Cooperative bi-directional DF cognitive radio networks with limited feedback and beamforming

In this paper, we consider cooperative beamforming for bi-directional decode and forward (DF) cognitive radio networks comprising two secondary transceivers and multiple secondary relays in the presence of a pair of primary users (PUs). The aim of this work is to improve the secondary system performance with limited feedback from the PUs while using a mean value-based power allocation strategy. We consider the presence of mutual interference between the primary and secondary systems, and employ beamforming to suppress the interference inflicted on the primary system. However, the interference caused to the secondary system is not mitigated. To examine the impact of this interference on the performance of the secondary system, we derive closed-form expressions for the outage probability and bit error rate (BER) over independent and identically distributed Rayleigh fading channels. Numerical and simulation results demonstrate the effect of the limited feedback on the secondary system performance.