Cooperative filter-and-forward beamforming in cognitive radio relay networks

In this paper, the filter-and-forward (FF) strategy is developed for cooperative relays in cognitive radio (CR) networks with the underlay structure and the frequency selective fading channels. A cost function is defined to minimize the required transmitting power of the relay networks and the secondary user. For this purpose, the cost function is constrained to keeping the power of noise and interferences at the primary receiver less than a predefined limit, and the SINR above a given threshold. Simulation results show that the proposed algorithm converges to an optimal solution based on the interior point method. The results show that compared to the AF strategy, we achieve a higher SINR threshold in the secondary receiver and need a lower transmitting power at the relays and the secondary transmitter.