The whole procedure (transmission, reception and ack/nack reporting, retransmission) is done by a speciall process called HARQ process. The transmission and reception process involves transmitting data, receiving ACK or NACK, and performing retransmissions if necessary. So I would like you to google something about FEC. FEC is also not LTE specific technology and a kind of generic error correction mechanism. Then what would be the "Something" ? The "Something" is FEC (forward error correction). The "H" in HARQ means "Hybrid" which implies that HARQ is a combination of "Something" and "ARQ". ARQ stands for Automatic Repeat Request and you would have heard this a lot if you had experience of studying IP communication (I think you can google a lot of tutorials on this, so I would not explain about what is ARQ here). What is H-ARQ ? Why it uses the term "Hybrid" ?įirst think about the term ARQ. Number of HARQ processor is configured in RRC and the max number of the process is 16.The time gap between PDSCH and corresponding Ack/Nack (k1) is determined by the combination of RRC Configuration and DCI.The time gap between PDSCH and corresponding Ack/Nack (k1) is not fixed any more (this is another difference between NR and LTE).It is a special physical layer message that indicates the success or failure of PDSCH decoding in UE (In NR, PUSCH does not required Ack/Nack.FEC involves adding redundant bits to the original data to allow error detection and correction at the receiver, while ARQ is a feedback mechanism where the receiver sends a retransmission request if an error is detected in the received data.Hybrid implies the combination of Error Correction(FEC) and ARQ.
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