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LTE - FDD UL HARQ

LTE - FDD UL HARQ [Under LTE]

Below is an illustration of LTE UL HARQ operating in Synchronous mode (HARQ process number is implied) with Non-adaptive retransmission (UL grant is *not* part of PHICH feedback).

Usual formula to calculate HARQ process number is "(system frame x 10 + subframe) modulo 8" for PUSCH allocation subframe. The sequence of redundancy versions has been set in specification as 0,2,3,1.

Scenario is a failed transmission, followed one failed retransmission, followed by a successful retransmission.

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. 312.5). Δ indicate processing time taken by MAC and δ indicate time taken by RF + DSP.

For more details, refer 36.321:5.4.2(MAC UL HARQ operation), 36.213:9.1.2 (PHY PHICH assignment), and 36.212:5.3.3.1 (DCI formats).

 eNB_MAC   

 eNB_L1   

 UE_L1   

 UE_MAC   


Subframe Tick
312.5 - Δ
Subframe Config
PDCCH DCI 0
(RNTI=100, mcs=22, ndi=1)
Subframe Tick
312.5 - Δ
Subframe Config
PDCCH DETECTION
312.5
PDCCH
Subframe Tick
312.5 + δ
Control Indication
(mcs=22)
Subframe Tick
312.9 - Δ
Subframe Config
PUSCH
(RNTI=100, harq=1, rv=0)

Subframe Tick
312.9 - Δ
Subframe Config
PUSCH
(RNTI=100, harq=1, tb size=349, rv=0)

312.9
PUSCH
Subframe Tick
312.9 + δ
Data Indication
(RNTI=100, crc=error)

Subframe Tick
313.3 - Δ
Subframe Config
PHICH HI=NACK
(RNTI=100)
Subframe Tick
313.3 - Δ
Subframe Config
PHICH DETECTION
312.3
PHICH
Subframe Tick
313.3 + δ
Control Indication
(HI=NACK)
Subframe Tick
313.7 - Δ
Subframe Config
PUSCH
(RNTI=100, harq=1, rv=2)

Subframe Tick
313.7 - Δ
Subframe Config
PUSCH
(RNTI=100, harq=1, tb size=349, rv=2)

313.7
PUSCH
Subframe Tick
313.7 + δ
Data Indication
(RNTI=100, crc=error)

Subframe Tick
314.1 - Δ
Subframe Config
PHICH HI=NACK
(RNTI=100)
Subframe Tick
314.1 - Δ
Subframe Config
PHICH DETECTION
314.1
PHICH
Subframe Tick
314.1 + δ
Control Indication
(HI=NACK)
Subframe Tick
314.5 - Δ
Subframe Config
PUSCH
(RNTI=100, harq=1, rv=3)

Subframe Tick
314.5 - Δ
Subframe Config
PUSCH
(RNTI=100, harq=1, tb size=349, rv=3)

314.5
PUSCH
Subframe Tick
314.5 + δ
Data Indication
(RNTI=100, crc=success)

Subframe Tick
314.9 - Δ
Subframe Config
PHICH HI=ACK
(RNTI=100)
Subframe Tick
314.9 - Δ
Subframe Config
PHICH DETECTION
314.9
PHICH
Subframe Tick
314.9 + δ
Control Indication
(HI=ACK)

Copyright © Samir Amberkar 2010-21§

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