Wireless Transmission Method With Statistical CSI In Reconfigurable Intelligent Surface-assisted Communication

The 5th Generation Mobile Communication System(5G)has begun to be deployed and commercialized around the world,and the research on the 6th Generation Mobile Communication System(6G)in various countries is also in full swing.It is expected that in 2030,6G will provide better performance than 5G and meet various emerging services and applications,becoming a key driving force for the intelligent information society.6G will require higher communication rates,lower transmission delays,lower operating energy consumption and higher security performance.Reconfigurable intelligent surface(RIS)is considered one of the key technologies of 6G,which can meet the requirements of the green and safe development of future communication networks.In this paper,the following researches are carried out on the wireless transmission method using statistical channel state information(CSI)in RIS-assisted communication:Firstly,the characteristics and physical realization of RIS are introduced,and several specific application scenarios are shown for its broad application prospects.In addition,the importance of studying physical layer security issues in wireless communication systems is explained,the channel model foundation of physical layer security research is introduced,and the definition and mathematical expression of system ergodic secrecy rate are introduced.Secondly,for the RIS-assisted Multiple-Input Multiple-Output(MIMO)downlink wireless communication system,an alternating optimization algorithm for designing the base station(BS)transmit covariance matrix and the RIS diagonal phase-shifting matrix is proposed to increase the system ergodic rate.Considering the Rayleigh channel model with spatial correlation,assuming that the BS only knows the statistical CSI,the ergodic rate of the system is analyzed under the premise that the transmit power in BS is constrained.In order to avoid the great computational complexity caused by the Monte Carlo averaging of the channel,the large-dimensional random matrix theory is used to derive the deterministic equivalent of the system ergodic rate in the large system state.By maximizing the deterministic equivalent,an alternating optimization algorithm for joint design of BS transmit covariance matrix and RIS diagonal phase-shifting matrix is proposed.The simulation results show that the deduced deterministic equivalent formula can approximate the system ergodic rate very well,and the proposed alternating optimization algorithm can effectively improve the system performance.Finally,for a RIS-assisted MIMO wireless secrecy communication system,a design method of BS transmit covariance matrix and RIS diagonal phase-shifting matrix is proposed to improve the secrecy ergodic rate of the legitimate user.Considering the Rician channel model with line-of-sight component and spatial correlation,assuming that the BS only knows the statistical CSI,the secrecy ergodic rate of the legitimate user is analyzed under the premise that the transmit power of BS is constrained.In order to avoid the great computational complexity caused by the Monte Carlo averaging of the channel,the large-dimensional random matrix theory is used to derive the deterministic equivalent of the secrecy ergodic rate of the legitimate user.Aiming at maximizing the deterministic equivalent formula,a jointly alternating optimization algorithm with the method of Taylor series expansion and the projected gradient ascent method is proposed to design the transmit covariance matrix at the BS,as well as the diagonal phase-shifting matrix.Simulations are conducted to demonstrate the accuracy of the derived analytical expressions,as well as the superior performance and good convergence of our proposed algorithm.