Joint Relay and Receive Beamforming in Cognitive Relay Networks with Hybrid Relay Strategy

This paper investigates the joint design of relay and receive beamforming vectors in cognitive relay networks with the secondary network (SN) using the same frequency band allocated to the primary network (PN). To guarantee the QoS of the primary user (PU), the interference from source and relays in the SN to PU must be lower than what the PU can tolerate. A hybrid relay strategy is adopted by relays that can use amplify-and-forward (AF) or decode-and-forward (DF) strategies to retransmit signal according to signal to interference pulse noise ratio (SINR). The capacity of the source-destination in the SN is maximized with the transmit power and the interference at PU constraints. The simulation results show that the maximum relay transmit power will affect the gain of both the joint beamforming and the hybrid relay strategy, while the maximum interference power at PU will only affect that of the hybrid relay strategy.