Abstract: To maximize the spectral efficiency of the multiple-input multiple-output ( MIMO) system assisted by reconfigurable intelligent surface (RIS), the active beamforming of base station and the phase shift design of RIS have to be considered jointly. Therefore, a beamforming scheme based on the improved particle swarm optimization (PSO) algorithm is proposed. First, the joint beamforming problem is decomposed into active beamforming at the base station and phase shift design at RIS by using an alternating optimization algorithm. Then, the two problems are solved alternately by the water-filling algorithm and improved PSO algorithm. Finally, the proposed scheme is extended to the RIS of the practical phase-shift model. The experimental results show that the beamforming problem can be effectively solved by the proposed scheme, and the spectral efficiency of the system is greatly improved.

Key words: beamforming, swarm intelligence algorithm, reconfigurable intelligent surface, particle swarm optimization algorithm, multiple input multiple output