Research On Key Technologies Of Cognitive Relay Network Based On Cooperative Communication

In the traditional cognitive network, the communication performance of the secondary user is always limited because of the need to guarantee the communication performance of the primary user. The cognitive relay network can effectively improve the coverage and throughput of the secondary system by employing the cooperative relay technology into the cognitive wireless environment, which provides a good solution for the above problems. In the cognitive relay network, the appropriate relay selection mechanism is also essential. At the same time, because the available resources of secondary systems are often limited in the cognitive relay network, how to carry out efficient resource allocation while relaying selection is also very important. Therefore, this thesis investigates the key technologies of the cognitive relay network.In order to further improve the performance of the system, this thesis first studies the single relay selection problem in full-duplex cognitive networks. The article proposes a kind of joint relay and antenna mode selection scheme with the optimal power allocation. The closed-form expressions of the optimal power allocation are derived. Then an iterative algorithm is designed to obtain the solution of the joint optimization problem. And the numerical results demonstrate that the system performance can be greatly improved through employing the proposed algorithm.Aiming at the problem of high complexity of cognitive multi-relay selection, this article studies the low complexity implementation of cognitive multi-relay selection. Firstly, the signal-to-noise ratio and channel capacity of the cognitive multi-relay system are deduced, and the multi-relay selection and power allocation are combined into a joint optimization problem. In this thesis, we first quantify the available power of relay nodes and convert the continuous power allocation problem into discrete power allocation to reduce the complexity of algorithm implementation. At the same time, a heuristic relay selection algorithm based on relay transmission efficiency is proposed to solve the problem that relay nodes do not fully consider the interference caused by relay nodes. The algorithm proposed in this thesis can reduce the implementation complexity of multi-relay selection effectively, and the performance is closer to the optimal solution than the previous ones.Simulation results show that the algorithm proposed in this thesis can improve the channel capacity by about 12%, which provides a feasible solution for the application of multi-relay technology.