Reconfigurable intelligent surface (RIS) is a promising technology that can reshape the electromagnetic environment in wireless networks, offering various possibilities for enhancing wireless channels. Motivated by this, we investigate the channel optimization for multiple-input multiple-output (MIMO) systems assisted by RIS. In this paper, an efficient RIS optimization method is proposed to enhance the effective rank of the MIMO channel for achievable rate improvement. Numerical results are presented to verify the effectiveness of RIS in improving MIMO channels. Additionally, we construct a 2$\times$2 RIS-assisted MIMO prototype to perform experimental measurements and validate the performance of our proposed algorithm. The results reveal a significant increase in effective rank and achievable rate for the RIS-assisted MIMO channel compared to the MIMO channel without RIS.

翻译：可重构智能表面（RIS）是一种有前景的技术，能够重塑无线网络中的电磁环境，为增强无线信道提供多种可能性。受此启发，我们研究了RIS辅助下的多输入多输出（MIMO）系统信道优化问题。本文提出了一种高效的RIS优化方法，通过提升MIMO信道的有效秩来提高可实现速率。数值结果验证了RIS在改善MIMO信道方面的有效性。此外，我们构建了一个2×2的RIS辅助MIMO原型系统，进行实验测量，并验证了所提算法的性能。结果表明，与无RIS的MIMO信道相比，RIS辅助的MIMO信道在有效秩和可实现速率上均有显著提升。