Blockage-Aided RIS Cooperative Joint Beamforming for mmWave MIMO Systems.

A reconfigurable intelligent surface (RIS) is a kind of metasurface that provides an adaptable way of controlling the propagation of radio signals in wireless systems, allowing for improved coverage and system efficiency. Instead of the traditional RIS-assisted single-to-multiple reflection channel, we present a time-variant location-centric hybrid reflection channel (TL-HRC) model in this paper. The designed TL-HRC model can easily enable mobile blockages and establish a cooperative relationship between the static and mobile RIS in millimeter wave multiple-input and multiple-output systems. Based on the designed TL-HRC model, we establish a joint active and passive beamforming problem for the weighted sum rate maximization and propose an alternative optimization with an RIS element selection (AO-RES) algorithm to tackle the challenging high dimensional coupled parameters. Through simulation experiments, the effectiveness of the proposed TL-HRC-based AO-RES algorithm is validated in terms of the weighted sum rate with the case of perfect channel state information.