Reconfigurable intelligent surfaces (RISs) represent a new technology that can shape the radio wave propagation and thus offers a great variety of possible performance and implementation gains. Motivated by this, we investigate the achievable sum-rate optimization in a broadcast channel (BC) that is equipped with an RIS. We exploit the well-known duality between the Gaussian multiple-input multiple-output (MIMO) BC and multiple-access channel (MAC) to derive an alternating optimization (AO) algorithm which optimizes the users' covariance matrices and the RIS phase shifts in the dual MAC. The optimal users' covariance matrices are obtained by a dual decomposition method in which each iteration is solved in closed-form. The optimal RIS phase shifts are also computed using a derived closed-form expression. Furthermore, we present a computational complexity analysis for the proposed AO algorithm. Simulation results show that the proposed AO algorithm can provide significant achievable sum-rate gains in a BC.
翻译:重新配置的智能表面(RIS)代表着一种能够影响无线电波传播的新技术,因此提供了各种可能的性能和实施收益。我们受此驱动,对配备RIS的广播频道(BC)中可实现的和速率优化进行了调查。我们利用高西亚多投入多输出(MIMO)BC和多接入频道(MAC)之间众所周知的双重性能优化,以获得一种交替优化算法,优化用户的常变矩阵和双MAC的RIS阶段转移。最佳用户的共变矩阵是通过一种双分解法获得的,其中每种变异法都是在闭式中解决的。最佳的RIS阶段转变也是用一种衍生的封闭式表达法来计算的。此外,我们为拟议的AO算法提供了计算复杂性分析。模拟结果表明,拟议的AO算法可以在BC中提供显著的可实现的和率收益。