We consider non-orthogonal multiple access (NOMA) downlink with a multiple-antenna base station (BS) and single-antenna mobile users. Cell-edge users that are blocked from the BS are assisted by intelligent reflective surface (IRS) for data reception. Cell-center and IRS-assist users are paired to share the same frequency-time resource block and zeroforcing transmit beamforming from the BS. We propose to optimize IRS-element coefficients and transmit power to minimize the total power for a given rate threshold. Differing from the existing work, the proposed joint optimization is based on channel covariance instead of fast-changing channel coefficients. Our scheme can reduce larger total power when the number of IRS elements increases. The performance of IRS-assist users decreases significantly if the rank of BS-IRS channel matrix is low.

翻译：我们考虑多天线基站与单天线移动用户的非正交多址（NOMA）下行链路。被基站遮挡的小区边缘用户通过智能反射面（IRS）辅助实现数据接收。小区中心用户与IRS辅助用户配对共享相同频率-时间资源块，并采用迫零发射波束赋形。我们提出优化IRS单元系数与发射功率，在给定速率阈值下最小化总功率。与现有研究不同，本文提出的联合优化基于信道协方差而非快速变化的信道系数。所提方案可随IRS单元数量增加而降低更大总功率。若BS-IRS信道矩阵秩较低，IRS辅助用户的性能将显著下降。