Research On Cooperative Beamforming In Cognitive Multi-User Systems

With the development of wireless communication technologies, wireless business demand for spectrum is also rapidly growing. The lack of spectrum resources becomes one of the bottlenecks in the development of wireless communications. However, most of the existing wireless communication systems with fixed spectrum allocation result in lower spectrum efficiency. The cognitive radio technology proposed in recent years is able to sense and access the unused spectrum. It has realized the dynamic management of spectrum resources and can effectively improve the spectrum utilization.Beamforming is the key technology to improve spectrum efficiency in the next generation of wireless network. It can adjust the direction of the signal of the channel vector to maximize the system performance and can effectively eliminate the interference among users. At the same time, in cooperative communication system, multi-user can form a virtual multi-antenna, then if use the beamforming, it can makes the multi-user transmission signal orthogonal to each other and eliminate the interference between users. It can effectively improve the performance of the system. In this paper, we mainly study the application of cooperative beamforming in cognitive multi-user system.Firstly, this paper studies the application of cooperative beamforming in cognitive relay networks. Considering the dynamic variation of spectrum resources and different fading features of cooperative this paper proposes a QoS-based cognitive relay transmission method for optimization of bandwidth, delay and bit error rate. The method consists of three steps:first for the dynamic spectrum allocation process; followed by the relay selection process based on the average channel gain; finally, design the beamforming vector for the selected relay node. Simulation shows that the algorithm satisfies the requirements of the bandwidth of the user, minimizes the delay and reduces the bit error rate of the system. On the whole it ensures the user’s QoS requirements, at the same time increases the system throughput, improves the spectrum efficiency.Secondly, this paper studies the application of cooperative beamforming in the cognitive heterogeneous cellular network. We analyze the different types of interference in the two-tier heterogeneous network including macrocell and small cell. We make full use of the advantages of cell clustering and proposed a clustering-based cooperative transmission and resource allocation mechanism in order to maximize the system rates. The proposed scheme use beamforming to eliminate interference within the cluster while carry out public sub-channels allocation between clusters, so as to eliminate interference between clusters. This scheme not only ensures interference from cognitive users to primary users is less than the threshold and also eliminates the common channel interference, and maximizes the system total rate at the same time. The simulation results show the algorithm is better than no interference coordination system performance.