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Figure 4.54 Illustration of the chase combining and incremental redundancy HARQ schemes [15].

4.1.8.2 UE Processing Times, HARQ Protocol and Timing

3GPP NR uses an asynchronous HARQ-IR scheme in the downlink and uplink. The gNB provides the UE with the HARQ-ACK feedback timing either dynamically in the DCI or semi-statically through RRC configuration messages. The gNB schedules each uplink transmission and retransmission using the uplink grant on DCI. In LTE, the basic mode of operation for uplink HARQ is synchronous retransmission, which can be used to reduce the scheduling overhead for retransmissions. In this case, HARQ ACK/NACK is carried ...

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