A TDoA based Positioning Method for Wireless Networks assisted by Passive RIS

Reconfigurable intelligent surfaces (RISs) are identified as a passive way to enable holographic multiple-input multiple-output (MIMO) as well as support future wireless networks, such as the 5th generation advanced (5G-Adv) and the 6th generation (6G) network, thanks to their abilities to dynamically conFigure the wireless propagation environment and establish artificial and enhanced radio link among network nodes. It is also commonly assumed that some RISs are fully or nearly fully passive, only capable of reflecting incident signals but not transmitting or receiving. Such passive RISs enjoy the advantages of lower costs, lower power consumption, lighter weight and easier deployment compared to competing solutions like relays or repeaters. However, acting in a passive mode means that RISs are hard to be identified and distinguished from one another, bringing challenges to tasks which require the identification of network nodes, such as positioning. In this paper, a novel time difference of arrival (TDoA) based localization method is proposed to realize positioning in wireless networks assisted by passive RISs. The proposed method is generic and applies to both downlink and uplink. Simulation results presented in this paper verify the feasibility and demonstrate the accuracy of the proposed method.