面向多用户NOMA-IRS系统的公平性优化

Fairness optimization for the multi-user NOMA-IRS system

多用户非正交多址接入-智能反射面系统,可通过多天线发射机与智能反射面间“发射-反射”联合波束成形,改善系统的用户接入能力。针对多用户非正交多址接入-智能反射面系统用户公平性问题,尝试在射频链路受限的实际场景中,最大限度提升用户最小接收信干噪比,从而无差别地保证各用户的通信质量。为此,根据射频链路数对用户进行分簇,构建了最大-最小接收信干噪比分式规划问题,此问题的发射波束矢量与反射阵元矩阵在接收信干噪比处高度耦合。因此,提出了一种基于半定松弛与算术几何平均算法,通过在每次迭代中交替优化发射波束矢量与反射阵元矩阵,实现各簇中最小信道容量的最大化。并进一步采用二分搜索算法求解簇内功率分配问题,以提升用户最小接收信干噪比。仿真结果表明,相对于迫零方案,提出方案能够以较低的计算复杂度提升用户最小接收信干噪比,从而改善各用户通信质量;且区别于最大比传输方案,提出方案中用户最小接收信干噪比不会随基站发射功率增加而呈现饱和现象,从而实现各用户通信质量的稳定增长。

Non-Orthogonal Multiple Access(NOMA)-Intelligent Reflection Surface(IRS)systems can improve user access capability through joint"transmit-reflect"beamforming between multiple antenna transmitters and IRS.For the user fairness problem of multi-user NOMA-IRS systems,the minimum received signal-to-Interference plus Noise Ratio(SINR)of users should be maximized in a practical scenario with restricted RF links,so as to guarantee the communication quality of each user without any difference.To this end,a maximum-minimum SINR fractional planning problem is constructed by clustering users according to the number of RF links,and the transmit beam vector of this problem is highly coupled with the reflected array element matrix at SINR.Therefore,a semi-definite relaxation and arithmetic-geometric mean-based algorithm is proposed to maximize the minimum channel capacity in each cluster by alternately optimizing the transmit beam vector and the reflected array element matrix in each iteration.Furthermore,a dichotomous search algorithm is used to solve the intra-cluster power allocation problem to enhance the user minimum SINR.Simulation results show that,compared with the zero-forcing scheme,this scheme can improve the minimum SINR among users with lower computational complexity,thus improving the communication quality of each user.Different from the maximum ratio transmission scheme,the minimum SINR of users in this scheme does not saturate with the increase of transmit power at base stations,thus enabling the steady growth of communication quality of each user.