frame is 10 ms. One frame is divided into 10 subframes of 1 ms each, and each subframe is divided into two slots of 0.5 ms each. Each slot contains either six or seven OFDM symbols, depending on the Cyclic Prefix (CP) length. The useful symbol time is 1/15 kHz= 66.6 mircosec. Since normal CP is about 4.69 microsec long, seven OFDM symbols can be placed in the 0.5-ms slot as each symbol occupies (66.6 + 4.69) = 71.29 microseconds. When extended CP (=16.67 microsec) is used the total OFDM symbol time is (66.6 + 16.67) = 83.27 microseconds. Six OFDM symbols can then be placed in the 0.5-ms slot. Frames are useful to send system information. Subframes facilitate resource allocation and slots are useful for synchronization. Frequency hopping is possible at the subframe and slot levels.


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LTE Bible

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In LTE, radio resources are allocated in units of Physical Resource Blocks (PRBs). Each PRB contains 12 subcarriers and one slot. If the normal Cyclic Prefix is used, a PRB will contain 12 subcarriers over seven symbols. If the extended CP is used, the PRB contains only six symbols. The UE is specified allocation for the first slot of a subframe. There is implicit allocation for the second slot of the subframe. For example, if the eNB specifies one RB as the resource allocation for the UE, the UE actually uses two RBs, one RB in each of the two slots of a subframe. When frequency hopping is turned on, the actual PRBs that carry the UE data can be different in the two slots. In a 10 MHz spectrum bandwidth, there are 600 usable subcarriers and 50 PRBs. LTE - TDD Subframe Configuration

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Frame structure Type 2 is applicable to TDD is as shown in the figure. Each radio frame of 10 ms in length consists of two half-frames of 5 ms in length. Each half-frame consists of eight slots of the length Ts=5 ms and three special fields DwPTS, GP, and UpPTS of 1 ms in length. Different configurations, numbered zero to six, are defined in the standard for the subframe number allocated for the uplink and downlink transmission. Subframe 1 in all


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LTE Bible -

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configurations and subframe 6 in configurations 0, 1, 2 and 6 consist of DwPTS, GP and UpPTS. All other subframes are defined as two slots. Switch-point periodicities of 5 ms and 10 ms are supported. The standard defines the table for the uplink and downlink allocations for switch-point periodicity. In the case of a 5-ms switch-point periodicity, UpPTS and subframes 2 and 7 are reserved for uplink transmission. In the case of a 10-ms switch-point periodicity, UpPTS and subframe 2 are reserved for uplink transmission and subframes 7 to 9 are reserved for downlink transmission. Subframe 0 and 5 are always for the DL. The subframe following the special SF is always for the UL. The DwPTS field carries synchronization and user data as well as the downlink control channel for transmitting scheduling and control information. The UpPTS field is used for transmitting the PRACH and the Sounding Reference Signal (SRS

Each subframe is divided into two time slots. For 1 Frame (10ms) = 10 sub-frames (1ms) = 20 Time slots (0.5ms) 1 sub frame = TTI = 2 Time Slots = 14 symbols ( 1 Time slot = 7 symbols) SPECIAL SUB-FRAME


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LTE Bible LTE- TDD SUBFRAME DETAILED:

Special Subframe Length >


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LTE Bible Switching Points

PRACH Preamble Format

Refer to 36.211 5.7 Physical random access channel for the details.

RACH Configuration © Farhatullah Mohammed

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LTE Bible

Special Slot Usage < RB Allocation on Special Subframe > Refer to 36.213 7.1.7 Modulation order and transport block size determination for the details.


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LTE Bible HARQ Timing < ACK/NACK from UE for PDSCH > Following table shows the Ack/Nack Transmission Timing from UE for the PDSCH it recieved.

Problem is how to interpret this table. Following shows how to interpret each raw of the table. Case 1 : UL/DL Configuration 0

In case of UL/DL Configuration 0, Ack/Nack response timing for the PDSCH that is received by UE is transmitted according to the following rule.


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LTE Bible How do you interpret this table and DL/UL correlation ?

It says 

UE transmit Ack/Nack at subframe 2,4,7,9

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At subframe 2, UE transmit Ack/Nack for PDSCH it received at subframe 6 in previous SFN

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At subframe 4, UE transmit Ack/Nack for PDSCH it received at subframe 0 in current SFN

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Case 2 : UL/DL Configuration 1


How do you interpret this table and DL/UL correlation ?

It says 

UE transmit Ack/Nack at subframe 2,3,7,8

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At subframe 2, UE transmit Ack/Nack for PDSCH it received at subframe 5,6 in previous


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LTE Bible SFN 

At subframe 3, UE transmit Ack/Nack for PDSCH it received at subframe 9 in previous SFN

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At subframe 7, UE transmit Ack/Nack for PDSCH it received at subframe 0,1 in current SFN

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At subframe 8, UE transmit Ack/Nack for PDSCH it received at subframe 4 in current SFN Case 3 : UL/DL Configuration 2


How do you interpret this table and DL/UL correlation ?

It says 

UE transmit Ack/Nack at subframe 2,7

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At subframe 2, UE transmit Ack/Nack for PDSCH it received at subframe 4,5,6,8 in previous SFN

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At subframe 7, UE transmit Ack/Nack for PDSCH it received at subframe 9 in previous SFN and 0,1,3 in current SFN

< ACK/NACK from eNB for PUSCH >


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LTE Bible




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LTE Bible SR/DCI 0 Timing The Time delay between SR(Scheduling Request) and DCI 0 is not clearly specified in 3GPP specification. So basically, NW can send DCI 0 in any available DL subframe after reception of SR, but depending on the eNodeB and Test Equipment some minimum time interval may be required. DCI 0/PUSCH Timing If UE recieves DCI 0 at subframe n, it should send PUSCH at subframe n + k where k is defined as follow. I will post some graphical explanation for this table later. Until then, give it a try on your own to understand this table.

36-213 V9.3.0 (2010-10) Table 8-2 k for TDD configurations 0-6

Let's assume that you are using DL/UL Configuration 2. and suppose UE sent a NACK at Subframe 2. How did you know whether the NACK is for PDSCH at subframe 4 or 5 or 6 or 8 ? (As you know, in FDD.. the answer is so simple since the ACK/NACK from the UE is always for the PDSCH that it received 4 subframe before. If it is FDD, the answer is supposed to be 'it is for PDSCH received at subframe 9 in previous SFN), but in TDD case it is different as you may guess. Then how do you correlate the NACK to the specific PDSCH which caused the NACK. It is completely dependent on how much detailed information that your UE log or Network log provide. If UE log or Network log provide ACK/NACK information and HARQ process number for every subframe.. you can try following procedure. i) First, check UCI info at specific SFN and subframe number (let's label this as 'SFN_n:Subframe_2') and locate the HARQ process number that caused NACK. ii) Go to transmitted PDSCH list 'around' SFN_n:Subframe_2 (at this point, you would not © Farhatullah Mohammed

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LTE Bible know exactly which subframe you have to pin point out). iii) Look through several subframes upwards and downwards to find the subframe that is marking the same HARQ process number as you got at step i). That is the subframe that caused NACK. Ack/Nack Feedback Mode As described above, in TDD LTE ibe subframe can transmit ACK/NACK for multiple subframe as shown below. In the following figure as an example, UE send ACK/NACK for 4 PDSCHs in subframe 2. What should eNB do if the subframe 2 send NACK ? Does it have to retransmit the whole 4 PDSCHs ? or transmit only PDSCH which is NACKed ?

The answer to the question gets different depending on tdd-AckNackFeedbackMode setting in RRC message (e.g, RRC Connection Setup or RRC Connection Reconfiguration). If it is set to be 'bundling', eNB should retransmit all the PDSCH. If it is sent to be 'multiplexing', eNB should retransmit the only PDSCH which is NACKed.


42

LTE Bible Followings are some of the items that is worth noticing from 3GPP 36.213 10.1.3 TDD HARQ-ACK feedback procedures (I modified the statement a little bit to make it simple and hopefully clearer) For TDD UL/DL configuration 5 and a UE that does not support aggregating more than one serving cell, only HARQ-ACK bundling is supported.  A UE that supports Carrier Aggregation is configured by higher layers to use HARQ-ACK

bundling, PUCCH format 1b with channel selection according to the set of Tables 10.1.32/3/4 or according to the set of Tables 10.1.3-5/6/7, or PUCCH format 3 for transmission of HARQ-ACK when configured with Carrier Aggregation.  PUCCH format 1b with channel selection according to the set of Tables 10.1.3-2/3/4 or

according to the set of Tables 10.1.3-5/6/7 is not supported for TDD UL/DL configuration 5. 

DD HARQ-ACK bundling is performed per codeword across M multiple DL subframes associated with a single UL subframe n, by a logical AND operation of all the individual PDSCH transmission (with and without corresponding PDCCH/EPDCCH) HARQ-ACKs and ACK in response to PDCCH/EPDCCH indicating downlink SPS release 

or TDD HARQ-ACK multiplexing and a subframe n with M >1, spatial HARQ-ACK bundling across multiple codewords within a DL subframe is performed by a logical AND operation of all the corresponding individual HARQ-ACKs. PUCCH format 1b with channel selection is used in case of one configured serving cell 

or TDD HARQ-ACK multiplexing and a subframe n with M = 1, spatial HARQ-ACK bundling across multiple codewords within a DL subframe is not performed, 1 or 2 HARQ-ACK bits are transmitted using PUCCH format 1a or PUCCH format 1b, respectively for one configured serving cell. You would notice the variable 'M' in many of the statement above. M is defined to be "the number of elements in the set K defined in Table 10.1.3.1-1". Following examples would give you clearer idea on the meaning of M.


43

LTE Bible System Information Variation


44

LTE Bible

8.

-

LTE Architecture

Overall Architecture Overview: LTE architecture consists of EUTRAN and EPC. The core network (called as EPC in SAE) is responsible for overall control of UE and establishment of the bearers. - The main logical nodes of EPC are  MME – Mobility Management Entity  S-GW – Serving Gateway  P-GW – PDN Gateway - Apart from the main nodes, EPC also includes logical nodes and functions such as Home Subscriber Server (HSS), Policy Control and Rules charging Function (PCRF). - PCRF: Policy control and charging Resource Function is responsible for policy control and decision making, as well as for controlling the flow based charging functionalities in the policy control enforcement function, which resides in PDN-GW. - PCRF provides the QoS authorization (QCI and bit rates) that decides how data flow will be treated in the PCEF and ensures that is in accordance with the user subscription profile. - HSS: Home Subscriber Server contains user’s SAE subscription data such as EPS subscribed QoS profiles and any access restrictions for roaming. - It holds information about PDN to which user can connect, this could be in the form of APN. - The HSS may integrate the authenticate center (AuC) which generates the vectors for authentication and security keys. - P-GW: PDN Gateway is responsible for IP address allocation for all UE, as well as QoS enforcement and flow based charging according to the rules from PCRF. - It is responsible for filtering downlink IP packets into different QoS based bearers. - This is done through TFT (Traffic Flow Templates) - P-GW performs QoS enforcement for guaranteed bit rate (GBR) bearers. - S-GW: All the IP packets are transferred through Serving gateway, which serves the local mobility anchor for the data bearer, when UE moves between eNodeBs. - It also retains bearer information when UE is idle state. - It temporarily buffers downlink data rate while MME initiates administrative functions in the visited network such as collecting information for charging. 45 © Farhatullah Mohammed

LTE Bible -

MME: Mobility Management Entity is the control node that processes the signaling between the UE and the core network. Protocols running between the UE and the Core network are known as Non Access Stratum (NAS).


46

LTE Bible

9. -

-

-

-

-

LTE Interfaces

Air Interface Uu: It is the interface connection between the user equipment and eNodeB. The UE and eNodeB make use of the Uu whenever transmit or receive across the LTE interface. X2 Interface: Connects one eNodeB with another eNodeB  Allows both signalling and data to be transferred between the neighbouring eNodeB. X2 – CP (Control Plane): Interface allows signaling between eNodeB. X2 – UP (User Plane) : Interface allows the transfer of application data between eNodeB. S1 Interface: Connects eNodeB to the Evolved Packet Core (EPC).  Allows signaling and the data to be transferred between EPC and EUTRAN  S1 – MME (Control Plane): allows signaling with MME.  S1 – U (User Plane) : allows transfer of application data through S – GW. S11 Interface: Connects MME to S-GW.  Allows signaling information for mobility and bearer management to be transferred.  Application data does not use S11. S5 Interface: Connects S-GW to PDN-GW  Both control plane and user plane uses S5 interface.  PDN provide connectivity to the set of IP ServicesGateway S8 Interface: Similar to S5 interface but it terminates at a PDN Gateway belonging to different PLMN. S6a Interface: Connects MME to HSS  HSS is a database for all user subscription information. S13 Interface: Connects MME to EIR  EIR stores IMEI S7 or Gx Interface: Connects PCEF within PDN Gateway to the PCRF  PCRF provides QoS and charging information to the PDN – Gateway SGi Interface: Interface connects between PDN Gateway and packet data network S3 Interface: Connects MME and SGSN. S10: Connects MME with other MME S4 Interface: Connects S – GW with SGSN


47

LTE Bible

10.

LTE Bearers

Bearers: Bearer is a concept that defines how UE data is treated when it travels across the network. Some data is provided with guaranteed bit rate and other may face low transfer.

Default Bearer: When LTE UE is attached to the network for the first time, it will be assigned default bearer which remains as long as UE is attached. Each default bearer comes with IP address QCI 5 to 9(Non GBR) can be assigned to default bearer.

Dedicated Bearer: Dedicated bearers provides dedicated tunnel to one or more specific traffic (i.e… VOIP, video). Dedicated bearer acts as an additional bearer on top of default bearer. -

Dedicated bearer does not require IP address and is linked to one of the default bearer established previously. Dedicated bearer can be with Guaranteed bit rate and Non-Guaranteed Bit Rate. Dedicated bearer uses Traffic Flow Template (TFT) to give special treatment to the services. Dedicated bearer is linked to default bearer using “Linked EPS bearer identity” setup information.

What is the information that default EPS has but dedicated bearer does not? © Farhatullah Mohammed

48

LTE Bible -

APN name, PDN type and PDN address.

What kind of PDN address does dedicated EPS bearer will use? -

Dedicated EPS bearer has the same PDN address of default EPS bearer. Which of the bearers does not contains QCI?

-

Both default bearer and dedicated bearer contains QCI. Default Bearer QCI 5 to 9 Dedicated bearer QCI 5 to 9 and 1 to 6.

Can default bearer and dedicated bearer have a same value? -

No the two bearers must have different values.

What is the relation between the default bearer and APN? -

There is one to one relation between the default bearer and APN. 1 APN for 1 bearer.

How is dedicated bearer linked to default bearer? The value of "Linked EPS bearer identity" defined in setup info of dedicated bearer is used to link dedicated bearer to default bearer In many cases, we get confused by the role of Default EPS Bearer and Dedicated EPS Bearer. I think the best way to clear the confusion would be to understand the detailed information elements (parameters) defining these two bearer. First take a look at the decoded message for Default EPS Bearer and Dedicated EPS Bearer.


49

LTE Bible


50

LTE Bible

11.

Quality of Service - QoS

Quality of Service in LTE There are some subscribers who want to have better user experience in 4G LTE device. These users are willing to pay for high bandwidth and better network access on their devices. -

Not only subscribers, but some services itself need better priority handling in the network like voip. In LTE network, QoS is applied on Radio bearer, S1 bearer and S5/S8 bearer, collectively called EPS bearer. The QoS is implemented between UE and PDN gateway which is applied to set of bearers.

GBR: Guaranteed Bit Rate: It is the minimum bit rate per EPS bearer specified independently for uplink and downlink. MBR: Maximum Bit Rate: It is the maximum guaranteed bit rate per EPS bearer specified independently for uplink and downlink. AMBR: Aggregate – Maximum Bit Rate: It is the maximum allowed total non GBR throughput to specific APN. ARP: Allocation and Retention Priority: It decides whether new bearer modification or establishment request should be accepted considering the current resource situation. TFT: Traffic Flow Template: TFT is always associated with the dedicated bearer and may or may not be associated with the default bearer. -

Dedicated bearer provides QoS to special service or application and TFT defines rules so that UE and network knows which IP packet should be sent or particular dedicated bearer.

L-EBI: Linked EPS Bearer Identity: Dedicated bearers are always linked to one of the default bearers. © Farhatullah Mohammed

51

LTE Bible -

LEBI tells dedicated bearer to which default bearer it is attached to.

-

Applying QoS Through QCI Levels: QCI (Quality of Service Class Identifier)

-

Aims to provide users with low download volume with highest speed by giving them higher scheduling priority.

-

As users download continues, the user will move to a lower profile with a lower scheduling priority which will reduce his affect to the normal users.

-

Profile B

Profile C

Profile D

Always

Norm al

More than 1GB per day

More than 2GB per day

QCI

6

7

8

9

9

ARP

6

11

11

11

11

Throughp ut

1.2 Profile B

1

50% of Profile B

30% of Profile B

MBR: 256kbps

Weight

11

9

4

2

2

Profiles

Profile A

Consumpt ion


Profile E More than 15GB per week

52

LTE Bible

12.

Protocol Stacks

User plane Protocol stack:

Control Plane Protocol Stack:


53

LTE Bible

13.

Protocol Layer Functionality

-


54

LTE Bible

14.

LTE Elements Functionality

-

-

-

MME - Mobility Management Entity MME is the key control node for LTE access network. It is responsible for tracking and paging procedure including retransmissions, and also for idle mode of User Equipment (UE). MME is also involved in bearer activation and its deactivation procedures, to its task also belongs choosing the SGW for a UE in process of initial attach and when the intra-handover take place which involves Core Network (CN) node relocation. MME is responsible for authenticating user towards the HSS, if user is roaming MME terminates S6a interface towards user's home HSS. All Non Access Stratum (NAS) signaling terminates at the MME point, which is also responsible for generation and allocation of temporary UE identities (GUTI). Among its duties is also authorization UE to Public Land Mobile Network (PLMN) and enforcing UE roaming restrictions if there are any. MME is also termination point of ciphering and integrity protection for NAS signaling. Lawful Interception (LI) of signaling could be also supported by MME entity. It also provides the control plane function for mobility between LTE and 2G/3G networks by the S3 interface( from SGSN to MME). Functions mentioned above as a list, according to 23.401 3GPP documentation. MME functions include:  NAS signalling;  NAS signalling security;  Inter CN node signalling for mobility between 3GPP access networks (terminating S3);  UE Reach ability in ECM-IDLE state (including control and execution of paging retransmission);  Tracking Area list management;  Mapping from UE location (e.g. TAI) to time zone, and signalling a UE time zone change associated with mobility;  PDN GW and Serving GW selection;  MME selection for handovers with MME change;  SGSN selection for handovers to 2G or 3G 3GPP access networks;  Roaming (S6a towards home HSS);  Authentication;  Authorization;  Bearer management functions including dedicated bearer establishment;  Lawful Interception of signalling traffic;


55

LTE Bible  

-

Warning message transfer function (including selection of appropriate eNodeB); UE Reach ability procedures.

The MME shall signal a change is UE Time Zone only in case of mobility and in case of UE triggered Service Request, PDN Disconnection and UE Detach. If the MME cannot determine whether the UE Time Zone has changed (e.g. the UE Time Zone is not sent by the old MME during MME relocation), the MME should not signal a change in UE Time Zone. A change in UE Time Zone caused by a regulatory mandated time change (e.g. daylight saving time or summer time change) shall not trigger the MME to initiate signalling procedures due to the actual change. Instead the MME shall wait for theUE's next mobility event or Service Request procedure and then use these procedures to update the UE Time Zone information in PDN GW.

SGW - Serving Gateway -

-

Serving GW is the gateway which terminates the interface towards E-UTARN. For each UE associated with the EPS, at given point of time, there is a single Serving GW. SGW is responsible for handovers with neighboring eNodeB's, also for data transfer in terms of all packets across user plane. To its duties belongs taking care about mobility interface to other networks such as 2G/3G. SGW is monitoring and maintaining context information related to UE during its idle state and generates paging requests when arrives data for the UE in downlink direction. (e.g. somebody's calling). SGW is also responsible for replication of user traffic in case of LI. SGW functions as a list, according to 23.401 3GPP documentation. SGW functions include:  

the local Mobility Anchor point for inter-eNodeB handover; Sending of one or more "end marker" to the source eNodeB, source SGSN or source RNC immediately after switching the path during inter-eNodeB and inter-RAT handover, especially to assist the reordering function in eNodeB.  Mobility anchoring for inter-3GPP mobility (terminating S4 and relaying the traffic between 2G/3G system and PDN GW);  ECM-IDLE mode downlink packet buffering and initiation of network triggered service request procedure;  Lawful Interception;  Packet routing and forwarding;  Transport level packet marking in the uplink and the downlink, e.g. setting the DiffServ Code Point, based on the QCI of the associated EPS bearer;  Accounting for inter-operator charging. For GTP-based S5/S8, the Serving GW generates accounting data per UE and bearer;  Interfacing OFCS according to charging principles and through reference points specified in TS 32.240 PDN GW - Packet Data Network Gateway -

The PGW is the gateway which terminates the SGi interface towards PDN. If UE is accessing multiple PDNs, there may be more than one PGW for that UE, however a mix of S5/S8 connectivity and Gn/Gp connectivity is not supported for that UE simultaneously.


56

LTE Bible -

-

PGW is responsible to act as an "anchor" of mobility between 3GPP and non-3GPP technologies. PGW provides connectivity from the UE to external PDN by being the point of entry or exit of traffic for the UE. The PGW manages policy enforcement, packet filtration for users, charging support and LI. PGW functions include:    

Per-user based packet filtering (by e.g. deep packet inspection); Lawful Interception; UE IP address allocation; Transport level packet marking in the uplink and downlink, e.g. setting the DiffServ Code Point, based on the QCI of the associated EPS bearer;  Accounting for inter-operator charging;  UL and DL service level charging as defined in TS 23.203 (e.g. based on SDFs defined by the PCRF, or based on deep packet inspection defined by local policy);  Interfacing OFCS through according to charging principles and through reference points specified in TS 32.240 [51].  UL and DL service level gating control as defined in TS 23.203 [6];  UL and DL service level rate enforcement as defined in TS 23.203 [6] (e.g. by rate policing/shaping per SDF);  UL and DL rate enforcement based on APN-AMBR (e.g. by rate policing/shaping per aggregate of traffic of all SDFs of the same APN that are associated with Non-GBR QCIs);  DL rate enforcement based on the accumulated MBRs of the aggregate of SDFs with the same GBR QCI (e.g. by rate policing/shaping);  DHCPv4 (server and client) and DHCPv6 (client and server) functions;  The network does not support PPP bearer type in this version of the specification. Pre-Release 8 PPP functionality of a GGSN may be implemented in the PDN GW;  packet screening. ENODEB FUNCTIONALITY: -

-

eNode B is the RAN node in the EPS architecture that is responsible for radio transmission to and reception from UEs in one or more cells. The eNode B is connected to EPC nodes by means of an S1 interface. The eNode B may also be connected to its neighbour eNode Bs by means of the X2 interface. Some significant changes have been made to the eNode B functional allocation compared to UTRAN. Most Rel-6 RNC functionality has been moved to the E-UTRAN eNode B. Below follows a description of the functionality provided by eNode B. • Cell control and MME pool support

-

eNode B owns and controls the radio resources of its own cells. Cell resources are requested by and granted to MMEs in an ordered fashion. This arrangement supports the MME pooling concept. S-GW pooling is managed by the MMEs and is not reallyseen in the eNode B. • Mobility control

-

The eNode B is responsible for controlling the mobility for terminals in active state. This is done by ordering the UE to perform measurement and then performing handover when necessary. Control and User Plane security


57

LTE Bible -

The ciphering of user plane data over the radio interface is terminated in the eNode B. Also the ciphering and integrity protection of RRC signalling is terminated in the eNodeB.

-

Shared Channel handling Since eNode B owns the cell resources, eNode B also handles the shared and random access channels used for signalling and initial access.

-

-

-

-

-

-

-

-

-

Segmentation/Concatenation Radio Link Control (RLC) Service Data Units (SDUs) received from the Packet Data convergence Protocol (PDCP) layer in the AGW consist of whole IP packets may be larger than the transport block size provided by the physical layer. Thus, the RLC layer must support segmentation and concatenation to adapt the payload to the transport block size. HARQ A Medium Access Control (MAC) Hybrid Automatic Repeat reQuest (HARQ) layer with fast feedback provides a means for quickly correcting most errors from the radio channel. To achieve low delay and efficient use of radio resources, the HARQ operates with a native error rate which is sufficient only for services with moderate error rate requirements such as for instance VoIP. Lower error rates are achieved by letting an outer Automatic Repeat reQuest (ARQ) layer in the eNode B handle the HARQ errors. Scheduling A scheduler with support for the QoS model provides efficient scheduling of UP and CP data. Multiplexing and Mapping The eNode B performs mapping of logical channels onto transport channels. Physical layer functionality The eNode B handles the physical layer such as scrambling, Tx diversity, beamforming processing, and OFDM modulation. The eNode B also handles L1 functions like link adaptation and power control. Measurements and reporting eNode B provides functions for configuring and making measurements on the radio environment and eNode B-internal variables and conditions. The collected data is used internally for RRM but can be reported for the purpose of multi-cell RRM. Radio Resource Management Functions: Radio Bearer Control: The establishment, maintenance and release of radio bearers involve the configuration of the radio resources associated with them. When setting up the radio bearer for a service, radio bearer control (RBC) takes into account for overall resource situation in EUTRAN, the QoS requirement of in-progress sessions and the QoS requirement for the new service. RBC is also concerned with the maintenance of the radio bearers of in-progress sessions at the change of the radio situations due to mobility or other reasons. RBC is involved in the release of the radio resources associated with the radio bearers at the session termination, handover or other occasions. RBC is located in eNB Radio Admission Control(RAC): The task of RAC is to admit or reject the establishment request for new radio bearers. In order to do this RAC takes into account the overall resource situation in EUTRAN, the QoS requirement, the priority levels and the provided QoS of in progress sessions and the QoS requirement of new bearer request.


58

LTE Bible -

-

-

-

The goal of RAC is to ensure high resource utilization(by accepting radio bearer requests as long as radio resources are available) and at the same time to ensure proper QoS for inprogress sessions(by rejecting radio bearer request when they cannot be accommodated) RAC is located in ENB. Connection Mobility Control: Connection Mobility control is concerned with the management of radio resources in connection with the idle or connected mode mobility. In idle mode the cell reselection algorithms are controlled by setting of parameters (thresholds and hysteresis values) that defines the best cell and/or determine when the UE should select the new cell. In connected mode, the mobility of the radio connections has to be supported. Handover decisions may be based on UE and eNB measurements In addition, handover decision may take other inputs such as neighbour cell load, traffic distribution, transport and hardware resources and operator defined policies into the account.


59

LTE Bible

15. LTE Timers

-

-

-

-

-

-

LTE Timers and Constants -

Function at Start/Stop/Expiry

-

>>Starts at the RRC connection REQ transmit >>Stops at the Receipt of RRC connection setup or reject message OR at the cell reselection time OR upon abortion of connection establishment by Higher layers (L2/L3). >>At the expiry performs the actions

-

>>Starts at the RRC Connection Re-establishment REQUEST >>Stops at the Receipt of RRC Connection Re-establishment OR RRC Connection Re-Establishment REJECT message OR When selected cell becomes unsuitable to continue further >>At expiry, it Go to RRC_IDLE mode

-

>>Starts when access is barred while performing RRC CONNECTION ESTABLISHMENT for MO(Mobile Originating) calls >>Stops while entering RRC_CONNECTED and upon cell re-selection mode >>At expiry, Informs higher layers about barring alleviation

-

>>Starts at the Receipt of RRC CONNECTION RECONFIGURATION message along with Mobility Control Info OR at the receipt of mobility from EUTRA command message including CELL CHANGE ORDER >>Stops at the successful completion of HANDOVER to EUTRA or CELL CHANGE ORDER is met >>At expiry, it performs action based on need. 1. In the case of CELL CHANGE ORDER from E-UTRA OR intra E-UTRA handover, initiate the RRC connection re-establishment procedure. 2. In case of HANDOVER to E-UTRA, perform the actions defined as per the specifications applicable for the source RAT.

-

>>starts when access is barred while performing RRC CONNECTION ESTABLISHMENT for MO signaling >>Stops when entering RRC_CONNECTED and when UE does cell reselection >> At expiry, Informs higher layers about barring alleviation

-

>>Starts when UE detects PHY layer related problems (when it receives N310 consecutive out-of-sync INDs from lower layers) >>Stops 1. When UE receives N311 consecutive in-sync INDs from lower layers/ 2. Upon triggering the HANDOVER procedure 3. Upon initiating the CONNECTION RE-ESTABLISHMENT procedure >> At expiry, if security is not activated it goes to RRC IDLE else it

T300

T301

T303

T304

T305

T310


60

LTE Bible initiates the CONNECTION RE-ESTABLISHMENT Procedure

-

-

-

-

-

>>Starts while initiating RRC CONNECTION RE-ESTABLISHMENT procedure >>stops upon selection of suitable E-UTRA cell OR a cell using another RAT >>At expiry it enters RRC IDLE state

-

>> Starts upon receipt of t320 or upon cell reselection to E-UTRA from another RAT with validity time configured for dedicated priorities (in which case the remaining validity time is applied). >>Stops upon entering RRC_CONNECTED state, when PLMN selection is performed on request by NAS OR upon cell re-selection to another RAT >> At expiry, it discards the cell re-selection priority info provided by dedicated signaling

-

>>starts upon receipt of measConfig including a reportConfig with the purpose set to reportCGI >> Stops at either of following cases: 1. Upon acquiring the information needed to set all fields of globalCellId for the requested cell 2. upon receipt of measConfig that includes removal of the reportConfig with the purpose set to reportCGI >> At expiry initiates the measurement reporting procedure, stop performing the related measurements and remove the corresponding measID

T311

T320

T321

T300: Timer T300 of the cell in the eNodeB. The UE start T300 timer after sending RRC Connection Request. When it receives RRC connection setup message or RRC connection Reject message, the timer is cleared. When the T300 timer terminates, UE reset the MAC, clears the MAC configuration and reestablishes the RLC Default timer value is 400ms. T301: Timer 301 of the Cell in eNB The UE starts T301 timer after sending the RRC Connection Reestablishment message or the RRC connection Reestablishment reject message, the timer is cleared. When the T301 timer terminates, UE becomes idle. Default value of the timer is 200ms T302: Timer starts after receiving the RRC Connection Reject message. The timer terminates when UE status becomes RRC connect or the cell is reselected. When the timer is cleared the UE marks the cell as barred and perform cell reselection. T304: The timer start by UE after receiving RRC reconfiguration message during the handover. The timer terminates when the handover to EUTRAN succeeds. Default value is 200ms


61

LTE Bible -

T310: Timer value which starts after UE continuously receives out-of-sync indication as much as N310. Cleared if in-sync indication is received continuously as much as N311, if handover is triggered or the reestablishment procedure is triggered. Default value of the timer is 1000ms. T311: The timer starts by UE when initiating a reestablishment procedure. The timer is cleared if a suitable EUTRAN cell or inter RAT cell is found. If the timer is cleared without finding a suitable cell, it enters RRC_IDLE state. Default value of this timer is 3000ms. N 310: The maximum count of out-of-sync indication the UE receives from the lower layer Default value of counter is 10. N 311: The maximum count of in-sync indication on the UE receives from the lower layer. Default value of this counter is 1. T303: Timer starts when access is barred while performing RRC connection establishment for MO (Mobile Originating) calls. Timer stops while entering RRC_Connected and upon cell reselection mode. T 305: Timer starts when the access is barred while performing RRC Connection establishment for MO Signalling The timer stops when entering RRC_Connected and UE does cell reselection.

