| With the commercialization of the 5th generation wireless communication system(5G),the research and development of the 6th generation wireless communication system(6G)has gradually attracted extensive attention in academia and industry.6G is expected to provide wider coverage,higher spectrum and energy efficiency,and better security performance.Reconfigurable Intelligent surface(RIS)has attracted much attention because of its passive,energy-efficient,low-cost and other characteristics,and is considered to be one of the key technologies of 6G.Many studies have shown that RIS can effectively improve the coverage and security performance of wireless communication system.However,at present,many researches on RIS are mostly based on perfect channel state information(CSI).Due to the large number of reflective elements in RIS,the acquisition of perfect CSI will lead to excessive channel training overhead.In addition,the feedback of perfect CSI will also increase the overhead of the feedback link between BS and RIS.Therefore,in order to reduce the system overhead,this paper will study the RIS assisted wireless secure transmission method based on partial CSI.The specific contributions are as follows:Firstly,a design method of transmission covariance matrix and phase shift matrix based on statistical CSI is proposed.For RIS assisted multiple input multiple output(MIMO)CR downlink wireless secure transmission communication system,a communication system which consists of a multiple antennas primary/secondary transmitter,a multiple antennas primary/secondary user,a RIS with multiple reflection units,and a multiple antennas eavesdropper is considered.The direct link between secondary transmitter and primary user,transmitter,and eavesdropper is blocked by obstacles and can only communicate through RIS reflection link.Using the rician spatial correlation channel,the deterministic equivalent expression of system secrecy rate is deduced by using largescale system approximation theory based on statistical CSI.Then,in order to maximize the deterministic equivalent expression,and under the condition of meeting the total power constraint and interference power constraint,the transmission covariance matrix and phase shift matrix are designed based on only statistical CSI,respectively.The simulation results show that the proposed deterministic equivalent expression has high accuracy,and the proposed algorithm has good convergence.Secondly,a design method of phase shift matrix and transmission covariance matrix based on legitimate user statistical CSI is proposed.Aiming at the RIS assisted MIMO downlink wireless secure transmission communication system with unknown eavesdropper CSI,a communication system which consists of a multiple antennas base station,a multiple antennas legitimate user/eavesdropper,and a RIS with multiple reflection units is considered,and direct connection is not considered.Using the rician spatial correlation channel,the deterministic equivalent expression of the reachable ergodic rate of legitimate users is deduced by using the large-scale system approximation theory based on legitimate user’s Statistical CSI.In order to maximize the deterministic equivalent expression and meet the communication quality of legitimate users,the transmission covariance matrix at BS and the phase shift matrix at RIS are designed based on only legitimate user statistical statistical CSI,respectively.Then,the artificial noise power is calculated,and the covariance matrix of the artificial noise is designed.Simulation results show that the proposed optimization algorithm can effectively improve the system security performance and ensure the normal communication of legitimate user. |
