基于STARS的安全认知无线电联合波束成形优化算法

Joint beamforming optimization algorithm for secure cognitive radio based on STARS

基于可重构智能表面(RIS,reconfigurable intelligent surface)的安全认知无线电(SCR,secure cognitive radio)系统均假设次用户(SU,secondary user)和主用户(PU,primary user)在基站(BS,base station)的同一侧,仅能够实现通信区域的部分覆盖,限制了RIS部署的灵活性和有效性。为了解决上述问题,提出了一种新的基于同时透射和反射表面(STARS,simultaneously transmitting and reflecting surface)的SCR系统。在该系统中,STARS能够实现通信区域的全覆盖,利用透射波束成形向量提高SU的接收信号强度,同时利用反射波束成形向量降低SU对PU的干扰,为SCR系统的设计提供了新的优化自由度(DoF,degree of freedom)。考虑SU保密率约束、PU干扰功率约束(IPC,interference power constraint)和STARS透射/反射参数约束,从降低系统总功耗角度出发,以最小化BS发射功率为目标,构建BS主动波束成形向量和STARS透射/反射波束成形向量联合优化问题。这一最小化问题是变量耦合非凸问题,很难直接求解,提出了基于凸差松弛(DCR,difference-of-convex relaxation)方法和顺序秩一约束松弛(SROCR,sequential rank-one constraint relaxation)方法的交替优化(AO,alternating optimization)算法,联合设计BS主动波束成形向量和STARS透射/反射波束成形向量。仿真结果表明,所提算法具有良好的收敛性能,能够有效降低SU对PU的干扰,且与传统RIS、随机相位、最大比传输(MRT,maximum-ratio transmission)和等能量分裂(Equal ES,equal energy splitting)方案相比,BS发射功率分别降低了8.3%、15.4%、5.9%和5.3%。

Secure cognitive radio(SCR)system based on reconfigurable intelligent surface(RIS)assumes that secondary user(SU)and primary user(PU)locate on the same side of the base station(BS),which can only cover part of the communication area and limits the deployment flexibility and effectiveness of the RIS.In order to solve the above problem,a new SCR system based on simultaneously transmitting and reflecting surface(STARS)was proposed.In the system,STARS could achieve full coverage of communication area,improve the received signal strength of the SU with the transmission beamforming vector and reduce the interference of the SU to the PU with the reflection beamforming vector,which provided new optimization degree of freedom(DoF)for the design of the SCR system.Considering secrecy rate constraint of the SU,interference power constraint(IPC)of the PU and transmission/reflection parameters constraint of the STARS,BS active beamforming vector and STARS transmission/reflection beamforming vectors were jointly optimized to minimize the BS’s transmit power from the perspective of reducing the total power consumption of the system.The minimization problem is a variable coupling non-convex problem,which is difficult to tackle directly.An alternating optimization(AO)algorithm based on difference-of-convex relaxation(DCR)method and sequential rank-one constraint relaxation(SROCR)method was proposed to jointly design the BS active beamforming vector and STARS transmission/reflection beamforming vectors.Simulation results show that the proposed algorithm has good convergence performance and effectively reduces the interference of SU on PU.Compared with the traditional RIS,random phase,maximum-ratio transmission(MRT)and equal energy splitting(Equal ES)schemes,the BS transmitting power is reduced by 8.3%,15.4%,5.9%and 5.3%,respectively.