rhead. However, even in that case, the four-step RACH would still involve more signaling and latency relative to that of the two-step approach. In two-step RACH, the MsgA may consist of two parts, that is, PRACH preamble and PUSCH which are time-division multiplexed. The PRACH preamble is used for UE detec- tion, allowing the network to prepare for the reception of the corresponding PUSCH mes- sage. In NR Rel-15, up to 64 preamble signatures are mapped to one PRACH occasion. The preambles are orthogonal, or quasi-orthogonal, allowing the network to receive multiple preambles (from different UEs) in the same PRACH occasion. If all the preambles are mapped to a PUSCH in the same time-frequency occasion and more than one preamble is detected, the PUSCH transmissions of the detected preambles overlap in time and fre- quency, increasing the probability of PUSCH decoding failure. Alternatively, each pream- ble, or subset of preambles, can be mapped to a PUSCH in a unique time-frequency resource. This reduces the probability of PUSCH decoding failure due to collision but sig- nificantly increases the two-step RACH physical-layer overhead in the uplink. The MsgB in New Radio Access Physical Layer Aspects (Part 2) 631 two-step procedure comprises several fields including the detected unique ID for contention resolution, where the size of the detected ID depends on the use case; a timing advance field; an uplink-grant for scheduling the data packets after the RACH procedure; and small user-plane/control-plane packets for downlink communication. The presence and the size of each field depend on the use case; thus the total size of MsgB may vary. 4.2.4 Physical Uplink Shared Channel The physical uplink shared channel is used to transmit the user traffic and control informa- tion in the uplink. It supports two transmission modes namely codebook-based and non- codebook-based multi-antenna transmission. For codebook-based transmission, the gNB provides the UE with a transmit precoding matrix indication in DCI. The UE uses the i