智能超表面辅助双小区NOMA系统下行低功耗传输方案研究

A downlink transmission scheme with low power consumption for IRS⁃aided two⁃cell NOMA systems

由于在频谱效率与功率效率方面的优势,智能超表面(Intelligent Reflecting Surface,IRS)和非正交多址接入(Non⁃Orthogonal Multiple Access,NOMA)被视为未来无线通信的两项关键技术,文中针对IRS与NOMA的融合系统展开研究。具体地,将IRS部署在两小区的边缘,用于提升小区边缘用户的传输性能,建立了IRS辅助两小区NOMA系统的下行传输功率最小化问题。为了求解建立的发射功耗最小化问题,推导了基站传输功率与IRS相移矩阵之间的关系,并将传输功率分配系数和相移矩阵的联合优化问题转化为单纯的相移优化问题。由于相移向量中每个元素需服从恒模约束,转换后的相移优化问题仍为非凸优化问题,提出了一种顺序相位旋转算法进一步求解相移优化问题。仿真结果表明,在相同的实验配置下,文中提出的下行传输方案在发射功耗方面的性能明显优于其他基准方案。

Thanks to the advantages of the spectrum and power⁃efficiency,both intelligent reflecting surface(IRS)and non⁃orthogonal multiple access(NOMA)are envisioned as the key techniques for wireless communication systems.In this paper,we focus on the integration of IRS and NOMA.Specifically,an IRS is deployed at the edge of two cells to enhance the transmission performance of cell⁃edge users.And a power consumption minimization problem is formulated for the IRS⁃assisted two⁃cell NOMA downlink system.In order to solve this problem,the relationship between the power allocation coefficients at base station and the phase shift matrix of IRS is derived.Thus,the joint optimization problem of power allocation and phase shift is converted into a pure phase shift determination problem.Since each phase shifter should satisfy a constant module constraint,the transformed phase shift optimization problem is still non⁃convex,which is further addressed by the proposed phase shift optimization scheme based on the sequential rotation algorithm.Simulations demonstrate that under the same experimental setups,the performance of the proposed scheme is obviously better than several benchmarking schemes in terms of transmission power consumption.