Distributed beamforming for cognitive relay networks

A distributed beamforming technique for half-duplex underlay cognitive relay networks is developed in this paper. The considered cognitive relay network consists of one pair of primary users, one pair of secondary users and multiple relays. With the help of multiple relays, the secondary transmitter sends data to the secondary receiver. In our approach, the receive quality-of-service at the secondary user is maximized while keeping the total relay transmit power and the interference power below a predefined threshold. The resultant problem is shown to have closed-form solutions with certain conditions or can be formulated as a quasi-convex problem, which can be solved efficiently using bi-section search method and second-order-cone programming. Simulation results demonstrate that the proposed beamforming method improves the system performance.