TDD HARQ theory

Chen Zhenhua 171949 TDD Product Line

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Contents

HARQ overview HARQ classification HARQ combination HARQ feedback HARQ Timing Analysis HARQ retransmissionZTE confidential

HARQ overview

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HARQ=FEC+ARQ Based on Turbo code before the to forward error correction (FEC) and automatic request retransmission (ARQ) with combination,The receiving point use Turbo code correction the few mistakes , more than the mistake exceed the FEC ability then Through the method of sending retransmission request to correct FEC forward error correction coding, used to correct the mistakes in the channel often appear to reduce weight and improve the system through the efficiency; ARQ Automatic request retransmission, used to correct the mistake, of FEC can't correct to enhance the system reliability

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HARQ classification Synchronization HARQ&Asynchronous HARQ

Asynchronous HARQAsynchronous HARQ accurately inform receiver the HARQ process ID number

Synchronization HARQ

Synchronization HARQ implicitly inform receiver the HARQ process ID number, for example: for TDD Uplinkwe can

obtain current HARQ ID from UL sub frame num

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HARQ classification Adaptive & Non adaptive HARQ retransmission

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Adaptive HARQ retransmission Redistribution of frequency resource for retransmission HARQ. so, it needs to use PDCCH resource to indicate the retransmission UE HARQ assigned frequency resource. Non adaptive HARQ retransmission Retransmission HARQ use of frequency resource and the HARQ last transmission using same frequency resourceAt this timethe HARQ does not require using PDCCH resources

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HARQ combination CC & IR

RV RV (redundancy version)Used to determine the starting position of the new transition data, value is 012 and 3 CC CCChase combiningcombination: Retransmission and new transmission RV are same, then HARQ combinationif there is more than one retransmission the CC can combination only when retransmission RVand new transmission RV have the same value.

IR IR combination: when retransmission and new transmission RV are not equal ,then the HARQ can combine

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HARQ combinationTurbo code

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HARQ combinationRV division

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HARQ CombinationCombined condition

HARQ Combined condition The receiver need Judge HARQ new transmission and retransmission have the equal TB block size. Judging the new transmission TB: determined by RBNumMCS and ITBS Judging the retransmission TB: if 0IMCS 28 , then Judging by RBNumMCS and ITBS. if 29IMCS 31, then consider the retransmission TB and new transmission TB have the equal TB size. In which, for the DL HARQ 2930 and 31 express QPSK 16QAM and 64QAM modulation mode; for UL HARQ 29 30 and 31 express RV equal to 123

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HARQ combinationCC

A retransmission combine as an example:

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HARQ combinationIR

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HARQ combinationCC&IR combined gain102

Comparisons between CC, PIR and FIR on AWGN

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1

BLER (%)

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1 Tx CC1 PIR1 FIR1 CC2 PIR2 FIR2

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-1

-8

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-4 Ior/Ioc (dB)

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-1

0

Figure 1: Comparison between FIR, PIR and CC on AWGN

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HARQ combinationCC&IR combined gain(2)102

Comparisons between CC, PIR and FIR on flat fading at 3 km/h 1 Tx CC1 PIR1 FIR1 CC2 PIR2 FIR2

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BLER (%)100

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-10

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5 Ior/Ioc (dB)

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20

Figure 2: Comparison between FIR, PIR and CC on flat fading at 3 km/h

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HARQ feedback

Reason TDD UL and DL sub frame are Asymmetricwhen UL sub frame num less than DL sub framesome uplink sub frame may be report multiple downlink sub frame information. Solution method

LTE offer two methods ACK/NCK Bundling ACK/NCK Multiplexing

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HARQ feedbackBundling feedback

ACK/NCK Bundling feedback moduleIn bundling windowfor each stream let the need report sub frame ACK/NCK(s) information to make and operate ,then through one bit to report. NCK-0ACK-1

Bundling Window conceptionas shown in the diagram below

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HARQ feedbackBundling feedback(2)

Bundling defectBundling reports ACK/NACK is multiple ACK NACK make and operatoringif there is one NACK is reported NACK, it reports NACKAfter the eNB analytic NACK informationit considers the corresponding all HARQ as NACK to retransmit processing. Thus it may waste some time frequency resource and lead to layer 1 throughputs reduction

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HARQ feedbackMultiplex feedback

ACK/NCK Multiplexingevery HARQ process 2 streams make and operator single stream without this operation TDD SwitchCfg 2:2 multiplex feedback:

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DL HARQ Timing Analysis

n=0 eNB TX PDSCH eNB RX

n=4

n=6 PDSCH

n=10

UE RX UE TX

PDCCH NACK

PDCCH ACK

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UL HARQ Timing Analysis

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ULSCH ULeNB Rx SCH UE Tx

A teNB_UL=3ms eNB Tx C K UE Rx Tp

A C K

tUE_UL = 6-2Tp -Ta

ULSCH ULeNB Rx SCH UE Tx

UPLINK MAX DELAY (D km) Max HARQ Processes: 4 teNB_UL=3msA C K Tp A C K

RTT=10ms ULSCH ULeNB Rx SCH UE Tx

teNB_UL=5ms

eNB Tx UE Rx

A C K Tp

A C K

tUE_UL = 4-2Tp -TaUE Tx ULSCH ULeNB Rx SCH

teNB_UL=5ms

eNB Tx UE Rx

A C K Tp

RTT=10ms

A C K

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ULSCH ULeNB Rx SCH UE Tx

A eNB Tx C K UE Rx Tp

A C K

tUE_UL = 6-2Tp -Ta

ULSCH ULeNB Rx SCH UE Tx

UPLINK MAX DELAY (D km) Max HARQ Processes: 2 teNB_UL=3msA C K A C K

RTT=10ms Tp

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HARQ retransmissionUL-CC

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HARQ retransmission UL IR Non-Adaptive retransmission

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HARQ retransmission UL IR adaptive retransmission

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ENDThank you !

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