Research On Optimization Of Wireless Network Relay Cooperative Commlunication

Due to the openness of wireless communication network,the security problem has drawn much attention.Relays can effectively increase the capacity of the channel,and the security can be improved by using the physical layer security technique.This thesis mainly studies the wireless communication system of two users to exchange information through several relays.Using the physical layer security and relay beamforming technique,an optimization model is proposed,and an efficient optimization algorithm is designed to achieve the purpose of safe and effective communication.This thesis first studies the two-way relay wiretap network,while the Channel State Information(CSI)of the eavesdropper is imperfectly known.We design the relay beamforming weights to minimize the total relay transmit power,while requiring the Signal-to-Noise-Ratio(SNRs)of the legitimate users to be higher than the given thresholds and the achievable rate of the eavesdropper to be upper-bounded.Due to the imperfect CSI,a robust optimization problem is proposed.The problem of robust optimization is usually non-convex.We eliminate three uncertain parameters by shrinking the feasible region,and transform the robust optimization problem into a quadratic constrained quadratic programming(QCQP)problem.Then we solve the problem via the semi-definite relaxation technique.Simulation results show that the proposed algorithm performs very close to the non-robust model with perfect CSI,in terms of the obtained relay transmit power.In addition,the above algorithm is further improved.Because of the shrinkage and other factors,the feasible region of the problem is shrank,and the feasible solution of the shrank problem may not exist.A novel iterative algorithm is proposed,where the line search technique is applied,and the feasibility is preserved during iterations.In each iteration,two QCQP subproblems and a one-dimensional subproblem are optimally solved.The two QCQP subproblems are both solved optimally by the semi-definite relaxation technique;the one-dimensional subproblem is solved by the intersection technique.Compared with the existing algorithm,our algorithm has a higher security rate.Moreover,the proposed algorithm converges very quickly,and more than 85%of instances are solved optimally.