RIScan: RIS-aided Multi-user Indoor Localization Using COTS Wi-Fi

Multi-user indoor localization is considered to be one of the most useful wireless applications. Low latency and high robustness to dynamic interference from surrounding people are essential requirements for multi-user localization. However, state-of-the-art (SOTA) indoor localization systems cannot satisfy both requirements at the same time. In this paper, we propose RIScan, a Reconfigurable Intelligent Surface (RIS)-aided localization system that can achieve both low latency and high reliability. We leverage RIS to perform Wi-Fi beam scanning so all clients can figure out their direction in a single scan. However, compared with traditional AP-based systems, the introduction of RIS creates a more complicated signal superposition at the receiver, preventing clients from directly obtaining target beams for direction derivation and localization. To overcome this challenge, we fully utilize the reconfigurability of RIS to endow target beams with distinguishing features, so that RIScan can extract stable and accurate direction information from complex and dynamic environments. RIScan is implemented in the real system with our own developed 16 × 16 RIS prototype and COTS Wi-Fi devices. Extensive experiments show that RIScan achieves a median localization error of 47cm and 71cm in static and dynamic environments with only two RIS anchors. Compared to the SOTA methods, RIScan reduces the localization latency by more than an order of magnitude.