Channel Estimation for RIS Assisted Wireless Communication Systems Based on the Channel Map

Reconfigurable Intelligent Surfaces (RIS) as a transformative technology in wireless communication, can significantly improve the wireless communication environment by adjusting the phase and amplitude of reflective elements. However, RIS assisted communication systems face a challenge where their numerous reflective elements necessitate significant pilot overhead for accurate channel estimation. In other words, the performance of channel estimation decreases when pilot resources are limited. We propose the channel map based channel estimation (CMCE) to address this issue. The CMCE scheme utilizes the signal processing capability of the RIS to acquire directional information of wireless channel paths at different user locations, and construct the channel map. Then the CMCE scheme optimizes the reflection coefficients of the RIS and focuses the reflected signals of the RIS in the receiving direction of the base station. The proposed scheme is simulated and compared to schemes without reflection coefficient optimization. The simulation results show that, under the same pilot overhead, the proposed scheme can significantly reduce the normalized mean square error (NMSE) of cascaded channel estimation.