Low-Complexity Channel Estimation and Passive Beamforming for RIS-Assisted MIMO Systems Relying on Discrete Phase Shifts
Low-Complexity Channel Estimation and Passive Beamforming for RIS-Assisted MIMO Systems Relying on Discrete Phase Shifts
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DOI：
10.1109/tcomm.2021.3127924
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发表时间：
2022-02-01
影响因子：
8.3
通讯作者：
Hanzo, Lajos
中科院分区：
文献类型：
--
作者：
An, Jiancheng;Xu, Chao;Hanzo, Lajos
可重构智能表面(RISS)能够以较低的成本提高无线网络的容量。在实际的RIS辅助通信系统中，信道状态信息(CSI)的获取和RIS反射优化构成了一对挑战。本文提出了一种低复杂度的信道估计和被动波束形成设计方案。首先，我们设想了一个低复杂度的框架，用于最大化在每个RIS元素具有离散相移的RIS辅助多输入多输出(MIMO)系统的可实现速率。与现有解决方案相比，提出的方案将信道训练阶段划分为几个阶段，其中预先设计RIS反射系数并估计有效叠加信道，而不是单独训练源-目的地和源-RIS-目的地链路。基于此，可以低复杂度地设计主动波束形成器，并通过从预先设计的训练集中选择该波束形成器来执行RIS反射优化，从而最大化可实现的速率。其次，我们提出了生成RIS反射系数训练集的新技术。分析了该方案的理论性能，并与最优RIS配置进行了比较。最后，我们的仿真结果表明，当依赖于不完美的CSI时，所提出的框架比现有的同类框架更具竞争力，特别是对于具有较短的信道相干时间的快时变信道。
Reconfigurable intelligent surfaces (RISs) are capable of enhancing the capacity of wireless networks at a low cost. In practical RIS-assisted communication systems, the acquisition of channel state information (CSI) and RIS reflection optimization constitute a pair of challenges. In this paper, a low-complexity channel estimation and passive beamforming design is proposed. First of all, we conceive a low-complexity framework for maximizing the achievable rate of RIS-assisted multiple-input multiple-output (MIMO) systems having discrete phase shifts at each RIS element. In contrast to existing solutions, the proposed arrangement partitions the channel training stage into several phases, where the RIS reflection coefficients are pre-designed and the effective superposed channel is estimated instead of separately training the source-destination and source-RIS-destination links. Based on this, the active beamformer can be designed at low complexity and the RIS reflection optimization is performed by selecting that one from the pre-designed training set which maximizes the achievable rate. Secondly, we propose novel techniques for generating the training set of RIS reflection coefficients. The theoretical performance of the proposed scheme is analyzed and compared to the optimal RIS configuration. Finally, our simulation results demonstrate that the proposed framework is more competitive than its existing counterparts when relying on imperfect CSI, especially for rapidly time-varying channels having short channel coherence time.