Research On Optimal Node Selection Scheme For Cooperative Communication

With the help of the surrounding idle relay nodes,cooperative communication technology forms a virtual MIMO system by sharing the antennas among numbers of single-antenna users.Cooperative communication can combat channel fading and improve signal coverage area effectively,especially well for blind spots or weak signals.in the cell.Amplify-and-forward(AF)and decode-and-forward(DF)are the most frequently used relay forwarding protocols of cooperative communication.Because the performance of these two protocols under different channel conditions is different,a reasonable choice of a suitable cooperative method can effectively improve the system performance.The hybrid decode-amplify-and-forward(HDAF)relay protocol effectively overcomes the disadvantages of using a single cooperative method based on the characteristics of AF and DF.On the other hand,due to the participation of relay nodes,cooperative communication changes the traditional single-hop communication to multi-hop communication,which makes it more susceptible to eavesdropping by illegal users.These issues are still hot and difficult in the research of cooperative communications.This dissertation focuses on HDAF relay protocol and physical layer security of cooperative communication.The specific work includes the following two aspects:Aiming at the problem of selecting the multi-relay set under the HDAF protocol,a relay selection algorithm based on the sequential arrangement of the statistic channel information is proposed.Firstly,the parameter calculation of statistical characteristics of each relay channel are analyzed under the equal power allocation of each node,and the relay set that meets the system with the smallest outage probability is obtained,which greatly reduces the computational complexity.Simulation results show that this algorithm has lower average outage probability than the traditional relay selection algorithm under the same conditions.Second,the reallocation of power to participate in the communication nodes,the system performance is further improved.For wireless cooperative networks with multiple sources and multiple relays,an optimal node selection scheme based on power allocation is proposed.This scheme aims at maximizing the secrecy transmission rate and considers comprehensively the communication quality of the main channel and the eavesdropping channel.First,theoptimal power allocation scheme for any link under the limited total transmit power is given.Based on this,an optimal node selection scheme is designed.Then,a closed-form expression of the system secrecy outage probability under SNR is deduced.Simulation results show that the proposed scheme reduces the probability of security outage to a certain extent and has higher security performance compared with the traditional MAX-MIN selection scheme.