Multiple Reconfigurable Intelligent Surfaces for Improving Performance of Multiple Antenna Wireless Communication Networks

Abstract

This thesis analyzes the performance of an uplink/downlink reconfigurable intelligent surface (RIS)-based wireless system with a multiple-antenna base station (B). The RIS selection strategy is considered to reduce overhead and optimize resources. To enhance system performance, the study investigates maximal-ratio-combining (MRC) and selection-combining (SC) for uplink transmission, and maximum-ratio-transmission (MRT) and beamforming for downlink transmission. The work proposes two methods of beamforming design: direct-path beamforming design (DBD) and reflective-path beamforming design (RBD). Additionally, the impacts of uncertain phase shift (UPS) and optimal phase shift (OPS) alignments were also studied. Closed-form expressions for each uplink and downlink scenario's outage probability (OP) are derived. The numerical results indicate that using MRC at the B and OPS at RIS in the uplink transmission yields the best performance. For small antenna settings, employing SC-enabled OPS outperforms MRC-integrated UPS. In the downlink transmission, RBD outperforms DBD, and MRT at the B and OPS at the RIS again provide superior performance over UPS.