Reconfigurable Intelligent Surfaces Relying on Non-Diagonal Phase Shift Matrices

Reconfigurable intelligent surfaces (RIS) have been actively researched as a potential technique for future wireless communications, which intelligently ameliorate the signal propagation environment. In conventional design, each RIS element configures and reflects its received independently of all other elements, results in diagonal phase shift matrix. By contrast, we propose novel architecture, where incident impinging on one can be reflected from another after an appropriate adjustment, increases flexibility design shifts, hence, potentially improving system performance. The resultant matrix also has off-diagonal opposed to pure structure design. Compared state-of-art fully-connected/group-connected structures, our proposed architecture lower complexity, while attaining higher channel gain than group-connected structure, approaching that fully-connected structure. We formulate solve problem maximizing achievable rate by jointly optimizing transmit beamforming non-diagonal based alternating optimization semi-define relaxation (SDR) methods. Moreover, closed-form expressions gain, outage probability bit error ratio (BER) are derived. Simulation demonstrate improved performance terms compared both single-user well multi-user scenarios.