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）是一种有望重塑无线网络电磁环境的前沿技术，为无线信道增强提供了多种可能性。受此启发，本文研究了RIS辅助的多输入多输出（MIMO）系统信道优化问题。提出了一种高效的RIS优化方法，通过提升MIMO信道的有效秩来提升可达速率。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2×2 RIS辅助MIMO原型系统进行实验测量，以验证所提算法的性能。结果表明，与无RIS的MIMO信道相比，RIS辅助的MIMO信道在有效秩和可达速率方面均有显著提升。