论文标题
通过准静态相移设计对双IRS合作辅助系统的分析和优化
Analysis and Optimization of A Double-IRS Cooperatively Assisted System with A Quasi-Static Phase Shift Design
论文作者
论文摘要
已经对单个智能反射表面（IRS）辅助系统的分析和优化进行了广泛的研究，而对于多IRS辅助系统，知之甚少。本文调查了双IRS合作的下行链路系统的分析和优化，其中多元素使用IRSS的多元素IRS为单个Antenna使用者提供了多个Antenna基站（BS），并通过Inter-IRS Inter-IRS通道连接。任何两个节点之间的通道都是用里奇亚人褪色建模的。 BS采用瞬时CSI自适应最大比率传输（MRT）波束形式，两个IRS采用合作的准静态相移设计。目的是最大化平均可实现的速率，以低相调整成本和计算复杂性，BS和用户之间的同等通道的平均通道功率可以反映出。首先，我们分别获得了总体而言，纯粹的视线（LOS）和纯粹的视线（NLOS）态度的等效通道的平均通道功率的可拖动表达式。然后，我们共同优化了两个IRS的相移，以最大程度地提高等效通道的平均通道功率。优化问题挑战了非凸面问题。在某些情况下，我们获得了全球最佳的封闭式溶液，并提出了计算有效的迭代算法，以获得其他情况的固定点。接下来，我们将计算复杂性比较以优化相移的计算复杂性以及双IRS合作辅助系统的最佳平均通道功率与在三个制度中的大量反射元素中，双IR合作辅助系统的最佳平均通道功率与对应单IRS辅助系统的最佳通道功率。最后，我们从数值上证明了在不同系统参数下，在现有解决方案上，提出的解决方案的显着增长。
The analysis and optimization of single intelligent reflecting surface (IRS)-assisted systems have been extensively studied, whereas little is known regarding multiple-IRS-assisted systems. This paper investigates the analysis and optimization of a double-IRS cooperatively assisted downlink system, where a multi-antenna base station (BS) serves a single-antenna user with the help of two multi-element IRSs, connected by an inter-IRS channel. The channel between any two nodes is modeled with Rician fading. The BS adopts the instantaneous CSI-adaptive maximum-ratio transmission (MRT) beamformer, and the two IRSs adopt a cooperative quasi-static phase shift design. The goal is to maximize the average achievable rate, which can be reflected by the average channel power of the equivalent channel between the BS and user, at a low phase adjustment cost and computational complexity. First, we obtain tractable expressions of the average channel power of the equivalent channel in the general Rician factor, pure line of sight (LoS), and pure non-line of sight (NLoS) regimes, respectively. Then, we jointly optimize the phase shifts of the two IRSs to maximize the average channel power of the equivalent channel in these regimes. The optimization problems are challenging non-convex problems. We obtain globally optimal closed-form solutions for some cases and propose computationally efficient iterative algorithms to obtain stationary points for the other cases. Next, we compare the computational complexity for optimizing the phase shifts and the optimal average channel power of the double-IRS cooperatively assisted system with those of a counterpart single-IRS-assisted system at a large number of reflecting elements in the three regimes. Finally, we numerically demonstrate notable gains of the proposed solutions over the existing solutions at different system parameters.