Timer

Message that Carreirs the Timer

T300 T301 T310 T311 N310 N311

SIB2

T3402 T3412 T3423

Attach Accept, Tracking Area Update Accept


62

16. TIMER NUM.

TIMER VALUE

LTE Timers Detailed_UE Side STATE

T3402

Default 12 min. NOTE 1

EMM DEREGISTERED EMM REGISTERED

T3410

15s

EMMREGISTEREDINITIATED

T3411

10s

EMM DEREGISTERED. ATTEMPTING TO-ATTACH EMM REGISTERED. ATTEMPTING TO-UPDATE

T3412

Default 54 min. NOTE 2 NOTE 5

EMM REGISTERED

CAUSE OF START At attach failure and the attempt counter is equal to 5. At tracking area updating failure and the attempt counter is equal to 5. ATTACH REQUEST sent

NORMAL STOP

ON EXPIRY

ATTACH REQUEST sent TRACKING AREA UPDATE REQUEST sent

Initiation of the attach procedure or TAU procedure

ATTACH ACCEPT received ATTACH REJECT received

Start T3411 or T3402 as described in subclause 5.5.1.2.6 Retransmission of the ATTACH REQUEST or TRACKING AREA UPDATE REQUEST

At attach failure due to ATTACH REQUEST sent lower layer failure, T3410 TRACKING AREA UPDATE timeout or attach rejected REQUEST sent with other EMM cause values than those treated in subclause 5.5.1.2.5. At tracking area updating failure due to lower layer failure, T3430 timeout or TAU rejected with other EMM cause values than those treated in subclause 5.5.3.2.5. In EMM-REGISTERED, when When entering state EMM EMM-CONNECTED mode is DEREGISTERED left. or when entering EMMCONNECTED mode.

Initiation of the periodic TAU procedure

LTE Bible T3416

30s

EMM REGISTERED INITIATED EMM REGISTERED EMM DEREGISTERED INITIATED EMM-TRACKINGAREA UPDATING INITIATED EMM-SERVICE REQUEST INITIATED

RAND and RES stored as a result of a UMTS authentication challenge

T3417

5s

EMM-SERVICEREQUESTINITIATED

SERVICE REQUEST sent EXTENDED SERVICE REQUEST sent in case f and g in subclause 5.6.1.1

T3417ext

10s

EMM-SERVICEREQUESTINITIATED

Inter-system change from S1 mode to A/Gb mode or Iu mode is completed Inter-system change from S1 mode to A/Gb mode or Iu mode is failed SERVICE REJECT received

Abort the procedure

T3418

20s

AUTHENTICATION REQUEST received

On first expiry, the UE should consider the network as false

T3420

15s

AUTHENTICATION REQUEST received

On first expiry, the UE should consider the network as false

T3421

15s

EMM REGISTEREDINITIATED EMM REGISTERED EMM-TRACKINGARE AUPDATINGINITIATED EMM DEREGISTEREDINITIATED EMM-SERVICEREQUESTINITIATED EMM REGISTERED INITIATED EMM REGISTERED EMM DEREGISTERED INITIATED EMM-TRACKINGAREA UPDATING INITIATED EMM-SERVICE REQUEST INITIATED EMM DEREGISTERED INITIATED

EXTENDED SERVICE REQUEST sent in case d in subclause 5.6.1.1 EXTENDED SERVICE REQUEST sent in case e in subclause 5.6.1.1 and the CSFB response was set to "CS fallback accepted by the UE" AUTHENTICATION FAILURE (EMM cause = #20 "MAC failure" or #26 "non-EPS authentication unacceptable") sent AUTHENTICATION FAILURE (cause = #21 "synch failure") sent

DETACH REQUEST sent

DETACH ACCEPT received

Retransmission of DETACH REQUEST


SECURITY MODE Delete the stored RAND COMMAND received and RES SERVICE REJECT received TRACKING AREA UPDATE ACCEPT received AUTHENTICATION REJECT received AUTHENTICATION FAILURE sent EMM DEREGISTERED or EMM-NULL entered Bearers have been set up Abort the procedure SERVICE REJECT received

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LTE Bible T3423

NOTE 3

EMM REGISTERED

T3412 expires while the UE is in EMM-REGISTERED.NOCELLAVAILABLE and ISR is activated.

When entering state EMM DEREGISTERED or when entering EMMCONNECTED mode.

Set TIN to "P-TMSI"

T3430

15s

EMM-TRACKING AREA UPDATING INITIATED

TRACKING AREA UPDATE REQUEST sent

TRACKING AREA UPDATE ACCEPT received TRACKING AREA UPDATE REJECT received

Start T3411 or T3402 as described in subclause 5.5.3.2.6

T3440

10s

EMM REGISTERED INITIATED EMM-TRACKING AREA UPDATING INITIATED EMM DEREGISTERED INITIATED EMM-SERVICE REQUEST INITIATED EMM REGISTERED

Signalling connection released Bearers have been set up

Release the signalling connection and proceed as described in subclause 5.3.1.2

T3442

NOTE 4

EMM REGISTERED

ATTACH REJECT, DETACH REQUEST, TRACKING AREA UPDATE REJECT with any of the EMM cause #11, #12, #13, #14 or #15 SERVICE REJECT received with any of the EMM cause #11,#12, #13 or #15 TRACKING AREA UPDATE ACCEPT received after the UE sent TRACKING AREA UPDATE REQUEST in EMMIDLE mode with no "active" flag SERVICE REJECT received with EMM cause #39 "CS domain temporarily not available"

TRACKING AREA UPDATE REQUEST sent

None

Note 1

The default value of this timer is used if the network does not indicate another value in an EMM signalling procedure.

Note 2 Note 3 Note 4 Note 5

The value of this timer is provided by the network operator during the attach and tracking area updating procedures. (This Timer value is set in Attach Accept message as well). The value of this timer may be provided by the network in the ATTACH ACCEPT message and TRACKING AREA UPDATE ACCEPT message. The default value of this timer is identical to the value of T3412. The value of this timer is provided by the network operator when a service request for CS fallback is rejected by the network with EMM cause #39 "CS domain temporarily not available". The default value of this timer is used if the network does not indicate a value in the TRACKING AREA UPDATE ACCEPT message and the UE does not have a stored value for this timer.


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LTE Bible (This Timer value is set in Attach Accept message as well).

17. TIMER VALUE

TIMER NUM.

LTE Timers Detailed_Network Side STATE

CAUSE OF START

NORMAL STOP

ON THE 1st, 2nd, 3rd, 4th EXPIRY (NOTE 1)

T3413

NOTE 2

EMM REGISTERED

Paging procedure for EPS services initiated

Paging procedure for EPS services completed

Network dependent

T3422

6s

EMM DEREGISTERED INITIATED

DETACH REQUEST sent

DETACH ACCEPT received

Retransmission of DETACH REQUEST

T3450

6s

EMM-COMMON PROC-INIT

ATTACH ACCEPT sent TRACKING AREA UPDATE ACCEPT sent with GUTI TRACKING AREA UPDATE ACCEPT sent with TMSI GUTI REALLOCATION COMMAND sent

ATTACH COMPLETE received TRACKING AREA UPDATE COMPLETE received GUTI REALLOCATION COMPLETE received

Retransmission of the same message type, i.e. ATTACH ACCEPT,TRACKING AREA UPDATE ACCEPT or GUTI REALLOCATION COMMAND


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LTE Bible T3460

6s


AUTHENTICATION REQUEST sent SECURITY MODE COMMAND sent

AUTHENTICATION RESPONSE received AUTHENTICATION FAILURE received SECURITY MODE COMPLETE received SECURITY MODE REJECT received

Retransmission of the same message type, i.e.AUTHENTICATION REQUEST or SECURITY MODE COMMAND

T3470

6s


IDENTITY REQUEST sent

IDENTITY RESPONSE received

Retransmission of IDENTITY REQUEST

Mobile reachable

Default 4 min greater than T3412

All except EMM DEREGISTERED

Entering EMM-IDLE mode

NAS signalling connection established

Network dependent, but typically paging is halted on 1st expiry

Implicit detach timer

NOTE 3

All except EMM DEREGISTERED

The mobile reachable timer expires while the network is in EMM-IDLE mode

NAS signalling connection established

Implicitly detach the UE on 1st expiry

NOTE 1:

Typically, the procedures are aborted on the fifth expiry of the relevant timer. Exceptions are described in the corresponding procedure description.

NOTE 2:

The value of this timer is network dependent.

NOTE 3:

The value of this timer is network dependent. If ISR is activated, the default value of this timer is 4 minutes greater than T3423.


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18.

LTE Events

Event A1: “Serving becomes better than threshold”.

𝑴𝒆𝒂𝒔𝒔𝒆𝒓𝒗 − 𝑯𝒚𝒔𝒕 > 𝑻𝒉𝒓𝒆𝒔𝒉𝒐𝒍𝒅 Event A2: “Serving becomes worse than threshold”.

EventA4: “Neighbour becomes worse than threshold”

𝑴𝒆𝒂𝒔𝒏𝒃𝒓 + 𝑶𝒇𝒇𝒔𝒆𝒕𝒏𝒃𝒓 𝒇𝒓𝒆𝒒 + 𝑶𝒇𝒇𝒔𝒆𝒕𝒏𝒃𝒓 𝒄𝒆𝒍𝒍 − 𝑯𝒚𝒔𝒕 > 𝑻𝒉𝒓𝒆𝒔𝒉𝒐𝒍𝒅 Event A5: “Serving becomes worse than threshold1, and neighbour becomes better than threshold2”.

𝑴𝒆𝒂𝒔𝑺𝒆𝒓𝒗 + 𝑯𝒚𝒔𝒕 < 𝑻𝒉𝒓𝒆𝒔𝒉𝒐𝒍𝒅 Event A3: “Neighbour’s offset becomes better than serving”.

𝑴𝒆𝒂𝒔𝒔𝒆𝒓𝒗 + 𝑯𝒚𝒔𝒕 < 𝑻𝒉𝒓𝒆𝒔𝒉𝒐𝒍𝒅 𝟏 𝑴𝒆𝒂𝒔𝒏𝒃𝒓 + 𝑶𝒇𝒇𝒔𝒆𝒕𝒏𝒃𝒓 𝒇𝒓𝒆𝒒 + 𝑶𝒇𝒇𝒔𝒆𝒕𝒏𝒃𝒓 𝒄𝒆𝒍𝒍 − 𝑯𝒚𝒔𝒕 > 𝑻𝒉𝒓𝒆𝒔𝒉𝒐𝒍𝒅 𝟐

𝑴𝒆𝒂𝒔𝒏𝒃𝒓 + 𝑶𝒇𝒇𝒔𝒆𝒕𝒏𝒃𝒓 𝒇𝒓𝒆𝒒𝒖𝒆𝒏𝒄𝒚 + 𝑶𝒇𝒇𝒔𝒆𝒕𝒏𝒃𝒓 𝒄𝒆𝒍𝒍 − 𝑯𝒚𝒔𝒕 > 𝑴𝒆𝒂𝒔𝒔𝒆𝒓𝒗 + 𝑶𝒇𝒇𝒔𝒆𝒕𝒔𝒆𝒓𝒗 𝒇𝒓𝒆𝒒 + 𝑶𝒇𝒇𝒔𝒆𝒕𝒔𝒆𝒓𝒗 𝒄𝒆𝒍𝒍 + 𝑶𝒇𝒇𝒔𝒆𝒕

LTE Bible Event B1: “Inter RAT neighbour becomes better than threshold”.

Event B2: “Serving becomes worst than threshold1 and IRAT becomes better than threshold2”

𝑴𝒆𝒂𝒔𝒏𝒃𝒓 + 𝑶𝒇𝒇𝒔𝒆𝒕𝒏𝒃𝒓 𝒇𝒓𝒆𝒒 − 𝑯𝒚𝒔𝒕 > 𝑻𝒉𝒓𝒆𝒔𝒉𝒐𝒍𝒅 𝑴𝒆𝒂𝒔𝒔𝒓𝒗 + 𝑯𝒚𝒔𝒕 < 𝑻𝒉𝒓𝒆𝒔𝒉𝒐𝒍𝒅 𝟏 𝑴𝒆𝒂𝒔𝒏𝒃𝒓 + 𝑶𝒇𝒇𝒔𝒆𝒕𝒏𝒃𝒓 𝒇𝒓𝒆𝒒 − 𝑯𝒚𝒔𝒕 > 𝑻𝒉𝒓𝒆𝒔𝒉𝒐𝒍𝒅𝟐

- Value of Hysteresis is between 0 and 30dB. - Range of Offset for frequency specific and cell specific is -24dB to 24dB - Offset value is -30dB to +30dB


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19.

LTE Cell Reselection

Cell Reselection is a kind of mechanism to change cell after UE is camped on a cell and stay in IDLE mode. This is to let UE get connected to cell which has the best condition among all the cells to which the UE is allowed to camp on. But UE does not change cells randomly, it uses a set of pretty complicated criteria and algorithms for this reselection process. The details of these criteria andalgorithms will be described later but the high level guideline is as follows : 

First Level Criteria : Absolute Priority



Second Level Criteria : Radio Link Quality



Third Level Criteria : Cell Accessibility

When the UE is powered on, usually it goes on with the following sequence. i) Cell Detection/Search ii) Cell Selection iii) RACH and Completion of Registration iv) < In IDLE > v) Keep measuring RSRP/RSRQ for the cell it registered vi) if RSRP/RSRQ is very poor or undetectable, go to step i) for finding other cell if RSRP/RSRQ is measureable at least, it evaluate < Cell Reselection Criteria > perform Cell Reselection if the criteria is met or stay in the current cell if the criteria is not met Step vi) is the most complicated process going on during the idle stage and in this page I will mostly deal with < Cell Reselection Criteria >. Understanding this criteria is the most imporant thing in implementing and testing Cell Reselection.



How Cell Reselection Priority is determined ?

LTE Bible 

How to detect and reselect to another LTE cell while in LTE Cell (LTE to LTE Cell Reselction) ?



How to detect and reselect to LTE cell while in WCDMA (WCDMA to LTE Cell Reselction) ?



How to detect and reselect to WCDMA cell while in LTE (LTE to WCDMA Cell Reselction) ?

  o o 

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

 

A little bit detailed criteria can be described as follows and you will see ever further details after this. UE always have to measure frequecies and RAT with higher priority UE has to have to measure frequecies and RAT with lower priority in the following fashion UE has to perform intra-frequency measurement only when SrxLev of the serving cell <= SintraSearch UE has to perform lower or equal priority inter-frequency/InterRAT measurement only when SrxLev of the serving cell <= SnonintraSearch LTE cell reselection uses priority based levels. (These priorities can be specified in LTE SIB4,5,6,7 and RRC Connection Release). Priority 0 indicate the lowest priority and 7 indicate the highest priority. The priority cannot be same for WCDMA and LTE, meaning that it must be set differently for different RAT. Among the cell power and priority, which one plays more critical role in cell reselection ? Cell Power defines the minimum condition. Once the minimum condition is met, Priority plays more critical role. For example, let's assume that UE is now camped in WCDMA cell and detected a neighbouring LTE cell with higher priority than the serving WCDMA cell, UE will perform cell reselection to LTE cell as long as the LTE cell is above the minimum signal strength threshold. In the same logic, if a UE camped on LTE cell detected a neighbouring WCDMA cell with higher priority than the serving LTE cell, UE will perform cell reselection to WCDMA cell as long as the WCDMA cell is above the minimum signal strength threshold. WCDMA SIB19 specifies the LTE frequencies (EARFCN) and priorities. A maximum of 8 EARFCNs (4 FDD + 4 TDD) can be listed in SIB 19. For each EARFCN, you can configure a max 16 blacklisted cells. The blacklisted cell is the cell UE should not make reselection to. Using the eutraDetection parameter in SIB19, you can make UE to detect and display the presence of lower priority LTE frequencies while it is in WCDMA cell. LTE SIB6 specifies the WCDMA frequencies (DL ARFCN) and the parameters used for absolute priority based cell reselection.

How Cell Reselection Priority is determined ? There are roughly three different ways of informing UE of Reselection Priority as listed before : (refer to 36.304 5.2.4.1 Reselection priorities handling for details). i) System Information ii) RRC Connection Release message iii) Inheriting from another RAT Note 1 : if the priority is specified in both i) and ii), the one specified in ii) takes effect. Note 2 : The UE shall only perform cell reselection evaluation for E-UTRAN frequencies and inter-RAT frequencies that are given in system information and for which the UE has a priority provided. Note 3 : The UE shall not consider any black listed cells as candidate for cell reselection

How to detect and reselect to another LTE cell while in LTE Cell (LTE to LTE Cell Reselction) ? In order for UE to reselect from one LTE cell to another LTE Cell, the internal evaluation result in UE side (SrxLev and Squal) should meet a certain criteria, otherwise it may not even monitor (measure) neighboring cell and in result would not perform reselection. LTE SIB3 defines various parameter to influence the evaluation result and the expected UE side behavior is described in 36.304 5.2.4.2 Measurement rules for cell re-selection. If your device does not perform Cell Reselection, first Check if Cell Measurement Criteria is met and the © Farhatullah Mohammed

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LTE Bible check if Cell Reselection Criteria is met and also check if following condition is met (Following statement come from 36.304 5.2.4.1 Reselection Priority Handling. I saw some UE ignore this requirement but some UE strictly follows this requirement.) The UE shall only perform cell reselection evaluation for E-UTRAN frequencies and inter-RAT frequencies that are give in system information and for which the UE has a priority provided. If your UE strictly follow this requirement stated above, populate SIB4 for proper neighbour cells. Following is the contents of SIB3 for your reference (The parameter shown here is just an example. You have to set it properly based on your own test requirement) sib-TypeAndInfo item: sib3 (1) sib3 cellReselectionInfoCommon q-Hyst: dB0 (0) cellReselectionServingFreqInfo s-NonIntraSearch: 62dB (31) threshServingLow: 62dB (31) cellReselectionPriority: 7 intraFreqCellReselectionInfo q-RxLevMin: -140dBm (-70) s-IntraSearch: 62dB (31) .0.. .... presenceAntennaPort1: False neighCellConfig: Not all neighbour cells have the same MBSFN subframe allocation as serving cell (0) t-ReselectionEUTRA: 0s lateNonCriticalExtension: s-IntraSearch-v920 s-IntraSearchP-r9: 62dB (31) s-IntraSearchQ-r9: 0dB s-NonIntraSearch-v920 s-NonIntraSearchP-r9: 62dB (31) s-NonIntraSearchQ-r9: 0dB q-QualMin-r9: -34dB threshServingLowQ-r9: 0dB

< LTE to LTE Intra Frequency Measurement > If the serving cell's evaluation result is as follows, UE may not perform intra frequency measurement. SrxLev > S_IntraSearchP Squal > S_IntraSearchQ Note : If neither of S_IntraSearchP nor S_IntraSearchQ is specified, UE applies the default value (S_IntraSearchP = Infinity, S_IntraSearchQ = 0 based on 36.331) If the serving cell's evaluation result does NOT meet following criteria, UE perform intra frequency measurement. SrxLev > S_IntraSearchP Squal > S_IntraSearchQ Note : If neither of S_IntraSearchP nor S_IntraSearchQ is specified, UE applies the default value (S_IntraSearchP = Infinity, S_IntraSearchQ = 0 based on 36.331) < LTE to LTE NonIntra Frequency Measurement > © Farhatullah Mohammed

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LTE Bible If the serving cell's evaluation result is as follows, UE may not perform intra frequency measurement. SrxLev > S_NonIntraSearchP Squal > S_NonIntraSearchQ Note : If neither of S_IntraSearchP nor S_IntraSearchQ is specified, UE applies the default value (S_IntraSearchP = Infinity, S_IntraSearchQ = 0 based on 36.331) If the serving cell's evaluation result does NOT meet following criteria, UE perform intra frequency measurement. SrxLev > S_NonIntraSearchP Squal > S_NonIntraSearchQ Note : If neither of S_IntraSearchP nor S_IntraSearchQ is specified, UE applies the default value (S_IntraSearchP = Infinity, S_IntraSearchQ = 0 based on 36.331)

How to detect and reselect to LTE cell while in WCDMA (WCDMA to LTE Cell Reselction) ? UE must measure the LTE frequencies and detect the available LTE cell in order to perform cell reselection to LTE.     





UE measures two physical properties called for WCDMA signal. One is CPICH RSCP and CPICH EcNo. RSCP determines Srxlev and EcNo determines Squal. Srxlev = Qrxlevemeas - qRxLevMin. Qrxlevemeas is RSCP level measured by UE and qRxLevMin is the value specified in SIB. Squal = Qqualmeas - qQualMin. Qqualmeas is EcNo level measured by UE and qQualMin is the value specified in SIB. The detection measurement of LTE frequencies should be done at least once every 60s for higher priority LTE frequencies. In following condition, detection measurements of lower priority LTE frequency is not required. Srxlev > absPrioCellRes.sPrioritySearch1 Squal > absPrioCellRes.sPrioritySearch2 In following condition, UE should detect once every 30s for both lower and higher priority LTE frequencies Srxlev <= absPrioCellRes.sPrioritySearch1 Squal <= absPrioCellRes.sPrioritySearch2 The maximum number of LTE FDD Frequencies are 4. In this case, UE should have performed measurement for detecting LTE cells on all 4 LTE frequencies once every 240 (4 x 60) s or 120(4 x 30) s depending if UE measures above or below parameter threshold absPrioCellRes.sPrioritySearch1

How to detect and reselect to WCDMA cell while in LTE (LTE to WCDMA Cell Reselction)? Measurement Criteria (From High Priority LTE Cell to Lower Priority WCDMA Cell): When LTE cell has higher priority than WCDMA, it would stay in LTE cell but it performs measurement for the low priority WCDMA if UE is under the following condition : Srxlev of the serving cell < sNonIntraSearch (SIB3), If we express this using dB/dBm, Srxlev of the serving cell < (2 x sNonIntraSearch (SIB3)) where Srxlev = Qrxlevmeas - qRxLevMin (SIB3), If we express using dB/dBm, Srxlev = Qrxlevmeas [dBm] - (2 x qRxLevMin (SIB3)) [dBm] where Qrxlevemeas = measured RSRP level, qRxLevMin = minimum RSRP level for camping Measurement Criteria (From Lower Priority LTE Cell to Higher Priority WCDMA Cell): When LTE cell has lower priority than WCDMA (WCDMA cell priority defined in SIB6 is higher than the serving cell priority),The UE always have to perform measurements on WCDMA cell. How often UE has to © Farhatullah Mohammed

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LTE Bible measure for WCDMA depends on whether Srxlev of the serving cell is greater or lower than sNonIntraSearch(SIB3). If no parameter is set (meaning in default condition), detection of WCDMA cell should be performed at least every 60 seconds. Reselection Criteria (From High Priority LTE Cell to Lower Priority WCDMA Cell): If UE in LTE cell is under the following condition with the duration longer than tReselectionUtra (SIB6), it should reselect to WCDMA cell. Srxlev of LTE cell (serving cell) < threshServingLow (SIB3), where Srxlev = Qrxlevmeas - qRxLevMin (SIB3), where Qrxlevemeas = measured RSRP level, qRxLevMin = minimum RSRP level for camping Srxlev of WCDMA cell > threshXLowP (SIB6), where Srxlev = Qrxlevmeas - qRxLevMin (SIB3), If we express using dB/dBm, Srxlev = Qrxlevmeas [dBm] - (2 x qRxLevMin (SIB3)) [dBm] where Qrxlevemeas = measured RSCP level, qRxLevMin = minimum RSCP level for camping Note : If more than one WCDMA meet this condition, UE should select to the cell with highest Srxlev Note : If these values are not specified in SIB and UE has to apply default values, UE has to perform reselection when LTE RSRP is lower than -145 dBm and WCDMA cell is better than -119 dBm for at least 2 seconds. Reselection Criteria (From Lower Priority LTE Cell to Higher Priority WCDMA Cell): If UE in LTE cell is under the following condition with the duration longer than tReselectionUtra (SIB6), it should reselect to WCDMA cell. Srxlev of WCDMA cell > threshXHighP (SIB6), where Srxlev = Qrxlevmeas - qRxLevMin (SIB3), where Qrxlevemeas = measured RSCP level, qRxLevMin = minimum RSCP level for camping

Parameters related to Cell Reselection These parameters are defined in 36.304 5.2.4.7 Cell reselection parameters in system information broadcasts. Some of the important parameters and descriptions are as follows : ThreshXHighP : The threshold of target cell Srxlev to perfrom reselection from a low priority to a high priority cell. (i.e, a large ThreshXHigh value makes reselection harder) ThreshXLowP : The threshold of target cell Srxlev to perfrom reselection from a high priority to a low priority cell. (i.e, a large ThreshXLow value makes reselection harder) ThreshXHighQ : The threshold of target cell Squal to perfrom reselection from a low priority to a high priority cell. (i.e, a large ThreshXHigh value makes reselection harder) ThreshXLowQ : The threshold of target cell Squal to perfrom reselection from a high priority to a low priority cell. (i.e, a large ThreshXLow value makes reselection harder) SIntraSearchP : The threshold of current cell Srxlev to perform intra-frequency. If the current cell Srxleve is lower than this value, UE perform measurement for intra-frequency. SIntraSearchQ : The threshold of current cell Squal to perform intra-frequency. If the current cell Squal is lower than this value, UE perform measurement for intra-frequency. SnonIntraSearchP : The threshold of current cell Srxlev to perform inter-frequency or interRAT measurement. If the current cell Srxleve is lower than this value, UE perform measurement for inter-frequency or interRAT cells. © Farhatullah Mohammed

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LTE Bible SnonIntraSearchQ : The threshold of current cell Squal to perform inter-frequency or interRAT measurement. If the current cell Srqual is lower than this value, UE perform measurement for interfrequency or interRAT cells.


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LTE Bible

20. -

LTE Scheduling

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To provide efficient resource usage, the LTE concept supports fast scheduling where the resources on the shared channels PDSCH and PUSCH are assigned to the users and the radio bearers on sub-frame basis according to the users momentary traffic demand, QoS requirements and estimated channel quality. The ENodeB allocates the physical layer resources for the uplink and downlink shared channels (DLSCH and UL-SCH). The resources comprises of Physical Resource Blocks (PRB) and modulation coding Scheme(MCS). MCS determines the bit rate and thus the capacity of PRB. Allocations may be valid for one or more TTI. Scheduling is also referred to as Dynamic Resource Allocation (DRA) and is a part of RRM. Scheduling are classified into two  Downlink Scheduling and  Uplink Scheduling There is no LTE scheduling Algorithm defined by standard, this enables the vendors to differentiate between each other and use different optimization goals. The parameters used as input for the scheduling decisions are the Channel Quality Indicator(CQI) reported by the UE, QoS , congestion/resource situation, fairness, charging policies and so on. With most schedulers aim to maximize the cell throughput under the consideration of fairness metrics between cell edge users and users with very good channel conditions. Downlink Scheduling with HARQ

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ACK/NACK PROCESS IN DOWNLINK SCHEDULING

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LTE UL scheduling is similar to downlink scheduling although UL scheduler is unique entity.

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LTE Bible -

UL scheduling grants are indicated by UE transmitting all the relevant UL scheduling information with in PDCCH. This is done by using dedicated DCI, DCI type 0 scrambled with RNTI. This does not apply incase of power saving mode DRX mode enabled, which switches of UE receiver periodically.

-

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UL resources are allocated using without designated PDCCH UL grant in case of SPS or for nonadaptive HARQ retransmissions. Non adaptive HARQ transmission is triggered by the transmission of negative acknowledgement (NACK) by UE. In UL, only localized scheduling is allowed, which means that an integer number of consecutive Resource Blocks is allocated to one UE. There is only one scheduling process per UE, there is not a dedicated scheduling process per radio bearer. UE feeds the scheduler with CQI, Buffer status Reports (BSR), ACK/NACK and scheduling Requests (SR). BSR indicate the current fill level status of the current transmit buffer.

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LTE Bible

20.1 -

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Uplink Scheduling

The functions of the uplink scheduler is similar to the downlink scheduler, for each 1ms interval, which terminals are used to transmit and on which uplink resources. The basis for uplink scheduling is scheduling grants, containing the scheduling decision and providing the terminal information about the resources and the associated transport format for the use of ULSCH on one component carrier. Only if the terminal or ue has a valid grant, it is allowed to transmit on the corresponding UL-SCH, however autonomous transmissions are not possible without a corresponding grant. Dynamic grant are valid for one subframe – for each subframe in which the terminal is to transmit on the UL-SCH, the scheduler issues new grant. Uplink component carriers are scheduled independently, if the terminal is to transmit simultaneously on multiple component carriers, multiple scheduling grants are required.

Figure: Timing relations for Uplink Grants in TDD and FDD frame configuration #0 and #1. For FDD, the grant timing is straight forward. An uplink grant received in the sub-frame n triggers an uplink transmission in the sub-frame n+4. This is the same timing relation as used by uplink retransmission triggered by PHICH. For TDD, the situation is different. Here the sub-frame n+4 may not be uplink sub-frame. Therefore for TDD configurations #1 – 6, the timing relation is modified in such a way that the uplink transmission occurs in the sub-frame n+k, where k is the smallest value larger than or equal to 4 such that the subframe n+k is the uplink subframe. This requires some processing time for the terminal as in the case of FDD, the delay is minimized from the receipt of the uplink grant to the actual transmission. This implies that the time between the grant receipt and the uplink transmission may differ between two subframes. Another downlink heavy configurations 1 – 5, the property is that the uplink scheduling grants can only be received on some of the downlink subframes. In TDD configuration #0, there are more uplink sub-frames than downlinkn subframes, which has the possibility to schedule transmissions in multiple uplink subframes from a single downlink sub-frame. Similar to downlink case, the uplink scheduler can exploit information about the channel conditions, buffer status and priorities of the different data flows, and if some form of interference coordination is employed in the neighbouring cells interference.


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LTE Bible Persistent Scheduling -

There are a couple of Data Transmission Scheduling Scheme in LTE. The most simple in terms of algorithm would be the persisent scheduling. In this scheduling mode, Network send 'Grant' in DCI Format 0 for every subframe.

i) Network send the first data on DL PDSCH and PDCCH which has DCI format 1 for DL Data Decoding and DCI format 0 for UL Grant. (If there is no downlink data to be transmitted, network transmits only DPCCH with DCI format 0 without any DPSCH data) ii) UE decode PCFICH to figure CFI value. iii) UE decode PDCCH and get the information on DCI format 1 iv) Based on DCI format 1, UE decode DL data. v) UE decode the information on DCI format 0 from PDCCH vi) UE send ACK/NAK for DL data through UCI (UCI will be carried by PUCCH) vii) UE check the Grant field. viii) If Grant is allowed, UE transmit the uplink data through PUSCH ix) Network decode PUSCH data and send ACK/NACK via PHICH x) UE decode PHICH and retransmit the data if PHICH carries NACK - Overall flow can be illustrated as follows. This diagram would not show all the details but give you the big picture for the procedure.

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For detailed data structure of DCI Format 0, refer to TS 36.212 section "5.3.3.1.1 Format 0" The process listed above is in reality a pretty complicated process and need a lot of troubleshoot and debugging. So in case of development and testing phase, we normally break down this process into multiple simple/small procedure and verifies it step by step.


