Reconfigurable intelligent surface (RIS) is considered as a promising technology for future 6G communications. In RIS assisted communication systems, precise channel state information (CSI) is the prerequisite of efficient beamforming. Most existing channel estimation schemes rely on the spatial stationarity assumption. However, with the large array aperture of RIS, spatial non-stationarity effect naturally exists, which cannot be captured by most existing channel estimation schemes due to the spatial ambiguity effect of RIS and causes a significant decrease in the estimation accuracy. To tackle this problem, in this paper, we study the non-stationary channel estimation for RIS assisted communication systems. Specifically, we propose a two-dimensional group time block code (GTBC) based RIS decoupling scheme to convert the entire spatial non-stationary channel into a series of spatial stationary sub-channels. The proposed scheme is realized by artificially creating the time-domain relevance and exploiting it to recognize the spatial non-stationarity effect in the space domain. Based on the decoupled signals, a GTBC based dynamic orthogonal matching pursuit (GD-OMP) scheme is then proposed to update the dynamic codebook and estimate each path iteratively. Moreover, the computational complexity of the proposed GD-OMP scheme is analyzed. Finally, simulation results verify that the proposed scheme can capture the spatial non-stationarity effect and reach a higher channel estimation accuracy than existing schemes.

中文翻译：

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RIS 辅助无线通信的信道估计：固定还是非固定？


可重构智能表面（RIS）被认为是未来 6G 通信的一项有前途的技术。在RIS辅助通信系统中，精确的信道状态信息（CSI）是高效波束成形的前提。大多数现有的信道估计方案依赖于空间平稳性假设。然而，随着RIS的大阵列孔径，自然存在空间非平稳效应，由于RIS的空间模糊效应，大多数现有的信道估计方案无法捕获空间非平稳效应，导致估计精度显着下降。为了解决这个问题，在本文中，我们研究了 RIS 辅助通信系统的非平稳信道估计。具体来说，我们提出了一种基于二维群时间块码（GTBC）的RIS解耦方案，将整个空间非平稳信道转换为一系列空间平稳子信道。该方案是通过人为创建时域相关性并利用它来识别空间域中的空间非平稳效应来实现的。基于解耦信号，提出基于 GTBC 的动态正交匹配追踪（GD-OMP）方案来更新动态码本并迭代估计每条路径。此外，还分析了所提出的GD-OMP方案的计算复杂度。最后，仿真结果验证了所提出的方案能够捕获空间非平稳性效应，并达到比现有方案更高的信道估计精度。