Telecom Tutorials by Samir Amberkar

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)

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