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LTE Bible Step 1 : DL data reception and no ACK/NACK transmission == a) Network send PDCCH and PDSCH data b) See if UE properly decode PDSCH data This would seem to be very simple two step process, but to make this happen UE is capable of doing step ii), iii), iv) described above. Step 2 : DCI format 0 reception == a) Network send DCI Format 0(UL Grant) without PDSCH transmission b) See if UE properly decode DCI Format 0 (You need to make it sure that Resource allocation that UE decoded matches with DCI format 0 sent by network.) Step 3 : PUSCH transmission based on DCI format 0 == a) Network send DCI Format 0(UL Grant) without PDSCH transmission b) UE transmit UL Data on PUSCH c) Network decode PUSCH data d) see if the data decoded at Network side maches what UE transmit To make this happen, UL DMRS for PUSCH should have been properly implemented and you have to make it sure that UE transmit the PUSCH data on the RBs that DCI format 0 specified. Step 4 : DL data reception and ACK/NACK transmission == a) Network send PDCCH and PDSCH data b) UE decode PDSCH data c) UE has to transmit ACK/NACK accordingly Step 5 : UL data transmission and ACK/NACK reception == a) Network send DCI Format 0(UL Grant) without PDSCH transmission b) UE transmit UL Data on PUSCH c) Network decode PUSCH data d) Network send ACK/NACK on PHICH e) UE has to decode ACK/NACK properly f) UE has to retransmit the data if it gets NACK Non Persistent Scheduling -

In Persistent Scheduling mode, UE can send the data to Network anytime since Network is sending UL Grant all the time. But what if Network does not send UL Grant all the time ? In this case, UE has ASK the network to send UL Grant (DCI 0). If network send UL Grant, then UE can send UL data as allowed by the UL Grant. 80 © Farhatullah Mohammed

LTE Bible - Overall procedure is as follows : i) UE send SR (Scehduling Request) on PUCCH ii) Network send UL Grant (DCI 0) on PDCCH iii) UE decode DCI 0 and transmit PUSCH based on the RBs specified by DCI 0 iv) Network decode the PUSCH v) Network send ACK/NACK on PHICH vi) If Network send NACK, go to [Retransmission] Procedure ( For the details of [Retransmission] process, refer to HARQ Process page)


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20.2 -

-

-

-

Uplink Priority Handling

Multiple logical channels of different priorities can be multiplexed into the same transport block using the same MAC multiplexing functionality in the downlink. Unlike the scheduling in downlink, where the prioritization is under the control of the scheduler and upto the implementation, the Uplink multiplexing is done according to set of well defined rules in the terminal as a scheduling grant applies to a specific uplink carrier of a terminal and not specific to the radio bearer within the terminal. Using the radio bearer specific scheduling grants would increase the control signalling overhead in the downlink and hence per-terminal scheduling is used in LTE. Here the simplest multiplexing rule would be to serve the logical channels in strict priority. This may result in the starvation of low-priority channels, as all the resources would be given to higher priority channels until the transmission buffer is empty. However, the operators would like to provide atleast some throughput for low priority services as well, therefore each logical channel in LTE terminal, a prioritized data rate value is configured in addition to the priority values. The logical channels are then served in decreasing priority order upto their prioritized data rate which avoids the starvation as long as the scheduled data rate is atleast as large as the sum of prioritized data rates. Beyond the prioritized data rates, the channels are served in stricty priority until the grant is fully exploited or the buffer is empty.


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20.3

Scheduling Requests

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The scheduler needs the information about the data awaiting transmission from the terminals to assign the proper amount of uplink resources.

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There is no need to provide uplink resources to the terminals with no data to transmit as this would only result in the terminal performing padding to fill up the granted resources.

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Therefore the scheduler needs to know whether the terminal has a data to transm it and should be given a grant, known as Scheduling Request .

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Scheduling Request is a simple flag raised by the terminal to request uplink resources from the uplink scheduler.

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If the terminal requesting resources has no data to transmit on PUSCH, the Scheduling request is made on PUCCH.

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Each terminal is assigned dedicated PUCCH every nth sub-frame.

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With the dedicated scheduling mechanism there is no need to provide the identity of the terminal requesting to be scheduled as the identity of the terminal is implicitly known from the resources upon which the request is being transmitted. When the data with higher priority is existing in the transmit buffers and new data arrives at the terminal and the terminal has no grant and hence cannot transmit the data, the terminal transmits a scheduling request at the next possible instant.

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Figure: Scheduling Request transmission


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20.4 -

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Selective Scheduling

In LTE, both frequency selective and non selective scheduling are supported in uplink. Frequency selective scheduling is based on the eNodeB exploiting the available channel knowledge to schedule UE to transmit specific RB in frequency domain, where UE experience good channel conditions. In non frequency selective scheduling, UE does not make use of specific channel knowledge but aims to benefit from frequency diversity during the transmission of each transport block. FREQUENCY SELECTIVE SCHEDULING:

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-

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In frequency selective scheduling, the same localized allocation of the transmission resources is typically used in both slots of the sub frame. There is no frequency hopping during the subframe. The MCS and frequency domain RB allocation are chosen based on the location and quality of the above average gain in the uplink channel response. Frequency Selective scheduling required timely channel quality information at eNodeB which is done by SRS. The performance of frequency selective scheduling using the SRS depends on the sounding bandwidth and the quality of the channel estimate – which is a function of transmitted power spectral density used for SRS. With the large sounding bandwidth, link quality can be evaluated on large number of RBs. This can lead to SRS being transmitted at a lower power density, due to limited UE transmit power which reduces the estimate for each RB within the sounding bandwidth especially for cell edge UE. If a sounding smaller bandwidth can improve channel estimation on the sounded RBs can result missing channel information for certain parts of channel bandwidth, thus risking the exclusion of best quality RBs.

FREQUENCY DIVERSE OR NON-SELECTIVE SCHEDULING: -

-

Due to the limited or absence of frequency specific channel quality information, due to high Doppler effect, it is preferable to exploit the frequency diversity of LTE wideband channel. In LTE, frequency hopping of a localized transmission in used to the provide frequency diversity. Two hopping modes are supported here- hopping between the subframes (inter-subframe hopping) and hopping both between and within subframes (inter and intra subframes hopping). Intra-subframe hopping: Frequency hop occurs at the slot boundary in the middle of the subframe; this provides frequency diversity within a codeword (within a single transmission of transport block). Inter-Subframe hopping: It provides frequency diversity between HARQ retransmission of a transport block as a frequency allocation hops every allocated subframe. Signalling the frequency hop via the uplink resource grant can be used for the frequency semi selective scheduling in which the frequency resource is assigned selectively for the first slot of a subframe and frequency diversity is also achieved by hopping to a different frequency in the second slot.


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21.

LTE Modulation

Channel Quality Index: -

CQI is an entity reported by UE to eNodeB UE indicates modulation scheme and coding scheme to eNodeB. Range of CQI is 0 to 15. CQI is based on PMI(Precoding Matrix Indicator) and RI (Rank Indicator) It is used to demodulate the data in downlink with maximum block error rate of 10%. Higher CQI value, higher the modulation scheme (QPSK to 64 QAM) and higher coding rate is used by eNodeB.

What is Link Adaptation? Link adaptation is the ability to adapt the modulation scheme and the coding rate of the error correction according to the quality of radio link. If the condition of the radio link are good, high level efficient modulation scheme and small amount of error correction is used.

Rank Indication: -

When UE is experiencing bad SINR, it is difficult to decode transmitted downlink data. Reported by UE to eNB as RI 1 or RI2. Rank indication acts as input to eNodeB. When SINR is good RI 2 is used. In transmission mode 3 (OL-SM) for UE, if UE reports RI=1; eNodeB starts sending data in Transmit diversity mode. If RI=2 is reported by UE, eNodeB sends the data in MIMO mode for TM-3.

Precoding Matrix Indicator (PMI): -

UE reports which precoding matrix should be used for downlink transmission which is determined by R1. R1 and PMI can be configured to support MIMO operation for CL-SM and OL-SM SM. Periodic CQI reporting can be done on PUCCH and PUSCH and could be 2ms.


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22.

Modulation Coding Scheme

SINR VS MODULATION RELATION


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23.

Carrier Aggregation

Carrier Aggregation in LTE (CA): Carrier Aggregation is a cost effective way to utilize the fragmented spectrum spread across different or same bands in order to improve end user experience. -

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In CA, throughput is increased by sending data simultaneously over two carriers. Regular cell is known as Primary cell (PCell) and is combined with the logical cell (SCell) serving the same cell site. Each aggregated carrier is called as component carrier. CC. The PCell is the main carrier with which UE will communicate i.e. RRC/NAS messages exchange, measurement, RACH etc. PCell always remains active in RRC Connected mode while SCell is activated/deactivated whenever required e.g. when high throughput is required. PCell has PDCCH in downlink and PUCCH in uplink but SCell has only PDCCH in downlink 'RRC Connection Reconfiguration' procedure is used to add/remove SCell

Intra-Band Contiguous CA When two or more component carriers belong to same frequency band and they are contiguous. There must be spacing of 300 khz x N between two contiguous component carriers (N is integer). This is the simplest form of CA aggregation from operators perspective

Intra-Band Non-Contiguous CA When two or more component carriers belong to same frequency band but they are separated by one or more frequency gaps

Inter-Band Non-Contiguous CA When two or more component carriers belong to different frequency bands. This type of CA is implemented by operators who own fragmented spectrum


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LTE Bible Carrier Aggregation (CA): - LTE Release 10 Feature. - Known as LTE Advance. - DL Speeds upto 1 Gbps and UL Speeds upto 500Mbps. - Backward Compatibility with Rel 8 and Rel 9. - Can be used for both FDD and TDD. - The component carrier can have a bandwidth of 1.4, 3, 5, 10, 15 or 20 MHz. - A maximum of 5 Component Carriers(CC) can be aggregated. - The maximum aggregated bandwidth is 100 MHz. - Each component carrier is treated as an R8 carrier. - The spacing between center frequencies of contiguously aggregated component carriers will be a multiple of 300 kHz to be compatible with the 100 kHz frequency raster of Release 8/9 and at the same time preserve orthogonality of the subcarriers, which have 15 kHz spacing. - For non-contiguous cases the CCs are separated by one, or more, frequency gap(s). PCell and SCell : - The Cell UE selects during initial establishment (RRC Connection Request/RRC Connection Reestablishement Request) will become the PCell. - eNodeB can add / delete Scell(s) using RRC Connection Reconfiguration message.

PCell Vs SCell: - PCell always have both Uplink(UL) and Downlink(DL). Scell always have DL (While activated) but may or may not have UL. - PCell is always activated whereas SCell has to be activated or deactivated using MAC-CE. - UE does not required to acquire System Information and decode Paging from SCell. - For Scell SI is passed to UE while adding the Scell. © Farhatullah Mohammed

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LTE Bible - When an Scell is added using RRC Connection Reconfiguration Message it remains in the deactivated state till it is activated using MAC-CE. - If Scell activation/deactivation MAC-CE is received on Subframe n the Scell is activated/deactivated on Subframe n+24 or n+34.(TS 36.133 Section 7.7.2) - When sCellDeactivationTimer expires then Scell is deactivated. - Once Scell is deactivated - PDCCH on Scell and PDCCH for Scell is not monitored. - PUSCH is not transmitted and PDSCH is not received. - The SRS is not transmitted. - The CQI/PMI/RI for Scell is not reported. Activation/Deactivation MAC-CE: - The MAC-CE can activate and deactivate Scell(s) which is already configured using RRC Connection Reconfiguration Meassage. - Control Element is identified by a MAC PDU subheader with LCID. . Values of LCID for DL-SCH

Index

LCID values

11011

Activation/Deactivation

- fixed size and consists of a single octet containing seven C-fields and one R-field.

Activation/Deactivation MAC control element

- The Ci field is set to "1" to indicate that the SCell with SCellIndex i shall be activated. - The Ci field is set to "0" to indicate thatthe SCell with SCellIndex i shall be deactivated. - R: Reserved bit, set to “0”. Pcell and Scell Concepts: - Pcell can be changed using RRC Connection Reconfiguration With MobilityControlInfo i.e. Handover. - Scell can be changed using RRC Connection Reconfiguration message. - During Radio Link Failure, the Scell is release first before initiating RRC Connection Reestablishment procedure. - On receiving Handover Command i.e. RRC Connection Reconfiguration With MobilityControlInfo, © Farhatullah Mohammed

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LTE Bible UE deactivates the Scell, if configured. - TTI Bundling is not supported when configured with one or more Scell with Configured Uplink. - The RSRP and RSRQ measurement for Pcell shall follow time domain measurement resource restriction in accordance with measSubframePatternPCell, if configured.

Cross Carrier Scheduling(CCS): - Downlink Scheduling or Uplink Grant information of One Component Carrier(CC) can be carried by the PDCCH of another Component Carrier(CC). - 3 bit CIF field indicates target CC. - Pcell shall always be scheduled by Pcell only. © Farhatullah Mohammed

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LTE Bible - Scell can be cross scheduled by Pcell or by other Scell. - UE indicates whether it supports CCS or not. - Cross Carrier Scheduling is not applicable for PDCCH order. It is transmitted on Pcell. - CCS is applicable for aperiodic SRS transmission.

- The cif-Presence-r10 in physicalConfigDedicated indicates whether CIF will be present in PDCCH of Pcell. - The RadioResourceConfigDedicatedSCell-r10.PhysicalConfigDedicatedSCellr10.CrossCarrierSchedulingConfig-r10 indicates CCS status of Scell.

- cif-Presence indicates whether carrier indicator field is present (value TRUE) or not (value FALSE) in PDCCH DCI formats. - pdsch-Start indicates the starting OFDM symbol of PDSCH for the concerned SCell. Values 1, 2, 3 are applicable when dl-Bandwidth for the concerned SCell is greater than 10 resource blocks, values 2, 3, 4 are applicable when dl-Bandwidth for the concerned SCell is less than or equal to 10 resource blocks. - schedulingCellId Indicates which cell signals the downlink allocations and uplink grants, if applicable, for the concerned SCell.(When Scell cross scheduled other Scell.) - The other-r10.schedulingCellId-r10 and cif-Presence-r10 of that cell should be consistent. © Farhatullah Mohammed

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Carrier Aggregation and Measurement Events: - Definition of Serving Cell Measurement is Modified. - For Event A1 and Event A2 The Carrier Frequency in Measurement Object indicates whether this event is for Pcell or any Scell. - The eNodeB shall configure separate A1/A2 events for each serving cell. - Event A3 - Neighbor becomes offset better than Pcell. - Event A5 - Pcell becomes worse than theshold1 and neighbour becomes better than threshold2. - For Event A3 and Event A5 the frequency mentioned in the associated measObjectEUTRA indicates neighbours. - For Event A3 and Event A5 the Scell become neighbouring cell. - Event B2 - Pcell becomes worse than theshold1 and inter RAT neighbour becomes better than threshold2. - Event A6 - Intra Frequency Neighbour becomes offset better than Scell. - No change in the definition of Event A4 and Event B1.

Carrier Aggregation and Periodic Measurement: - If (Purpose == reportStrongestCells && reportAmount > 1) UE initiates a first MR immediately after the quantity to be reported becomes available for the Pcell. - If (Purpose == reportStrongestCells && reportAmount == 1) UE initiates a first MR immediately after the quantity to be reported becomes available for the Pcell and for the strongest cell among the applicable cells. - If (Purpose == reportStrongestCellsForSON) UE initiates a first MR when it has determined the strongest cells on the associated frequency.

Carrier Aggregation and Measurement Gap: - UE shall be able to carry out Measurement on any serving frequency without measurement gap i.e. intra-frequency measurement for any serving frequency. - UE may required measurement gap to perform inter-frequency or inter-RAT measurement.


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LTE Bible Typical CA Call Flow:


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24.

Cell Search

Cell Search In LTE : - eNodeB broadcasts Primary Synchronization Signal (PSS) and Secondary Synchronization Signal (SSS) to help UE with the Cell Search Process and Cell Id detection. - There is total 504 Cell Ids (0 - 503) defined in LTE. - These 504 Cell IDs are grouped in 168 Physical Layer Cell Identity Group. - Each Physical Layer Cell Identity Group Consists of 3 Physical Layer Cell Identity. - PSS and SSS is transmitted using central 62 sub carriers around the DC. The 5 REs above and below the Synchronization Signals are not used for transmission, i.e. they represents DTX periods. Primary Synchronization Signal (PSS): - PSS is allocated to Central 62 subcarriers. - Belonging to the "Last Symbol" of slot 0 and slot 10 of every radio frame. - So PSS is transmitted twice every 10 ms. - Both Transmissions are Identical. - PSS is used for : - Achieve SYMBOL, SLOT, and SUBFRAME synchronization. - Determine the Physical Layer Cell Identity (PCI) within the Physical Layer Cell Identity Group. - There are 3 Physical Layer Cell Identity in each Group So PSS is generated using 1 of 3 different Sequences. Secondary Synchronization Signal (SSS): - SSS is allocated to Central 62 subcarriers. - Belonging to the "Second Last Symbol" of slot 0 and slot 10 of every radio frame. - So SSS is also transmitted twice every 10 ms. - The 2 SSS transmissions within each radio frame use Different Sequences. - This is to allow UE to differentiate between the 1st and 2nd transmission. - This helps UE to determine the starting of each radio frame, i.e. to achive the Frame Synchronization. - SSS is used for : - Achieve FRAME synchronization. - Determine the Physical Layer Cell Identity Group. - There are 168 Physical Layer Cell Identity Group So SSS is generated using 1 of 168 different pairs of Sequences. Cell Id Identification: - Once UE read the PSS and SSS, UE will be able to get the Cell ID from the Physical Layer Cell Identity and Physical Layer Cell Identity Group. - Cell ID = 3 * Physical Layer Cell Identity Group + Physical Layer Cell Identity.


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25.

Cell Selection

The term 'Cell Selection Criterion' may be a vague expression, since there can be many different criteria from many different perspective. In broad sense, cell selection would be influenced by following factors. i) Is the cell transmitting power strong enough to be recognized/detected by the UE ? (Signal Strength/Quality Criteria) ii) Is the PLMN of the cell acceptable to the UE ? (PLMN selection criteria) iii) Is the service type of the cell acceptable to the UE ? (Service Type criteria) But in most of the situation when we say "Cell Selection Criteria", it is likely to say the first criteria (Signal Strength/Quality Criteria). This signal quality criterion as descrbed in 36.304 as follows. According to this criterion, UE would not start registration even though it sucessfully detected a cell and even decoded MIB and SIBs unless the Srxleve > 0 and Squal > 0. So if a device does not even initiate the PRACH process even when it successfully decoded all the MIB and SIBs, checking on this criteria would be a good first step for the troubleshooting. (Of course, this is not the only issues for this case. there may be USIM issue and Band Indicator Issue, PLMN issues etc).


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LTE Bible Out of the variables used in the equation, only Qrxlevmeas and Qqualmeas is the value UE really measures when it turns on and most of other parameters are determined by a specific SIB (SIB1 in LTE case) or calculated by some other predefined values. Following is the part of LTE SIB1 which is related to Cell Selection Criterion and Cell Selection Procedure. Following is overall information and functionality of SIB1 information element. – Q-RxLevMin The IE Q-RxLevMin is used to indicate for cell re-selection the required minimum received RSRP level in the (EUTRA)cell. Corresponds to parameter Qrxlevmin in 36.304 [4]. Actual value Qrxlevmin = IE value * 2 [dBm].

q-RxLevMinOffset

Parameter Qrxlevminoffset in 36.304 [4]. Actual value Qrxlevminoffset = IE value * 2 [dB]. If absent, apply the (default) value of 0 [dB] for Qrxlevminoffset. Affects the minimum required Rx level in the cell.

In summary, the cell selection criteria (Signal Strength/Quality Criteria) can be illustrated as follows.


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26.

Channels

The information flows between the different protocols are known as channels and signals. LTE uses several different types of logical, transport and physical channel, which are distinguished by the kind of information they carry and by the way in which the information is processed. 

Logical Channels: : Define whattype of information is transmitted over the air, e.g. traffic channels, control channels, system broadcast, etc. Data and signalling messages are carried on logical channels between the RLC and MAC protocols.



Transport Channels: Define howis something transmitted over the air, e.g. what are encoding, interleaving options used to transmit data. Data and signalling messages are carried on transport channels between the MAC and the physical layer.



Physical Channels: Define whereis something transmitted over the air, e.g. first N symbols in the DL frame. Data and signalling messages are carried on physical channels between the different levels of the physical layer.


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27.

Master Information Block

- Master information block is one of the important message that is broadcasted by LTE eNodeB irrespective of any user presence. - MIB is first among other system information blocks which are broadcasted by eNodeB. - MIB is transmitted using physical layer channel PBCH or Physical Broadcast channel on downlink. - MIB is 24 bit information with the following information within, - System Bandwidth (3bits) - PHICH Information (3bits) [ Configuration]  1 bit to indicate normal PHICH or extended PHICH  2 bits to indicate PHICH Ng Value. - System Frame number (8 bits) - Reserved for future use (10 bits) - Apart from information in the payload, MIB CRC also conveys number of transmit antennas used by eNodeB. - MIB CRC is scrambled or XORed with an antenna specific mask. -


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System Information Blocks

SYSTEM INFORMATION BROADCASTS [SIB] SIBs carry relevant information for UE which helps to access the cell, perform cell reselection, information related to Intra, Inter frequency and Inter RATcell selections. There are 13 types of SIBs. All SIBs are transmitted on BCCH, DL-SCH and PDSCH. -

SIB 1: Cell access related parameters and scheduling of SIB. SIB 2: Common and shared channels configuration, RACH related configuration are present. SIB 3: Parameters related to intra frequency, inter frequency and IRAT Cell Reselections. SIB 4: Information regarding INTRA frequency neighbour cells. SIB 5: Information regarding INTER frequency neighbour cells. SIB 6: Information about UTRAN Cell reselection SIB 7: Information about GERAN cell reselection SIB 8 : Information about CDMA Cell reselection. SIB 9: Information about Home cell (Femto cell) SIB 10: ETWS (earth quake & Tsunami warning system) primary notification SIB 11: ETWS (Earth quake and TSUNAMI warning system) Secondary notification. SIB 12: CMAS – Commercial Mobile Alert service SIB 13: Contains information required to acquire MBMS control information associated with one or more MBSFN areas.


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LTE Bible SIB 1:


Cell Access and scheduling of other system info

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LTE Bible SIB 2:


Radio Resource Configuration Information

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LTE Bible SIB 3:

Cell Reselection Parameters for INTRA, INTER Freq& Inter RAT


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LTE Bible SIB 4:

SIB 5:

Cell Reselection Parameters for Neighbouring INTRA Frequency

Cell Reselection Parameters for INTER Frequency


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LTE Bible SIB 6:

SIB 7:

Cell Reselection Parameters for INTER RAT(UTRAN) Frequency

Cell Reselection Parameters for INTER RAT(GERAN) Frequency

SIB 8:

CDMA 2000 CELL RESELECTION PARAMETERS

SIB 9:

HOME ENODEB NAME


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LTE Bible SIB 10:

ETWS PRIMARY NOTIFICATION

SIB 11:

ETWS SECONDARY NOTIFICATION


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LTE Bible SIB 12:

SIB 13:


CMAS NOTIFICATION

MBMS CONTROL INFORMATION

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29.

S1 Interface Procedures

CLASS 1 PROCEDURES: SENDER EXPECTS RESPONSE FROM THE RECEIVER ELEMENTARY PROCEDURE Handover Preparation Handover Resource Allocation Path Switch Request Handover Cancellation ERAB Setup ERAB Modify ERAB Release Initial Context Setup Reset S1 Setup UE Context Release UE Context Modification eNB Configuration update MME Configuration update Write Replace warning

INITIATING MESSAGE

SUCCESSFUL OUTCOME RESPONSE MESSAGE

HANDOVER REQUIRED

HANDOVER COMMAND HANDOVER REQUEST ACKNOWLEDGE PATH SWITCH REQUEST ACKNOWLEDGE HANDOVER CANCEL ACKNOWLEDGE ERAB SETUP RESPONSE ERAB MODIFY RESPONSE

HANDOVER REQUEST PATH SWITCH REQUEST HANDOVER CANCEL ERAB SETUP REQUEST ERAB MODIFY REQUEST ERAB RELEASE COMMAND INITIAL CONTEXT SETUP REQUEST RESET S1 SETUP REQUEST UE CONTEXT RELEASE COMMAND UE CONTEXT MODIFICATION REQUEST ENB CONFIGURATION UPDATE MME CONFIGURATION UPDATE WRITE PLACE WARNING REQUEST


ERAB RELEASE RESPONSE INITIAL CONTEXT SETUP RESPONSE RESET ACKNOWLEDGE S1 SETUP RESPONSE UE CONTEXT RELEASE COMPLETE UE CONTEXT MODIFICATION RESPONSE ENB UPDATE CONFIGURATION ACKNOWLEDGE MME CONFGURATION UPDATE ACKNOWLEDGE WRITE-REPLACE WARNING RESPONSE

UNSUCCESSFUL OUTCOME RESPONSE MESSAGE HANDOVER PREPARATION FAILURE HANDOVER FAILURE PATH SWITCH REQUEST FAILURE

INITIAL CONTEXT SETUP FAILURE S1 SETUP FAILURE

UE CONTEXT MODIFICATION FAILURE ENB CONFIGURATION UPDATE FAILURE MME CONFIGURATION UPDATE FAILURE

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LTE Bible CLASS 2 PROCEDURES: “SENDER DOES NOT EXPECTS RESPONSE FROM THE RECEIVER” ELEMENTARY PROCEDURES

MESSAGE

HANDOVER NOTIFICATION ERAB RELEASE REQUEST PAGING INITIAL UE MESSAGE DOWNLINK NAS TRANSPORT UPLINK NAS TRANSPORT NAS NON DELIVERY NOTIFICATION ERROR INDICATION UE CONTEXT RELEASE REQUEST DOWNLINK S1 CDMA 2000 TUNNELING UPLINK S1 CDMA 2000 TUNNELING UE CAPABILITY INFO INDICATION ENB STATUS TRANSFER MME STATUS TRANSFER DEACTIVATE TRACE TRACE START TRACE FAILURE INDICATION LOCATION REPORTING CONTROL LOCATION REPORTING FAILURE INDICATION LOCATION REPORT OVERLOAD START OVERLOAD STOP ENB DIRECT INFORMATION TRANSFER MME DIRECT INFORMATION TRANSFER ENB CONFIGURATION TRANSFER MME CONFIGURATION TRANSFER CELL TRAFFIC TRACE

HANDOVER NOTIFY ERAB RELEASE REQUEST PAGING INITIAL UE MESSAGE DOWNLINK NAS TRANSPORT UPLINK NAS TRANSPORT NAS NON DELIVERY INDICATION ERROR INDICATION UE CONTEXT RELEASE REQUEST DOWNLINK S1 CDMA TUNNELLING UPLINK S1 CDMA 2000 TUNNELING UE CAPABILITY INFO INDICATION ENB STATUS TRANSFER MME STATUS TRANSFER DEACTIVATE TRACE TRACE START TRACE FAILURE INDICATION LOCATION REPORTING CONTROL LOCATION REPORTING FAILURE INDICATION LOCATION REPORT OVERLOAD START OVERLOAD STOP ENB DIRECT INFORMATION TRANSFER MME DIRECT INFORMATION TRANSFER ENB CONFIGURATION TRANSFER MME CONFIGURATION TRANSFER CELL TRAFFIC TRACE


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30.

X2 Interface Procedures

CLASS 1 PROCEDURE:

INITIATING MESSAGE

ELEMENTARY PROCEDURE

HANDOVER PREPARATION RESET X2 SETUP ENB CONFIGURATION UPDATE RESOURCE STATUS REPORTING INITIATION

HANDOVER REQUEST RESET REQUEST X2 SETUP REQUEST ENB CONFIGURATION UPDATE RESOURCE STATUS REQUEST

SUCCESSFUL OUTCOME RESPONSE MESSAGE HANDOVER REQUEST ACKNOWLEDGE RESET RESPONSE X2 SETUP REQUEST RESPONSE ENB CONFIGURATION UPDATE ACKNOWLEDGE RESOURCE STATUS RESPONSE

UNSUCCESSFUL OUTCOME RESPONSE MESSAGE HANDOVER PREPARATION FAILURE X2 SETUP FAILURE ENB CONFIGURATION UPDATE FAILURE RESOURCE STATUS FAILURE

CLASS 2: PROCEDURES

ELEMENTARY PROCEDURES

MESSAGE

LOAD INDICATION HANDOVER CANCEL SN STATUS TRANSFER UE CONTEXT RELEASE RESOURCE STATUS REPORTING ERROR INDICATION

LOAD INFORMATION HANDOVER CANCEL SN STATUS TRANSFER UE CONTEXT RELEASE RESOURCE STATUS UPDATE ERROR INDICATION


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31.

SIB SCHEDULING

SIB Scheduling In LTE, MIB, SIB1, SIB2 is mandated to be transmitted for any cells. Since many of the SIB are transmitted, it should be transmitted in such a way that the location (subframe) where a SIB is transmitted should not be the same subframe where another SIB is transmitted.

Overall SIB Scheduling concept is as follows. As you see i) MIB is transmitted at a fixed cycles (every 4 frames starting from SFN 0) ii) SIB1 is also transmitted at the fixed cycles (every 8 frames starting from SFN 0). iii) All other SIB are being transmitted at the cycles specified by SIB scheduling information elements in SIB1

You may notice that LTE SIB1 is very similar to WCDMA MIB. Especially at initial test case development, you have to be very careful about item iii). If you set this value incorrectly, all the other SIBs will not be decoded by UE. It means, even though all the


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LTE Bible SIB is being transmitted UE would be trying to decode them at the wrong timing. And as a result, UE would not recognize the cell and show "No Service" message.

According to 36.331 section 5.2.1.2, the MIB scheduling is as follows : The MIB uses a fixed schedule with a periodicity of 40 ms and repetitions made within 40 ms. The first transmission of the MIB is scheduled in subframe #0 of radio frames for which the SFN mod 4 = 0, and repetitions are scheduled in subframe #0 of all other radio frames.

According to 36.331 section 6.2.2 Message definitions - MasterInformationBlock field descriptions, the System Frame Number in MIB is specified as follows : Defines the 8 most significant bits of the SFN. As indicated in TS 36.211 [21, 6.6.1], the 2 least significant bits of the SFN are acquired implicitly in the P-BCH decoding, i.e. timing of 40ms P-BCH TTI indicates 2 least significant bits(within 40ms P-BCH TTI, the first radio frame: 00, the second radio frame: 01, the third radio frame: 10, the last radio frame: 11). One value applies for all serving cells (the associated functionality is common i.e. not performed independently for each cell).

According to 36.331 section 5.2.1.2, the SIB1 scheduling is as follows : The SystemInformationBlockType1 uses a fixed schedule with a periodicity of 80 ms and repetitions made within 80 ms.The first transmission of SystemInformationBlockType1 is scheduled in subframe #5 of radio frames for which the SFNmod 8 = 0, and repetitions are scheduled in subframe #5 of all other radio frames for which SFN mod 2 = 0.

This means that even though SIB1 periodicity is 80 ms, different copies (Redudancy version : RV) of the SIB1 is transmitted every 20ms. Meaning that at L3 you will see the SIB1 every 80 ms, but at PHY layer you will see it every 20ms. For the detailed RV assignment for each transmission, refer to 36.321 section 5.3.1 (the last part of the section)

The transmission cycles for other SIBs are determined by schedulingInfoList in SIB1 as shown in the following example (This example is the case where SIB2 and 3 are being transmitted).

+-schedulingInfoList ::= SEQUENCE OF SIZE(1..maxSI-Message[32]) [2] | +-SchedulingInfo ::= SEQUENCE | | +-si-Periodicity ::= ENUMERATED [rf16] | | +-sib-MappingInfo ::= SEQUENCE OF SIZE(0..maxSIB-1[31]) [0]


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LTE Bible | +-SchedulingInfo ::= SEQUENCE | +-si-Periodicity ::= ENUMERATED [rf32] | +-sib-MappingInfo ::= SEQUENCE OF SIZE(0..maxSIB-1[31]) [1] |

+-SIB-Type ::= ENUMERATED [sibType3]

+-tdd-Config ::= SEQUENCE OPTIONAL:Omit +-si-WindowLength ::= ENUMERATED [ms20]

One thing you would notice that sib-MappingInfo IE in the first node is not specified, but the first entity of schedulingInfoList should always be for SIB2 as specified in the 36.331 as follows (See 36.331 SystemInformationBlockType1 field description).

