 reports are required to enable the MAC scheduler to make scheduling deci- sions in the downlink and uplink. These reports include transport capabilities and measure- ments of UEs instantaneous radio conditions. The uplink BSRs are needed to support QoS- aware packet scheduling. In NR, uplink BSRs refer to the data that is buffered for an LCG in the UE. There are eight LCGs and two reporting formats in the uplink: a short format to report only one BSR (of one LCG) and a flexible long format to report several BSRs (up to eight LCGs). The uplink BSRs are transmitted using MAC CEs. When a BSR is triggered upon arrival of data in the transmission buffers of the UE, an SR is transmitted by the UE. The PHRs are needed to support power-aware packet scheduling. In NR, there are three types of reporting, that is, for PUSCH transmission, PUSCH and PUCCH transmission, and SRS transmission. In case of carrier aggregation, when no transmission takes place on an activated SCell, a reference power is used to provide a virtual report. The PHRs are trans- mitted using MAC CEs [8]. The HARQ functionality in the MAC sublayer ensures reliable transport of MAC PDUs between peer entities over the physical layer. A HARQ mechanism along with soft combin- ing can provide robustness against transmission errors. A single HARQ process supports one or multiple transport blocks depending on whether the physical layer is configured for downlink/uplink spatial multiplexing. An asynchronous incremental redundancy HARQ pro- tocol is supported in the downlink and uplink. The gNB provides the UE with the HARQ- ACK feedback timing either dynamically via DCI or semi-statically through an RRC con- figuration message. The UE may be configured to receive code-block-group-based trans- missions where retransmissions may be scheduled to carry a subset of the code blocks 214 Chapter 2 included in a transport block. The gNB schedules each uplink transmission and retransmis- sion using the uplink grant on DCI [8]. The HARQ protocol in NR uses multiple paralle