Research Of Beamforming In The Multi-relay Cognitive Radio Networks

With the rapid development of wireless communication,wireless communicating spectrum resources is becoming less and less.But the study found that a lot of licensed spectrum resources are not fully utilized.Cognitive radio technology by allowing unauthorized users to detect and opportunistical freely access authorization system band,can be a good method to increase the spectral efficiency.Since the distributed beamforming can effectively improve system performance and suppress the interference,it has been widely used.Distributed beamforming is distributed beamforming factor node by a certain direction of beam pointing,so that the receiving terminal can effectively receive information.At the same time due to the eavesdropping node,we want to avoid eavesdropping node to get to useful information,by taking beamforming or noise interference suppress the eavesdropping node,so that the physical layer of security based on joint beamforming and jamming emerged.Based on the distributed beamforming in cognitive wireless network,the study focuses on the following issues:With the limition of the primary network interference and relay transmission power,the article maximize the safety rate of the cognitive system by optimizing the relay beamforming factor and rationalizing secondary users transmit power and interference power.The article use SDP convex optimization problem and Taylor expansion formula to solve the problem of the one-way relay objective function and makes simulation comparison in the end,simulation illustrates that cooperate joint beamforming and jamming can improve the System's Safety rate.In the cognitive network system,the fourth part in the article considers the bidirectional multi-hop beamforming scheme,Since two-way relaying objective function is complex and can not be converted to a convex problem,only can be solves by low complexity Taylor expansion formula problem,simulation results show that the cooperative joint beamforming and interference scheme can effectively improve the security capacity of the system.