List of the SIBs mapped to this SystemInformation message.There is no mapping information of SIB2; it is always present in the first SystemInformation message listed in the schedulingInfoList list.

Understanding overall cycle in the unit of Subframe number is pretty straightforward to understand. But understanding exactly at which subframe a SIB should be transmitted is not that straightforward as you might think. It is related to 'si-WindowLength'. si-WindowLength tells that a SIB should be transmitted somewhere within the window length starting at the SFN specified by siPeriodicity. But this parameter does not specify the exact subframe number for the transmission.

The subframe for a specific SIB transmission is determined by a algorithm defined in 36.331 5.2.3 Acquisition of an SI message as follows.

When acquiring an SI message, the UE shall: 1> determine the start of the SI-window for the concerned SI message as follows: 2> for the concerned SI message, determine the number n which corresponds to the order of entry in the list of SI messages configured by schedulingInfoList in SystemInformationBlockType1; 2> determine the integer value x = (n – 1)*w, where w is the si-WindowLength; 2> the SI-window starts at the subframe #a, where a = x mod 10, in the radio frame for which SFN mod T = FLOOR(x/10), where T is the si-Periodicity of the concerned SI message;


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LTE Bible NOTE: E-UTRAN should configure an SI-window of 1 ms only if all SIs are scheduled before subframe #5 in radio frames for which SFN mod 2 = 0.

1> receive DL-SCH using the SI-RNTI from the start of the SI-window and continue until the end of the SI-window whose absolute length in time is given by si-WindowLength, or until the SI message was received, excluding the following subframes: 2> subframe #5 in radio frames for which SFN mod 2 = 0; 2> any MBSFN subframes; 2> any uplink subframes in TDD; 1> if the SI message was not received by the end of the SI-window, repeat reception at the next SIwindow occasion for the concerned SI message;

< Example >

Following is a SIBs captured from a live network. Go through the capture and check if it matches your understanding.


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32.

Downlink Control Information (DCI)

DCI: DOWNLINK CONTROL INFORMATION: -

There are various DCI formats used in LTE PDCCH. DCI format is a predefined format in which the downlink control information is packed/formed and transmitted in PDCCH. DCI formats are required because it tells UE how to get its data which is transmitted on PDSCH in the subframe. DCI format gives the UE details suchas number of resource blocks, resource allocation type, modulation scheme, TB, redundancy version and coding rate. DCI Formats: 0, 1, 1A,1B,1C,1D,2,2A,3,3A Format 1 : Used for scheduling PDSCH codeword. Only single TB can be scheduled here using resource allocation type0/type1. Format 1A: Used for scheduling PDSCH codeword. Only single TB can be scheduled here using resource allocation type2. Format 1B: Used for scheduling PDSCH codeword with Rank 1 assignment. Format 1C: Very compact scheduling of PDSCH code word. Only single TB can be scheduled here using the resource allocation type 2 distributed always. Format 1D: Used for scheduling MIMO cases. Format 2: Used for scheduling PDSCH in closed loop spatial multiplexing. Format 2A: Used for scheduling PDSCH in open loop spatial multiplexing.

Uplink DCI Formats: Format 0: Used for scheduling PUSCH (uplink grant) Format 3: Uplink transmit power control with 2 bit power adjustment Format 3A: Uplink transmit power control with 1 bit power adjustment.


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33.

Uplink Grant

UL Grant is a specific physical control channel information from Network (eNodeB) telling a UE "Now you can transmit data" (More accurately saying "You can transmit the data 4 ms after you got this grant"). UL Grant is another name of DCI format 0. (Many people get confused by the name of "DCI format 0". They think DCI format 0 would be some information about downlink data transmission, but keep in mind that DCI format 0 is a control information about uplink data transmission).

UL Grant (DCI format 0) carries the following information and the most important information is 'Resource Allocation' and MCS. UE should transmit the data using RBs and MCS specified in this DCI 0.


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34.

Scheduling Request

SR (Scheduling Request)

SR is a special Physical Layer message for UE to ask Network to send UL Grant (DCI Format 0) so that UE can transmit PUSCH.

Overall SR process (when to send SR) is controlled by MAC layer as illustrated below. (See 36.321 5.4.4 for details)

Once SR is transmitted and eNB recieves it, eNB should send UL Grant(DCI 0) and UE has to send PUSCH in response to the UL Grant. The timing among SR, UL Grant, PUSCH varies on whether it is FDD or TDD. 

For FDD, refer to Non-Persistant Scheduling for PUSCH transmission.



For TDD, refer to SR/DCI 0 Timing, DCI 0/PUSCH Timing

The timing and physical control channel configuration for SR transmission can be configured in higher layer signaling message (e.g, RRC Connection Setup as shown below) © Farhatullah Mohammed

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sr-PUCCH-ResourceIndex : PUCCH Resource Location described in 36.213 10.1.5 Scheduling Request (SR) procedure.

sr-ConfigIndex : This IE is used to determine the subframe where SR shall be transmitted based on following table and formula.

< 36.213 Table 10.1.5-1: UE-specific SR periodicity and subframe offset configuration >

UE can transmit SR at there subframe where following condition is met.

dsr-TransMax : Maximum number of SR transmission count (See 36.321 5.4.4 Scheduling Request)


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35.

Paging

PAGING IN LTE: -

Paging is used by the network to communicate with the User Equipment in idle mode. In these situations, the network does not know on which cell UE is camped. Lte network uses paging to notify UE in idle mode of incoming data session, system information change and ETWS notifications. There are two types of paging: CN initiated paging eNB initiated paging. In case of CN initiated paging, eNB receives S1AP paging message from MME and determines the paging occasion (PO) where UE monitors PCCH. The paging identifies are queued separately for each PO. In case of ENB initiated paging due to ETWS notification or system information change , paging is sent on all paging occasions. UE decode the content (Paging cause) of the paging message and UE has to initiate the appropriate procedure.

Paging Mechanism: -

During the idle mode, UE gets into and stay in sleeping mode defined in DRX cycle. DRX cycle is defined in SIB 2. UE periodically wake up and monitor PDCCH in order to check for the presence of paging message. (UE looks for any information encrypted in P-RNTI) - If PDCCH indicates that paging message is transmitted in the subframe, the UE needs to demodulate PCH to see the paging message is directed to it. - Paging messages are sent by MME to all eNodeB in a tracking area and those eNodeB in the tracking area is transmitting the same paging message. Paging Occasion and Paging Frame: -

There are two terminologies which is Paging frame (PF) and Paging Occasion (PO). Paging Occasion (PO) is a subframe where there may be P-RNTI transmitted on PDCCH addressing the paging message. Paging Frame (PF): is one frame, which contain one or multiple paging occasions. The parameters used to calculate PO and PF is UE_ID: IMSI mod 1024 UE_ID: is the index value parameter of PAGING message initiated by MME-S1AP. Since network node MME knows about UE IMSI, it will calculate UE_ID and send it to eNodeB S1AP part of paging message.


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36.

DRX_IDLE MODE

DRX: - In LTE, DRX mode can be enabled in both RRC_IDLE and RRC_CONNECTED states. - DRX is used to reduce power consumption.

Idle Mode DRX: - Applicable when UE is in RRC_IDLE state. - The UE is registered with the evolved packet system mobility management (EMM_REGISTERED) but does not have an active session (ECM_IDLE). - In this state the UE can be paged. - UE monitors paging messages using idle mode DRX configuration. - Idle mode DRX configuration is broadcast within System Information Block 2(SIB2). - Idle mode DRX configuration is used to calculate Paging Frame(PF) and Paging Occation(PO). - One Paging Occasion (PO) is a subframe where there may be P-RNTI transmitted on PDCCH addressing the paging message. - One Paging Frame (PF) is one Radio Frame, which may contain one or multiple Paging Occasion(s). -When DRX is used the UE needs only to monitor one PO per DRX cycle.

PF is given by following equation: SFN mod T= (T div N)*(UE_ID mod N) T : DRX cycle of the UE. T = min(The UE specific DRX , Default DRX value). The UE specific DRX value allocated by upper layers, and default DRX value broadcast in system information. If UE specific DRX is not configured by upper layers, the default value is applied. N: min(T,nB) nB: Broadcast within System Information Block 2(SIB2) and can take values 4T, 2T, T, T/2, T/4, T/8, T/16, T/32. N can have values of T, T/2, T/4, T/8, T/16, T/32. UE_ID: IMSI mod 1024. IMSI is given as sequence of digits of type Integer © Farhatullah Mohammed

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LTE Bible Index i_s pointing to PO from subframe pattern defined below will be derived from following calculation: i_s = floor(UE_ID/N) mod Ns Ns: max (1,nB/T)


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37.

DRX_CONNECTED MODE

Connected Mode DRX:

- DRX in connected mode is a power-saving method. - DRX is a method by which the UE can switch off its receiver for a period of time. - Applicable when UE is in RRC_CONNECTED state. - When UE is in RRC Connected state UE may be configured with a UE specific DRX. - if DRX is configured, the UE is allowed to monitor the PDCCH discontinuously in RRC Connected state. - Controls the UE’s PDCCH monitoring activity for the UE’s C-RNTI, TPC-PUCCH-RNTI, TPC-PUSCHRNTI and Semi-Persistent Scheduling C-RNTI (if configured). - In the RRC_CONNECTED state DRX mode is enabled during the idle periods during the packet arrival process,when there are no outstanding/new packets to be transmitted/received, eNB/UE may initiate the DRX mode. - If the UE is configured with DRX, the UE may delay the measurement reporting for event triggered and periodical triggered measurements until the Active Time. - cqi-Mask - Limits CQI/PMI/PTI/RI reports to the on-duration period of the DRX cycle.

DRX Cycle :

-On Duration followed by a possible period of inactivity.


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onDurationTimer :

- The duration of 'ON time' within one DRX cycle. - The number of consecutive PDCCH-subframe(s) UE monitors at the beginning of a DRX Cycle. - If both Long DRX and Short DRX is configured for a particular UE, onDurationTimer i.e. on duration time during Short DRX cycle or Long DRX cycle should be same. - When to onDurationTimer should be started depends on :

- If (Short DRX Cycle) && If ([(SFN * 10) + subframe number] modulo (shortDRX-Cycle) == (drxStartOffset) modulo (shortDRX-Cycle)) or - If (Long DRX Cycle) && If ([(SFN * 10) + subframe number] modulo (longDRX-Cycle) == drxStartOffset) -

start onDurationTimer.


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LTE Bible drx-InactivityTimer :

- During Active time if UE receives PDCCH indicates a new transmission (DL or UL) drxInactivityTimer started or restarted. - Determines the number of consecutive PDCCH-subframe(s) UE monitors before going to sleep, after successfully decoding a PDCCH during active time. - Value in number of PDCCH sub-frames.

drx-RetransmissionTimer :

- PDCCH subframe(s) the UE should remain active as soon as a DL re-transmission is expected by the UE. - Value in number of PDCCH sub-frames.

longDRX-Cycle :

- Once drxShortCycleTimer expires Long DRX cycle starts. - longDRX-Cycle and drxStartOffset . The value of longDRX-Cycle is in number of sub-frames. - If shortDRX-Cycle is configured,the value of longDRX-Cycle shall be a multiple of the shortDRXCycle value. - The value of drxStartOffset value is in number of sub-frames.

shortDRX-Cycle :

- It is a optional one. - If Short DRX is configured, if drx-InactivityTimer expires or a DRX Command MAC control element is received, drxShortCycleTimer is started and short DRX cycle is used.

drxShortCycleTimer :


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LTE Bible - Specifies the number of time(s) the UE shall follow the Short DRX cycle. - Value in multiples of shortDRX-Cycle. A value of 1 corresponds to shortDRX-Cycle, a value of 2 corresponds to 2 * shortDRX-Cycle and so on.

Active Time: 

Time when UE continuously monitors PDCCH.



Includes when onDurationTimer or drx-InactivityTimer or drx-RetransmissionTimer or macContentionResolutionTimer is running.



SR is sent on PUCCH and is pending.



Uplink grant for a pending HARQ re-transmission can occur, and there is data in the corresponding HARQ buffer.



A PDCCH indicating a new transmission addressed to the C-RNTI of the UE has not been received after successful reception of a RAR for the preamble not selected by the UE i.e. Dedicated RACH. DRX Command MAC Control Element : - DRX Command MAC control element is identified by a MAC PDU subheader with LCID (11110). - It has a fixed size of zero bits.


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38.

Buffer Status Reporting - BSR

Buffer Status Reporting (BSR) : - The Buffer Status reporting procedure is used to provide the serving eNB with information about the amount of data available for transmission in the UL buffers of the UE. Type Of BSR: - UL data, for a logical channel which belongs to a LCG, becomes available for transmission in the RLC entity or in the PDCP entity and either the data belongs to a logical channel with higher priority than the priorities of the logical channels which belong to any LCG and for which data is already available for transmission, or there is no data available for transmission for any of the logical channels which belong to a LCG, in which case the BSR is referred below to as "Regular BSR". - UL resources are allocated and number of padding bits is equal to or larger than the size of the Buffer Status Report MAC control element plus its subheader, in which case the BSR is referred below to as "Padding BSR". - retxBSR-Timer expires and the UE has data available for transmission for any of the logical channels which belong to a LCG, in which case the BSR is referred below to as "Regular BSR" - periodicBSR-Timer expires, in which case the BSR is referred below to as "Periodic BSR". When UE will Report Which Type: - periodicBSR-Timer expires, "Periodic BSR". For Regular and Periodic BSR: If (More than one LCG has data available for transmission in the TTI where the BSR is transmitted) Report Long BSR. else, Report Short BSR. For Padding BSR: If (Number of padding bits => size of the Short BSR plus its subheader) && If (Number of padding bits < size of the Long BSR plus its subheader) Then Short BSR or Truncated BSR Can be transmitted instead of Padding. If (More than one LCG has data available for transmission in the TTI where the BSR is transmitted): Then : Report Truncated BSR of the LCG with the highest priority logical channel with data available for transmission; Else Report Short BSR. Elseif (Number of padding bits => Size of the Long BSR plus its subheader) Report Long BSR.


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-

Figure: Signalling of buffer status and power headroom reports.


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39. -

-

-

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Signalling Radio Bearers - SRB

LTE Signalling Radio Bearer types which include LTE SRB0, SRB1 and SRB2. LTE Signalling radio bearers(SRB) are used for the transfer of RRC and NAS signalling messages. • RRC messages are used as signalling between UE and eNodeB. • NAS(Non Access Stratum) messages are used as signalling between UE and MME. RRC messages can be used to encapsulate NAS messages for their transfer between UE and eNodeB. The S1 application protocol is later used to transfer NAS messages between eNode and MME.

As mentioned in the LTE SRB table, there are three types of SRB in the LTE technology. • SRB0 used to transfer RRC messages which use CCCH channel. • SRB1 used to transfer RRC messages which use DCCH channel. • SRB2 used to transfer RRC messages which use DCCH channel and encapsulates a NAS message. SRB1 is also used to encapsulate NAS message if SRB2 has not been configured. SRB2 has lower priority then SRB1 and it is always configured after security activation SRB0 uses transparent mode RLC while SRB1 and SRB2 use acknowledged mode RLC.


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40.

SRB Mapping

MasterInformationBlock  Signalling radio bearer: N/A  RLC-SAP: TM  Logical channel: BCCH  Direction: E-UTRAN to UE

UEInformationRequest  Signalling radio bearer: SRB1  RLC-SAP: AM  Logical channel: DCCH  Direction: E-UTRAN to UE

SystemInformationBlockType1  Signalling radio bearer: N/A  RLC-SAP: TM  Logical channel: BCCH  Direction: E-UTRAN to UE

DLInformationTransfer  Signalling radio bearer: SRB2 or SRB1 (only if SRB2 not established yet. If SRB2 is suspended, E-UTRAN does not send this message until SRB2 is resumed.)  RLC-SAP: AM  Logical channel: DCCH  Direction: E-UTRAN to UE

RRCConnectionRequest  Signalling radio bearer: SRB0  RLC-SAP: TM  Logical channel: CCCH  Direction: UE to E-UTRAN RRCConnectionSetup  Signalling radio bearer: SRB0  RLC-SAP: TM  Logical channel: CCCH  Direction: E-UTRAN to UE RRCConnectionSetupComplete  Signalling radio bearer: SRB1  RLC-SAP: AM  Logical channel: DCCH  Direction: UE to E-UTRAN RRCConnectionReconfiguration  Signalling radio bearer: SRB1  RLC-SAP: AM  Logical channel: DCCH  Direction: E-UTRAN to UE MeasurementReport  Signalling radio bearer: SRB1  RLC-SAP: AM  Logical channel: DCCH  Direction: UE to E-UTRAN MobilityFromEUTRACommand  Signalling radio bearer: SRB1  RLC-SAP: AM  Logical channel: DCCH  Direction: E-UTRAN to UE UECapabilityEnquiry  Signalling radio bearer: SRB1  RLC-SAP: AM  Logical channel: DCCH  Direction: E-UTRAN to UE

Paging  Signalling radio bearer: N/A  RLC-SAP: TM  Logical channel: PCCH  Direction: E-UTRAN to UE

41. Intercell Interferece Coordination - ICIC -

ICIC allows neighbouring eNodeB to exchange load information to help coordinate the use of both uplink and downlink resources. ICIC is introduced to deal with interference issues at cell edge. ICIC mitigates interference on traffic channels only. ICIC uses power and frequency domain to mitigate cell edge interference from neighbor cells. TYPES:

-

No two neighbgour eNodeB will use same resource assignments for their UE. This improves cell Edge SINR. The disadvantage is decreased cell throughput, Since full resource blocks are not being utilized. All eNodeB utilize complete range of resource blocks for centrally located users but for cell edge users, no two neighbours uses the same set of resource block at a given time. eNodeB can use power boost for cell edge users with specific set of resources(not used by neighbours) while keeping low signal power for center users with availability of all resource blocks.

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42.

Transmission Modes

Multiple Input Multiple Output: -

7 modes of MIMO Key factor to performance of the MIMO is spatial layers of wireless channel which determines the ability to improve spectral efficiency. Increase in data rate of MIMO system is linearly proportional to minimum number of transmit antennas and receive antennas. The transmit and receive antennas are subject to the limit of rank of the propagation channel estimate. Rank is the measure of the number of independent spatial layer. 4 Tx/2 Rx antenna MIMO system provides double data rate (min 4,2)=2 gives two spatial layers (rank =2) in wireless channel. In LOS, the channel matrix rank =1, even with 4 antennas we cannot increase spectral efficiency.

-

-

Mode 1: Single Antenna Port, Port 0 One transmit and one receive antennas with one or more antennas (SISO or SIMO) Mode 2: Transmit Diversity Transmission of same information stream on multiple antennas. Information stream is coded differently on each antennas using so-called Space Frequency Code Block codes (SFBC). SFBC repeats data symbols over different subcarriers on each antenna. This mode is used by LTE by default for broadcast channel and common control channels. It is single layer transmission, but does not improve peak rate. Mode 3: Open Loop Spatial Multiplexing OL-SM In this case two information streams (2 code words) are transmitted over two or more antennas. There is no feedback from UE. Transmit Rank Indication (TRI) transmitted by UE is used by eNB to select spatial layers. OL-SM provides better peak throughput than transmit diversity. Mode 4: Closed Loop Spatial Multiplexing CL-SM: Similar to OL-SM, two streams are transmitted over 2 code words from N antennas (upto 4). In CL-SM, PMI is feedbacked from UE to eNB. Feedback mechanism allows transmission to precode the data and optimize transmission on wireless channel. Mode 5: Multiuser MIMO Multiuser MIMO is similar to CL-SM , but the information streams are targeted at different terminals. Multiple users share the same resources.


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Each user experiences same data rate overall data rate is improved. Mode 6: Closed Loop Rank 1 with Precoding: This represents single code word transmitted over single spatial layer. It is considered as fallback scenario of CL-SM as it is associated with beamforming. Mode 7: Single Antenna Port, Port5: This is a beamforming mode where single code word is transmitted over a single spatial layer. Dedicated reference signal forms additional antenna port(port5) and allows transmission for 4 more antennas.


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43.Resource Allocation Vs TM Modes Vs DCI Mapping


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44.

Synchronization Signals

Synchronization Signals: Synchronization is the first step in which UE wants to camp on to any cell. From synchronization UE is able to acquire Physical Cell Identity (PCI), time slot and frame. UE will tune its radio by turning to different frequency channels depending on which band to select that UE supports. -

Two types of synchronization signals Primary Synchronization signals Secondary synchronization signals. UE finds PSS located in the last OFDM symbol of first time slot of the first subframe. PSS is repeated in subframe 5, which means UE is synchronized on 5ms basis since subframe is 1ms. SSS is also located in the same subframe of PSS, but in symbol before PSS.

UE is able to obtain PCI group number 0 to 167. Using the physical layer identity and physical layer group number, UE knows PCI. In LTE 504 PCIs are allowed and are divided into 168 cell layer groups which consist of three physical layer identity. PCI = 3 (SSS – from 0 to 167) + PSS(from 0,1,2)

-

-

(***PCI ranging from 0 to 503)

PSS (Primary Synchronization Signal)  Estimate 5ms timing and physical layer identity  Channel estimation information for SSS. SSS (Secondary Synchronization Signal)  Physical layer Identity (Cell ID) is obtained  Mapped to one of 168 cell ID groups (168 ID groups for 504 cell IDs)  Radio frame timing (10ms) identification


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45.

Reference Signals

- The channels (DPSCH, DPCCH and PBCH) is carrying a special information and they have some higher layer channel connected to them. - The reference signal is a special signal that exists at PHY layer. The purpose of this signal is to deliver the reference point from the downlink power. - When UE tries to figure out DL power(the power of signal from eNodeB) , it measure the power of this reference signals and take this downlink cell power. - Downlink Reference Signals: - There are two types of downlink reference signals- Cell Specific Reference Signals (CsRS) and - UE Specific Reference Signals (UeRS). - The CSRS is cell specific, which means that, these do not depend/change per user but remain same for all the users and entire system, once configured. These reference signals are used by the UE to estimate the downlink channel and do a relative equalization to remove the channel effect over the signal. Hence the UE will generate the CSRS on his side and do a comparison of the generated and received CSRS to get an estimate of channel effect. The CSRS is transmitted with some specific power, which the UE must know, to calculated the multipath effect and this power is conveyed to the UE using SIB messages. The CSRS is mapped onto symbol 0, 4, 7 ,11 of all downlink subframes in FDD. The CSRS is mapped to every sixth subcarrier in these symbols, the start index is determined by the physical cell ID using the below formula, - CSRS start position = Cell ID % 6 - The below diagram shows 2 examples of CSRS mapping for 2 different cell ID 12 and 8. For Cell ID 12 since the above formula results in 0, the CSRS mapping starts at 0th subcarrier in 0th RB and continues to map every 6th subcarrier till end of the bandwidth. Similarly for the second case of cell ID 8, the formula results in 2 and the CSRS mapping starts at 3rd subcarrier (Since the subcarrier count starts from 0 and not 1) and continues to map.

- LTE Downlink Reference Signals - The CSRS is a QPSK modulated sequence. - The downlink reference signal in LTE corresponds to the set of resource elements used by the higher layer but does not carry any higher layer information. - To allow the coherent demodulation at the user equipment, reference symbols are used at the OFDM time frequency grid to allow channel estimation. - Two downlink RS are inserted from the first and third from last OFDM symbol of each slot. - Both of the signals have frequency domain spacing of six sub carriers within the same symbol. - Uplink Reference Signals: © Farhatullah Mohammed

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LTE Bible - Uplink reference signals are used with the PHY layer and do not convey information from higher layers. - There are two main types of reference signals – Sounding Reference Signals and Demodulation Reference Signals. - Demodulation Reference signals: - This facilitates coherent demodulation and associated with transmission of PUSCH or PUCCH. It is transmitted in fourth SC-FDMA symbol of the slot and is the same sign as the assigned resource. - DMRS is intended for specific terminal and is only transmitted in the resource blocks assigned for the transmission to that terminal. - Demodulation reference signals are intended to be used for channel estimation for PDSCH transmissions for the case when cell specific reference signals are not used.

- Sounding Reference Signals: - This is used to facilitate frequency dependent scheduling and not associated with the transmission of PUSCH or PUCCH. Both variants of the UL are based on Zadoff Chu sequences. - SRS signals are of two types based on periodicity. The minimum periodicity is of 2ms and max periodicity is of 320ms. - The similarity between the SRS and DMRS is that both of them use CAZAC sequences(Constant Amplitude Zero Autocorrelation sequences).

-


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LTE Bible What is SRS? - An Uplink Reference Signal. - Not Associated with transmission of PUSCH or PUCCH. - Use to measure Uplink Channel Quality over a Section of the Channel Bandwidth. - Can be used by eNodeB to do Frequency Selective Scheduling and Link Adaptation Decisions. - eNodeB instructs UE to transmit SRS over a specific Section Of The Channel Bandwidth - eNodeB instructs UE to transmit SRS using a combination of Common Information in SIB2 and UE specific Dedicated Information in an RRC Connection Reconfiguration Message. - SRS is always transmitted using the Last Symbol Of The Subframe. - UE never instructed to send SRS over Entire Channel Bandwidth, as it is NOT necessary to transmit SRS within the RBs reserved for PUCCH. PUCCH RBs are located at the Two Edges of the Channel Bandwidth. - SRS is used for Frequency Selective Scheduling of PUSCH, Not PUCCH. SRS Information In SIB2:

SRS Information In RRC Connection Reconfiguration Message:

RS-BandwidthConfig:(C-SRS) - Broadcast on SIB2. - Value from 0-7. - Common to all UE within the Cell SRS-Bandwidth:(B-SRS) - Can be included in RRC Connection Reconfiguration Message. - Can take values 0-3 - Can be UE specific. According to 36.211:


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M-SRS : No of Resource Block over which the Sounding Reference Signal is Transmitted. N0 - N3: One of parameter to decide the Starting position of the SRS in the Frequency Domain. FreqDomainPosition: Received in RRC Connection Reconfiguration Message also has an impact on the Starting Position In The Frequency Domain. SRS-SubframeConfig & SRS-ConfigIndex: The set of Subframes within which the SRS is transmitted is determined by Cell Specific SRS-SubframeConfig in SIB2 and UE specific SRS-ConfigIndex within in RRC Connection Reconfiguration Message. SRS-SubframeConfig: - Takes a value between 0-14. - Common within the Cell. - Talks about in which subframe(s) SRS can be transmitted. According to 36.211:


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SRS-ConfigIndex: (I-SRS) According to 36.213:

The SRS can transmitted in Subframes which satisfy: (10 * nf +k-SRS -T-offset ) mod T-SRS =0 where, nf = SFN No (0-1023). k-SRS= SF No (0-9). Duration: - Received in RRC Connection Reconfiguration Message. - Takes a value TRUE or FALSE. - TRUE - UE should Continue Transmitting SRS until instructed - FALSE - UE should complete only a Single Transmission. TransmissionComb: - Received in RRC Connection Reconfiguration Message. - Allows 2 UE to Frequency Multiplex their SRS with in the Same

otherwise.

Resource Block

CyclicShift:(n-CS-SRS) © Farhatullah Mohammed

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LTE Bible - Received in RRC Connection Reconfiguration Message. SRS-HoppingBandwidth:(B-hop) - Received in RRC Connection Reconfiguration Message. - Allow SRS to move in the Frequency Domain Between Transmission.


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46.

Downlink Power Allocation

"How do we allocate power to each of the those channels ?". The simplest way for our understanding would be to allocate the same power to all of the these channels, but this would be only for the sake of our understanding. For decoding any downlink data, the first step is to detect/decode reference signal. If the power of this reference signal is same as all other channel power, it would not be easy (though not impossible) to detect it. So more practical implementation is to make Reference Signal outstanding comparing to other channels as shown in the red bar in the following plot (you see a certain degree of offset, P_A between Reference Signal and other channel power). However there is a complication with this method and it is because the reference channels occurs only in specific symbols, not in every symbols. It means that there are some symbols with reference signal in it and there are some other symbols without reference signal in it. It implies, if you measure the power of each symbol, some symbol (symbol with reference signal) has higher power than the other symbols (symbol without reference signal). This would cause some complication on the implementation of reciever equalizer. To solve this problem of power difference between two groups of symbols, we can put lesser power to the non-reference signal channels at the symbol carrying reference signal. Due to this, you see another type of offset P_B in the plot shown below. Combining all of these factors, we have pretty complicate peak-and-valley type of power terrain rather than the flat plain terrain in downlink power allocation.

Power offset between PDSCH channel in the symbols with reference signal and PDSCH channel in the symbols without reference signal (P_B) is specified in SIB2 as follows. © Farhatullah Mohammed

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Power offset between the Reference Signal and PDSCH channel in the symbols without reference signal (P_A) is specified in RRC Connection Setup as follows. P_A is UE specific power offset. This is why this is specified by RRC Connection Setup message.

In Physical Layer performance test, we set Rho A, Rho B as a test condition and the relationship between Rho A/Rho B and P_a/P-b is as follows.

Normally P_B is specified first by SIB2 and P_A is determined by following table and specified in RRC message (e.g, RRC Connection Setup, RRC Connection Reconfiguration) according to following table.


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Examples:


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47.

Uplink Power Control

UPLINK POWER CONTROL: -

Uplink power parameters are changed in order to decrease the interference and the service drop and enhance RRC rate.  Adjust UE Transmission to compensate for channel fading.  Reduces cell interference.  Avoid UE from transmitting excessive power.  Maximizes uplink data rate.  eNB radio receive Power maintained for optimum SINR.  Prolongs UE battery life.

There are two type of uplink power control - Open Loop power control - Closed Loop Power Control

Open Loop Power Control -

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The terminal transmits power depending upon estimate of downlink path loss and channel configuration. OL-PC is used for PRACH and initial access PUSCH and PUCCH as part of power control. - 𝐏𝐋(𝐏𝐔𝐒𝐂𝐇) = 𝒎𝒊𝒏{𝑷𝒎𝒂𝒙 , 𝟏𝟎𝒍𝒐𝒈𝑴 + 𝑷𝒐 𝒏𝒐𝒎𝒊𝒏𝒂𝒍(𝑷𝑼𝑺𝑪𝑯) + 𝜶. 𝑷𝑳 Where M is number of PRB used by UE 𝑷𝒐 𝑵𝒐𝒎𝒊𝒏𝒂𝒍 = 𝑻𝒂𝒓𝒈𝒆𝒕 𝑺𝑰𝑵𝑹 + 𝑻𝒐𝒕𝒂𝒍 𝑵𝒐𝒊𝒔𝒆 𝑷𝒐𝒘𝒆𝒓 𝑷𝑳 = 𝑹𝑺 − 𝑹𝑺𝑹𝑷 As PRB increases, UE power increases. α = -8

Closed Loop Power Control -

It controls the terminal transmit power by means of power command in the downlink. PUSCH and PUCCH as part of power control of UL.


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48.

RSRP, EPRE and Total Power

Some equipment would request you to specify the power in EPRE (power/15 Khz) and some equipment would request you to specify the total power (total power across all the allocated RBs).

Some of the most confusing power concepts are RSRP, EPRE and total power. Definition and Differences among these powers can be illustrated as follows. For the simplicity, I use the structure of only one RB and TM1 (Single Antenna)

Directly or indirectly from this illustrations, you can infer some additional facts as follows : 

EPRE indicate power for one resource element (RE). This can be used for any channel (e.g, Reference Signal, PDSCH etc). This value does not vary with system bandwidth or number of RBs.

