Physical Channels

Physical channels and signals - recap

For internal use 4 © Nokia Siemens Networks

LTE Radio Parameters / v001 / Document Number

Overview - Channels Upper Layers DL

UL

RLC DCCH

DTCH

CCCH

MTCH

MCCH

DTCH

DCCH

CCCH

PCCH

BCCH

Logical channels

MAC UL-SCH

RACH

MCH

DL-SCH

PCH

BCH

Transport channels

PHY PUSCH

PUCCH

PRACH


PMCH


PDCCH

PCFICH

PHICH

PDSCH

PBCH

Air interface

Downlink Physical Signals and Channels • Downlink Physical Signals – Reference Signals – Synchronisation Signals • Downlink Physical Channels – Physical Broadcast Channel (PBCH) – Physical Downlink Shared Channel (PDSCH) – Physical Downlink Control Channel (PDCCH) – Physical Control Format Indicator Channel (PCFICH) – Physical Hybrid-ARQ Indicator Channel (PHICH) – Physical Multicast Channel (PMCH)



Overview – Control Information CQI, PMI, RI, ACK/NACK

CQI, PMI, RI, ACK/NACK SR

eNode B

DL control configuration 1x per cell RNTI DL scheduling UL Grant UL PWRC n x per cell HARQ Info



Resource Block • Physical Resource Block or Resource Block (PRB or RB): 12 subcarriers in frequency domain (180kHz) x 1 slot period in time domain (0.5ms) Capacity allocation is based on Resource Subcarrier 1 0 1 2 3 4 5 6 0 1 2 3 4 5 6 Blocks 0 1 2 3 4 5 6 0 1 2 3 4 5 6 0 1 2 3 4 5 6 0 1 2 3 4 5 6

180 KHz

0 1 2 3 4 5 6 0 1 2 3 4 5 6 0 1 2 3 4 5 6 0 1 2 3 4 5 6 0 1 2 3 4 5 6 0 1 2 3 4 5 6 0 1 2 3 4 5 6 0 1 2 3 4 5 6 0 1 2 3 4 5 6 0 1 2 3 4 5 6 0 1 2 3 4 5 6 0 1 2 3 4 5 6 0 1 2 3 4 5 6 0 1 2 3 4 5 6 0 1 2 3 4 5 6 0 1 2 3 4 5 6

• Note: Although 3GPP definition of RB refers to 0.5ms, in some cases it is possible to found that RB refers to 12 subcarriers in frequency domain and 1ms in time domain. In particular, since the scheduler in the eNodeB works on TTI basis (1ms) RBs are considered to last 1ms in time domain. They can also be known as ‘scheduling resource blocks’

Subcarrier 12 0 1 2 3 4 5 6 0 1 2 3 4 5 6 1 slot

1 slot

1 ms subframe For internal use 8 © Nokia Siemens Networks


Resource Element

Physical Layer Downlink Summary DL-Channel DLOverview

Frequency

Central 72 subcarriers (6 RBs)

Total System Bandwidth e.g. 10MHz (50 RBs)

DL-Physical Data & Control Channel



Reference Signals: OFDMA Channel Estimation • Channel estimation in LTE is based on reference signals (like CPICH functionality in WCDMA) • Reference signals position in time domain is fixed (0 and 4 for Type 1 Frame) whereas in frequency domain it depends on the Cell ID • In case more than one antenna is used (e.g. MIMO) the Resource elements allocated to reference signals on one antenna are DTX on the other antennas • Reference signals are modulated to identify the cell to which they belong. symbols

6

0

symbols

6

subcarriers

subcarriers

0

Antenna 1 For internal use 10 © Nokia Siemens Networks


Antenna 2

Synchronization Signals allocation (DL) • Synchronization signals: – Transmitted during the 1st and 11th slots within a radio frame

– Occupy the central 62 Subcarriers (around the DC subcarrier) to facilitate the cell search

– 5 Subcarriers above and 5 Subcarriers below the synch. Signals are reserved and transmitted as DTx

– Synchronisation Signal can indicate 504 (168 x 3) CellID different values and from those one can determine the location of cell specific reference symbols For internal use 11 © Nokia Siemens Networks


