a indicator to determine whether the current transmission should be soft combined with the received data currently in the soft buffer for the HARQ process or the soft buffer should be cleared [9,11]. The NR uplink uses asynchronous HARQ protocol in the same way as downlink. The HARQ-related information including process number, new-data indicator, CBG-based retransmission (if configured), and the CBGTI are included in the scheduling grant. The uplink CBGTI is used in the same way as in the downlink, that is, to indicate the CBGs that need to be retransmitted in the case of CBG-based retransmission. Note that no CBGFI is needed in the uplink as the soft buffer is located in the gNB which can decide whether to flush the buffer or not based on the scheduling decisions. The use of HARQ in NR allows reliable delivery of layer-1 packets between peer entities. Each HARQ process supports one TB when the physical layer is not configured for New Radio Access Physical Layer Aspects (Part 2) 545 Downlink data Downlink data assignment Uplink grant Uplink data Figure 4.57 NR HARQ protocol timing [9]. downlink/uplink spatial multiplexing; otherwise, each HARQ process supports one or multi- ple TBs. The NR HARQ operation and timing are illustrated in Fig. 4.57, where the para- meters used in the figure are defined as follows [8,9]: K denotes the delay between downlink grant and corresponding PDSCH data reception. K1 is the delay between PDSCH data reception and the corresponding ACK/NACK transmission on the uplink. K2 denotes the delay between uplink grant reception in downlink and the uplink data transmission on PUSCH. K3 is the delay between ACK/NACK reception in the uplink and the corresponding retransmission of downlink data on PDSCH. The parameters Ko, K1, and K2 are signaled via DCI and if K1 0, a self-contained subframe/slot is configured. The choice of N1 value has a significant impact on the UE processing time, where N1 is defined as the number of OFDM symbols from the end of PDSCH reception to the start of the correspo