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RSRP is an averaged value for all the Resource Elements for Reference Signal within a symbol. Since this is the averaged value, the value would be similar to EPRE value you set for the Reference Signal. If there is no noise at all, RSRP would be same as EPRE you set for Reference Signal.

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Total Channel Power is summed value of all EPREs within a symbol. This value may vary with different symbols since each symbol may have different channel combination (e.g, Symbol 0 in first slot is made up of multiple component - PCFICH, HICH, RS. Symbol 4 is made up of PDSCH and Reference signal).


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LTE Bible For simplicity, if we take the symbol which is made up of only PDSCH (e.g, Symbol 3,5,6) we may come out with the following formula. For different symbols, you may have a little bit different values depending on P-a, P-b configurations. But you can apply this formula for other symbols if you can tolerate around +/- 1dB differences. Total Power of PDSCH (in linear scale ) = EPRE for PDSCH x Number of PDSCH RE = EPRE for PDSCH x Number of RB x 12 (assuming for the symbol with no Reference Signal)

Total Power of PDSCH (in dB/dBm scale ) = EPRE for PDSCH (in dBm) + 10 Log(Number of PDSCH RE) = EPRE for PDSCH + 10 Log(Number of RB x 12)

Total Power is not affected by the system bandwidth, it is affected by number of RBs being used at the specific moment of the calculation.

For example, if you allocated -90 dBm/EPRE for PDSCH and allocated 100 RBs for the PDSCH, the Total Power of PDSCH become as follows. Total Power of PDSCH (in dB/dBm scale ) = EPRE for PDSCH + 10 Log(Number of RB x 12) = -90 + 10 Log(100 x 12) = -90 + 30.8 = - 59.2 dBm


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49. -

GPRS Tunnelling Protocol

GTP – GPRS Tunnelling Protocol in LTE: GTP is a tunnelling protocol based on IP/UDP. It is used to encapsulate user data when passing through the core network. 3 types of GTP:

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GTP-C GTP-U GTP’

Why GTP is used in LTE? -

It provides mobility When UE is mobile, IP address remains same packets are still forwarded since the tunnelling is provided between P-GW and eNB via S-GW. Multiple tunnels can be used by same UE to obtain different QoS. Main IP is hidden, so it provides more security. Creation, establishment, modification and termination of tunnels in case of GTP-C.


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RRC

According to the 3GPP functions, the RRC protocol includes the following main functions. Broadcast of system information: > Including NAS common information > Information applicable for UE in RRC_Connected (common channel configuration information) >Information applicable for UE in RRC_Idle (cell reselection parameters, neighbouring cells) Including ETWS notification RRC Connection Control: Paging Establishment, modification and release of RRC connection, including assignment, modification of UE, release of SRB1; SRB 2 Initial Security activation – initial configuration of AS integrity (SRB) and AS ciphering RRC connection mobility including intra-frequency and inter-frequency handover, associated security handling, ie… key/algorithm change, specification of RRC context information transferred between network nodes. Establishment/ modification and release of RB carrying user data (DRB) Radio configuration control, including assignment/ modification of ARQ configuration, HARQ configuration and DRX configuration. QoS control including assignment/modification of parameters for UL rate control in the UE. (allocation of priority and Prioritized bit rate PBR) Recovery from Radio link failure. Inter RAT mobility including security activation, transfer of RRC context information. Measurement configuration and Reporting Establishment/modification/ release of measurements (Intra frequency, inter frequency and interRAT measurements) Setup and release of measurement gaps. Measurement reporting Other functions like transfer of dedicated NAS and non 3GPP dedicated information, transfer of UE radio access capability information. Generic protocol error handling Support for self configuration and self optimization.


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51. Packet Data Convergence Protocol PACKET DATA CONVERGENCE PROTOCOL: PDCP is responsible for -

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Header compression and decompression for all user plane data packets. This is based on RoHC- Robust Header Compression protocol which stores static part of the header. The dynamic part is compressed by transmitting the difference from the reference. RoHC is especially important for the voice services where IP/UDP and RTP header comprises a large number of actual packet size. It also does handover management: reorders and sequences PDU during a handover from one cell to another. There are two types of handovers: Seamless handover and Lossless handover. Seamless Handover: applies to control plane data and RLC- UM user plane data that is tolerant to loss but not delay such as voip. This handover is relatively simple and designed to minimize the delay as no security context is exchanged between the source and the target eNodeB during handover. PDCP SDU that has not been transmitted are forwarded over the X2 interface for transmission by target eNodeB. PDCP SDU that has not been transmitted are buffered and transmitted after the handover is complete. Lossless Handover: This mode is used for the delay tolerant data but are sensitive to loss such as file download where it is desired to minimize the packet loss to save bandwidth utilization and enhance the data rate. This handover applies to RLC-AM bearers. In this mode, a sequence number is used to provide lossless handover by retransmitting PDCP PDU that has not been acknowledged prior to handover. PDCP also provides encryption and decryption services for control plane and user plane data in addition to integrity protection and verification of control plane data.


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52.

Radio Link Control - RLC

RADIO LINK CONTROL LAYER: In the transmit path, RLC tasks with reformatting PDCP PDU- referred as segmentation and/or concatenation to fit the size required by MAC layer (Transport Block –TB). TB size depends on bandwidth requirements, distance, power requirements, modulation scheme etc. RLC also reorders packets received out of sequence during HARQ. RLC communicates with PDCP through Service access points(SAP) and MAC through logical channels. There are 3 modes supported by RLC : -

Transparent Mode [TM] Acknowledged Mode [AM] Unacknowledge mode [UM] Transparent Mode: This is a pass through mode which maps RLC SDU to RLC PDU and vice versa without any overhead or modifications done to the packet. It is only used for signalling suchas broadcast system information and paging messages. . Unacknowledge Mode: This mode is used for delay sensitive traffic such as VoiP. Multimedia Broadcast/ Multicast service (MBMS) also uses this mode. In this mode, the layer performs segmentation and concatenation of RLC SDU , reordering and duplicate detection of RLC PDU and reassembly of RLC SDU. Acknowledge Mode(AM): This mode is used to support delay tolerant but error sensitive traffic(non real time traffic suchas web browsing). It allows bidirectional data transfer where RLC can transmit and receive data. It features ARQ applies to correct erroneous traffic.


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53.

MAC Layer

MEDIUM ACCESS CONTROL LAYER: MAC layer performs important functions that includes the scheduler which distributes the available bandwidth to number of active UE. RACH Procedure is a MAC layer function which is used by UE that is not allocated with uplink radio resources to access and synchronize with the network. MAC layer performs uplink timing alignment which ensures UE transmissions do not overlap when received at the base station. Discontinuous reception –DRX is implemented at MAC layer to save battery power by limiting the time. MAC implements HARQ operation to retransmit and combine received data blocks, and generate ACK/NACK signalling in case of CRC failure. MAC layer maps the RLC data received through logical channels onto transport channels connecting MAC with PHY layer. MAC Control Elements MAC Control Elements: - Way of FAST Signaling Communication Exchange Between UE and eNodeB. - Send as a part of MAC PDU. - MAC control elements are always placed before any MAC SDU. MAC Control Element Types: Buffer Status Report MAC Control Elements C-RNTI MAC Control Element DRX Command MAC Control Element UE Contention Resolution Identity MAC Control Element Timing Advance Command MAC Control Element Power Headroom MAC Control Element Extended Power Headroom MAC Control Element MCH Scheduling Information MAC Control Element Activation/Deactivation MAC Control Element MAC CE Header:


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- LCID field in MAC Subheader denotes MAC CE Type.

Values of LCID for DL-SCH:

Index

LCID values

00000

CCCH

0000101010

Identity of the logical channel

0101111010

Reserved

11011

Activation/Deactivation

11100

UE Contention Resolution Identity

11101

Timing Advance Command

11110

DRX Command

11111

Padding

Values of LCID for UL-SCH:

Index


LCID values

00000

CCCH

0000101010

Identity of the logical channel

0101111000

Reserved

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Extended Power Headroom Report

11010

Power Headroom Report

11011

C-RNTI

11100

Truncated BSR

11101

Short BSR

11110

Long BSR

11111

Padding

Buffer Status Report MAC Control Elements:

- Long BSR format:

- If extendedBSR-Sizes is not configured, the values taken by the Buffer Size field are in Table 6.1.3.11(3GPP TS 36.321). If extendedBSR-Sizes is configured, the values taken by the Buffer Size field are in Table 6.1.3.1-2(3GPP TS 36.321). - Short BSR Header:

3D : MAC sub-header - Short BSR R=0 R=0 E=1

LCID = 11101 = Short BSR

1D : MAC sub-header - Short BSR © Farhatullah Mohammed

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LCID = 11101 = Short BSR

- Long BSR Header:

3E : MAC sub-header - Long BSR R=0 R=0 E=1 LCID = 11110 = Long BSR

1E : MAC sub-header - Long BSR R=0 R=0 E=0 LCID = 11110 = Long BSR

- Truncated BSR Header:

3C : MAC sub-header - Truncated BSR R=0 R=0 E=1 LCID = 11100= Truncated BSR

1C : MAC sub-header - Truncated BSR R=0 R=0 E=0


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C-RNTI MAC Control Element Format :

C-RNTI MAC control element

UE Contention Resolution Identity MAC Control Element :

UE Contention Resolution Identity MAC control element - Has a fixed 48-bit size - UE Contention Resolution Identity: This field contains the uplink CCCH SDU.

3C : MAC subheader - Contention Resolution R=0 R=0 E=1 LCID = 11100 = Contention Resolution


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Timing Advance Command MAC control element - Timing Advance Command is of 6 bits in length. TA (0, 1, 2… 63). Power Headroom MAC Control Element :

Power Headroom MAC control element Activation/Deactivation MAC Control Element : - The Ci field is set to "0" to indicate that the SCell with SCellIndex i shall be deactivated.

Activation/Deactivation MAC control element

Padding MAC Sub-Header:

1F : MAC subheader - Padding R=0 R=0 E=0 LCID = 11111 = Padding


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53.1 Stream Control Transmission Protocol The Stream Control Transmission Protocol (SCTP) is a transport layer protocol, similar in nature to the STCP

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traditional Transmission Control Protocol (TCP). They both provide a number of useful features, including congestion control, error detection and retransmission. SCTP, however, offers some capabilities that TCP does not. It allows the application to send data as independent streams. SCTP also makes better use of the redundancy benefits of having multiple network interfaces. Role of STCP:

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require framing of reliable data streams, require ordered transport of data, but can transfer multiple message sequences that are unrelated, need to transfer messages that hold no particular sequence or relationship to one another or can be correlated and sequenced at the application level, require network layer redundancy (to avoid loosing too much efficiency when a fault occurs at the transport layer or below) Mission critical systems recognize that their components inevitably fail and plan accordingly. Any individual component that would disrupt service when it dies is known as a single point of failure. Effective contingency plans eliminate (within practical capabilities) single points of failure. Consider the connectivity between a hypothetical Cell Site and Mobile Switching Office (MSO) illustrated in Figure 1. It’s been decked out with redundant routers at both the cell site and the switching office. It also has two independent links between the sites – Ethernet and SONET. Each of the nodes has two network interfaces (IP addresses shown). It appears to have eliminated all single points of failure; communications between the eNodeB and MME cannot be disrupted by the failure of any single component. Looks can be deceiving, however.

Figure 1 Cell site with redundant connectivity to the Mobile Switching Office Where TCP Comes Up Short The concept of a TCP connection is fundamental to the operation of the protocol. The connection embodies all of the state information needed by the congestion control, sequential delivery and error recovery algorithms. TCP connections are identified by the IP address and TCP port number of the source and destination nodes. Figure 2 illustrates three TCP connections between the eNodeB and the MME. TCP connection [192.0.2.125:14457, 198.51.100.65:34851] uses one network interface on each device. TCP connections [192.0.2.10:36412, 198.51.100.39:36412] and [192.0.2.10:24500, 198.51.100.39:18479] use the other network interface.


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Figure 2 Examples of TCP connections between eNodeB and MME The problem with TCP stems from its strict association of IP address with the TCP connection. Figure 3 illustrates what happens when one of the network interfaces on the MME fails. TCP connections associated with that port’s IP address will time out. TCP cannot redirect data from the failed port to the remaining active port. Communication between the eNodeB and MME has been affected, even though an alternate path between the two nodes exists.

Figure 3 Effect of a port failure on TCP connection Now, it is possible for us to do something about this. We could write the application such that it reopens the failed TCP connection using the new address. We could devise a scheme in which the IP address of the failed port gets mapped to the in-service port. However, the central issue with TCP remains: TCP cannot, by itself, effectively use redundant network interfaces. SCTP to the rescue Before an application sends data using SCTP, it must first set up an association between the source and destination nodes. The SCTP association is analogous to the TCP connection. One significant difference, however, is that the two nodes may exchange a list of acceptable IP addresses when they establish the association. SCTP monitors the reachability of the destination IP address it is using to send data. If the address becomes unreachable, for any reason, SCTP selects one of the association’s © Farhatullah Mohammed

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LTE Bible alternate addresses. Figure 4 illustrates the fact that all three SCTP associations remain up, despite an MME network interface failure.

Figure 4 SCTP Associations Conclusion SCTP’s multi-homing feature assigns multiple IP addresses to a single association. SCTP automatically detects when an IP address is unreachable and starts sending data to one of the association’s other IP addresses. SCTP improves the overall availability of mission critical systems like the LTE network. The LTE standards documents suggest using SCTP on a number of its signaling interfaces, as shown in Figure 5.

Figure 5 SCTP in the LTE-EPC network


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54.

LTE UE Measurements

RSRP(Reference Signal Received Power):RSRP (Reference Signal Receive Power) is the average power of Resource Elements (RE) that carry cell specific Reference Signals (RS) over the entire bandwidth, so RSRP is only measured in the symbols carrying RS. Its typical range is around -44 to -130dbm. This measurement is used in RRC Idle/Connected, Cell Re selection/Selection, handover scenarios. Reference signal receive quality (RSRQ): Although RSRP is an important measure, on its own it gives no indication of signal quality. RSRQ is defined as (N x RSRP)/RSSI, where N is the number of RBs over the measurement bandwidth. As you see, this is not the direct measurement, it is a kind of derived value from RSRP and RSSI. By dividing RSRP by RSSI, it could give some information about interference as well in addition to the strength of the wanted signal. The RSSI parameter represents the entire received power including the wanted power from the serving cell as well as all co-channel power and other sources of noise. Measuring RSRQ becomes particularly important near the cell edge when decisions need to be made, regardless of absolute RSRP, to perform a handover to the next cell. Reference signal receive quality is used only during connected states. Intra- and inter-frequency absolute RSRQ accuracy varies from ±2.5 to ±4 dB, which is similar to the inter frequency relative RSRQ accuracy of ±3 to ±4 dB.

RSSI (Received Signal Strength Indicator): RSSI (Received Signal Strength Indicator) is a parameter which provides information about total received wide-band power (measure in all symbols) including all interference and thermal noise. RSSI is the total power UE observes across the whole band. This includes the main signal and cochannel non-serving cell signal, adjacent channel interference and even the thermal noise within the specified band. This is the power of non-demodulated signal, so UE can measure this power without any synchronization and demodulation. Following is an example of one downlink radio frame. The red part is the resource elements in which reference signal is being transmitted. Blue and light blue part is for synchronization signal. Yellow part is for PDCCH. Green part is for MIB. Whitepart is PDSCH where user data is being transmitted. RSSI is the total power for all color and any possible noise/interference existing over all these area.


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55.

Random Access Process

Random Access: -

two types of Random Access Contention based Non contention based or contention free.

When UE is powered ON, UE does not have any resources or channel available to inform, so it will sent request over a shared medium.

Contention Based Random Access Procedure: -

There is possibility of collision among the request coming from various UE. Contention based RACH process user RACH preambles. There are 64 RACH preambles. Non Contention Based or Contention Free RACH:

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In contention free, network informs UE to use some unique identity to prevent its request from colliding with request from UE. Second scenario is called as non contention based RACH. Mostly used in Handover (UE), where eNB informs about which preamble it can use, since UE is already in connected state.

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Contention Based procedure involves the UE selecting a Random Access Resource i.e. UE selecting a PRACH resource, a Preamble Sequence and the next available Subframe for PRACH transmission.

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Non-Contention Based procedure involves the eNodeB allocating the Random Access Resource i.e. eNodeB allocating ra-PreambleIndex and ra-PRACH-MaskIndex. - Contention Based RACH Procedure can be applicable for all RACH reasons but Non Contention Based RACH Procedure can be applicable for : - Completing an Intra-System Hand Over. - Downlink data arrives while UE is in Non-synchronized RRC Connected State. RACH Procedure:

Step1: MSG1 © Farhatullah Mohammed

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UE selects one of the 64 preambles. UE gives its own identity to the network, so the network can address it in next step. This identity is called RA-RNTI. If UE does not receive any response from the network, it increases its power in fixed step and sends RACH preamble again. Step2: MSG2: eNodeB sends Random Access Response to UE on DL-SCH (Downlink shared channel) addressed to RA-RNTI calculated from the time slot in which preamble was sent. The message carries following information: Temporary C-RNTI: eNB gives another identity to UE which is called as temporary CRNTI for further communication. Timing advance value: eNB also informs UE to change its timing so it can compensate for the round trip delay caused by eNB. Uplink grant resource: eNodeB assigns initial resources to UE so it can use UL-SCH. Step3: MSG3:

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Using UL-SCH, UE sends RRC connection message UE is identified by Temporary C-RNTI UE identity contains TMSI Connection establishment cause. Step4: MSG4:

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eNodeB responds with contention resolution message to UE whose message was successfully received in step3. This message is address towards TMSI or random number but contains CRNTI which will be used for further communication.

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RACH Configurations: Number of RACH preambles available for contention based random access. -

There are 64 preambles sequence available. Range is from 4 to 64, others are reserved for non contention based. Size of RA Preambles: the RACH preambles are divided into two groups. Group A: Group A preambles are intended for sending small packets and group B are intended for sending large packets. Range is from 4 to 60. Message size of group A is 56, 144, 208 or 256 bits. Power ramping step: Power offset selecting preamble group B (0,5,8,10,12,15 and 18dB). Power Ramp: This parameter is the power increase step of random access preambles.

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UE received acquisition indicator in random access procedure. Value ranges from 1dB to 8dB. Default value is 2dB. If the value is too high, the access process is shortened, but the probability of power waste is high. If the value is too low, the access process is lengthened but transmitting power is saved.

Random Access Resource Selection: Random Access Group Selection: If (ra-PreambleIndex == Allocated By eNB && ra-PRACH-MaskIndex == Allocated By eNB) © Farhatullah Mohammed

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LTE Bible { If (ra-PreambleIndex != 000000) { Random Access Preamble && PRACH Mask Index = Allocated By eNB. } } Elseif { If (MSG3 == Not Transmitted Yet) { If (Random Access Preambles group B == present) { If ( sizeof(MSG3) > messageSizeGroupA && pathloss < (P-CMAX,c– preambleInitialReceivedTargetPower – deltaPreambleMsg3 – messagePowerOffsetGroupB)) { select the Random Access Preamble from Random Access Preambles group B } Else { select the Random Access Preamble from Random Access Preambles group A } } Else { select the Random Access Preamble from Random Access Preambles group A } } Elseif (MSG3 == Re-transmitted) { select the Same Group of Random Access Preambles = used for the preamble transmission attempt corresponding to the first transmission of Msg3 } } Random Access Preamble Selection Within the Group: - Randomly select a Random Access Preamble within the selected group. - The random function shall be such that each of the allowed preamble will have equal probability. - set PRACH Mask Index to 0.

Figure: RACH Preamble transmission © Farhatullah Mohammed

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LTE Bible PRACH Resource Selection: - Subframe for PRACH transmission selected using restrictions given by the prach-ConfigIndex and the PRACH Mask Index. - physical layer timing requirements i.e. UE may take into account the possible occurrence of measurement gaps when determining the next available PRACH subframe. Random Access Preamble Power : - PREAMBLE_RECEIVED_TARGET_POWER = preambleInitialReceivedTargetPower (RACHConfigCommon) + deltaPreambleMsg3 (UplinkPowerControlCommon) + (PREAMBLE_TRANSMISSION_COUNTER – 1) * powerRampingStep (RACH-ConfigCommon) - Physical layer transmit a preamble using the selected PRACH, corresponding RA-RNTI, preamble index and PREAMBLE_RECEIVED_TARGET_POWER Random Access Response (RAR) Reception: - Once RACH is transmitted UE shall monitor PDCCH regardless of the possible occurrence of a measurement gap. - RAR is identified by RA-RNTI. - RA Response window starts at subframe that contains the end of the preamble transmission + three subframes. - RA Response window has a length ra-ResponseWindowSize(SIB2) subframes - The RA-RNTI is calculates as : RA-RNTI= 1 + t_id+10*f_id where t_id = Subframe within which start of preamble was transmitted(0<= t_id<=9). f_id = Frequency domain index of the PRACH within the subframe.(0<= f_id<=5). - For FDD there can be maximum one set of RBs allocated to PRACH within a subframe so f_id is always 0. - So for FDD RA-RNTI= 1 + t_id.

Figure: RACH Preamble Formats


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56.


UE Categories

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57. -

Circuit Switch Fall Back

CIRCUIT SWITCH FALL BACK:


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The legacy 2G/3G network and the LTE network co-exist in mixed networks, residing between the mobile customer’s User Equipment (UE) and the common core network, where an MME (Mobility management Entity) is serving users while in LTE access, while for 2G/3G an SGSN (Serving GPRS Support Node) is serving users when utilizing data services and an MSC Server (Mobile Switching Center Server) when utilizing voice services. The MSC Server connects to the carrier’s telephony network. To support CS Fallback signaling and SMS transfer for LTE devices, the MME connects to the MSC Server

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Figure 1: EPS and Legacy core networks

Figure 2: CSFB to UTRAN/GERAN

Figure 3: Return to EUTRAN (LTE)

CSFB SIGNALLING FLOW

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If UE decides to perform a mobile Originated CS call or receives paging from UTRAN. CSFB Procedure is initiated by UE.  UE transmits NAS Extended Service Request (ESR) to MME.


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MME sends S1 request with CSFB indicator to EnodeB. The eNodeB transmits S1 response message to MME. eNodeB requests UTRAN measurement to UE. eNodeB transmits RRC Connection release to UE. ENodeB transmits the UE context Release request to MME. The UE is switched to UTRA carrier and connect to the UTRAN.


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ARQ and HARQ

AUTOMATIC REPEAT REQUEST (ARQ) – RLC Layer Retransmission protocol in which the receiver checks for error within the received data and if the receiver discards the data and requests a retransmission from the sender. The simplest way (or more common) control using what we described above is known as ARQ, or 'Automatic Repeat Request'. In ARQ, when we have a 'bad' package, the system simply discards it, and asks for a retransmission (of the same package). And for this, it sends a feedback message to the transmitter.

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These feedback messages are messages that the receiver uses to inform whether the transmission was successful or not: 'ACKnowledgement' (ACK) and 'NonACKnowledgement' (NACK). These messages are transmitted from the receiver to the transmitter, and respectively informs a good (ACK) or bad (NACK) reception of the previous packages. If in the new retransmission the packet keep arriving with errors, the system requests a new retransmission (still for this same package). That is, sends another 'NACK' message.

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The data packets that are not properly decoded are discarded. The data packets or retransmissions are separately decoded. That is, every time a packet that arrives is bad, it is discarded, and it is requested that this same package be retransmitted.

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But see that if there were no retransmissions, the performance of the data flow would be much better. In the example below, compared with the previous, we transmit more information - 3 times in the same time interval.

Unfortunately we don't have much to do about the link conditions. Or better, we are able to improve the links performance, for example with configuration parameters optimization, but we'll always be subject to face adverse conditions. In this case, our only way out is to try to minimize retransmissions. And that's where arise other techniques or more 'enhanced' schemes for retransmission. The main one is HARQ. HYBRID AUTOMATIC REPEAT REQUEST (HARQ) – MAC Layer Retransmission protocol in which the receiver checks for error in the received data and if an error is detected then the receiver buffers the data and request retransmission from the sender. The HARQ is the use of conventional ARQ along with an Error Correction technique called 'Soft Combining', which no longer discards the received bad data (with error). With the 'Soft Combining' data packets that are not properly decoded are not discarded anymore. The received signal is stored in a 'buffer', and will be combined with next retransmission. That is, two or more packets received, each one with insufficient SNR to allow individual decoding can be combined in such a way that the total signal can be decoded!

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The following image explains this procedure. The transmitter sends a package [1]. The package [1] arrives, and is 'OK'. If the package [1] is 'OK' then the receiver sends an 'ACK'.

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The transmission continues, and is sent a package [2]. The package [2] arrives, but let's consider now that it arrives with errors. If the package [2] arrives with errors, the receiver sends a 'NACK'.

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But if the combination of these two packages still does not give us the complete information, the process must continue - and another 'NACK' is sent.

And there we have another retransmission. Now the transmitter sends a third package [2.2]. Let's consider that now it is 'OK', and the receiver sends an 'ACK'.

Only now this package [2] (bad) is not thrown away, as it is done in conventional ARQ. Now it is stored in a 'buffer'. Continuing, the transmitter send another package [2.1] that also (let's consider) arrives with errors.

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Here we can see the following: along with the received package [2.2], the receiver also has packages [2] and [2.1], that have not been dropped and are stored in the buffer.

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We have then in a buffer: bad package [2], and another package [2.1] which is also bad. Does by adding (combining) these two packages ([2] + [2.1]) we have the complete information? Yes. So we send an 'ACK'.


‘Chase Combination’: when we combine the same information (the retransmission is an identical copy of the original packet). We transmit an information, which arrived wrong, and we need to do a retransmission. We retransmit the same information - and there we don't have much gain. 171

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HARQ Incremental Redundancy ‘Incremental Redundancy’: where we retransmit only the portion that we didn't transmitted before. Thus we retransmit less information. Less information means fewer bits, less energy. And this gives a gain! Redundancy bits are retransmitted gradually to the receiver, until an ACK is received. With this, we adapt to changes in the condition of the link. The first retransmission can, for example, contain or not bits of redundancy. If necessary, a small number of these bits is retransmitted.


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LTE Numbering and Addressing

The Network IDs The network itself will be identified using Public Land Mobile Network Identity (PLMNID) which will have a three digit mobile country code (MCC) and a two or three digit mobile network code (MNC). For example, the Mobile Country Code for the UK is 234, while Vodafone's UK network uses a Mobile Network Code of 15.

The MME IDs Each MME has three main identities. An MME code (MMEC) uniquely identifies the MME within all the pool areas. A group of MMEs is assigned an MME Group Identity (MMEGI) which works along with MMEC to make MME identifier (MMEI). A MMEI uniquely identifies the MME within a particular network.

GUMMEI If we combile PLMN-ID with the MMEI then we arrive at a Globally Unique MME Identifier (GUMMEI), which identifies an MME anywhere in the world:

The Tracking Area IDs Each tracking area has two main identities. The tracking area code (TAC) identifies a tracking area within a particular network and if we combining this with the PLMN-ID then we arrive at a Globally Unique Tracking Area Identity (TAI).

The Cell IDs Each cell in the network has three types of identity. The E-UTRAN cell identity (ECI) identifies a cell within a particular network, while the E-UTRAN cell global identifier (ECGI) identifies a cell anywhere in the world.

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The physical cell identity, which is a number from 0 to 503 and it distinguishes a cell from its immediate neighbours. The Mobile Equipment ID The international mobile equipment identity (IMEI) is a unique identity for the mobile equipment and the International Mobile Subscriber Identity (IMSI) is a unique identity for the UICC and the USIM. The M temporary mobile subscriber identity (M-TMSI) identifies a mobile to its serving MME. Adding the MME code in M-TMSI results in a S temporary mobile subscriber identity (S-TMSI), which identifies the mobile within an MME pool area.

Finally adding the MME group identity and the PLMN identity with S-TMSI results in the Globally Unique Temporary Identity (GUTI).


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60.

TTI Bundling

TTI Bundling has been introduced in FDD and TD-LTE to improve Uplink coverage. In this blog, we shall present the salient features of TTI Bundling with respect to FDD and TD-LTE. We will first explore the motivation for TTI Bundling and then compare it with other techniques. Finally, we shall address the implementation of TTI bundling in FDD and TD-LTE . Introduction TTI bundling is a technique used to send a transport block multiple times in consecutive subframes without waiting for HARQ ACK/NACK messages. Normally, a transport block is converted to multiple redundancy versions after coding and the first redundancy version is sent in a subframe. Subsequent transmissions of the transport block are dependent on the HARQ ACK/NACK which is sent 4 subframe durations later or more after the first transmission. In TTI bundling, the different redundancy versions can all be sent in consecutive subframes without waiting for the HARQ ACK/NACK feedback and a combined ACK/NACK can be sent after processing all the transmissions of a transport block. The motivation for TTI bundling which is illustrated in Figure 1 is the low transmission power of some handsets, short TTI length, and the long RTT of the HARQ transmissions. TTI bundling is expected to improve the UL coverage of applications like VOIP over LTE wherein low power handsets are likely to be involved. This feature has more relevance for TDD over FDD as coverage issues are likely to be more challenging in TD-LTE. Simulation results reported in publications indicate a 4 dB gain due to TTI bundling on the UL.

Alternative Approach The alternative to TTI bundling is RLC segmentation wherein a VOIP payload is split into smaller size RLC PDUs as shown in Figure 2. The smaller RLC PDUs will result in smaller transport blocks which can be decoded with better accuracy. One drawback of this method is the potential overhead increase due to RLC segmentation due to multiple RLC headers needed. For a typical VOIP payload, it has been shown that as we increase the segmentation factor from 1 to 8, the overhead increases from 14% to 55%. Each RLC PDU which is mapped into a transport block will need a separate © Farhatullah Mohammed

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LTE Bible PDCCH assignment message which will contribute to control signal overhead for such a scheme. There might be retransmissions of each of those transport blocks which will also potentially increase the control signaling overhead. In addition, since we are transmitting many small transport blocks, the chances of interpreting a NACK as a ACK also increases proportionately with the increase in the RLC segmentation size. Hence, RLC segmentation has many disadvantages when we consider the transmission of a VOIP like payload from a power limited terminal.

Overview of TTI Bundling TTI bundling is used to achieve successful transmissions from power limited terminals. The process as shown in Figure 3 is typically triggered by UE informing the eNB about its power limitations at the present state. This could for example happen at the edge of a cell when the terminal has to send high power but is limited by the power capability of the terminal. This triggers the eNB to transmit the various redundancy versions of the same transport block in consecutive subframes or TTIs giving rise to the name TTI bundling. A single PDCCH allocation is sufficient for the multiple transmissions thus saving control overhead as compared to the RLC segmentation approach. A single HARQ ACK/NACK for the combined transmissions is generated after processing the TTI bundle which can reduce the error rate of the transport block as compared with processing a single redundancy version. This approach can also reduce the delay in the HARQ process compared to transmissions of the redundancy versions separated in time using the normal approach.

TTI Bundling Operation


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Summary: TTI bundling is a useful technique for improving coverage of VOIP handsets in LTE systems. It is applicable to both FDD and TD-LTE deployments and can improve the link budget by up to 4 dB. Differences in implementation exist between FDD and TD-LTE systems. TTI bundling helps achieve good latency performance for VOIP even at the edges of cells.


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61. Basic Procedures between UE and EnB -

SYNCHRONIZATION PROCEDURE: Procedure for synchronization and obtaining system information.

