Systems and methods of selecting a PRACH resource opportunity are described. One of multiple Synchronization Signal Blocks (SSBs) is received. Each SSB has PSSs, SSSs and a PBCH that contain system information. A RACH occasion (RO) is selected from among multiple ROs associated with the SSB. A PRACH is transmitted on resources of the RO. The ROs are configured in a TDM and/or FDM manner. The RO is selected randomly or, if TDM is used, an earliest of the ROs from a UE-initiated RACH transmission in a previous period. A preamble of the RO is selected randomly with equal probability.