Cooperative beamforming in cognitive radio network with hybrid relay

In this paper we investigate the cooperative beamforming in cognitive radio network (CRN) composed of a primary network (PN) and a secondary network (SN). In the SN, the transmitter has to communicate with the receiver with the help of the hybrid relays which use cooperative beamforming to retransmit data. The relays will select amplify-and-forward (AF) or decode-and-forward (DF) according to the signal to interference pulse noise ratio (SINR). The aim of this paper is to maximize the received SINR in the SN with different power constraints and the QoS requirement of the primary user (PU). Numerical results compare the performance of the SN between relays with beamforming and relays without beamforming which indicates that the gap between them is related to the maximum interference power at primary destination, while is irrelevant to maximum the total transmitted power of the relays. Besides there is a tradeoff between the performance of the SN and the number of the relays.