Research Of Reconfigurable Intelligent Surfaces Aided Wireless Secure Communications

The sixth-generation mobile communication(6G)network has higher requirements for air interface security.Wireless Physical Layer Security(PLS)technologies such as cooperative jamming and Artificial Noise(AN)can provide efficient security protection for 6G.However,traditional PLS technology heavily relies on the random disturbance characteristics of wireless channels,and the uncontrollable wireless propagation environment limits the performance of traditional PLS technology.Reconfigurable intelligent surfaces(RIS),as a key enabling technology for 6G,can intelligently and actively adjust the wireless propagation channel according to demand,and is expected to enhance physical layer security capabilities.How to utilize RIS to empower physical layer secure transmission is one of the important issues in this field.This thesis studies the physical layer secure communication assisted by RIS from typical physical layer security models such as cooperative jamming and AN.The specific research is as follows:(1)Research on physical layer secure communication assisted by RIS and cooperative jammingTo enhance wireless communication security,a novel physical layer secure communication method that jointly uses RIS and cooperative jamming is proposed.The successful secure transmission probability is used as a performance analysis metric,and its closed-form expression is derived.The quantitative relationship between security performance and key system parameters such as communication distance,transmission power,and the number of reflecting surfaces is revealed,and an asymptotic analysis is made.Simulations verify the accuracy of the theoretical analysis,and the results show that the secrecy performance can be significantly improved by setting a reasonable jamming distance and jamming power.Moreover,when the transmission power is large or the RIS elements are many,the jamming power selection is almost unaffected by the eavesdropper’s location.(2)Secure NOMA communication assisted by AN and STAR-RISThe Simultaneously Transmitting And Reflecting RIS(STAR-RIS)can effectively improve the communication performance of legitimate users and enhance coverage,but it also improves the eavesdropping performance of eavesdroppers.To solve this problem,a secure communication strategy that combines AN with STAR-RIS is proposed.By jointly optimizing the base station’s beamforming and AN vector,and the reflecting phase of STAR-RIS,the sum of legitimate user’s secure rates is maximized.An iterative algorithm based on alternating optimization is proposed,which uses classic Successive Convex Approximation and Semi-Definite Relaxation techniques to solve the optimal artificial noise model and RIS parameters.Simulation results show that the proposed scheme improves the secure rate by about 17.3%compared to the baseline scheme while reducing the AN power consumption by about 8%.(3)Wireless secure communication assisted by STAR-RIS with imperfect channel estimationBased on the above research,this study further considers practical issues such as the inability to obtain perfect channel state information(CSI)and the correlation between the reflecting and transmitting phases of STAR-RIS,and studies a robust wireless secure communication scheme assisted by STAR-RIS and AN.By jointly optimizing the base station’s active beamforming and AN vector,and the passive beamforming vector of STAR-RIS to minimize the base station’s transmission power.To solve this problem,first,the Bernstein inequality lemma is used to simplify the probability constraint in the problem,and then,an alternating optimization algorithm is proposed.Simulation results show that the proposed scheme can achieve secure communication under a given interruption probability constraint,while the optimization scheme without considering channel estimation errors cannot achieve the required interruption probability constraint,demonstrating the effectiveness of the proposed robust scheme.