The Research Of Beamforming Algorithm In Cognitive Radio System

With the rapid development of wireless applications in recent years, the spectrum resources are increasingly strained, while most licensed bands experience low utilization due to the fixed allocation scheme. Cognitive radio is proposed as an effective technique to improve the utilization of licensed spectrums, so the bottleneck problem of insufficient spectrum resource can be handled effectively through dynamic spectrum management.To improve the system capacity, cognitive radio system adopts MIMO technology which can obtain spatial gain. The beamforming technology can effectively reduce interference to primary users from cognitive users and interference between cognitive users, so the system throughput can gain improvement. In this paper, the innovative work is to develop transmit beamforming algorithms in the downlink channel of cognitive radio system that adopts MIMO technology.In this paper, the main research is to develop beamforming algorithms for two kinds of beamforming problems in the cognitive MIMO system. In the downlink channel of multi-user multi-antenna cognitive radio system, basing on the idea of SVD decomposition and the BD algorithm, we developed the CR BD algorithm and improved CR TX-RX algorithm to solve the sum rate maximization beamforming optimization problem, in which the cognitive users should not interfere with the primary user and the transmit power at cognitive base station is constrained. For the transmit power minimization beamforming optimization problem, in which the interference constraints at primary users and the SINR constraints at cognitive users exist, we proposed the KKT-Based iterative algorithm to find the optimal beamforming vector basing on the KKT conditions of the optimization problem. The proposed algorithms have all been verified by simulating the performance and comparing with existing algorithms in difference simulation scenarios.