Buffered-Relay Selection in an Underlay Cognitive Radio Network

We consider an underlay relay-assisted time-slotted cognitive radio network operating on the same band used by a primary link. For implementation simplicity, one relay is selected at any time slot for reception from the secondary source, or for transmission to the secondary destination. Relay selection depends on the instantaneous channel gains and the occupancy status of the relays' buffers. Selection is constrained by a maximum tolerable interference level at the primary receiver. We provide a theoretical framework based on a Markov chain to model the system and obtain the secondary throughput and average queuing delay. We verify our obtained expressions via numerical system simulations and investigate the impact of the various system parameters on performance.