Cooperative Beamforming Aided Incremental Relaying in Cognitive Radios

We propose a cooperative beamforming aided incremental relaying scheme to improve spectrum efficiency of cognitive radio systems. In this scheme, the source and relays can utilize cooperative beamforming to activate packet retransmission in busy timeslots or spatial spectrum holes, if the destination fails to receive the packets transmitted from the source. Therefore, cooperative diversity gain is obtained without consuming extra idle timeslots. Given a packet loss constraint, our proposed scheme endeavors to further improve the system throughput by dynamically adjusting the maximum number of retransmissions. We derive the average throughput of the proposed scheme and obtain the maximum throughput by optimizing the scheduling parameters. Theoretical and simulation results reveal that the proposed scheme obtains a significant throughput gain compared to direct transmission as well as conventional incremental relaying schemes utilizing idle timeslots only.