LTE KPI Measurement Methodology and Acceptance Procedure Here I write in simple word on LTE KPI Measurement Methodology and its Acceptance Procedure. As it’s for only at network at network start up stage and now a day worldwide so many operator starts to launch LTE and so this is the way for them to check of KPI in LTE LTE KPI Measurement Methodology The KPIs are formulated to measure the network performance in terms of Accessibility, Integrity, Mobility, Retainability, and Subscriber perceived quality. LTE KPIs are mainly classified into 5 classes, which are, Accessibility, Retainability, Mobility, Latency, and Integrity. The KPI KP I architecture is shown in the following figure.
The above KPI classification fully considers the customer experience andfocuses on the Quality of Experience, providing a wide range of network KPIs to reflect network factors that are relative to the service the service quality, using industry standards as reference to define network counters and KPIs. LTE KPI Acceptance Procedure LTE network KPI acceptance procedure for the two phases, preliminary acceptance and final acceptance, are recommended as shown above. During the phase of preliminary acceptance before commercial launch, KPIs will be derived from the drive test analysis and stationary measurements, and this analysis and measurement are on the basis of cluster which constitutes a group of sites sites (20-40 sites).
Statistics KPIs are not proposed and measured at this stage as the traffic is insufficient, statistics will not eligible statistical result without enough samples. After on-going optimization while the traffic keeps increasing after commercial launch, the final acceptance of the whole network performance on the basis of statistics will be implemented. However, the KPI values of statistics probably might not be same with those in drive test due to different calculations and considerations. LTE Service KPIs and LTE Network KPIs The Field Test KPIs into two categories: LTE Serv ice KPIs and LTE Network KPIs. Service KPIs are the KPIs that are not subject to be effected by cluster tuning and optimization activities, mainly determined by product performance, configuration and parameter setting, e.g. ping delay, throughput, etc. I recommend that only one cluster (named pilot cluster) is selected for the evaluation and acceptance for the Service KPIs, no necessary for repeating the measurement in all clusters Based on the above reasons, the Service KPIs’ test is suggested to be performed by Stationary Test (ST) in the area with good RF conditions and close to the cell in order to eliminate the affect of poor RF or non-equipment factor and the test is proposed to be implemented under the condition of one serving cell. LTE Network KPIs , such as Call setup success rate, Call Drop Rate,Handover Success Rate, which is determined by the radio network environment, planning and optimization capabilities, should be performed on the Drive Test (DT) routes in rollout clusters.
How and Which KPI to Check before and after LTE Launch Operator always needs to check LTE performance before commercial launch and after commercial launch and here I write how and which KPI to check.As This is general guide so it is change for different operator but it cover all KPI. There are two types of methods for KPIs’ measurement: Field Test and Statistic Collection. Different measurement methods and KPI categoriesshall be taken into consideration so as to match the following two acceptance phases. Preliminary Acceptance For Preliminary Acceptance (before the commercial launch), low traffic(even empty) is not able to produce sufficient traffic data to evaluate the correlative Statistics KPIs. The main purpose of Preliminary Acceptance is to verify whether the optimized cluster achieves the coverage and performance requirements or not, so the Field Test (Drive Test and Stationary Test) KPIs are recommended for this phase. Final Acceptance (Stability Acceptance, Optional) For Final Acceptance (after the commercial launch), statistics collection method could be introduced under the condition that a minimum amount of traffic per site at the Busy Hour is reached (the sufficient data are available). Based on worldwide experiences of LTE commercial networks, the following KPIs are suggested for Preliminary Acceptance and Final Acceptance separately.
Proposed KPIs for Preliminary Acceptance The following table lists the proposed KPIs for Preliminary Acceptance.
Proposed KPIs for Final Acceptance (Stability Acceptance, Optional) The following table lists the proposed KPIs for Final Acceptance.
Cluster and Test Route The following contents present recommendation for Cluster Optimization and the selection of Drive Test Route for LTE project. Cluster Optimization Performing optimization/acceptance per Cluster is recommended. Cluster means a group of sites (Normally 20-40 sites) which are geographically neighbor and all the eNodeBs of this test cluster should be integrated and on air, along with surrounding neighbor cells, but the actual sites number of per cluster should be flexible to allow a faster rollout and acceptance. Drive Test Route Selection For cluster optimization, the planning of the test route shall consider the handover performance, neighboring relations, coverage, etc. In general the test routes shall be planned according to the following criteria: All sectors of each site in the cluster should be covered by the drive route, if possible.
