r scheduling transmission/retransmission; however, the initial transmission is slot-based, and the retransmissions may be non-slot based as shown in Fig. 4.58. In the following example, we assume subcarrier spacing is 15 kHz, D1 is a slot-based downlink scheduling period with front-loaded DM-RS and D2 is a non-slot-based schedul- ing period. If D2 is the initial transmission then the processing time is calculated as T2; nev- ertheless, if D2 is the retransmission of D1 then we need to perform TB decoding with 14 OFDM symbols; thus the processing time for retransmission is shown to be TPDCCH + demodulation + 13Tdecode + TUL-HARQ + Tother, meaning that for the same con- ditions, the processing time for initial transmission and retransmission are different [65]. As we mentioned earlier, the maximum number of HARQ processes per carrier supported in NR is 8 or 16. For continuous downlink transmission at the peak data rate, the minimum number of HARQ processes is min(NDL-HARQ) = K + K3 + 2Td/TTIDL in which T denotes the transmission delay. The required number of HARQ processes may vary depend- ing on UE HARQ processing capability, numerology, and network configurations. The determination of the number of HARQ processes is up to gNB scheduler and thus signaled via the DCI. To reduce the overhead, the gNB can semi-statically configure a UE with a smaller number of HARQ processes than 16 per bandwidth part. In order to reduce the latency due to HARQ retransmissions and to avoid retransmission of the entire TB and the performance degradation of HARQ due to large transport block size, NR defined CBG- based transmission and HARQ operation which supports single-/multi-bit HARQ-ACK feedback in Rel-15. The CBG-based (re)transmissions are only allowed for the same TB of a HARQ process. The CBG can include all code blocks of a TB regardless of the size of the TB. In such conditions, the UE reports single HARQ-ACK bits for the TB. The CBG can include one code block and its granularity is configurable. The UE is semi-statically con