双IRS辅助的NOMA无线携能通信网络优化

无线携能传输（simultaneous wireless information and power transfer，SWIPT）能够有效解决通信终端的能源受限问题，而智能反射面（intelligent reflecting surface，IRS）能够辅助增强SWIPT的效率。为了克服单个IRS覆盖范围有限的缺点，以及进一步提高SWIPT的时间和频谱资源利用率，考虑了一个双IRS辅助基于非正交多址接入技术（non-orthogonal multiple access，NOMA）的无线携能通信系统，其中发送端的波束成形矢量、每个IRS的相移以及接收端的功率分割系数将进行联合优化以最大化系统的最小用户速率。为解决上述有着高度耦合优化变量的非凸优化问题，提出一个基于半正定松弛技术（semidefinite relaxation，SDR）和连续凸逼近技术（successive convex approximation，SCA）的交替优化（alternative optimization，AO）算法来高效求解该问题。仿真结果表明，双IRS辅助的系统比传统的单IRS辅助的系统能够实现更高的最小速率，揭示了部署双IRS的优异性、所提算法的有效性以及联合优化IRS相移及功率分割系数在提升用户速率性能方面的重要性。

Performance optimization for double-IRS assisted NOMA SWIPT system

SWIPT can effectively deal with the energy limitation problem of communication terminals, and IRS can assist in enhancing the efficiency of SWIPT. Therefore, to overcome the shortcoming of limited coverage of deploying a single IRS and further improve the time and spectrum resource utilization efficiency of SWIPT, this paper studied a double-IRS-assisted NOMA SWIPT system, where the beamforming vector of the transmitter, the phase shifts of each IRS, and the power splitting coefficients of the receivers were jointly optimized to maximize the minimum user rate. To solve the above non-convex optimization problem with highly coupled variables, this paper proposed an AO algorithm based on SDR and SCA techniques to solve it efficiently. The simulation results show that the double-IRS-assisted system can achieve a higher minimum rate than that of its single-IRS, which reveals the superiority of deploying double IRSs, the effectiveness of the proposed algorithm, and the importance of jointly optimizing IRS phase shifts and power splitting coefficients in improving the user rate performance.