Investigation On The Optimization Algorithm Of Relay Selection And Power Allocation In Two-way Cooperative Networks

With the rapid development of wireless communication technology,how to further improve the information transmission rate of wireless communication system,enhance the security and reliability of the system and expand the communication coverage have become the focus of research in the field of wireless communication.Cooperative relay technology means that each user node with a single antenna can share its antenna to transmit information through mutual cooperation in multi-user communication network,so as to form a virtual multiple input multiple output(MIMO)system to resist channel fading,expand communication coverage and improve information transmission rate.Cognitive radio technology allows secondary users(unauthorized users)to share the spectrum resources with primary users(authorized users),without affecting the normal communication of the primary user,thus greatly improving the spectrum utilization of the system.In recent years,combining cognitive radio technology with cooperative relay technology to form cooperative cognitive system can further improve the spectrum efficiency of the system,which has gradually become a research hotspot in the field of cooperative communication.On the other hand,due to the open and broadcast natures of wireless communication system,it is difficult to ensure the security of the transmission in the presence of eavesdropping,which brings security threats to the cooperative communication network.In recent years,the physical layer security technology,which uses the physical characteristics of wireless communication channel to construct a secure wireless communication channel and to ensure the safe transmission of information,can effectively prevent eavesdroppers from illegally receiving and obtaining information,so as to improve the security performance of the system.Therefore,the current physical layer security technology has attracted extensive attention of researchers in the field of wireless communication.However,due to the high computational complexity for cooperative(cognitive)relay networks,most of the researches focus on the physical layer security of one-way cooperative(cognitive)networks,and few researches on two-way cooperative(cognitive)networks.From the above,the main works and contributions of this thesis are as follows:1.The two-way underlay cognitive cooperative relay transmission in the presence of interference from the primary user is studied,and a joint optimization strategy of relay selection and power allocation is designed to improve the performance of secondary user information transmission under the condition of ensuring normal communication between the primary users.With the goal of maximizing channel capacity of the system,the closed-form solutions for optimal power allocation of secondary source nodes and relay nodes under high SNR are derived by using the Lagrange optimization algorithm.At the same time,the optimal relay node can also be determined.The simulation results show that the proposed method can effectively improve the channel capacity of cognitive system.In addition,it can be seen that the interference produced by the primary user has a relatively large impact on the cognitive cooperative network.Therefore,interference cannot be ignored or treated as Gaussian noise when studying this network.2.The physical layer security of cooperative two-way relay networks in the presence of an eavesdropper is investigated.For the two-way cooperative eavesdropping network,the security transmission models based on amplify-and-forward(AF)and decode-and-forward(DF)protocols are deduced,and a joint optimization algorithm for relay selection and power allocation is proposed.However,the analysis shows that this is a non-convex optimization problem.Its computational complexity is high,and it is difficult to obtain a closed solution.In order to solve this problem,an improved particle swarm optimization algorithm(PSO)is proposed to maximize the secrecy rate,and the optimal power distribution scheme of the secondary source node and the relay node is obtained.At the same time,the optimal relay node is determined.Simulation results show that the proposed algorithm increases the security and confidentiality of the system,and significantly improves the performance of the system.3.The physical layer security of the two-way underlay cognitive cooperative relay networks in the presence of the primary user and eavesdropper is studied.For the two-way cognitive cooperative eavesdropping network,the security transmission models based on AF and DF protocols are deduced,and a joint optimization algorithm for relay selection and power allocation is proposed.It can be seen from the analysis that this complex non-convex optimization problem has many restrictions,and it is difficult to guarantee the feasibility of the initial solution generated randomly by the PSO algorithm,resulting in the difficulty of obtaining solution.Therefore,a hybrid optimization algorithm based on variable mesh optimization(VMO)and PSO is proposed.The algorithm first uses VMO algorithm to obtain an initial feasible approximate solution.Then a domain space is created,and the initial population of PSO algorithm is generated in the domain.In the end,the PSO algorithm is used to obtain the optimal feasible solution.In this way,the joint optimal relay selection and power allocation in the two-way cognitive cooperative relay networks can be realized to maximize the security rate of the cognitive system.Simulation results show that this algorithm improves the security performance of the cognitive system.