Hybrid RIS-assisted Cooperative Communication Model Design and Performance Analysis

The spectral efficiency and energy efficiency are well-studied performance measures of the next-generation wireless systems and networks. Recently, researchers found dynamically controlled electronic meta-surfaces or reconfigurable intelligent surfaces (RIS) as useful means to enhance these performance measures, specifically, energy efficiency, in the absence of a direct transmission path. Passive meta-surfaces can only reflect their received signals without amplifying, whereas active meta-surfaces can amplify and reflect. This paper proposes a hybrid, dual RIS-assisted cooperative wireless system (CORISS) with two non-Line of sight paths, one via active RIS and the other via passive RIS. We also propose a novel performance objective function (POF) that depends on each path’s spectral efficiency and energy efficiency with an average power constraint. We investigate the proposed hybrid CORISS system via numerical simulations. Our simulations show that the energy efficiency of the active RIS path is inferior to the passive RIS path in high SNR scenarios.