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MIB: System Frame number, Channel Bandwidth and PHICH information are included SIB: Cell specific information are included for system operation except MIB information. SIB1: Cell access configuration, frequency band indicator, scheduling information for system other SIB and systemInfoValue tag. SIB2: Radio configuration information are included (PUCCH, PUSCH, SRS etc)

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UE specific resource allocation information in MSG4 (RRC connection setup) are transmitted.

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CQI Resource Index, Transmit period and subframe offset. SR Resource Index, Transmit period and subframe offset. SRS Transmission bandwidth, Frequency location, comb, cyclic shift.

DOWNLINK DATA – TRANSMISSION PROCEDURE: UE Transmits CQI periodically CQI(Channel Quality indicator) which is DL channel status after receiving CQI resource allocation per UE. eNodeB allocates PDSCH considering DL channel status of UE and DL buffer status.  Transmit information of PDSCH allocation per specific subframe with PDCCH.

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When CRC is OK on PDSCH detection result in UE, transmit ACK to eNB.


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 Transmit ACK info. on PUSCH when PUSCH is allocated.  In other cases, Transmit ACK info on PUCCH. UPLINK DATA – TRANSMISSION PROCEDURE: UE transmits periodically SRS signal after receiving SRS resource allocation per UE. eNodeB allocates PUSCH resource considering UL channel status and UE and BSR. When CRC is OK on PUSCH detection result in UE, transmit ACK to eNB.  Transmit ACK using PHICH (Downlink Detection).

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*** BSR – BUFFER STATUS REPORT

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HANDOVER PROCEDURE

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UE sends measurement report to the serving cell with the condition of comparing Neighbour cell signal and serving cell signal. If the serving cell transmit “handover command” message to UE, UE orders target call to be handover.

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62.

LTE WiFi Offload

WiFi OffLoad means a kind of handover (or selection/reselection) technology between Non-WiFi network and WiFi Network. It is not a new concept, but it has become hot issue recently especially after LTE network is wide spread. So when we say WiFi Offloading, it usually mean that WiFi Offload (handover) between LTE network and WiFi network.

Just from the user's point of view, we can think of several user model as described below.

< Case 1 > UE-Initiated WiFi OffLoading i) UE is in connected mode with LTE network while there is no WiFi Network Available. ii) UE start seeing WiFi signal. iii) User switch the connection from LTE to WiFi Network. Note : I should say this is over-simplified description. You may have a lot of questions boggling in your mind. In what criteria, user decided to switch from LTE to WiFi ? You said 'Switch the connection to WiFi ?'. Exactly what do you mean by 'Switching' ? What is the exact mechanism ? etc. I will get back to these question later.. for now, just get the big picture.

< Case 2 > Network-Initiated WiFi OffLoading i) UE is in connected mode with LTE network while there is no WiFi Network Available. ii) UE start seeing WiFi signal. iii) Network tells UE to switch the connection from LTE to WiFi Network. Note : I should this is over simplified description as well. You would have a lot of questions for this as well. How network knows that UE is seeing WiFi Signal ? How network notify UE to switch to WiFi ? etc.

Now let's think about business issues... about money. What is the motivation to go for WiFi offloading?

What would be your motivation to Switch your communication channel from LTE to WiFi while you are in connection? © Farhatullah Mohammed

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LTE Bible For mobile phone user it may help him to get access to wider bandwith and probably in lower cost or free For mobile network operators it would help reduce the load on the LTE network by offloading the subscriber to WiFi network

Then you may ask "What about the money for the network operator? " they may not be able to charge for WiFi network usage as much as for LTE network but they may be able to get some gain from load balancing and still keep some portions of the money from the mobile user by directing to switch to the WiFi network serviced by the mobile network operator (not free WiFi) Overall Network Arichitecture for WiFi Offload Now let's get just a little bit deeper into WiFi Offload mechanism. The first thing you need to understand is overall network architecture related to WiFi Offload. You would see various network architecture depending various use model. Most of the components are the ones that you are already familiar with normal LTE/IMS operation. The component and interfaces that you need to pay attention for WiFi Offload would be as follows : (Don't try to memorize it.. just try to follow the path with pen whenever you are studing any specific use case).  Untrusted Non-3GPP IP  Trusted Non-3GPP IP  ePDG  3GPP AAA Server  SWu, SWn,Swa,SWm,STa,S2c,S2a,S2b


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Figure 4.2.2-1: Non-Roaming Architecture within EPS using S5, S2a, S2b Now let's think of how WiFi network get anchored to 3GPP network (e.g, LTE network). There are a couple of different ways to do it but if I am allowed for another oversimplifcation, it can be only two categories. One is through 'Trusted Access Point' and the other one is through 'Non-Trusted Access Point'. You can think of 'Trusted' as that the WiFi Security is protected by the 3GPP network, so you would not need any separate authentication process between 3GPP and Non-3GPP Network (WiFi). 'NonTrusted' means that the WiFi Security is not protected by the 3GPP network, so you need to go through separate authentication process between 3GPP and Non-3GPP Network (WiFi) 'Trusted vs Untrusted' Access If you see the network structure for Non-3GPP Access, you would see two different path. One is through 'Trusted' path and the other one is through 'Untrusted' path. What does it mean by 'Trusted' ? Who trust who ? 'Trust' in this case is that 'Operator TRUST the access(path)'. It doesn't necessarily mean (may or may not mean) 'UE trust the path'. The biggest difference between trusted access and untrusted access would be the requirement of authentication requirement. In trusted access, UE would not need any separate authentication/security process when it switches from 3GPP access to non-3GPP access (WiFi) since UE already has gone through this process when it was camping on the 3GPP access and network trust the © Farhatullah Mohammed

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LTE Bible process and assume that the non-3GPP access can be protected by the same security procedure. In this access, it is highly likely that Network Operator distribute their own WiFi Access points and let UE get access through those Access Point.

On the other hand, in Untrusted access, network would require UE to go through additional authentication/security process when UE switches to non-3GPP access and use special IP tunneling mechanism (e.g, IPSec) for data transaction. In most of this case, UE would get WiFi access via public WiFi access point and those access points would be anchored to ePDG. ANDSF, what is it ? why we need it ? ANDSF stands for 'Access Network Discovery and Selection Function'. This is a set of services that would answer to following questions. I am at such and such location now, which network (3GPP or Non-3GPP) are available for me ?  Now my mobile phone detected 3GPP network and WiFi network, which network I

have to get access to ? Session Mobility

Mobility is a mechanism of switching between 3GPP (e.g LTE) and non-3GPP (e.g, WiFi) networks. Largely there are two methods you can think of, NBM (Network Based Mobility - Network Initiated) and HBM(Host Based Mobility - UE Initiated) Interplay between ANDSF and Mobility

Interplay between UE and ANDSF


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What kind of Information are provided by ANDSF It provides huge set of information. so it is hard to describe everything in this section. You can get the full sets of information about this in 3GPP as summarized below

The specification that I referred to is ETSI TS 124 312 V11.6.0 (2013-04). Since this is relatively early stage, it is highly likely that new items or revision will be added as it goes to new version. Try following up the latest specification as it roll out. One of the 'Untrusted' access that attracts the widest attention as of this writing (Feb 2014) is through ePDG as shown below. Overall procedure and data path are as follows. i) UE is in 3GPP network (e.g, LTE) ii) UE is triggered to switch to WiFi network iii) UE switches to WiFi network and goes to authentication server first (follow the red line) iv) After completing the authentication process, start user data transaction through the green path. Most important step in this traffic flow is Authentication and Security Association step at the initial step where UE start communicating with 3GPP network over Non-3GPP Access (e.g, WiFi Access Point). This initial step is described in detail in IKE based 3GPP 33.402 section.


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Following is one example of WiFi Offloading From LTE network to WiFi Network. In terms of protocol implementation on UE and Test equipment side in early phase of testing (As of Jun 2014), the colored part has become the major target of validation. According to my experience on testing, step 4 and step 8 is the most tricky step to come over. Especially, passing step 4 (IKEv2) is the most difficult part to step over. < Handover from LTE to WiFi > Following diagram shows overall procedure for the case where UE start communication from LTE and switch to WiFi Network (Untrusted Non-3GPP). This case assumes that UE is connected to LTE before the switch (Handover) and not connected in WiFi. If UE is already connected both to LTE and WiFi before this handover, it will skip the step 2~9 and directly jump to step 10.

< 3GPP 23.402 Figure 8.2.3-1: Handover from 3GPP Access to Untrusted Non-3GPP IP Access with PMIPv6 on S2b >


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Step 1 : UE is initially attached to LTE network. (In the most of testing situation with test equipment, WiFi on UE turned off at this stage).

Step 2 : (In the most of testing situation with test equipment, we turn on WiFi on UE at this time). UE start detecting WiFi network and initiate switching process to WiFi network.

Step 3 : (This may be an optional step) UE and EPC perform Access authentication process. => This corresponds to 33.402 6 Authentication and key agreement procedures

Step 4 : UE and ePDG performs IKEv2 tunnel establishment procedure. (See the details in IKE page or 3GPP 33.402). Following is the decription for this step in 23.402 and I add some comments to relate 23.402 and 33.402. 

The IKEv2 tunnel establishment procedure is started by the UE. The ePDG IP address to which the UE needs to form IPsec tunnel with is discovered as specified in clause 4.5.4.


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After the UE is authenticated, UE is also authorized for access to the APN. The procedure is as described in TS 33.234.

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As part of access authentication the PDN GW identity is sent to the ePDG by the 3GPP AAA server. => This corresponds to step 5 of 33.402 Figure 8.2.2-1

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If the UE supports IP address preservation during handover from 3GPP Access to the untrusted non-3GPP IP access, the UE shall include its address (IPv4 address or IPv6 prefix /address or both) allocated when it's attached to 3GPP Access into the CFG_Request sent to the ePDG during IKEv2 message exchange. => This corresponds to step 2 of 33.402 Figure 8.2.2-1

Step 5 : ePDG sends the Proxy Binding Update message to PDN GW. Followings are conveyed in this message o

MN-NAI

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Step 6B : PDN GW and AAA Server performs the following transaction. 

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PDN GW sends following information to AAA Server o

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APN corresponding to the UE's PDN Connection

AAA Server sends Authorization information to PDN GW

Step 7 : PDN GW processes the Proxy Binding Update from ePDG and update the binding cache entry for the UE. and then sends Proxy Binding Acknowledgement message. This message carries following information. o

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Step 8 : ePDG and UE continues the IKEv2 exchange and IP address configuration => This corresponds to step 15 of 33.402 Figure 8.2.2-1 Step 9 : End of the Handover procedure. At this step, we would have two IP tunnels as follows © Farhatullah Mohammed

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IP sec tunnel between UE and ePDG

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PMIPv6 tunnel between ePDG and PDN GW

Step 10 : This is for the case for connectivity to multiple PDNs. UE establishes connectivity to each PDN that is being transferred from 3GPP access. Step 11 : Disconnect LTE EPS Bearer. PDN GW shall initiate the PDN GW Initiated PDN Disconnection procedure or PDN GW Initiated PDN Deactivation procedure (3GPP 23.401)

63. © Farhatullah Mohammed

LTE CQI Reporting 188

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The periodicity and the frequency resolution is used by the UE to report the CQI feedback which are both controlled by enodeB. In time domain, both periodic and aperiodic CQI reporting are supported. PUCCH (Physical Uplink Control Channel) is used to report the periodic CQI feedback, whereas PUSCH (Physical Uplink Shared Channel) is used to report the aperiodic CQI. Here the enodeB instructs UE to send an individual CQI report embedded into the resource which is scheduled for data uplink transmission. The granularity of the CQI reporting is determined by defining the number of subbands (N), each comprised of k contiguous Physical Resource Blocks. The value of k depends on type of CQI report considered and is a function of system bandwidth. And is given by 𝑵 = [𝑵𝑫𝑳 𝑹𝑩 /𝒌] Where , 𝑵𝑫𝑳 𝑹𝑩 is the number of resource blocks across the system bandwidth. Basically, there are three types of CQI Reporting WideBand CQI eNodeB Configured sub-band feedback UE selected sub-band feedback. For some downlink transmission modes, Precoding Matrix Indicator (PMI), Channel Quality and Rank Indicator are reported by UE. CQI reporting can be again classified into 2: Periodic Reporting and Aperiodic Reporting. Periodic CQI Reporting UE reports CQI, PMI and RI with the reporting periods configured by the higher layers on PUCCH (example: used for RRC Connection Reconfiguration, RRC Connection Setup) Aperiodic CQI Reporting: Aperiodic CQI reporting is used to provide large and more detailed reporting in a single reporting instance via PUSCH. Report timing is triggered by DCI(DCI 0, RACH Response) Aperiodic reporting on PUSCH is scheduled by enodeB by setting CQI request bit in uplink resource grant sent on PDCCH. WideBand Feedback: UE reports one wideband CQI value for the whole system bandwidth. eNodeB Configured sub-band feedback: UE reports wideband CQI value for the whole system bandwidth. UE reports CQI value for each sub-band calculated assuming transmission only in relevant sub band. Sub band CQI reports are encoded differentially, with respect to wideband CQI using 2 bits as follows. Sub band differential CQI offset = Sub-band CQI index – Wide band CQI index. Possible sub bands CQI offsets are {<-1, 0, +1, >+2}


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UE selected sub-band feedback: UE selects set of M preferred sub-bands of size k with in the whole system bandwidth. UE reports one wideband CQI value and one CQI value reflecting the average quality of selected M bands. UE also reports the position of selected M sub bands using a combinatorial index r defined as

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contains M sorted sub band indices

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Differential CQI = Index of average of M preferred sub-bands – Wideband CQI index. Possible CQI differential values are {<+1,+2,+3, >+4}

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Table Below shots the CQI reporting with reference to Transmission modes.

Periodic CQI Reporting: If eNodeB is configured for UE to report periodically, UE reports the CQI using the PUCCH. One wideband and UE selected sub-band is possible for periodic CQI reporting for all downlink PDSCH transmission modes. As with aperiodic reporting the type of periodic reporting is configured by eNodeB by RRC signaling. For wide band CQI reporting, the periodic can be configured upto {2,5,10,16,20,32,40,64, 80 ,128 ,160}ms or off.


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The wideband reporting is similar to sent via PUSCH, the UE selected sub band CQI using PUCCH is different. Here the total number of sub-bands N is divided to J fractions called bandwidth parts. The value of J depends on the system bandwidth. CQI value is computed and reported for single selected sub-bands from each bandwidth part, along with the corresponding sub band index.

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CQI Reporting for Spatial Multiplexing: If UE is configured in PDSCH transmission modes 3, 4, 8 or 9, the enodeB may use spatial multiplexing to transmit two codewords simultaneously to UE with independently selected MCS. If UE is not configured to send RI feedback, or if the reported RI is equal to 1, in any case in transmission mode 3, UE feedbacks only one CQI report corresponding to single codeword. If RI is configured to report R1 greater than 1 in transmission modes 4 or 8 - for aperiodic reporting, each CQI report [whether wideband or subband] comprises of two independent CQI reports for the two codewords. For Periodic CQI reporting, one CQI report is feedback for one code word, and a second three bit differential CQI report is fed back for the second codeword. – [for both wideband and sub band reporting] Differential cqi report for the second codeword can take the following values relative to the CQI report for the first codewords. <-4,-3,-2,-1,0,+1,+2,>+3

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64. LTE Interference Rejection Combining -IRC -

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Interference Rejection combining – IRC concept is to regenerate the transmitted signal based on the estimated data from the previous receptions, emulate the distortions occurring from the multi-path channels and finally subtract all the regenerated interfering signals from the uplink received signals, to obtain more reliable estimation of the original users’ data. This feature utilizes the spatial separation and the characteristics of inter cell interference to determine the power of interfering UE which belongs to another cell. Once the pattern and the power level is determined, the victim cell can then remove the interferer from the received cell. Whereas, Maximum Ratio Combining – MRC do not make use of spatial characteristics of the interference when calculating antenna weighting. In the case where there are only small number of dominating interfering sources, IRC can provide more improvement than MRC when there are reasonable number of receive antennae for IRC to compensate. In the case where there are large number of equal power signals arriving at the receiving antennae, the gain of the Interference rejection combining over the maximum rejection combining is not as significant. Interference rejection combining is implemented in the baseband processing module of the enodeB. It can reduce the interference impact of the neighbouring users in the uplink. Therefore, Interference Rejection Combining – IRC can increase the uplink users throughput significantly and hence improves the users experience.

When Uplink Interference Rejection combining is used, the simulations shows maximum SINR gain of 7dB can be achieved over the traditional MMSE interference reduction method. By outperforming MMSE and interference Rejection combining, the network coverage and better Qos for cell edge is enhanced.


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UE Inactivity Timer

User inactivity timer means the network discovers that for a certain period of time (defined by the value of user inactivity), there are no user plane packets exchanged between the UE and the network. On the expiry of the user Inactivity timer, the network releases the default EPS bearer and hence UE is forced to enter idle mode. Once the user is put in the idle mode, the default radio bearer is torn down i.e.. there is no RRC connection once the user enters in the idle mode. When the user comes out of the idle more (due to traffic, paging, expiry of timers), UE has to reestablish the RRC connection before the bearers get reactivated. If the UE unexpectedly loses power (if the battery is removed, as in your example), the eNB is not informed that the UE is gone. However, there are two things going on simultaneously. First, since the UE is no longer on the channel, it no longer responds to any signaling messages, and it no longer provides any feedback to the eNB (such as CQI reports); eventually, the eNB will realize that the UE has been lost, and will shut down the RRC Connection, indicating that the radio connection is broken. Secondly, since the UE is not sending or receiving data, the eNB's inactivity timer will eventually expire, and the eNB will shut down the connection with a reason of user inactvity. The timer is typically set to about 10 seconds. Whichever method detects the problem first will determine the reason given to the MME when the eNB sends a UE Context Release Request to the MME. The MME will in turn send a UE Context Release Command to the eNB, which is what actually shuts down the context in the eNB.


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TROUBLESHOOTING


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RRC Connection Release

Often time while doing a drive test the RRC collection released gets logged by our data collection tools and later, while debugging our drive tests we see, RRC connection Release. Many times we wonder why we received that message. Is it because we finished our 500 GB file download? Did we unintentionally press a button and we ended the call? What happened? There are many cases where and when the UE receives an RRC connection release: a) Going to idle mode: In this case, the UE will receive an RRC connection release from the eNodeB due to the expiration of the inactivity timer (in most networks configured to approximately 10 seconds). Release Cause: Other

b) Drop Call - > RLC Failure: When the number of retransmissions at the RLC layer in the Downlink direction reaches its maximum value given by the parameter MaxRetxThreshold, the eNodeB releases the context and sends an RRC connection release to the UE. Release Cause: Other.


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c) Drop Call - > RRC Connection Reestablishment Reject: Either because the feature is not adopted or because a race condition occurred in which the case just presented happened first, the eNodeB responds with a RRC connection reestablishment reject to the UE. Release Cause: Other.


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LTE Bible d) Tracking Area Update: During a successful tracking area update, the eNodeB will send an RRC connection release to the UE after sending a tracking area update message (from the MME) when no new GUTI is allocated or after the tracking area update complete message is received from the UE, if it received a new GUTI. Release Cause: Other.

e) During Detach: Either during normal detach or abnormal detach, both by an UE initiated detach or network initiated detach, the UE receives an RRC connection Release from the network. Elements in the Network that may cause a detach message sent from the MME to the UE are: Expiration of timers at the P-GW for the last bearer the UE had, capacity issues or errors. Errors or Capacity issues at the S-GW Expiration of timers at the MME (t3412) without TAU, errors at the MME, configuration problems, etc. Release Cause: Other or Normal.


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LTE Bible Given the above, the RRC connection release message is caused by many reasons. Before arriving to a conclusion just by analyzing a simple UE logfile, a cell trace or MME trace analysis is required to arrive to sounded conclusions.


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2.

LTE DROP SESSIONS

There are several reasons why a session may drop in LTE. However, whether the session is dropped or not depends on the particular vendor implementation. That is, the drop may be caused by a UE message or by measurements carried out by the eNodeB. Both the UE and the eNodeB may check if the radio link is in-synch. In this blog, we will describe the activities that the UE carries out to determine if the radio link is in-synch and their consequences. Part 2 of this blog, will present the activities that the eNodeB may carry out to determine if the radio link is in-synch or not. So…. When is the Radio Link in-synch? The UE is expected to monitor the RS in the downlink. Based on the signal strength of the Reference Signals (i.e., the RSRP), the UE will determine if it can decode the PDCCH based on a certain set of parameters that are provided in the specs. Each UE will have a different RSRP threshold in which it will assume it cannot read the PDCCH. If the Reference signals have enough strength such that the UE can decode consistently the PDCCH, then the link is In-Synch. How do we determine if the Radio Link is out of Synch? The full procedure for determining if the link has failed due to being out of sync is shown in the figure below. In the picture, there are three parameters shown: n310: This parameter indicates the number of 200 ms intervals when the UE is unable to successfully decode the PDCCH due to low RSRP detected. That is, this parameter indicates the number of times in which the UE cannot successfully decode 20 consecutive frames in the downlink. t310: It is a timer, in seconds, used to allow the UE to get back in synchronization with the eNodeB. n311: This parameter indicates the number of 100 ms intervals that the UE must successfully decode the PDCCH to be back in-synch with the eNodeB. That is, this parameter indicates the number of times in which the UE must successfully decode 10 consecutive frames in the downlink in order for the UE to assume the radio link is insynch. If the UE detects n310 consecutive out-of-sync indications, it starts the t310 timer. If the timer expires, the link has failed. If the UE detects n311 consecutive in-sync indications prior to the t310 timer expiring, then the timer is stopped and the link has not failed.


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So what happens after the UE detects that the link failed? If the UE determines that the Radio Link fails, the UE will try to reconnect with an RRC Connection Reestablishment Request message. There are a number of cases that could occur based on vendor implementation. What if the eNodeB does not support RRC Connection Reestablishment? The case shown in the figure below is the simplest case where the eNB does not support RRC Connection reestablishment. In this case, the eNB responds with an RRC Connection Reestablishment Reject message. Simultaneously, the eNB will realize that the radio link has failed and request the connection to be release to the MME. It first requests to drop the UE Context or the connection to the UE. The cause value is set to “Radio Connection with UE Lost.” The MME will respond with a UE Context Release Command. At this point, the eNodeB will respond with the UE Context Release Complete message to the MME and will release the RRC connection with the UE by sending an RRC Connection Release to the UE. Depending on the RF conditions, the UE may or may not receive this message.


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LTE Bible What if the eNodeB does support RRC Connection Reestablishment? If the eNodeB supports RRC connection Reestablishment, and assuming that the eNodeB finds both the UL and DL in synch when it receives the RRC connection reestablishment request message, two scenarios may occur: RRC connection reestablishment success and failure. In the case of an RRC connection reestablishment success, the following signaling is carried exchanged.

If the RRC connection gets successfully reestablished, then the session does not get dropped. If the RRC connection reestablishment procedure fails in one of its steps, then the eNodeB will send the UE context release request message to the MME. Note that the RRC connection reestablishment process may fail in several steps. Below, in the figure, only one case is shown.


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If the RRC connection reestablishment fails, then the session is dropped. The types of failure that the eNodeB may detect (again, these may be vendor specific) are: a) DL failure (RLC failures) b) UL failure (Physical layer failure).

DL Failure at the RLC layer: The RLC Layer has a failure when data or signaling that is sent over the air is unsuccessful and the RLC Layer stops trying. When data is sent over the air, but is received incorrectly, the receiver will send a NACK. Also, the transmitter can send a request for an acknowledgement of all received packets, by © Farhatullah Mohammed

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LTE Bible setting the poll bit. The receiver will then send a list of all received packets. If a sent packet is not received, it is considered lost. In either case, the transmitter will retransmit. See figure below.

This procedure can repeat, but at some point the transmitter will give up on the packet. If that happens, the transmitter declares that the radio link has failed and starts the procedures to communicate that to the other side. The parameter MaxRetxThreshold determines the number of times a packet is retransmitted at the RLC layer in the downlink. If this number is reached, the eNodeB declares a DL RLC failure and “kills” the context as shown in the picture below.


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UL Failure at the Physical layer: Not all vendor implementation support this type of failure detection. It essentially consists in measuring the power of the sounding reference signals (SRS) sent by the UE in the UL. If the power is below a given SINR threshold, a timer gets started. If the SINR remains under the stated SINR threshold for the entire duration of the timer, then the eNodeB declares the UL as out of synch and proceeds to “kill” the context. If the SINR of the SRS goes above a second specified threshold during the timer duration, the UL is said to be in-synch and no actions are carried out. Below, the actions carried out by eNodeB are shown when an UL Physical Layer failure is detected.


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Yes, you are right!!! But think about the consequences again! Yes, increasing the value of maxretxthreshold may result in a decrease in the number of drop sessions due to RLC DL failures. However, to avoid a large number of drops, the best thing to do is to clean the RF environment in your network.


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3. Downlink Throughput Troubleshooting Several are the conditions that produce low throughput in the downlink. This blog shows a simple flowchart that attempts to guide you while troubleshooting cells with poor performance in the downlink. Note that the flowchart is not comprehensive but rather an informative guide for you to start.


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LTE Bible In this blog we will briefly describe general troubleshooting guidelines for downlink throughput in LTE networks with MIMO 2x2. The reader is advised to look for particular counters in their respective OEM’s documentation to address each of the fields explored below. The general troubleshooting strategy is described below and the covered reasons for bad throughput are shown in the figure below.

Figure 1. Low Throughput causes in the Downlink for LTE networks. Step 1: Identify cell with low DL (downlink) throughput a) The first thing is to identify those cells with low throughput. This threshold is defined by your network policies and practices (it also depends on your design parameters). Reports should be run for a significant number of days so that data is statistically valid. Step 2: Identify Downlink interference a) Cells with downlink interference are those whose CQI values are low (an exception to this rule is when most traffic is at the cell edge –bad cell location-). Analyze the CQI values reported by the UE for 1. Transmit Diversity 2. MIMO one layer 3. MIMO two layers Typical values for transmit diversity oscillate between 7 and 8. Typical values for MIMO one and two layers oscillate between 10 and 12. b) If low CQI values are found after a CQI report is obtained, then downlink interference might be the cause of low throughput.


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LTE Bible c) Common sources of interference in the 700 MHz band (LTE deployment in the USA) are: inter-modulation interference, cell jammers and wireless microphones Step 3: BLER Values a) Run a report for BLER in the cells identified. The BLER should be smaller or equal than 10%. If the value is larger, then, there is an indication of bad RF environment. b) Typical causes of bad BLER are downlink interference, bad coverage (holes in the network, etc.) Step 4: MIMO Parameters a) Identify the transmission mode of your network. There are seven transmission modes as shown in the table below

b) Adjust the SINR thresholds for transition of transmission modes as recommended by the OEM. Request the Link Level simulations they used to set these thresholds and see if the conditions under which the values were calculated apply to your network. Otherwise, update them if the parameters are settable and not restricted. Step 5: Low Demand a) Run a report using the counters provided by the OEM to find 1. Maximum number of RRC connections supported per cell (parameter or feature) 2. Maximum number of RRC connections active per cell 3. Average number of RRC connections active per cell 4. Maximum number of users per TTI supported per cell (parameter or feature) 5. Maximum number of users scheduled per TTI in the cell(s) of interest 6. Average number users scheduled per TTI in the cell(s) of interest

b) If the maximum number of RRC connections active per cell is close or equal to the maximum number of RRC connections supported, then. The cause for low throughput is load. © Farhatullah Mohammed

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LTE Bible c) A high number of scheduled users per TTI does not necessarily mean that demand is the cause for low throughput. Step 6: Scheduler Type a) Find the scheduler types your OEM supports b) Select the one that is more convenient for the type of cell you are investigating. Examples of schedulers are: round robin, proportional fairness, maximum C/I, equal opportunity, etc. OEMs allow you to switch the scheduler in your network but recommend one in particular. c) The wrong scheduler may be the reason for bad throughput. Step 7: CQI reporting parameters a) Check if your network is using periodic or aperiodic CQI reporting (or both). b) Verify the frequency in which the CQI reporting is carried out for periodic reporting as well as the maximum number of users supported per second. c) If the value is too small compared with the maximum number of RRC active connections, then, increase the values of the parameters CQIConfigIndex as well as RIConfigIndex (deal with in future blog). d) If your network is not using aperiodic CQI reporting, then enable it. e) Slow frequencies of CQI reporting might yield bad channel estimations that prevent the eNodeB from scheduling the right amount of data and Modulation and Coding Schemes to UE. Step 7: Other a) Run a VSWR report or ask your OEM to run it for you. b) High values of VSWR result in low throughput due to losses. c) Check your backhaul capacity. Often times, the backhaul links are shared among multiple RATs. Make sure your backhaul is properly dimensioned. At the end of this methodology, you will be able to determine if the reasons for low throughput in your cells is one of the following or a combination, thereof: - BLER (bad coverage) - Downlink Interference (Bad CQI) - MIMO Parameters - Scheduling algorithm - Low Demand - CQI reporting frequency - Other (VSWR, Backhaul capacity) © Farhatullah Mohammed

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4. Uplink Throughput Troubleshooting Several are the conditions that produce low throughput in the uplink. This blog shows a simple flowchart that attempts to guide you while troubleshooting cells with poor performance in the uplink. Note that the flowchart is not comprehensive but rather an informative guide for you to start.


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LTE Bible The general troubleshooting strategy is described below and the covered reasons for bad throughput are shown in the figure below.

Figure 1. Low Throughput causes in the Uplink for LTE networks. Step 1: Identify cell with low UL (uplink) throughput a) The first thing is to identify those cells with low throughput. What is considered as low throughput is a threshold defined by your network policies and best practices (it also depends on your design parameters). Reports should be run for a significant number of days so that data is statistically valid. Step 2: Identify Uplink interference a) Run a report for RSSI in the uplink. Most OEM provide with counters and or tools to assess the RSSI in a span of days. Cells with uplink interference are those whose RSSI values are high (higher than -90dBm, for instance). b) Typical scenarios where these values are high are indoor environments (i.e.: arenas, airports, etc.) c) Common sources of interference in the 700 MHz band (LTE deployment in the USA) are: high values of traffic in the uplink, external source of interference, high values of P0nominalPUCCH and P0-nominalPUSCH (Consult your technical lead on the settings of these parameters) Step 3: BLER Values a) Run a report for BLER in the cells identified. The BLER should be smaller or equal than 10%. If the value is larger, then, there is an indication of bad RF environment. b) Typical causes of bad BLER are uplink interference, bad coverage (holes in the network, etc.) Step 4: Low Demand © Farhatullah Mohammed

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LTE Bible a) Run a report using the counters provided by the OEM to find 1. Maximum number of RRC connections supported per cell (parameter or feature) 2. Maximum number of RRC connections active per cell 3. Average number of RRC connections active per cell 4. Maximum number of users per TTI supported per cell (parameter or feature) 5. Maximum number of users scheduled per TTI in the cell(s) of interest 6. Average number users scheduled per TTI in the cell(s) of interest b) If the maximum number of RRC connections active per cell is close or equal to the maximum number of RRC connections supported, then. The cause for low throughput is load. c) A high number of scheduled users per TTI does not necessarily mean that demand is the cause for low throughput. Step 5: Scheduler Type a) Find the scheduler types your OEM supports b) Select the one that is more convenient for the type of cell you are investigating. Examples of schedulers are: round robin, proportional fairness, maximum C/I, equal opportunity, etc. OEMs allow you to switch the scheduler in your network but recommend one in particular. c) The wrong scheduler may be the reason for bad throughput. Step 6: Power Headroom a) Run a report to find out the average power headroom that UEs have in your network. b) A low value of power headroom means that UEs do not have available power to transmit in the uplink and hence, the throughput is low. c) Low values of power headroom are 5 dB or smaller. d) Typical causes of low power headroom are uplink interference and/or incorrect power control parameter settings, to mention a few. Step 7: Other a) Run a VSWR report or ask your OEM to run it for you. b) High values of VSWR result in low throughput due to losses. c) Check your backhaul capacity. Often times, the backhaul links are shared among multiple RATs. Make sure your backhaul is properly dimensioned.


