Strategy Of Physical Layer Security In Cooperative Communications

Physical layer security has become a hot issue in the area of information security during recent years. Traditional technologies of information security mainly adopt authentication and key-based cryptography to ensure data security. However, once the encryption algorithm is cracked, all data can be obtained by eavesdroppers easily. Unlike the traditional technologies, physical layer security starts from a perspective of information theory and can yield high level of secrecy rate performance through utilizing different kinds of channel characteristics in wireless network. No need for encryption algorithm, physical layer security can keep eavesdroppers from obtaining useful information so that the message can be transmitted securely. In cooperative communication, auxiliary nodes are utilized to complete the communication between two nodes and the diversity gain will improve the channel capacity. The combination of cooperative communication and physical layer security can bring the diversity gain into physical layer security effectively, which improves the secrecy rate and ensures information security even further.This dissertation studies physical layer security based on cooperative communication from many aspects and a certain number of achievements have been made.Above all, the power allocation in physical layer security based on amplify-and-forward(AF) and cooperative jamming(CJ) relay network is studied. A performance comparison of AF and CJ in different scenarios is considered. Simulation results show that power allocation is a great influence on secrecy rate and the optimal power allocation schemes corresponding to different scenarios are not the same. Besides, AF and CJ have different needs in power allocation because of different principles.Secondly, the scale of active relays in physical layer security based on CJ relay network is studied. A group-sparse penalty is introduced into the secrecy rate maximization problem and the proximal gradient algorithm(PGA) is proposed to deal with this problem. Simulation results show that the proposed algorithm can yield high level of secrecy rate performance with a smaller set of relays and lower power consumption. In addition to striking a balance between secrecy rate and the size of active relays, the proposed algorithm also makes the resource allocation more flexible.In the end, physical layer security based on amplify-and-forward with cooperative-jamming(ACJ) scheme is studied and the PGA is still use to deal with it. Simulation results demonstrate that utilizing jamming nodes in amplify-and-forward relay networks can improve secrecy rate slightly on the one hand, yet increase the power consumption badly on the other. In order to obtain higher secrecy rate and lower power consumption, the sum of AF nodes and CJ nodes should be allocated reasonably.The entire work of this dissertation is exploring three key problems in physical layer security based on cooperative communication, which is helpful for improving security performance and resource allocation performance. The research has theoretical and practical significance and will promote the development of physical layer security.