Ergodic Capacity Analysis for Relay-RIS System Under Three-Dimensional Channel Model

In this letter, we investigate the ergodic capacity of the Relay-Reconfigurable Intelligent Surface (Relay-RIS) system exploiting the three-dimensional channel model, which is different from existing works ignoring antenna height. Specifically, we propose a novel three-dimensional statistical channel for the Relay-RIS system. The upper bound expressions of the ergodic capacity are deduced in diverse propagation environments. Meanwhile, the impact of channel condition and deployment location on the capacity improvement is quantified, and the minimum number of reflecting elements to achieve a given rate threshold is obtained. Simulation results verify the effectiveness of the Relay-RIS system and the three-dimensional deployment strategy.