Optimal power allocation and relay selection for cognitive two-way AF relaying network

In an underlay cognitive two-way Amplify-and-Forward (AF) relaying network, secondary users (SUS) and primary user (PU) can share the licensed spectrum simultaneously under the interference threshold constraint. In this paper, the joint power allocation and optimal relay selection scheme is proposed for allocating radio resource on cognitive nodes effectively. For power allocation problem, the objective function is to maximize the achieved minimum Signal to Interference plus Noise Ratio (SINR) at SUS, and the constraints include the total transmit power of cognitive nodes and PU interference threshold, the optimal power allocation algorithm and a simple distributed power allocation algorithm are proposed. Furthermore, based on these results, an optimal two-way relay selection scheme is proposed. Simulation results show that the proposed joint power allocation algorithms and relay selection scheme can achieve excellent system performance.