Routes shall pass through Key business centers, major roads, shoppingcenters, tourist attractions and railway stations.
Cell Reselection Procedures in LTE Contents
1. 1 Introduction 2. 2 LTE Initial Access
3. 3 Initial synchronization 1. 3.1 Primary Synchronization Signal (PSS) 2. 3.2 Secondary Synchronization Signal (SSS) 4. 4 LTE Cell selection and reselection criteria
Introduction Cell reselection is a complex process in LTE. The following extract from [1] provides a very good understanding of the ove procedure.
LTE Initial Access Like all mobile communication systems, in LTE a terminal must perform ce rtain steps before it can receive or transmit data. These steps can be categorized in cell search and cell selection, derivation of system information, and random access. The complete procedure is known as LTE Initial Access and is shown in the Figure below. After the initial access procedure, the terminal is able to receive and transmit its user data.
Initial synchronization Successful execution of the cell searc h and selection procedure as well as acquiring initial system information is essential for the UE before taking further steps to communicate with the network. For this reason, it is important to take a closer look at this fundamental physical layer procedure. This section focuses on the cell-search scheme defined for LTE and the next chapter describes reception of the essential
system information. As in 3G (WCDMA), LTE uses a hierarchical cell-search procedure in which an LTE radio cell is identified by a cell identity, which is comparable to the scrambling code that is used to separate base stations and cells in WCDMA. To avoid the need for expensive and complicated network and cell planning, 504 physical layer cell identities of is sufficiently large. With a hierarchical cell sear ch scheme, these identities are divided into 168 unique cell layer identity groups in the physical layer, in which each group consists of three physical layer identities. To remember this hierarchical principle, consider the example of first names and surname s. According to statistics, the most common English surname is “Smith”, which corresponds to physical layer ce ll identity group 0. The second most common surname is “Johnson”, which represents
the physical layer cell identity group 1. This example can be extended to the last group, which would be “Rose”. The most common male first names are “James”, “John”, or “Robert” and female names are “Mary”, “ Patricia”, and “Linda”. Each first name
represents one of the three physical layer identities. This information is now transmitted using two different signals, generated by Layer 1. The two signals, carrying the physical layer identity and the physical layer cell identity group, are the primary and the secondary synchronization signals respectively. This means that the complete cell search procedure consists of two steps to identify the cells’ identity as shown Graphically in the Figure below:
Primary Synchronization Signal (PSS) The UE first looks for the primary synchronization signal (PSS) which is transmitted in the last OFDM symbol of the first time slot of the first subframe (subframe 0) in a radio frame. This enables the UE to acquire the slot boundary independently from the
chosen cyclic prefix selected for this cell. Based on the downlink frame structure (Type 1, FDD). The primary synchronization signal is transmitted twice per radio frame, so it is repeated in subframe 5 (in time slot 11). This enables the UE to get time synchronized on a 5 ms basis, which was selected to simplify the required inter-frequency and inter-RAT measurements. LTE must accommodate handover to and from other radio access technologies, such as GSM/GPRS/EDGE, WCDMA/HSPA or CDMA®2000 1xRTT/1xEV-DO.
Secondary Synchronization Signal (SSS) After the mobile has found the 5 ms timing, the second step is to obtain the radio frame timing and the cells’ group ident This information can be found from the SSS. In the xtime domain, the SSS is transmitted in the symbol before the P SS . Th also has 5 ms periodicity, which means it is transmitted in the first and sixth subframes (subframes 0 and 5) as shown in t Figure below. Like the PSS, the SSS is transmitted on 62 of the 72 reserved subcarriers around the DC subcarrier.
LTE Cell selection and reselection criteria The previous section described how initial cell selection will work and the difference between LTE FDD and TD -LTE. Howe only when specific criteria are fulfilled is the UE allowed to camp on that ce ll. These criteria for cell selection as well as cell reselection for LTE are specified in [3]. It is further illustrated by a description of the two procedures: In the initial cell selection procedure, as described in the previous sections, no knowledge about RF channels carrying an E-UTRA signal is available at the UE. In that case the UE scans the supported E-UTRA frequency bands to find a suitable cell. Only the cell the strongest signal per carrier will be selected by the UE. The second procedure relies on information about carrier frequencies and optionally cell parameters received and sto red from previously-detected cells. If no suitable cell is found the stored information the UE starts with the initial cell selection procedure. S is the criterion defined to decide if the cell suitable . This criterion is fulfilled when the cell selection receive level is computed based on the Equation below:
is the measured receive level value for this cell, i.e. the Reference Signal Received Power (RSRP).
