Cooperative Beamforming Design for Multiple RIS-Assisted Communication Systems

Reconfigurable intelligent surface (RIS) provides a promising way to build programmable wireless transmission environments. Owing the massive number of controllable reflecting elements on surface, RIS is capable providing considerable passive beamforming gains. At present, most related works mainly consider modeling, design, performance analysis and optimization single-RIS-assisted systems. Although there are few that investigate multiple RISs individually serving their associated users, cooperation among not well considered as yet. To fill gap, this paper studies cooperative design for multi-RIS-assisted communication systems, where deployed assist downlink communications from base station its users. do so, we first model general channel users arbitrary reflection links. Then, formulate an problem maximize sum rate all Analysis shows formulated difficult solve due non-convexity interactions decision variables. it effectively, decouple into three disjoint subproblems. by introducing appropriate auxiliary variables, derive closed-form expressions variables propose low-complexity algorithm. Simulation results have verified effectiveness proposed algorithm through comparison with various baseline methods. Furthermore, these also unveil that, maximization, distributing superior deploying them at one single RIS.