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LTE - FDD DL HARQ

LTE - FDD DL HARQ [Under LTE]

LTE DL HARQ operate in an Asynchronous way - HARQ process number is provided as part of DCI. HARQ acknowledgment (from UE) is transmitted in four subframes later [Ref: 36.213:10.2].

Below is an example message exchange, illustrating DL HARQ process. Scenario is a failed transmission, followed two failed retransmissions, followed by a successful new transmission (NDI is toggled).

MAC entities below include MAC and Layer 1 control procedures. L1 entities include mainly RF and DSP functions. Time stamping is system frame.subframe (e.g. 498.6). Δ indicate processing time taken by MAC and δ indicate time taken by RF + DSP.

For more details, refer 36.321:5.3.2(MAC DL HARQ operation), 36.213:10.2 (PHY PUCCH HARQ Ack), 36.212:5.2.3.1 (UCI coding), and 36.212:5.3.3.1 (DCI formats).

 eNB_MAC   

 eNB_L1   

 UE_L1   

 UE_MAC   


Subframe Tick
498.6 - Δ
Subframe Config
PDCCH DCI 2a
(RNTI=100, harq=1, mcs1=28, ndi1=1, rv1=0, mcs2=28, ndi2=0, rv2=0)
Subframe Tick
498.6 - Δ
Subframe Config
PDCCH DETECTION
498.6
PDCCH + PDSCH

Subframe Tick
498.6 + δ
Data Indication

(harq=1, tb-size1=9422, rv1=0, ndi1=1, tb-size2=9422, rv2=0, ndi2=0, crc1=error, crc2=error)
Subframe Tick
499.0 - Δ
Subframe Config
PUCCH DETECTION
(RNTI=100)

Subframe Tick
499.0 - Δ
Subframe Config
PUCCH UCI 1b
(RNTI=100, harq-ack=b00)

499.0
PUCCH
Subframe Tick
499.0 + δ
Control Indication
(RNTI=100, harq-ack=b00)

Subframe Tick
499.4 - Δ
Subframe Config
PDCCH DCI 2a
(RNTI=100, harq=1, mcs1=31, ndi1=1, rv1=2, mcs2=31, ndi2=0, rv2=2)
Subframe Tick
499.4 - Δ
Subframe Config
PDCCH DETECTION
499.4
PDCCH + PDSCH

Subframe Tick
499.4 + δ
Data Indication

(harq=1, tb-size1=9422, rv1=2, ndi1=1, tb-size2=9422, rv2=2, ndi2=0, crc1=error, crc2=error)
Subframe Tick
499.8 - Δ
Subframe Config
PUCCH DETECTION
(RNTI=100)

Subframe Tick
499.8 - Δ
Subframe Config
PUCCH UCI 1b
(RNTI=100, harq-ack=b00)

499.8
PUCCH
Subframe Tick
499.8 + δ
Control Indication
(RNTI=100, harq-ack=b00)

Subframe Tick
500.2 - Δ

Subframe Config
PDCCH DCI 2a
(RNTI=100, harq=1, mcs1=31, ndi1=1, rv1=3, mcs2=31, ndi2=0, rv2=3)
Subframe Tick
500.2 - Δ
Subframe Config
PDCCH DETECTION
500.2
PDCCH + PDSCH

Subframe Tick
500.2 + δ
Data Indication

(harq=1, tb-size1=9422, rv1=3, ndi1=1, tb-size2=9422, rv2=3, ndi2=0, crc1=error, crc2=error)
Subframe Tick
500.6 - Δ
Subframe Config
PUCCH DETECTION
(RNTI=100)

Subframe Tick
500.6 - Δ
Subframe Config
PUCCH UCI 1b
(RNTI=100, harq-ack=b00)

500.6
PUCCH
Subframe Tick
500.6 + δ
Control Indication
(RNTI=100, harq-ack=b00)

Subframe Tick
501.0 - Δ

Subframe Config
PDCCH DCI 2a
(RNTI=100, harq=1, mcs1=26, ndi1=0, rv1=0, mcs2=26, ndi2=1, rv2=0)
Subframe Tick
501.0 - Δ
Subframe Config
PDCCH DETECTION
501.0
PDCCH + PDSCH

Subframe Tick
501.0 + δ
Data Indication

(harq=1, tb-size1=4904, rv1=0, ndi1=0, tb-size2=4904, rv2=0, ndi2=1, crc1=success, crc2=success)
Subframe Tick
501.4 - Δ
Subframe Config
PUCCH DETECTION
(RNTI=100)

Subframe Tick
501.4 - Δ
Subframe Config
PUCCH UCI 1b
(RNTI=100, harq-ack=b11)

501.4
PUCCH
Subframe Tick
501.4 + δ
Control Indication
(RNTI=100, harq-ack=b11)

Copyright © Samir Amberkar 2010-21§

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