This measured value is the linear average over the power of the resource elements that carry the cell specific reference signals over the considered measurement bandwidth. Consequently, it depends on the configured signal bandwidth. In the case of receiver diversity configured for the UE, the reported value will be equivalent to the linear average of the power values of all diversity branches.
is the minimum required receive level in t his cell, given in dBm. This value is signaled as Q rxLevmin by higher layers as part of the System Information Block Type 1 (SIB Type 1). Q rxLevmin is
calculated based on the value provided within the information element (-70 and -22) multiplied with factor 2 in dBm.
is an offset to Q rxlevmin that is only taken into account as a result of a periodic search for a higher priority PLMN while camped normally in a Visitor PLMN (VPLMN). This offset is based on the information element provided within the SIB Type 1, taking integer values between (1…8) also multiplied by a factor of 2 in dB. This gives a wider range by keeping the number of bit transmitting this information. The offset is defined to avoid “ping -pong” between different PLMNs. If it is not available then Q rxlevminoffset is
assumed to be 0 dB.
is a maximum function as shown in Equation 5. Whatever parameter is higher, PEMAX- PUMAX or 0, is the value used for PCompensation. PEMAX [dBm] is the maximum power a UE is
allowed to use in this cell, whereas P UMAX [dBm] is the maximum transmit power of an UE according to the power class the UE belongs too. At the moment only one power class is defined for LTE, which corresponds to Power Class 3 in WCDMA that specifies +23 dBm.
P EMAX is
defined by higher layers and corr esponds to
the parameter P-MAX defined in [2]. Based on this relationship, PEMAX can take values between -30 to +33 dBm. Only when PEMAX > +23 dBm PCompensation is it considered when calculating Srxlev. The P-MAX information element (IE) is part of SIB Type 1 as well as in the "RadioResourceConfigCommon" IE, which is part of the SIB Type 2.
As explained above, all parameters except for Q rxlevmeas are provided via system information. In a real network a UE will r several cells perhaps from different network operators. The UE only knows after reading the SIB Type 1 if this cell belong operator’s network (PLMN Identity). First the UE will look for the strongest cell per carrier, then for the PLMN identity by
decoding the SIB Type 1 to decide if this PLMN is a suitable identity. Afterwards it will compute the S criterion and decide a suitable cell or not.
The Figure above shows one possible scenario in a real network. Assume that the UE belongs to network operator 1. The two other carriers also operating an LTE network but of course at different frequencies. The terminal receives all base stations but at different power levels. Based on the above definition the UE will select t he strong cell for each carrier . Us this the UE will start with network operator 3 and figure out after decoding the SIB Type 1 that the PLMN saved on the U does not match to the transmitted one. From this information it will stop with its attempt and proceed to the next stron signal, which is operator 2 . Now t he PLMN does not correspond so the UE will continue with signal 3 (green) – and the P will match. The UE continues to use the information in SIB Type 1 and Type 2 to compute the cell selection criteria. In thi example, the parameters transferred and belonging to eNB1 do not fulfill S > 0 where the UE will move along with demodulating and decoding the information provided by eNB2. S > 0 is fulfilled and the UE starts camping on this cell.
• Rank indication (RI) Reports are applicable for closed- and open-loop spatial multiplexing. In case of open-loop TRI=1 corresponds to transmit diversity and TRI>1 to large delay CDD. • Precoding matrix indicator (PMI) PMI reporting is relevant for spatial multiplexing (open- and closed-loop), MU -MIMO, closed-loop RANK=1 precoding. PMI and RI are confined to a subset of the codebook which is created by means of a codebookSubsetRestriction parameter. • Channel quality indication (CQI) CQI may be wideband or may be related to subbands. Similar to HSPA the CQI definition is targeted at 10 % BLER whereby the overall energy per bit is nearly minimized.
For the purpose of periodic reporting the PUCCH is utilized, a periodic reports are sent on the PUSCH. The latter reports are explicitly requested by setting the CQI request field in connection with an uplink grant. In case of “collision” the aperiodic report will be transmitted. Furthermore the scheduling mode can be frequency selective (periodic and aperiodic).
frequency non-selective (periodic) or
The offset is signaled by nomPDSCH-RS-EPRE-Offset.
