This disclosure describes improving a 4-step RACH procedure by using a 2-step RACH procedure. A UE transmits a PRACH preamble and associated MsgA physical uplink shared channel (PUSCH) on a configured time and frequency resource. After successful detection of the PRACH preamble, and decoding of the MsgA PUSCH, the gNB transmits MsgB in the second step. Generally, a mapping is used between the PRACH preamble and the PUSCH resource unit for 2-step RACH. This disclosure describes the mapping for 2-step RACH.