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LTE Bible At the end of this methodology, you will be able to determine if the reasons for low throughput in your cells is one of the following or a combination, thereof: - BLER (bad coverage) - Uplink Interference (high RSSI) - Low Power headroom - Scheduling algorithm - Low Demand - Other (VSWR, Backhaul capacity)


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5.

Handover Troubleshooting

There are three ways of optimizing handovers in LTE: a) Via the modification of the parameters a3offset and hysteresisa3 b) By changing the parameter timetotriggereventa3 c) Via the modification of the parameter filtercoefficient for event a3. These set of blogs will dealt with parameter setting for Periodic Reporting of Event A3 only. The intention is to deal with each of the cases mentioned above, one at a time. Hence, this blog will concentrate in case a). Definitions: Event A3 is defined as a triggering event when a neighbour cell becomes an offset better than the serving cell. The UE creates a measurement report, populates the triggering details and sends the message to the serving cell. The parameters that define the trigger include: 

a3offset: This parameter can be found in 3GPP 36.331. It configures the RRC IE a3-Offset included in the IE reportConfigEUTRA in the MeasurementConfiguration IE. The value sent over the RRC interface is twice the value configured, that is, the UE has to divide the received value by 2.The role of the offset in Event A3 is to make the serving cell look better than its current measurement in comparison to the neighbor.

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Hysteresisa3: The role of the hysteresis in Event A3 is to make the measured neighbor look worse than measured to ensure it is really stronger before the UE decides to send a measurement report to initiate a handover.

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timetoTriggera3: The role of ttt in Event A3 is to avoid a ping-pong effect.

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CellIndividualoffsetEutran: This parameter is applied individually to each neighbor cell with load management purposes. The higher the value allocated to a neighbor cell, the “more attractive” it will be. This parameter can only be used if the neighbor list is broadcast in SIB4 or in an RRC connection reconfiguration.


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Based on the picture above, event A3 will trigger when: RSRP(target) > RSRS(Serving) +a3offset + hysteresisa3 – cellindividualoffsetEutran And this condition is valid for timetotriggera3. At the expiration of timetotriggera3, if the UE does not receive an RRC connection reconfiguration message (handover command) from the eNodeB, then it will start a timer called reportingintervala3. At the expiration of this timer, if the conditions for event A3 are still met and the eNodeB has not responded, then another measurement report will be sent to the eNodeB. This process will continue until the eNodeB responds or until a number of measurement reports given by the parameter reportingamount have been sent. Examples: The table below assumes that cellindividualoffsetEutran is not used and shows when the eventa3offset is triggered and when the UE ceases sending measurement reports.

As it can be seen from the table, eventa3 triggers at a3offset+hysteresisa3 However!!! After the first measurement result, subsequent measurement results can be sent if the RSRP of the neighbor cell is only a3offset-hysterisisa3 dB stronger! Hence, weaker neighbors could be reported in the measurements sent by the UE (this case is very rare but it exists in real systems). Therefore, it is recommended to follow the optimization rules:


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LTE Bible a) a3offset should always be larger than hysteresisa3 if we want UE to handover to cells with an RSRP at least equal to the RSRP value of its serving cell. b) Ensuring a3offset > hysteresisa3 avoids ping-pongs c) The higher the value of a3offset+hysteresisa3 the more we drag the calls to neighboring cells. This is very useful where we have coverage holes (not a one to one deployment scenario on top of 3G cells) d) The smaller the value of a3offset+hysteresisa3 the faster we release the calls to neighboring cells. This is useful in those scenarios where a large number of LTE cells exists in a given geographical area. e) The higher the value of a3offset+hysteresisa3 the more difficult we make it for calls do handover to other cells. Remember, eventa3 triggers at a3offset+hysteresisa3. Subsequent message reports are sent when the RSRP of the neighbor cell is a3offset-hysteresisa3 (See figure below).

TimetoTrigger Event a3 As explained in part 1 of these blogs, if the RSRP of a neighbor cell is a3offset+ hysteresisa3 dB stronger than the serving cell for a time period equal to timetotriggera3 then the UE sends the first measurement report to the eNodeB indicating that eventa3 has occurred. timetotriggera3 typical values are [0, 40, 64, 80, 100, 128, 160, 256, 320, 480, 512, 640, 1024, 1280, 2560, 5120] milliseconds. Clearly, the utilization of timetotriggera3 is highly dependent on the parameters a3offset and hysteresisa3. However, some general troubleshooting guidelines are provided here to minimize ping pong effects. Rules: a) If a3offset+ hysteresisa3 is relatively large (i.e.: 6dB or stronger), then a value of timetotriggera3 under 100 ms is acceptable. Explanation: Since the RSRP of the neighbor cell is already stronger than the value of the source cell, the time to trigger should not be large.


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LTE Bible b) If a3offset+ hysteresisa3 is relatively small (i.e.: 2dB), then a value of timetotriggera3 should be around 320 to 640 ms. Explanation: Since the RSRP of the neighbor cell is not much stronger than the value of the source cell, the time to trigger should not large to ensure the value remains the same for a long period of time. c)

If a3offset = hysteresisa3, see b)

d) If a3offset > hysteresisa3, see a) e)

If a3offset < hysteresisa3, see a)

However, these recommendations depend much on the speed of the mobile and the coverage scenarios. The value allocated to timetotriggera3, hence, depends on: 

Parameter setting of a3offset and hysteresisa3,

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Morphology (dense urban, urban, suburban, rural)

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Speed of UE in the cells (freeways and or suburban roads). Filter Coefficient for Event a3 Once the UE is configured to do measurements, the UE starts measuring reference signals from the serving cell and any neighbors it detects. The next question is whether the UE should look at just the current measurement value, or if the recent history of measurements should be considered. LTE, like other wireless technologies, takes the approach of filtering the currently measured value with recent history. Since the UE is doing the measurement, the network conveys the filtering requirements to the UE in an RRC Connection reconfiguration message. The UE filters the measured result, before using for evaluation of reporting criteria or for measurement reporting, by the following formula:

where 

Mn is the latest received measurement result from the physical layer;



Fn is the updated filtered measurement result, that is used for evaluation of reporting criteria or for measurement reporting;

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Fn-1 is the old filtered measurement result, where F0 is set to M1 when the first measurement result from the physical layer is received; and

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a = 1 / 2(k/4), where k is the filterCoefficent for the corresponding measurement quantity received by the quantityConfig.


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LTE Bible Then, the UE adapts the filter such that the time characteristics of the filter are preserved at different input rates, observing that the filterCoefficent k assumes a sample rate equal to 200 ms. The parameter “a” defines the weight given to current value and (1-a) (i.e., the remaining weight is given to the last filtered value). For example, if filter coefficient k = 4, then a = ½^(4/4) =1/2. This means that new measurement has half the weight and the last filtered measurement gets the other half of the weight. Example of Filter coefficient values are: 

Case 1: value k = 8 , a = ¼, Fn = ¾ Old + ¼ New



Case 2: value k = 4, a = ½, Fn = ½ Old + ½ New Optimization Rules: a) A high value of the parameter filtercoefficient will provide higher weight to old measurements (more stringent filter)(the opposite is true) b) The higher the values of filtercoefficient the higher the chances of eliminating fast fading effects on the measurement reports

1. This eliminates reporting a cell which RSRP was suddenly changed due to multipath or fast fading 2. Which in turns eliminates the chances to handover to a cell which RSRP was strong for some milliseconds 3. Therefore reducing the chances for Ping-Pong effects c) A value of 8 is typically used in the network although a value of 16 might also be used in dense urban areas.


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6. Effect of Closed Loop Pwr Control on RSSI Effect of Closed Loop Power Control on the UL RSSI The Received Signal Strength Indicator (RSSI) in the uplink is also affected by the parameter settings that govern closed loop power control in LTE. Immediately after the UE completes an RRC connection with the eNodeB, the UE uses closed loop power control on both, the PUCCH and the PUSCH. 1.

PUSCH

In particular, the power that the UE transmits the PUSCH with is given by:

The power control formula for the uplink for the PUSCH in LTE can be broken into five key parts. The first part is the amount of additional power that is needed based on the size of the RB allocation. The higher the number of RBs, the higher the power that is required. The second part is called P0. It is basically the assumed interference that the UE is expected to overcome. P0 is composed of two subcomponents. The first is called P0_Nominal_PUSCH and it is communicated over SIB2. It is valid for all UEs in the cell. The second component is called P0_UE_PUSCH and it is a UE-specific value. It is optional. The third part of this equation is the Path Loss (PL) and the impact of the PL or Alpha. PL is just calculated, but the Alpha value communicated to the UE in SIB2. If the Alpha value is set to 1, then all of the PL needs to be taken into account in the power control formula. Some vendors might not allow you to change this value, though (as it is hardcoded). The fourth part is an MCS-specific component. If the eNB wants the UE to adjust its power based on the MCS that is assigned, it will be taken into account here. Lastly is the f(i) value, which is simply the closed-loop feedback. This is the additional power the UE will add to the transmission based on specific feedback by the eNB.


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LTE Bible Hence, for the PUSCH, two parameters affect the UE transmit power, and therefore, our UL RSSI: a)

PO_nominal_PUSCH

b) Alpha. 2.

PUCCH:

The power control formula for the uplink for the PUCCH in LTE can be broken into four key parts. The first part is called P0. It is basically the assumed interference that the UE is expected to overcome. P0 is composed of two subcomponents. The first is called P0_Nominal_PUCCH and it is communicated over SIB2. It is valid for all UEs in the cell. The second component is called P0_UE_PUSCH and it is a UE-specific value. It is optional. The second part of this equation is the Path Loss (PL) and the impact of the PL or Alpha (the same value used for the PUSCH – See above-). The third part is an MCSspecific component. If the eNB wants the UE to adjust its power based on the MCS that is assigned, it will be taken into account here. Lastly is the f(i) value, which is simply the closed-loop feedback. This is the additional power the UE will add to the transmission based on specific feedback by the eNB. This value is different for each format type of the PUCCH. A different value is given to the UE in SIB2 for formats 1, 1a, 1b, 2, 2a and 2b.

Hence, the parameters that controls the transmit power in the PUCCH are: a)

PO_nominal_PUCCH

b) Alpha The higher the value of PUCCH and the higher the value of PUSCH, the more power the UE will transmit, the better the UL BLER, the higher the throughput and the higher the UL SINR. However, in high capacity cell, this might not be true and the opposite effects might be encountered. Examples of such situations are: Airports, events, convention centers, etc. It is recommended to analyze the UL RSSI in these types of venues during high capacity scenarios and adjust accordingly. Bear in mind that the Alpha value affects both, the PUCCH and the PUSCH. © Farhatullah Mohammed

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7.

Cell Radius

The cell radius in LTE is affected and/or determined by three factors: a) The Preamble Format b) The Cyclic Shift the corresponds to the ZeroCorrelationZoneConfig parameter and, c) The Cell Radius Parameter A) Preamble Format

LTE FDD supports four preamble formats (as of today, not all of them currently supported by the equipment manufacturers). The preamble consists of a cyclic prefix (to handle multipath interference) followed by an 800 μs sequence. In preamble formats 2 and 3, the sequence is repeated. The total length of the cyclic prefix and the sequence(s) determines how long it takes to transmit the preamble. Since the actual physical transmission occurs in units of sub-frames (1 ms), the remaining time determines how far away the UE can be without overlapping another UE's access attempt (the guard time). For further details, refer 3GPP TS 36.211 - Physical Channels and Modulation. The operator typically must pick a preamble format to determine the coverage area desired. In the event of remote sites deployment, the length of the fiber to the remote cells must be considered as part of the cell radius (this includes Distributed Antenna Systems -DAS- ). Since the speed of electromagnetic waves over fiber is only two thirds of the speeds in free space, the total cell radius reduces to the values shown in the table below.


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The parameters ZeroCorrelationZoneConfig and RootSequenceIndex are used to generate 64 random access signatures in each cell (all these access signatures should be different in each cell). Both, the ZeroCorrelationZoneConfig and the RootsequenceIndex paramaters are broadcast in SIB2. The random access sequences are built via the selection of a Zadoff-Chu sequence (one out of 839) given by RootSequenceSequence and a cyclic shift (used 64 times to generate the 64 random access signatures from the Zadoff-Chu sequence selected). The cyclic shift is indirectly given to the UE by the parameter ZeroCorrelationZoneConfig, as shown in the table below (see columns two and three and note that the cyclic shift has limited values). The available cyclic shifts are listed in 3GPP TS 36.211 table 5.7.2.-2.

The cyclic shift is also related to the cell size. The relationship between the cyclic shift and the cell size is given by equation (1): (NCS - 1) * (800 μs/839) ≥ RTD + Delay Spread

(1)

In the equation, RTD stands for Round Trip Delay (twice the cell radius). Hence: RTD = 2 R/c

(2)

Then, the cell radius is given by: R ≤ [c/2]*[(NCS - 1)*(800 μs/839)-Delay spread] © Farhatullah Mohammed

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LTE Bible For instance, if we assume that ZeroCorrelationZoneConfig is 12, then from the table above, Ncs = 119. Furthermore, if the delay spread = 6 μsec, then the cell size will be approximately 15.97km. Note that the smaller the cyclic shift, the smaller cell size. The delay spread in the equation above should be calculated by the RF engineer after a drive test is carried out in the areas of interest. The value of the delay spread is typically different for rural, suburban, urban and dense urban environments. The third factor that affects the cell radius in LTE is the parameter cell radius. Equipment manufacturers typical offer a parameter called cellradius, that allows the modification of the cell radius. The units of this parameter are typically Kilometers. EXAMPLE: Let's assume that the preamble format picked (or the only one currently available) is type 0 (which offers a maximum cell radius of approximately 14 km). The possible values of the parameters PrachconfigurationIndex are, therefore, 0 to 15. A network operator may decide to classify their cells into rural, suburban, urban and dense urban cells. Furthermore, the operator may allocate a cell radius to different morphologies, say: Rural = 14 km, Suburban = 8 km, urban = 5 km and dense urban = 2 km. In this case, the values of the parameters associated with the cell radius could be: PrachConfigurationIndex = Any number between 0 and 15 (Preamble Format 0). Cellradius = 14 (rural), 8 (suburban), 5 (urban), 2 (Dense urban), ZeroCorrelationZoneConfig = 12 (rural), 9 (suburban), 8 (urban) and 4 (dense urban). Notes: a) The value of PrachconfigurationIndex affects the RACH capacity (addressed in a future blog). b) The value of ZeroCorrelationZoneConfig affects the cell radius as explained in a previous blog (See table below).


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8. A3 Event Parameter Optimization The most important parameters involved in event a3 reporting are listed below: -

eventA3offset hysteresis timeToTrigger sMeasure cellIndividualOffset triggerQuantity reportAmount reportInterval filterCoefficientRsrp

LTE R8 uses hard handover. Therefore, one of the main optimization concerns is to avoid ping pongs between cells. Ping pongs significantly reduce user throughput and increases signaling in the E-UTRAN (in the case of X2 handovers) and in the EPC (in the event of an S1 handover). The table below shows an example with three different combinations for the parameters eventA3offset and hysteresis.

Assuming a cellindividualoffset = 0, then: Event a3 will trigger when RSRPsource + eventa3offset +hysteresis <= RSRPtarget + hysteresis Event a3 will not be further valid when RSRPsource + eventa3offset +hysteresis > RSRPtarget + hysteresis

Under these circumstances: a)

CASE 1:

a. Event a3 will trigger when the RSRP of the target cell is 2dB stronger than the RSRP of the serving cell b. The UE will cease sending measurement reports when the RSRP of the target cell is less than 2dB stronger than the RSRP of the serving cell b)

CASE 2:


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LTE Bible a. Event a3 will trigger when the RSRP of the target cell is 2dB stronger than the RSRP of the serving cell b. The UE will cease sending measurement reports when the RSRP of the target cell is weaker than the RSRP of the serving cell c)

CASE 3:

a. Event a3 will trigger when the RSRP of the target cell is 2dB stronger than the RSRP of the serving cell b. The UE will cease sending measurement reports when the RSRP of the target cell is -2dB or weaker than the RSRP of the serving cell Clearly, case 3 could be counterproductive since a candidate can be reported to the source cell when the target is weaker than the source cell!! A healthier approach is to provide a value of say, 3dB to a3offset and a value of 1 dB to the hysteresis parameter (for core cells). This will ensure that the target cell is at least 4 dB to trigger the event a3 and the handset will not report a candidate when the target is not at least 2dB stronger than the source cell (assuming that the number of measurement reports given by reportamount haven't expired). Also, in order to ensure that the target cell is strong enough than the source cell for a good amount of time, the parameter timetotrigger should be set to values of 480, 512 or 640 miliseconds. However, a drive test is recommended before and after these parameters have been modified along with the creation of counter reports for X2 and S1 handovers.


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9.

Parameters value Impact

The effect of the value of the parameters CQI-PMI-Configindex and RIconfigIndex on the Downlink throughput. This set of parameters is used when periodic CQI reporting is used. CQI-PMI-ConfigIndex determines how often the UE is supposed to report CQI (channel quality Indicator) and PMI (pre-coding matrix indicator) on the PUCCH. RI-ConfigIndex determines how often the UE is supposed to report RI (Rank Indicator) on the PUCCH. CQI, PMI and RI are transmitted to the eNodeB in format 2,2a or 2b in the PUCCH as shown below (the picture below assumes a bandwidth of 10 MHz for the UL and 1 resource block for the PUCCH).

The following tables show the periodicity of reporting for CQI/PMI and RI in the units of sub-frames, based on the configuration index for CQI/PMI and the RI that is sent to the UEs during RRC procedures. The tables are extracts from TS36.213 (Tables 7.2.2-1A and 7.2.2-1B).


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Mapping of cqi-pmi-ConfigIndex to Subframe Periodicity

Mapping of ri-ConfigIndex to Subframe Periodicity

For Instance, if CQI-PMI-ConfigIndex is set to a value between 17 and 36, the UEs are required to send a CQI and PMI report every 20 sub-frames. That is, every 20 mili-seconds (See highlighted row). On the other hand, if RI-ConfigIndex is set to a value between 322 and 482, then UEs are required to send a RI report every 4*20ms = 80 ms. Now, how do CQI-PMI-ConfigIndex and RI-ConfigIndex affect our downlink throughput? Well… As usual, there is a tradeoff with parameter settings:


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LTE Bible a) Low values of these parameters increase the periodicity of reporting CQI, PMI and RI. Hence, the eNodeB has more accurate information of the downlink conditions each UE has. This allows the eNodeB to provide better inputs to the scheduling algorithm and select the best choice of MCS as well as power to transmit in the downlink. b) The opposite is true.


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10.

PUCCH Capacity

The following table shows the PUCCH formats used for channel feedback. The channel feedback could carry channel quality indicator (CQI), Precoding Matrix Indicator (PMI) and Rank Indicator (RI), depending on transmission mode configured for the UE. Code Division Multiplexing and Frequency Division Multiplexing is used to multiplex UE’s on the same RB (more accurately RB-pairs) configured for PUCCH resources.

Format 2 carries CQI, PMI and ACK/NACKs. The multiplexing capacity could be 4, 6 or 12, depending on parameter settings. In this example, for illustrative purposes only, let’s assume that the multiplexing capacity is 4 As explained in the previous blog, CQI-PMI-ConfigIndex determines how often the UE is supposed to report CQI and PMI on the PUCCH. RI-ConfigIndex determines how often the UE is supposed to report RI on the PUCCH. CQI, PMI and RI are transmitted to the eNodeB in format 2, 2a or 2b in the PUCCH as shown below (the picture below assumes a bandwidth of 10 MHz for the UL and 1 resource block for the PUCCH).


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LTE Bible If we assume that CQI-PMI-Configindex is within the range 17 £ ICQI/PMI £ 36, then, the reporting period is 20 sub-frames or 20 ms.

Mapping of cqi-pmi-ConfigIndex to Subframe Periodicity

If we assume that RI-Configindex is within the range 322 £ ICQI/PMI £ 482, then, the rank indicator reporting period is 20 sub-frames*4 or 80 ms.

Mapping of ri-ConfigIndex to Subframe Periodicity

nRBCQI is a parameter that defines the number of resource blocks for CQI periodic reporting (Format 2, 2a or 2b). If we assume its value is 2, then, the number of users than can report CQI periodically in the PUCCH is: NRBCQI * no. of UE multiplexed per sub-frame *periodicity of CQIreporting © Farhatullah Mohammed

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LTE Bible = (2RB)(4 UE/RB)(20) = 160 UE per CQI reporting period.

See picture below. The number of UE per PUCCH can be increased by modifying the following parameters: a)

Increasing NRBCQI (but the PUSCH capacity will decrease)

b) Decreasing the periodicity of CQI reporting (decreasing CQI-PMIConfigIndex) but this might affect our uplink throughput. c)

Increasing the number of UE multiplexed per RB.

It is up to the operator to decide how to play with this values and achieve the goals planned.


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11.

RACH Capacity

The number of sub-frames utilized for random access is provided for by the parameter prachconfigurationindex by means of the following table.

When prachconfigurationindex has a value of 3 (See highlighted row), then: a) The preamble format used is 0 (which means that the maximum cell radius is 14 km)

b) The UE can send the preamble in any frame number. c) The UE HAS to send the preamble in subframe 1 only.


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Maximum RACH Capacity: a) Let us assume that the number of preambles available for initial access given by parameter numberofRA-Preambles is 56 (the other 8 are reserved for Contention Free Random Access, that is, for handover). In this is situation, up to 56 users could be trying to access the system simultaneously. b) Let’s assume then, that 56 UE are trying to access the system simultaneously and that each of them picked a different preamble. c) Let’s assume that the eNodeB responds to only one UE despite the fact that in 10 ms, up to 56 UE are trying to access. Given this situation, the maximum RACH capacity, can be approximated by: Max # of UE supported (RACH) = 1 UE per Frame*No. Frames/second = (1 UE/frame)*(100 frames/second) = 100 UE/second. Minimum RACH Capacity: a) Let us assume that all 56 UE are trying to access at the same time, as in the previous case. b) Let us also assume that the enodeB only responds to one UE per t300 period. © Farhatullah Mohammed

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LTE Bible Given this situation, the maximum RACH capacity, can be approximated by: Min # of UE supported (RACH) = 1 UE per t300 period*(number of t300 periods per second) = (1 UE/t300)*(1 sec/t300) Hence, if t300 is set to 400 ms, the Min # of UE supported per RACH = (1)(1000/400) = 2.5 users. The table below, taken from 3GPP specifications, shows the PrachConfigurationIndex paramter and their associated Preamble format, system frame number and sub-frame number. For RACH capacity allocation, let us assume that we have four types of cells in our system, based on capacity demand: a) Low traffic b) Medium traffic c) High traffic d) Very high traffic Now, let us allocate a color to each of these demands : a) Low traffic (gree) b) Medium traffic (yellow) c) High traffic (blue) d) Very high traffic (purple) Under these conditions, let us proceed to allocate a value of PrachConfigurationIndex to each traffic zone.


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RACH Capacity Design : a) Low capacity cells typically get allocated a prachconfigurationindex with a value between 0 to 5 for Preamble format 0 (See green rows in columns 1 to 4). b) Medium capacity cells typically get allocated a prachconfigurationindex with a value between 0 to 8 for Preamble format 0 (See yellow rows in columns 1 to 4). c) High capacity cells typically get allocated a prachconfigurationindex with a value between 9 to 11 for Preamble format 0 (See Blue rows in columns 1 to 4). d) Very High capacity cells typically get allocated a prachconfigurationindex with a value between 12 to 14 for Preamble format 0 (See Purple rows in columns 1 to 4). Similar reasoning is followed for preamble formats 1 to 3. prachconfigurationindex Allocation: The PRACH Configuration for a High Capacity eNodeB is given here as an example. See Figure below.


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This is a typical deployment in a small arena, where the RACH capacity is expected to be high. Similar deployments can be done with different expected capacities.


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12.

RS Power Reduction

There are some scenarios in which cell size reduction is required in LTE. Reasons may include, but are not limited to traffic reduction, deployment of new cell in congested areas, etc. Some of recommended approaches to decrease cell size include: a)

Antenna changes,

b) Electrical and Mechanical Down tilting, c)

Azimuth changes and

d) RS Power Reduction. However, there are certain cases where power reduction of the RS deems necessary (i.e.: indoor coverage via DAS deployment or when cell size reduction cannot be achieved via any of the other antenna methods). In such cases, a specific approach must be followed, as described below. The Reference Signal Power is typically specified in dB/RE (RE = Resource Element) in most of vendor implementations. All other power levels for other channels are either expressed in dB offsets from the RS power, dBm/antenna or dBm/2 antennas (in the case of MIMO 2x2). In these cases, the recommended way to decrease the RS transmit power is the following: a)

Reduce the Reference Signal Power

b) Set other power parameters for maximum DL power at the same value than the RS power. c) Do not modify the rest of other channel settings (since they are expressed as offsets of the RS power). d) A cell site reboot might be necessary after the power changes.


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13.

Retry/ Negative/ Reject Test

As the term says, 'Retry Test' is the test in which Network put DUT in a condition where the DUT has to 'retry' 'something'. Then what is the 'something' ? meaning 'In what situation UE has to retry something'. There can be many different cases for this. One of the most typical cases is when UE get some reject message to the message it sent to the network. One example for this is 'RRC Connection Request' retry and overall sequence is as follows. i) UE --> NW : 'RRC Connection Request' ii) UE <-- NW : 'RRC Connection Reject'. iii) < UE waits for a certain period of time. UE does not resend 'RRC Connection Request' during this period > iv) UE --> NW : 'RRC Connection Request' (Retry)

It seems that network operators are more interested in step iii). They want to specify this timing as they like and make it sure that UE should not retry during the time frame. I think it is understandable since if UE retry something too often it would generate huge load on the network, but if UE does not retry it too long, it will give the bad user experience.

For most of this kind of test, there a several common things to be clarified (if you are the person who has to develop a test case or write test plan/requirement, you have to have answers to these questions first).

i) What is the trigger for retry ? (Is it an explicit reject message ? or 'absense of response' (Ignoring Request)? or anything else ?) ii) When a DUT has 'Reject' ? or get its request 'ignored', does it have to retry the request ? or simply give up the request right away ? iii) If the DUT is expected to 'retry', does it simply has to send 'request' message again or does it goes even further backward and go through the whole process again ? iv) If it gets rejector or ignored even with the retry, does it have to 'try again' or give up right away ? if it has to retry, how many times it has to retry ?

For some case, you will get those answers from 3GPP specification, but © Farhatullah Mohammed

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LTE Bible unfortunately there are many cases where they are not specified by the specification explictely. In that case, you have to ask about the requirement to whoever wants to perform the test or setup the test criterial on your own by observing the DUT behavior on real network or network simulator.


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14.

TCP Performance Degradation

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When HARQ BLER (Block Error Rate) is 10% and HARQ failure rate is 0.1% as LTE protocol design, if DL (Downlink) HARQ RTT is 8ms and TCP RTT is 10ms, TCP throughput is seriously decreased up to only 36% of maximum bandwidth. And if DL HARQ RTT is 16ms and TCP RTT is 10ms, TCP throughput is decreased up to only 19% of maximum bandwidth.



To alleviate this problem, we propose "out-of-sequence delivery" in LTE link layer in order to decrease TCP RTT while HARQ or ARQ in LTE link layer is working for error recovery. The "out-of-sequence delivery" can decrease TCP RTT up to end-to-end RTT. While "out-of-sequence delivery" makes LTE link layer design simpler, but its throughput gain is considerable to the extent of 30% in average and 58% in maximum from our test results.



If the RLC sub-layer receiver detects a gap in the sequence of the received PDUs, it starts a reordering timer assuming that the missing PDU still is being retransmitted in the HARQ protocol. HARQ failures appear if a maximum number of HARQ transmission attempts are exceeded or HARQ feedback NACK-to-ACK errors occur. When the timer expires, usually in a HARQ failure case, an RLC UM receiver delivers SDUs to PDCP with a certain amount of loss. However, an RLC AM receiver sends a status message comprising the sequence number of the missing PDUs to the sender. The ARQ function of the RLC AM sender performs retransmissions based on the received status message.



The TCP RTT of packets which are contained PDUs from the gap SN to SN which received in-sequence, are proportional to the t_Reordering timer which is generally set as maximum HARQ transmission number times of MAC HARQ RTT


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15.

Out of Sequence - OOS

When HARQ or ARQ in LTE link layer is working frequently for error recovery, “insequence delivery” in LTE link layer increases TCP RTT and decreases TCP throughput seriously as shown in previous chapter. Therefore, in order to get better TCP throughput with the same packet error probability, we should decrease TCP RTT when HARQ or ARQ in LTE link layer is working for error recovery. To alleviate this problem, we propose "out-of-sequence delivery" in LTE link layer in order to decrease TCP RTT while HARQ or ARQ in LTE link layer is working for error recovery. As soon as a PDU is received, link layer can deliver reassembled SDUs in that PDU with “out-of-sequence delivery”. If an RLC receiver detects a gap in the SN (sequence number) of received PDUs, it starts a reordering timer (t_Reordering) assuming that the missing PDU is still being retransmitted in the HARQ protocol. But link layer with “out-of-sequence delivery” can deliver reassembled SDUs in newly received PDUs after the gap without delaying delivering SDUs after the gap is filled. The “in-sequence delivery” increases the TCP RTT of all SDUs in every PDU from the SN of the HARQ or ARQ retransmitted PDU. Therefore, this frequently incurs delay spikes in the TCP data and TCP ACK compression. On the other hand, an “out-of-sequence delivery” can increase the TCP RTT of the SDUs in the retransmitted PDU only. The "outof-sequence delivery" can decrease TCP RTT up to end-to-end RTT. We implemented "out-of-sequence delivery" in LTE link layer and measured TCP throughput of “in-sequence delivery” and “out-of-sequence delivery”. We tested only ARQ impact on TCP RTT increment and throughput with ARQ retransmission rate of 0.1%, 1% and 5%. We measured the TCP throughput in the ETRI LTE-Advanced system with varying ARQ retransmission rate. In the test, the TCP client in the UE is on Windows 7 and the TCP server is on Linux. We use various plug-in TCP variants [9] of TCP server on Linux. In our testbed, the RTT between the TCP client and TCP server is about 13ms. Also, a UE can use two carriers, and the maximum bandwidth between


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16. Visualization of Beam forming in LTE Visualization of Beam Forming in LTE Currently, beam forming is only applicable for TDD version of LTE. The time synchronous version of LTE TDD on uplink and downlink also makes the implementation of beam forming more attractive than in LTE FDD. Beam forming scheme is a signal processing technology that is used to direct radio transmission in a chosen angular direction. It is mainly based on an adaptive beam patterns that acts to make the strongest point of main-lobe of the system output always be toward the direction of the expected UE and hence reducing the overall interference level for the whole cell for Beam Forming in LTE Its algorithm is highly complex and utilizes channel state information to achieve array processing SINR gain.

Channel state information that is required includes:     

Fast fading channel coefficient Beam Forming in LTE Direction of arrival (DoA) of signal Beam Forming in LTE CQI information Beam Forming in LTE Channel state information can be obtained by different way, including: Feedback from receiver Estimation from reverse link assuming channel reciprocity (particularly true for TDD) As it is based on a multiple transmit configuration, this feature can significantly improve downlink system throughput and coverage performance and also provide good user experience by offering higher data rates. The main drawback here is there is also the requirement of either 4 (4×4) or 8 (8×2) transmit path from the eNodeB side which could make this more expensive to implement. There are two type of beam forming mode defined by 3GPP, Mode 7 (Rel 8) and Mode 8 (Rel 9). Mode 7 supports only single data flow so it can mainly improve coverage but Beam Forming in LTE Mode 8 can support multiplexing dual data stream as well which means it can improve both throughput and coverage.