Generic - Physical Layer Cell Id • Physical Layer Cell Identity defines a cell, but it is not necessarily unique in the network • It consists of the two parts; Physical layer Cell Identity Group and Physical layer Identity • Physical Layer Cell Identity = 3 x Physical layer Cell Identity Group + Physical layer Identity • Decoded during synchronisation using primary and secondary sync signal • PSS/SSS are used for: – Initial cell search and neighbor cell search • As a result of cell search the UE should acquire: – PHY cell ID Strongest Signal – DL center frequency – 10ms and 5ms timing – CP length – Duplex mode (TDD/FDD) Cell ID Group 0 (3 L1 id’s)

168 Cell ID groups

Cell ID Group i (3 L1 id’s)

Primary Synchronization Signal

L1 id, slot (0/10)

Secondary Synchronisation Signal Group 167 Phy L Cell ID Physical Layer Cell ID, Frame Alignment For internal use 12 © Nokia Siemens Networks


DL Physical Channels Allocation • PBCH: – Occupies the central 72 subcarriers across 4 symbols – Transmitted during second slot of each 10 ms frame on all antennas • PCFICH: – Transmitted during the first symbol of each TTI – Occupies up to 16 RE per TTI • PHICH: – Tx during 1st symbol of each TTI or alternativ during symbols 1 to 3 of each TTI Æ PhichDur – Each PHCIH group occupies 12 RE

• PDCCH: – Occupies the REs not used by PCFICH and PHICH and Reference Signals within the first 1, 2 or 3 symbols of each TTI (case 1.4 MHz: within the first 2, 3 or 4 symbols) – In RL09/10: configuration static by MaxNbrOfOFDMSymsForPDCCH • PDSCH: – Is allocated the RE not used by signals or other physical channels For internal use 13 © Nokia Siemens Networks


RB

UL Physical Channels • PUSCH: Physical Uplink Shared Channel – Intended for user data (carries traffic for multiple UEs) and control data – If control data is to be sent when traffic data is being transmitted, UE multiplexes both streams together

• PUCCH: Physical Uplink Control Channel – Carries H-ARQ Ack/Nack indications, uplink

CCCH

DCCH

DTCH

Logical RLC

Transport

RACH

scheduling request, CQIs and MIMO feedback – Only control information is sent. The UE uses Resources Element at the edges of the channel

UL-SCH

MAC

PHYS.

• PRACH: Physical Random Access Channel – For Random Access attempts. PDCCH indicates the resource elements for PRACH use – PBCH contains a list of allowed preambles (64 per cell) and the required length of the preamble.



PRACH

PUSCH

PUCCH

UL Channels The mapping of transport channels and UL control information (UCI) to physical channels is a task of the physical layer (PHY). Furthermore reference signals are provided by the physical layer which do not transfer any higher layer information. Logical channel mapping is provided by the MAC layer. Physical channel for data and signalling from higher layers: • Physical Uplink Shared Channel, PUSCH. • Physical Random Access Channel, PRACH. Physical channels with UL control - related signalling: • Physical Uplink Control Channel, PUCCH. and signals with no information of higher layers: • Demodulation Reference Signals (DRS). • Sounding Reference Signal (SRS).



UE Channel state information (CSI) feedback types in LTE • The purpose of CSI feedback is to provide • • •

• •

the eNodeB information about DL channel state to help in the scheduling decision. Compared to the WCDMA/HSPA, the main new feature in the channel feedback is the frequency selectivity of the report CSI is measured by the UE and signaled to the eNodeB using PUCCH or PUSCH Channel state information in LTE can be divided into three categories: – CQI - Channel Quality Indicator (2) UE CSI measurement – RI - Rank Indicator – PMI - Precoding Matrix Indicator In general the CSI reported by the UE is just a recommendation – The eNodeB does not need to follow it The corresponding procedure for providing information about the UL channel state is called Channel Sounding and it is done using the Sounding Reference Symbols, SRS (not considered in this presentation)



(1) eNodeB transmission

(3) UE feedback

PDCCH Uplink Grant • The eNodeB allocates the Uplink resources to the UEs by sending an UL Grant UL Grant contents •Resource Block assignment –Indicates the PRB the UE may use for transmission –Signaling format: index of starting PRB & number of contiguous PRBs •Modulation and Coding Scheme and the Redundancy version (5 bits) •Power control command (2 bits)

•Cyclic Shift for the demodulation reference symbols •CQI request flag •PUSCH Hopping flag •New data indicator TDD specific •UL index (indicates which UL subframe the grant refers to) •Downlink assignment index



Physical Channels

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