Metasurface-Enabled Multi-Target WiFi Sensing

As an emerging technology, WiFi sensing has garnered widespread attention in recent years. However, due to limitations in WiFi bandwidth and hardware capacity, multi-target sensing with WiFi remains an unresolved issue. In this paper, we present SlingShot, a first-of-its-kind approach for multi-target WiFi sensing enabled by metasurface. SlingShot exploits a metasurface's ability of beam scanning to periodically scan among targets in a high frequency, so their sensing signals can be separated in the time domain. However, the WiFi-initiated and the metasurface-initiated signals will interfere with each other, which could significantly degrade the sensing accuracy. Moreover, the WiFi devices and the metasurface operate in a distributed manner, so the inherent clock offset and clock drift among them make it difficult to accurately separate the sensing signals of the targets. To address the above challenges, SlingShot leverages the metasurface's ability of phase shifting to cancel interfering signals and designs a passive clock synchronization scheme to synchronize the metasurface and WiFi devices. We implement SlingShot and evaluate it under various settings. Results show that SlingShot can sense up to 8 targets. Respectively compared to the state-of-the-art methods, SlingShot has 6.75 % higher mean accuracy in activity recognition and 58.34 % lower mean error in respiration monitoring.