On the Diversity Gains of User Scheduling in the Cognitive Radio Parallel Access Channel

This paper investigates the multiuser diversity introduced by opportunistic user selection in the cognitive radio parallel access channel (CR-PAC), where multiple cognitive users request to access the spectral resources of the licensed user. Assuming a simple cognitive user selection strategy based on maximizing the received signal-to-interference-plus- noise ratio (SINR), we study the statistics of the SINR at the cognitive receiver. We then use this to analytically calculate the diversity gains introduced in the system due to the selection of one cognitive user amongst multiple candidates, compared to the case when only one cognitive user exists in the network and no selection occurs. Finally, we investigate potential gains for the primary network from this user selection. The results show a close match between analytical expressions and simulation results, while a tight lower bound for the multiuser gain is derived in closed form.