针对智能反射面(intelligent reflecting surface,IRS)辅助下行多天线非正交多址接入技术(non-orthogonal multiple access,NOMA)系统开展研究,根据用户解码顺序、基站波束成形矢量和IRS相移矩阵建立基站的发送功率最小化模型.通过用户组合信道强度的顺序得到最优用户解码顺序,利用交替优化方法设计最优波束成形矢量与相移矩阵.设计波束成形矢量时通过数学变换,将原本复杂的非凸优化问题转化为二阶锥规划(second order cone programming,SOCP)问题进行求解;优化相移矩阵时采用顺序相位旋转法来求解最优相移.仿真结果表明:在满足用户服务质量的条件下,所提出的设计方案可以显著降低基站的发送功率.
Power minimization design for IRS-Aided downlink NOMA networks
Both intelligent reflecting surface ( IRS ) and non-orthogonal multiple access ( NOMA )have been viewed as the key techniques for future communication systems. Together, IRS and NOMA effectively improve coverage quality and energy efficiency for communication systems. This paper focuses on an IRS-assisted downlink multi-antenna NOMA system. The transmit power of the base station is minimized based on the users' decoding orders, the base station's beam-forming vector, and the IRS's phase-shift matrix. Firstly, the optimal decoding order is obtained by the strengths of all users' channels. Then, the optimal beam-forming vector and phase shift matrix are designed by invoking the alternative optimization method. Specifically, when optimizing beam-forming vector, the original problem is transformed into a second order cone programming ( SOCP ) . Additionally, a sequential phase-rotation method is proposed to design the optimal phase shift matrix. Our simulation results show on condition of satisfying users' service quality, our design significantly reduces the transmission power of the base station.
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