Telecom Tutorials by Samir Amberkar

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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