Ergodic Capacity Analysis of Reconfigurable Intelligent Surface Assisted MIMO Systems Over Rayleigh-Rician Channels

Metamaterial-based antenna designs, such as Reconfigurable Intelligent Surface (RIS), are expected to play a significant role in next generation communication networks (i.e. 6G) because of their ability to improve wireless communication environments. This letter investigates the ergodic capacity of RIS-aided multiple input multiple output (MIMO), a.k.a. MIMO-RIS, systems over Rayleigh-Rician fading channels. We consider that the transmitter-RIS and receiver-RIS links experience Rayleigh and Rician fading, respectively. An exact analytical expression of the ergodic capacity is derived based on closed-form expressions of the probability density function (pdf) of the cascaded channel. Moreover, a high SNR expression and a large RIS approximation are provided to unveil further system insights. Simulations result validate the correctness of our expressions and show the impact of the Rician fading and the number of RIS elements on the capacity.