In this paper, we investigate the performance of multiple-input multiple-output (MIMO) fading channels assisted by a reconfigurable intelligent surface (RIS), through the employment of partition-based RIS schemes. The proposed schemes are implemented without requiring any channel state information knowledge at the transmitter side; this characteristic makes them attractive for practical applications. In particular, the RIS elements are partitioned into sub-surfaces, which are periodically modified in an efficient way to assist the communication. Under this framework, we propose two low-complexity partition-based schemes, where each sub-surface is adjusted by following an amplitude-based or a phase-based approach. Specifically, the activate-reflect (AR) scheme activates each sub-surface consecutively, by changing the reflection amplitude of the corresponding elements. On the other hand, the flip-reflect (FR) scheme adjusts periodically the phase shift of the elements at each sub-surface. Through the sequential reconfiguration of each sub-surface, an equivalent parallel channel in the time domain is produced. We analyze the performance of each scheme in terms of outage probability and provide expressions for the achieved diversity-multiplexing tradeoff. Our results show that the asymptotic performance of the considered network under the partition-based schemes can be significantly enhanced in terms of diversity gain compared to the conventional case, where a single partition is considered. Moreover, the FR scheme always achieves the maximum multiplexing gain, while for the AR scheme this maximum gain can be achieved only under certain conditions with respect to the number of elements in each sub-surface.

翻译：本文研究了在可重构智能表面（RIS）辅助下，采用基于分区的RIS方案的多输入多输出（MIMO）衰落信道的性能。所提出的方案无需发射端具备任何信道状态信息，这一特性使其在实际应用中具有吸引力。具体而言，RIS单元被划分为若干子表面，并通过周期性的高效调整来辅助通信。在此框架下，我们提出了两种低复杂度的分区方案，每种方案对子表面的调整分别基于幅度或相位方法。其中，激活-反射（AR）方案通过改变对应单元的反射幅度，依次激活每个子表面；而翻转-反射（FR）方案则周期性地调整各子表面单元的相移。通过对每个子表面进行顺序重构，在时域上生成了一个等效并行信道。我们分析了每种方案的中断概率性能，并给出了所实现的多样性-复用权衡表达式。结果表明，与采用单个分区的传统情况相比，基于分区方案的网络在分集增益方面的渐近性能得到显著提升。此外，FR方案始终能实现最大复用增益，而AR方案仅在满足特定子表面单元数量条件时才能达到此最大增益。