Research On Pre-Equalized Time Reversal Transmission Technology For Enhancing Security

Time reversal(TR)transmission technology can focus the signal energy in a desired spatial and temporal point by using the multi-path transmission,reduce the signal energy leakage at the non-target receiver,and can be applied in the physical layer secure communication system.By adding a pre-equalizer to the transmitter,the pre-equalized time reversal(ETR)transmission technology can improve the system performance at the cost of lower complexity.If the ETR transmission system is optimized for secure transmission,it can improve the security transmission performance of the system with lower complexity.This thesis studies the transmission scheme and the design of the preequalizer for the ETR system to enhance the security transmission performance.The main work of the thesis is as follows:1.Under the condition that the transmitter has known the eavesdropper’s channel state information,the tap coefficient of pre-equalizer in the ETR multi-antenna transmitter is optimized with the goal of maximizing security rate.This optimization problem is a non-convex problem,which is solved by an iterative algorithm for finding the maximum eigenvalue of the matrix.The simulation results show that the security rate of the ETR system optimized for secure transmission is significantly higher than that of the conventional TR system,and it can continue to increase with the increase of transmission power under a smaller sampling factor2.Under the conditions of unknown and known eavesdropper’s channel state information,the artificial noise(AN)scheme applied to the ETR multi-antenna secure transmission system is designed,and the pre-equalizer and AN are jointly optimized with the goal of secure transmission performance.When the channel state information of eavesdropper’s channel is unknown,zero-space artificial noise scheme is adopted.Then,the pre-equalizer is optimized to minimize the transmission power under the constraint of the legitimate receiver threshold signal-to-interference-noise ratio(SINR),so as to maximize the power of AN.The optimization problem can be solved by using a binary search algorithm which is used to find the maximum value of the generalized Rayleigh quotient that satisfies the necessary conditions of the optimal solution.When the channel state information of eavesdropper’s channel is known,the pre-equalizer and the covariance matrix of AN are jointly optimized to minimize the SINR of the eavesdropper under the constraint of the legitimate receiver threshold SINR.By equivalent transformation,the optimization problem is converted into a convex optimization problem,and then the CVX tool is used to solve the problem.The simulation results show that by adding AN and performing corresponding optimization,the safe transmission performance of the system can be significantly improved.The simulation results show that the ETR scheme combined with AN and optimized for secure transmission can achieve higher security rate,and the security rate of the scheme with known eavesdropper’s channel state information is significantly higher than that of the scheme with unknown eavesdropper’s channel state information.