Pilots Optimization and Surface Area Effects on Channel Estimation in RIS Aided MIMO System

Reconfigurable intelligent surface (RIS) is an emerging tool for 5G and wireless communication tech-nologies that have attracted researchers' interest. However, the passive nature and the high number of reflecting elements in RIS result in a large pilot overhead, which makes channel estimation challenging in multi-user multiple-input multiple -output (MU-MIMO) wireless communication systems. Previ-ous works have shown an improvement in reducing the pilot overhead by exploiting the structured sparsity in rows and columns, which was further improved by compensating off-set among users in angular cascaded channels of RIS aided system. To further reduce the pilot overhead, we analyze and adopt coherence-optimized pilots for channel estimation and propose an algorithm to analyze the combined effect of low-coherence pilots with an optimum size of RIS elements for a given number of users, transmit antennas, and normal-ized error threshold performance. The simulation results illustrate better NMSE performance as compared to contem-porary techniques.