Multichannel Uplink NOMA Random Access: Selection Diversity and Bistability

This letter investigates uplink random access (RA) systems based on power-domain non-orthogonal multiple access (NOMA) with multichannel. In NOMA RA systems, users transmit their packet with transmit power by inverting their channel gain, i.e., channel inversion, such that the received power of their packet at the base station (BS) can be one of the predefined values. While this facilitates the decoding process based on successive interference cancellation (SIC), it can incur excessive transmit power consumption upon low channel gains. To reduce transmit power (improve energy efficiency), this letter considers multichannel selection diversity, where users choose one channel whose channel gain is the maximum of all. We characterize the stability of multichannel NOMA RA systems with the cusp catastrophe and analyze diversity gain in terms of energy efficiency.