Cooperative Localization and Tracking Using RISs and Sidelink Communications

Cooperative localization and tracking are expected to play a crucial role in supporting location-based services in 6G networks. This work shows that integrating reconfigurable intelligent surfaces (RISs) with sidelink communications between user equipments (UEs) can enhance tracking and localization accuracy in the absence of access points (APs). To achieve this, we consider a localization and tracking problem of RIS-assisted sidelink communications, where moving UEs are localized and tracked without relying on APs. Specifically, we first design orthogonal RIS phase shift vectors to separate RIS-aided (reflected) paths from direct sidelink communication paths at the receiving UE(s). The initial locations of the UEs are then derived from the estimated channel parameters, enabling the tracking of the UEs using an extended Kalman filter (EKF). We benchmark the performance of the localization with multiple RISs using the Cramér-Rao lower bound (CRLB), and we assess the EKF's performance using the root mean squared error (RMSE) metric. Simulation results indicate that the initial localization accuracy reaches the CRLB, and the EKF achieves an RMSE below 10 cm for 90% of the time.