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17. What and How Cell Edge Rate in LTE What and How Cell Edge Rate in LTE Cell Edge Rate in LTE is simple if it’s High then Coverage Low and if It’s Low then Coverage high similar to Frequency selection. Not clear lets understand in detail. Cell Edge Rate in LTE Similar to other wireless communications systems, such as CDMA2000 EVDO, WiMAX and HSPA, the LTE features a rate layering feature. That is, the higher the required edge rate, the smaller the cell coverage radius. The lower the required edge rate, the larger the cell coverage radius. This comes about due to the fixed power offered by UE (normally 23dBm) being spread evenly to the number of RBs involved in the modulation scheme assigned, assuming there is no power control (i.e. Downlink ICIC also disabled). Some of the factors that affect the edge rate in the LTE system are as follows for Cell Edge Rate in LTE: 

Uplink/downlink TDD proportion

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MIMO schemes chosen

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eNodeB Power Amplifier power (affect downlink only)

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Number of RB used at the sector edge

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Modulation mode (1 of 29 coding methods)

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Repeated coding times The formula for calculating the downlink cell edge rate is as follows: Cell edge rate Phy = Number of Different data stream transmitted x Number of Resource Block assigned to user per frame x Number of available Traffic carrying Resource Element per Resource Block x Coding rate x Modulation model level / Duration of each frame Where,



Number of Resource Block Assigned in Cell Edge Rate in LTE (a single RB is the basic resource assignment level) reflects the number of resource blocks used by user at the edge of the sector. The smaller the number of resource blocks assigned, the lower the cell edge rate. In previous version of link budget tools, receive sensitivity of a base station is defined by the bandwidth of the RB which is 180 kHz. More recent version are using per subcarrier as basis of receiver sensitivity and the conversion value is simply 10log10. RB can be assigned down to a per TTI level (1 ms duration)



Number of Different data stream transmitted in Cell Edge Rate in LTE is related to the number of data stream being simultaneously transmitted. Number can be ranging from 1 (SFBC) to 2 (MCW 2×2). In case of BF, the value should be 1 for single antenna port transmission mode 7 (port 7 or 8), and 2 streams for dual antenna port transmission mode 8 (port 7 and 8).


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Number of available Traffic carrying Resource Element per Resource Block in Cell Edge Rate in LTE indicates the number of RE available for each resource block. In FDD system, a maximum of 3 symbols (36 Res) can be consumed per frame (10ms) for control channel signaling purposes and there is at least 6 more extra RE can be used for Downlink Reference signaling per TTI (1ms). A minimum of 1 symbol (12 Res) will be required per RB for control signaling purposes. In TDD system, due to frequency sharing and time gap requirement for switching between uplink and downlink, 6 symbols equivalent (72 Res) will be the minimum overhead requirement per TTI.

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Coding rate indicates the volume coding rate of the channel code. For example, the volume coding rate of QPSK1/2 is 1/2, and the volume coding rate of 16QAM3/4 is 3/4.

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Modulation model level indicates the number of bits in the modulation mode. For example, the modulation mode levels of QPSK, 16QAM, and 64QAM are 2, 4, and 6 respectively.

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Duration of each frame indicates the frame size. As regulated by the protocols, the frame size in LTE networks is 10 ms. In the link budget for Cell Edge Rate in LTE, the settings of the uplink/downlink cell edge rates (in particular the uplink cell edge rate) will determine the final cell coverage radius. Hence, an understanding of edge coverage requirement is very critical from a network planning perspective. If Downlink ICIC is enabled, downlink power control must be enabled also (which is executed at 20ms intervals based on UE BER reported value) and edge rate calculation will be more complex and beyond the formula listed above. However, the cell edge data rate requirement will still be the single most important factor in any cell planning activities.


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18.

Penetration Loss in LTE

Penetration loss in LTE indicates the fading of radio signals from an indoor terminal to a base station due to obstruction by a building. For an indoor receiver to maintain normal communications, the signal must be sufficiently strong. The indoor receiver obtains radio signals in the following scenarios for Penetration loss:  The indoor receiver obtains signals from an outdoor transmitter.  The transmitter and receiver are located in a same building. See Figure below

The link budget is only concerned with the scenario in which an outdoor transmitter is used and the signals penetrate only one wall. The propagation modes of electromagnetic waves are as follows: direct radiation, inverse radiation, diffraction, penetration, and scattering in Penetration loss. In areas where no indoor distributed system is deployed, electromagnetic wave signals are obtained through diffraction and scattering. Therefore, the indoor Penetration loss in LTE is related to the incident angle, building materials, terrain, and working frequency. Table below lists the penetration losses associated with typical buildings for Penetration loss. Typical building penetration losses In the link budget, Penetration loss in LTE values depend on the coverage scenario. Therefore, coverage target areas are classified into densely populated urban areas, common urban areas, suburban areas, rural areas, and highways. Table below lists the area classification principles. Principles for classifying coverage scenarios The building Penetration loss in LTE ranges from 5 dB to 40 dB. In link budget, if no actual test data in the target area is available, an assumed Penetration loss in LTE value must be used. The final assumption is also highly dependent on local customer requirement. For example of Penetration loss in sophisticated Asian Metropolis like Hong Kong, Singapore and Shanghai, the indoor coverage expectation will be very high, hence requiring a high Penetration loss in LTE provisioning. On the other hand, in less developed market such as Africa and Latin America, customer expectation is lower so the Penetration loss in LTE requirement can be reduced to reduce overall cost involved. © Farhatullah Mohammed

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19. Evaluation Process for Cell selection in LTE S-CRITERION -

The cell selection criterion S is a pre-condition for suitable cells. The conditions for E-UTRAN, UTRAN FDD and GSM cells are listed in the figure.

R – CRITERION – CELL RESELECTION -

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The cell reselection evaluation process depends on whether Hierarchical Cell Structure (HCS) is used or not. In order to perform cell reselection UE measures and ranks the neighbor cells. For each type of neighbor cells (Intra-Frequency; Inter-Frequency; Inter-RAT, i.e. GSM) thresholds are definable. Measurements of neighbor cells will be triggered if these thresholds are reached. HIGH MOBILITY / MEDIUM MOBILITY / NORMAL MOBILITY:

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For faster moving UEs the procedure alters – speed dependent scaling rules are applied. If the number of (different cells) cell reselections during the past time period TCRmax exceeds NCR_H, high mobility has been detected. If the number exceeds NCR_M, and not NCR_H, medium mobility has been detected. In high/medium-mobility states, a UE: • multiplies Qhyst by “Speed dependent ScalingFactor for Qhyst for mobility state” if sent. • multiplies TreselectionRAT by “Speed dependent ScalingFactor for TreselectionRAT for mobility state for RAT cells. (RAT = EUTRAN, UTRAN, GERAN).


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Cell reselection evaluation is performed according to the UE internal triggers or if the information on the BCCH used for the cell reselection evaluation procedure has been changed. FOR INTRA-FREQUENCY AND EQUAL PRIORITY INTER-FREQUENCY CELLS:

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(Re-) Selected cell is a suitable cell (e.g. fulfills the S criterion) and is the best ranked cell (has the highest R). The UE shall however reselect the new cell, only if the following conditions are met: • the new cell is better ranked than the serving cell during a time interval Treselections • more than 1 second has elapsed since the UE has camped on the current serving cell. The cell-ranking criterion R is defined as shown below: Note, s – indicates the serving cell, n – indicates the candidate cell.


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FOR INTER-FREQUENCY AND INTER-RAT NEIGHBOUR CELLS: - If UE camps longer than 1 sec in the serving cell and: - a higher priority neighbor fulfills (during TreselectionRAT): SnonServingCell,x > Threshhigh -> reselect neighbor cell. - no cell fulfills SnonServingCell,x > Threshhigh : SServingCell < Threshserving,low and SnonServingCell,x > Threshx,low ->reselect neighbor cell.


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20.

Figure 1: EPS and Legacy core networks

CSFB TROUBLESHOOTING

Figure 2: CSFB to UTRAN/GERAN

Figure 3: Return to EUTRAN (LTE)

Voice Network Acquisition: -

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The user device is paged via LTE with an incoming call or when the user initiates an outgoing call, the device switches from LTE to 3G/2G. Acquisition of the 3G/2G network is through the handover or redirection. In the handover procedure the target cell is prepared in advance and the device can enter that cell directly in the connected mode. IRAT measurements of the signal strength measurements may be required while LTE in this procedure prior to making the handover. In the redirection procedure, only the target frequency is indicated to the device. The device is then allowed to pick any cell on the indicated frequency or may be other frequencies/RAT if no cell can be found on target frequencies. In switching from LTE to 3G network, for voice calls expectably, there incur a penalty in call setup times. Example Mobile Originated Call Parameters as a function of time [seconds]

Example Mobile Terminated Call Parameters as a function of time [seconds] One option to reduce the call setup time is to shorten the DRX Paging time cycle. This gain in incoming call setup time comes at cost of power consumption, since shorter DRX paging cycles requires additional paging resources and as a result higher idle mode power consumption.


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-

-

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DATA INTERRUPTION TIME If the user is in active PS data session, for example streaming media when a voice call is initiated, the IRAT transition and the routing area will update the data transfer. If using Handover based CSFB, the data interruption is unlikely to be noticed. Data Interruption parameters as a function of time [ seconds]

Some other issues in CSFB, for voice call user experience is the call setup reliability – the ability to successfully establish an incoming or outgoing call on the first attempt or within the time frame that doesn’t indicate the call setup time failure. Handover Based CSFB: With handover based CSFB, IRAT measurements can change between the time measurements is taken using the LTE and the time 3G voice network acquisition is attempted. In the handover based CSFB, the measurement is performed before; and if the IRAT conditions change negatively, there is a high possibility of handover failure in the case of high mobility situations.

Redirection Based CSFB: Redirection based CSFB can deliver higher call setup reliability than handover based CSFB, since the redirection based CSFB takes the IRAT measurements before attempting access on the identified cell. Redirection based CSFB calls are more immune to the setup fails irrespective of RF conditions. LTE to 3G Handover Time:


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-

-

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Since the different frequencies have different terrain propagation and penetration characteristics, as well as different potentially fixed antenna sites , LTE and 3G radio access patterns for any given location are never identical. Since there is uncertainty about which 3G cell is best target for switchover from LTE cell is unavoidable since LTE cells can overlap two or more 3G cells.

If CSFB switching is done from an LTE cell in one TA to a 3G cell in LA [where the user device is not registered], a new location area must be done prior executing the connection setup. This LAU procedure can add one or two second delay to setup time depending on the load on the network. In some cases, LTE to 3G cell switch may occur in an MSC server [border] area, where LTE to 3G switch involves change of MSC server in which case both LAU and HLR update is necessary between the MSC servers prior to connection setup. These substantial call setup delays affect the user experience noticeably, and may be judged as call setup failures rather than acceptable delays. MTRF is a newer version of MT Roaming Retry [MTRR] standard and it solves the MSC border issue by forwarding the calls directly from old MSC to the new MSC in case fallback is done over the MSC border. MTRF has advantage over MTRR of not needing inter operator agreements and not rerouting calls back to GMSC for second HLR interrogation.

ISSUES TO STUDY: -

How does the CSFB voice affect the ongoing data service in LTE networks? How does the data session in LTE networks affect the voice service?

WHAT TO EXPECT, UNEXPECT AND WORST CASE -

How much is the performance degradation when voice calls occur? This is expected case for performance penalty. The data session falls back to 3G/2G networks during a CS voice call and then returns back to 4G network while the call ends. Can the data session go wrong when the call completes or never established? If it occurs, it will be the anticipated exceptions for CSFB, the LTE connectivity is lost and the UE get stuck in 3G even when the voice call complete or never start. Can voice call incur the negative performance impact beyond throughput degradation? The applications may abort when the voice calls are underway. Can the PS data also affect the CS voice calls under certain conditions? If in case, it shows both data and voice have mutual interference on each other’s operation.


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I Throughput Slump

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I: THROUGHPUT SLUMP: The observed throughput slump is caused due to CSFB

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II and III: More handoff and loosing connectivity.

Findings Through put Slump Loosing 4G Connecti vity Applicati on Aborts Missing Incoming call

II – Multiple Handoff

III – Losing 4G Connectivity

Sce nar io

Detail

Root Cause

I, II

Data Throughput decreases; I only during the call and II during and after the call

Handoff triggered by CSFB and speed gap between 3G and 4g.

I, II

Never Returns to 4G after CSFB call under certain data traffic; I: when the call fails to establish; II any CSFB call

State machine loophone 3--> 4G Transition

I, II

Application aborts occasionally I, II after the call

Network state changed by CS domain operation (here network detach caused by CSFB voice calls)

I, II

Misses all incoming calls temporally (for several seconds) while enabling PS service

Network state changed by PS domain operations

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-

-

-

-

RADIO LINK FAILURE

Two phases of radio link failures First Phase: Started upon radio problem detection Leads to radio link failure detection No UE based mobility Based on timer (or other counting criteria) T1 Second Phase: Started upon radio link failure detection or handover failure Leads to RRC_IDLE UE-based mobility Timer based T2. RLF Cases

In the second phase, in order to resume activity and avoid going via RRC_IDLE, when UE returns to the same cell or UE selects a different cell from the same eNB or when UE selects the cell from a different eNB, the following procedure applies. UE stays in RRC connected UE accesses the cell through Random access procedure UE identifier used in the random access procedure for the contention resolution (C-RNTI of the UE in the cell where the RLF occurred + Physical layer identity of that cell + MAC based on the keys of that cell) is used by the selected eNB to authenticate UE and check whether it has a context stored for that UE: If the eNB finds a context that matches the identity of the UE, it indicates to the UE that its connection can be resumed. If the context is not found, RRC connection is released and the UE initiates the procedure to establish new RRC connection. In this case, UE is required to go through RRC_IDLE.


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S1 HANDOVER

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Handover Preparation


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Handover Execution


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RRC Connection Reconfiguration


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Releasing Resources on eNodeB


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X2 HANDOVER

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Handover Messaging


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Measurement Metrics 1. KPIs Measurement for Voice and Data [Detailed] 1.1

Voice Telephony

This section gives the description of how KPIs (Key Performance Indicators) for the telephony (i.e. ordinary voice) service are calculated in this campaign. Note that KPIs are computed only for mobile-originated (MO) calls, not for mobile terminated (MT) calls. The KPI definitions are based on ETSI TS 102 250-2 V1.4.1. 1.1.1

Service Non-Accessibility [%]

Denotes the probability that the end-customer cannot access the service when requested although the phone indicates having network coverage:

Start trigger: RRC Connection Request/Channel Request message sent. There can be more than one such message per call attempt; the first message shall then be taken as start trigger. (Trigger point 1 in signaling diagram 1) Stop trigger: Connect message received from the MSC. In an unsuccessful call attempt, this trigger point is never reached. (Trigger point 30 in signaling diagram 1)

1.2

Setup Time [s]

Denotes the time between sending of complete address information and receipt of call setup notification:

Start trigger: RRC Connection Request message sent. There can be more than one RRC Connection Request message per call attempt; the first message shall then be taken as start trigger. (Trigger point 1 in signaling diagram 1) Stop trigger: Connect message received from the MSC. In an unsuccessful call attempt, this trigger point is never reached. (Trigger point 30 in signaling diagram 1) 1.2.1

Speech Quality on Sample basis [MOS]

LTE Bible Denotes the end-to-end speech transmission quality of the mobile telephony service computed on a sample-by-sample basis. The quality is judged using the PESQ algorithm.

Start trigger: Connect message received. (Trigger point 30 in signaling diagram 1) Stop trigger: Disconnect message sent. (Trigger point 35 in signaling diagram 1) 1.2.2

Call Cut-off Ratio [%]

Denotes the probability that a successful call attempt is ended by a cause other than the intentional termination by the user:

Start trigger: Connect message received. (Trigger point 30 in signaling diagram 1) Stop trigger: Disconnect message sent. (Trigger point 35 in signaling diagram 1)


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Signalling Diagram[3.1.7]

FTP (File Transfer Protocol Session)Download

1.3

1.3.1


Network Unavailability [%]

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LTE Bible Denotes the probability that no packet-switched network is available in the cell currently used by the customer. In GSM, the phone has access to a PS network if it has received System Information. This message is read once per KPI measurement cycle, at the beginning of the cycle. In WCDMA, matters are simpler: the phone is always known to have access to a PS network.

The information element "Mode - System" in TEMS Investigation indicates whether the phone is connected to a WCDMA or a GSM network. Because of the nature of this KPI, no start or stop triggers can be identified for it in the signaling diagrams. 1.3.2

Attach Failure Ratio [%]

Denotes the probability that a subscriber cannot attach to the GPRS/UMTS PS network:

Start trigger: Phone sending Attach Request message. (Trigger point 1 in sections 3.1.7, 3.2.7, 3.3.7, and 3.4.7) Stop trigger: Phone receiving Attach Accept/Reject message. (Trigger point 4 in sections 3.1.7, 3.2.7, 3.3.7, and 3.4.7)

1.3.3

Attach Setup Time [s]

Denotes the length of the time period taken to attach to the GPRS/UMTS PS network:

Start trigger: Phone sending Attach Request message. (Trigger point 1 in sections 3.1.7, 3.2.7, 3.3.7, and 3.4.7) © Farhatullah Mohammed

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LTE Bible Stop trigger: Phone receiving Attach Accept message. (Trigger point 4 in sections 3.1.7, 3.2.7, 3.3.7, and 3.4.7) 1.3.4

PDP Context Activation Failure Ratio [%]

Denotes the probability that the PDP context cannot be activated. It is the ratio of unsuccessful PDP context activation attempts to the total number of PDP context activation attempts:

Start trigger: Phone sending PDP Context Activation Request message. (Trigger point 5 in sections 3.1.7, 3.2.7, 3.3.7, and 3.4.7) Stop trigger: Phone receiving PDP Context Activation Accept message. (Trigger point 8 in sections 3.1.7, 3.2.7, 3.3.7, and 3.4.7) 1.3.5

PDP Context Activation Time [s]

Denotes the length of the time period taken to activate a PDP context:

Start trigger: Phone sending PDP Context Activation Request message. (Trigger point 5 in sections 3.1.7, 3.2.7, 3.3.7, and 3.4.7) Stop trigger: Phone receiving PDP Context Activation Accept message. (Trigger point 8 in sections 3.1.7, 3.2.7, 3.3.7, and 3.4.7) 1.3.6

PDP Context Cut-off Ratio [%]

Denotes the probability that a PDP context is deactivated without this being initiated intentionally by the user:

Start trigger: Phone receiving PDP Context Activation Accept message.


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LTE Bible (Trigger point 8 in sections 3.1.7, 3.2.7, 3.3.7, and 3.4.7) Stop trigger: Phone receiving the last data packet containing content. (Trigger point 41 in sections 3.1.7 and 3.2.7) (Trigger point 42 in sections 3.3.7 and 3.4.7) PDP context deactivation not initiated intentionally by the user can be caused by either SGSN failure or GGSN failure, so the PDP context may be deactivated either by the SGSN or by the GGSN. Note: The precondition for measuring this parameter is that a PDP context has been successfully established.


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Signalling Diagram [3.2.7]

1.4

FTP Upload

1.4.1



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LTE Bible Denotes the probability that a subscriber cannot access the service successfully due to a failure that has occurred either during PDP context activation or during service access. This means that the data transfer cannot be started:

Start trigger: Connect on command socket. (Trigger point 5 in section 3.3.7) Stop trigger: Sending the first data packet containing content. (Trigger point 35 in section 3.3.7) 1.4.2

Setup Time [s]

Denotes the period of time it takes to access a service successfully, from the moment the dial-up connection is established until the first data packet is sent:

Start trigger: Connect on command socket. (Trigger point 5 in section 3.3.7) Stop trigger: Sending the first data packet containing content. (Trigger point 35 in section 3.3.7) 1.4.3

IP Service Access Failure Ratio [%]

Denotes the probability that, after successfully activating a PDP context, a subscriber cannot access the service, so that the data transfer cannot be started:

Start trigger: First [SYN] sent. (Trigger point 5 in section 3.3.7) Stop trigger: Sending the first data packet containing content. (Trigger point 35 in section 3.3.7) 1.4.4

IP Service Setup Time [s]

Denotes the time period needed to establish a TCP/IP connection to the FTP server, from sending the initial query to a server until the first data packet is sent:


297

LTE Bible Start trigger: First [SYN] sent. (Trigger point 9 in section 3.3.7) Stop trigger: Sending the first data packet containing content. (Trigger point 35 in section 3.3.7) 1.4.5

Mean Data Rate [Kbit/s]

Denotes the average data rate measured throughout the entire connect time (application throughput):

Start trigger: Sending the first data packet containing content. (Trigger point 35 in section 3.3.7) Stop trigger: Sending the last data packet containing content. (Trigger point 42 in section 3.3.7) 1.4.6

Data Transfer Cut-off Ratio [%]

Denotes the probability that a data transfer cannot be completed when it has been started successfully:

Start trigger: Sending the first data packet containing content. (Trigger point 35 in section 3.3.7) Stop trigger: Sending the last data packet containing content. (Trigger point 42 in section 3.3.7)


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Signalling Diagram [3.3.7]

1.5

HTTP Specific KPIs

Two slightly different methods exist for calculating the KPIs. The difference is explained in the following extract from the ETSI specifications: (ETSI TS 102 250-2 V1.4.1 (2006-03)


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Denotes the probability that a subscriber cannot access the service successfully due to a failure that has occurred either during PDP context activation or during service access. This means that the data transfer cannot be started:

Start trigger: Connect on command socket. (Trigger point 5 in section 3.1.7) Stop trigger: Reception of the first data packet containing content. (Trigger point 20 in section 3.1.7) 1.5.2

Setup Time [s]

Denotes the period of time it takes to access a service successfully, from the moment the dial-up connection is established until the first data packet is received:

Start trigger: Connect on command socket. (Trigger point 5 in section 3.1.7) Stop trigger: Reception of the first data packet containing content. (Trigger point 20 in section 3.1.7) 1.5.3

IP Service Access Failure Ratio [%]

Denotes the probability that, after successfully activating a PDP context, a subscriber cannot access the service, so that the data transfer cannot be started:

Start trigger: First [SYN] sent. (Trigger point 9 in section 3.1.7) Stop trigger: Reception of the first data packet containing content. (Trigger point 20 in section 3.1.7) 1.5.4


Signalling Diagram[3.4.7]

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1.5.5

IP Service Setup Time [s]

Denotes the time period needed to establish a TCP/IP connection to the HTTP server, from sending the initial query to a server until the first data packet is received:

Start trigger: First [SYN] sent. (Trigger point 9 in section 3.4.7) Stop trigger: Reception of the first data packet containing content. (Trigger point 20 in section 3.4.7) © Farhatullah Mohammed

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Mean Data Rate [Kbit/s]

Denotes the average data rate measured throughout the entire connect time (application throughput):

Start trigger: Reception of the first data packet containing content. (Trigger point 20 in section 3.4.7) Stop trigger: Reception of the last data packet containing content. (Trigger point 27 in section 3.4.7) 1.5.7

Data Transfer Cut-off Ratio [%]

Denotes the probability that a data transfer cannot be completed when it has been started successfully:

Start trigger: Reception of the first data packet containing content. (Trigger point 20 in section 3.4.7) Stop trigger: Reception of the last data packet containing content. (Trigger point 27 in section 3.4.7)


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Additional Questions 1-What is LTE? LTE is an abbreviation of Long term Evolution and a part of 3GSM evolution path: GSM/EDGE, WCDMA, HSPA, HSPA Evolution and LTE. LTE uses OFDMA for downlink and SC-FDMA for the uplink which provides flexible spectrum allocation from 1.4MHz to 20MHz and good power efficiency for long battery life of terminals. By deploying LTE on wide carriers ie.. 10 – 20MHz very high data rates can be achieved enhancing the user experience for services like mobile broadband and mobile TV. The target 3GPP standard was to provide rates of 100Mbps in the downlink and 50Mbps in the uplink on 20MHz carrier. 2- What is SAE? LTE is the radio part of the 3G Evolution and SAE is the part handling the packet core network. The goals of SAE is to provide a simplification of the packet core with a flat architecture, improvement in the latency and optimization for IP services. 3- What are the name conventions in LTE/SAE? In LTE SAE projects some new name conventions have been developed. Radio Network: eUTRAN or LTE RAN or LTE RAN Radio base station: eNodeB. There are two packet core nodes defined in LTE User plane node – Serving Gateway also called as Aggregation Gateway AGW. Control Plane node: Mobility management entity MME.

4- How will subscribers benefit from the service provided in LTE? Already with HSPA broadband services such as internet access, VoiP, interactive gaming and mobile TV can be provided with high quality. With growing demand more spectrum and higher bit rates are required in order to secure the service availability for all users. 5- Will GSM and HSPA/WCDMA work seamlessly with LTE? LTE is an evolution of GSM- WCDMA and seamless mobility between these two technologies is therefore built into 3GPP standard. LTE is only operating in packet data mode and there is no circuit switch part for voice service. 6- Will LTE replace fixed broadband? LTE is compliment to DSL and other fixed broadband technologies, not a replacement. A fibre based fixed network provides an almost unlimited bandwidth and is very suitable for HDTV distribution. However LTE offers support for bandwidth demanding applications such as interactive TV, PoD TV to laptops and handheld terminals. 7- What kind of bitrates will LTE deliver? The exact capability interms of capacity and cell coverage varies depending on the number of factors such as amount of available spectrum, size of the radio channels, urban or rural areas, number of subscribers sharing the capacity in the cell, interference from neighbouring cells, LOS, NLOS, NLOS indoor. 8- What Latency will be there in LTE system? Latency or round trip time involves not only the radio but also the core network and the user equipment. A key focus on the development of LTE as well as development of the core network, System architecture

LTE Bible evolution is to bring down the latency in the system and the Round trip time. 9- Will LTE provide voice service? The high capacity and low latency characteristics of LTE is very suitable for voip and this technology will be used for providing voice service. 10- Will LTE include a new core network? LTE as per definition is the radio access part consisting of base stations, eNodeBs. Base stations are connected to the packet core, evolved packet core in a separate project named SAE. 11- What is the difference between FDD and TDD in LTE? LTE standard specifies two different duplex modes FDD and TDD. In FDD, both uplink and downlink are using different frequencies. In TDD mode, both uplink and downlink use the same frequency but in different time. Due to the commonalities, between the LTE TDD and FDD, their performance is similar in many aspects suchas spectrum efficiency. TDD has 3 – 6 dB weaker link budget compared to FDD in DL/UL allocations.

13 – What DL transmission scheme is used? For both FDD and TDD, DL transmission scheme is based on OFDMA. Each 10ms radio frame is divided in equally 10 sized sub frame. Channel dependent scheduling and link adaptation can operate on a sub frame level. Supported downlink data modulation schemes are QPSK, 16QAM and 64QAM. 14- What are the theoretical peak data rates assumptions? Downlink data rates of more than 300Mbps can be achieved assuming current physical assumptions 4x4 MIMO and a rough estimation overhead. Hence 3GPP requirement 100Mbps peak data rate in the downlink can be achieved. Uplink data rates of more than 80Mbps can be achieved assuming current physical layer assumptions, 1UE, Tx antenna and a rough estimation overhead. Hence also 3GPP uplink requirement of 50Mbps can be achieved. 15- What is control plane latency? CP latency that allows for a transition from a camped state to an active state is less than 100ms (from MME_IDLE to MME_Connected)

LTE TDD requires higher accuracy synchronization within the network and also towards other TDD systems for efficient coexistance.

16- What is user plane latency?

12- What UL Transmission scheme is used?

In general, latency in TDD is larger than in FDD because of the finite delay between the switching points per frame is limited due to efficiency reasons, the delay increases.

For both FDD and TDD the basic uplink transmission scheme is based on the low Peak Average to Power ratio, single Carrier transmission (SC-FDMA) with cyclic prefix to achieve uplink inter- user orthogonality and to enable efficient frequency domain equalization at the receiver side. Supported uplink data modulation schemes are QPSK, 16QAM and 64 QAM. © Farhatullah Mohammed

The transmission of IP packet with 0 byte payload should experience one way UP latency of less than 5ms.

17- What spectrum efficiency can be achieved? Like the user throughput requirements, the spectrum efficiency targets are formulated relative to a basic release 6 HSPA baseline system. 304

LTE Bible 18- What is EPS? EPS is made up of Evolved packet core and EUTRAN. EPC provides access to the external networks and operator services. It also performs functions related to security, charging and inter access mobility (GERAN/ UTRAN and EUTRAN). EUTRAN performs all radio related functions for active terminals. 19- What is the bearer supported by EPS? EPS supports bearer concept for supporting end user data services. The EPS bearer is defined as the user Equipment and the P-GW node in the EPC, which provide end users IP point of presence towards external networks. The EPS bearer service is further sub divided into EUTRA Radio bearer service (over the radio interface between UE and eNodeB) and EUTRAN access Radio bearer service(over the s1 interface between the enodeB and S-GW). End to end services are multiplexed on different SAE bearers. There is many one to one relation between end to end services and SAE bearers. There is one to one mapping between SAE bearers, SAE access bearers and SAE radio bearers. Each SAE Access bearer is associated with GTP tunnel over S1 interface and each SAE radio bearer over the radio interface is associated with RLC instance.

systems and their sizes range from 1/4 to 1/32 of a symbol period. Most receiver structures use the cyclic prefix to make an initial estimation of time and frequency synchronization which including pre-FFT synchronization, non-data assisted synchronization for Cyclic prefix in LTE A receiver typically uses the high correlation between the cyclic prefix and the last part of the following symbol to locate the start of the symbol and begin then with decoding. In multi-path propagation environments the delayed versions of the signal arrive with a time offset, so that the start of the symbol of the earliest path falls in the cyclic prefixes of the delayed symbols. As the CP is simply a repetition of the end of the symbol this is not an inter-symbol interference and can be easily compensated by the following decoding based on discrete Fourier transform for Cyclic prefix in LTE. Of course cyclic prefixes reduce the number of symbols one can transmit during a time interval. This method to deal with inter-symbol interference from multi-path propagation is theoretically sub-optimal. CDMA with RAKE receiver for instance provides a much better efficiency. On the other hand non-ideal implementations of RAKE receivers also degrade system performance drastically but still require a lot of hardware capacity for the basic implementation for Cyclic prefix in LTE. The rectangular pulse with cyclic prefix requires far less hardware, so the free capacity can be used to implement other performance optimization techniques like MIMO.

20- What is Cyclic prefix in LTE ? 21-Implementation Margin in LTE The guard period after each rectangular pulse carrying the modulated data symbol is a simple and efficient method to deal with multi-path reception. The cyclic prefix (CP) simply consists of the last part of the following symbol. The size of the cyclic prefix field depends on the system and can even vary within one system. Cyclic prefixes are used by all modern OFDM © Farhatullah Mohammed



Implementation margin is used to include non-ideal receiver effects such as channel estimation errors, tracking errors, quantization errors, and phase noise.



This implementation margin or sensitivity degradation can be used to apply some margin to the link budget to account for devices from other vendors that may have larger tolerances from the specifications or for 305

LTE Bible which the actual performance is not available. 

A larger implementation margin may be assumed at the subscriber end as opposed to the

base station end. 

This is done to reflect the scenario where one base station can connect to multiple subscriber devices.



The subscriber devices may be obtained from several different vendors, each with its own receiver design whereas the base station will typically be from fewer vendors.


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