Mobility-aware Hybrid Channel Estimation Scheme for RIS-aided Millimeter-Wave Systems

The Reconfigurable Intelligent Surface (RIS) is proven to be a crucial component for beyond fifth-generation (B5G) networks, as it can potentially enable higher joint beam-forming at the base station (BS) and RIS while consuming significantly less hardware and energy. However, channel estimation is challenging in a RIS-aided wireless system with many passive elements without signal processing or amplifying capability. All the dimensions from the transmitter to the receiver via each RIS are estimated for estimating a wireless channel. Thus, the transmitted pilot symbol overhead to be sent becomes prohibitively high, resulting in the degradation of the estimation performance and channel accuracy. In this paper, we proposed a hybrid solution guided by calculating comparatively lesser channel dimensions while considering the mobility factor of the BS-RIS and RIS-UE channels. We illustrate theoretically and with simulations that the pilot overhead is significantly lower in the proposed hybrid channel estimation method than in existing schemes in the literature. Based on our simulation results, we provide some exciting insights on designing channel estimation techniques for the RIS system.