On the Capacity of Reconfigurable Intelligent Surface Assisted MIMO Symbiotic Communications

Reconfigurable intelligent surfaces (RISs) appear as one of the most promising paradigms for future wireless communications, because their high adjustability diverse communication demands and additional information-carrying capability by reflecting patterns. This paper investigates capacity RIS-assisted multiple-input multiple-output (MIMO) symbiotic communications utilizing multiple patterns, where each pattern is non-uniformly activated to carry information. To enhance transmission performance, activation probability, transmit covariance matrix are jointly designed. Since exact expression system intractable, lower upper bounds on derived used optimization in this paper. Based bound capacity, a gradient ascent algorithm developed find optimal matrix. By taking advantage concise-form closed-form solutions probability can be after optimizing The superiority proposed design investigated verified computer simulations. Some selected numerical results demonstrate that achieve higher than benchmark adopting only pattern.