physical channels

4 Nokia Siemens Networks LTE Radio Parameters / v001 / Document NumberFor internal use

Physical channels and signals - recap


Overview - ChannelsUpper Layers

RLC

MAC

PHY

Logical channels

Transport channels

BCC

H

CC

CH

PCC

H

MTC

H

MC

CH

BCH

PCH

DL-SC

H

RAC

H

UL-SC

H

PBCH

PDSC

H

PHIC

H

PDC

CH

PCFIC

H

PMC

H

PUC

CH

PRAC

H

PUSC

H

MC

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CC

CH

DC

CH

DTC

HULDL

Air interface

DC

CH

DTC

H


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)


eNode B

CQI, PMI, RI,

ACK/NACK

SR

RNTIDL schedulingUL GrantUL PWRCn x per cell

DL control configuration

1x per cell

HARQ Info

CQI, PMI, RI,

ACK/NACK

Overview Control Information


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)

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 60 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 60 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

Subcarrier 1

Subcarrier 12

1

8

0

K

H

z

1 slot 1 slot

1 ms subframe

Capacity allocation is based on Resource Blocks

Resource Element

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


Physical Layer Downlink SummaryDL-Physical Data & Control Channel

DLDL--Channel Channel OverviewOverview

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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.

Antenna 1 Antenna 2

s

u

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r

r

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symbols 60 symbols 60

subcarriers


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


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

Strongest Signal

Primary Synchronization Signal

Secondary Synchronisation Signal

L1 id, slot (0/10)

Physical Layer Cell ID, Frame

Alignment

Cell ID Group 0(3 L1 ids)

Group 167

Cell ID Group i(3 L1 ids)168 Cell ID

groups

Phy L Cell ID

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 DL center frequency 10ms and 5ms timing CP length Duplex mode (TDD/FDD)


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 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

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

scheduling request, CQIs and MIMO feedback Only control information is sent. The UE uses

Resources Element at the edges of the channel

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.

RACH

CCCH DCCH DTCH

UL-SCH

PRACH PUSCH PUCCH

Logical

Transport

PHYS.

RLC

MAC


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 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

(2) UE CSI measurement


PDCCH Uplink Grant The eNodeB allocates the Uplink resources to the UEs by sending an UL

Grant

UL Grant contentsResource Block assignment

Indicates the PRB the UE may use for transmissionSignaling 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 symbolsCQI request flagPUSCH Hopping flagNew data indicator

TDD specificUL index (indicates which UL subframe the grant refers to)Downlink assignment index

physical channels

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