An Adaptive Cooperation Communication Strategy for Enhanced Opportunistic Spectrum Access in Cognitive Radios

To guarantee the continuity of secondary transmission (ST) in cognitive radio networks (CRNs), a beamforming-based cognitive cooperative communication protocol, referred to as BCC, is proposed in this paper. In BCC, a secondary user (SU) can increase the transmit power to reach its destination directly when the primary users (PUs) are absent. On the other hand, when new PUs come in, the SU will reduce its power and choose an intermediate relay to reach its destination to avoid the impact on the primary transmission (PT); in this case, the SU destination will leverage beamforming to receive data from both the SU and relay respectively. We analyze the performance of BCC and obtain the closed-form expressions of the ST outage probability. Simulation results are presented to validate the theoretical analysis and demonstrate that BCC achieves lower SU outage probability than the traditional cognitive radio scheme without using beamforming-based cooperation.