Deviation Beamfocusing Design for RIS-Aided Near-Field Communications

In this work, we novelly exploit a deviation beamfocusing scheme to resolve the performance degradation from small elevation of received signal in near-field communications. Compared to conventional reconfigurable intelligent surface (RIS)-aided scheme in near-field communications, which only adjusts optimal signal phase shifts for transmitter-RIS-user link being applicable to the far-field communications scenario, our proposed scheme takes the angle impact into account and designs the beamfocusing point deviated from user in terms of the distance, elevation and azimuth to overcome such handicap. In addition, we study the factors affecting the elevation angular difference, aiming to enlarge the angular difference with a fixed beamfocusing gain. Simulation and analytical results demonstrate that our proposed scheme outperforms the conventional RIS-aided scheme in the case of incidence signal with small elevation. We also verify the merits of RIS construction in significant enhancing beamfocusing gain compared with the frequency-varying, proving its effectiveness to improve the overall achievable rate.