The deployment of multiple reconfigurable intelligent surfaces (RISs) enhances the propagation environment by improving channel quality, but it also complicates channel estimation. Following the conventional wireless communication system design, which involves full channel state information (CSI) acquisition followed by RIS configuration, can reduce transmission efficiency due to substantial pilot overhead and computational complexity. This study introduces an innovative approach that integrates CSI acquisition and RIS configuration, leveraging the channel-altering capabilities of the RIS to reduce both the overhead and complexity of CSI acquisition. The focus is on multi-RIS-assisted systems, featuring both direct and reflected propagation paths. By applying a fast-varying reflection sequence during RIS configuration for channel training, the complex problem of channel estimation is decomposed into simpler, independent tasks. These fast-varying reflections effectively isolate transmit signals from different paths, streamlining the CSI acquisition process for both uplink and downlink communications with reduced complexity. In uplink scenarios, a positioning-based algorithm derives partial CSI, informing the adjustment of RIS parameters to create a sparse reflection channel, enabling precise reconstruction of the uplink channel. Downlink communication benefits from this strategically tailored reflection channel, allowing effective CSI acquisition with fewer pilot signals. Simulation results highlight the proposed methodology's ability to accurately reconstruct the reflection channel with minimal impact on the normalized mean square error while simultaneously enhancing spectral efficiency.

翻译：多可重构智能表面（RIS）的部署通过改善信道质量来增强传播环境，但同时也使信道估计复杂化。遵循传统的无线通信系统设计流程——即先获取完整信道状态信息（CSI）再进行RIS配置——会因巨大的导频开销和计算复杂度而降低传输效率。本研究提出一种创新方法，将CSI获取与RIS配置相融合，利用RIS改变信道的能力来降低CSI获取的开销和复杂度。研究聚焦于同时存在直射与反射传播路径的多RIS辅助系统。通过在信道训练阶段的RIS配置中应用快速变化的反射序列，复杂的信道估计问题被分解为更简单、独立的子任务。这些快速变化的反射能有效隔离来自不同路径的发射信号，从而以较低复杂度简化上下行通信的CSI获取流程。在上行场景中，基于定位的算法推导出部分CSI，据此调整RIS参数以构建稀疏反射信道，实现上行信道的精确重构。下行通信则受益于这种经策略性定制的反射信道，能够以更少的导频信号实现有效的CSI获取。仿真结果表明，所提方法能够以对归一化均方误差影响极小的方式精确重构反射信道，同时提升频谱效率。