Reconfigurable Intelligent Surfaces-Aided Relaying in Correlated Rice Fading: Performance Analysis and Design Optimization.

In this paper, we investigate the spatial correlation for a practical RIS-assisted communication system operating over Rician fading. Specifically, we derive a unified analytical framework for computing the outage probability and the achiev- able diversity order for arbitrary number of reflecting elements and over arbitrarily correlated Rice fading. We also investigate the impact of spatial correlation on a hybrid architecture that amalgamates both a practical RIS and a decode and forward relay. We then attain closed-form expressions for the outage probability and show that the activation of the relay boosts the outage performance by providing and additional diversity path. The tractable results empower the asymptotic outage analyses, which are conducted not only to reveal helpful insights into understanding the impact of spatial correlation, but also enable optimal power allocation strategies to enhance the system perfor- mance under both transmission modes. Numerical results validate the tightness and effectiveness of the closed-form expressions. In particular, the harmfulness of spatial correlation and the benefit of line-of-sight links are revealed and optimal power allocation is shown to yield impressive coding gains over equal power allocation.