Multi-Spotlight: A System for Sub-THz Multi-User Networking

Next-generation wireless networks operating in mmWave and sub-THz bands promise to deliver unprecedented data rates in densely populated networks, enabling advanced applications such as immersive AR/VR and UAV communications. However, achieving this objective requires not only wide bandwidth, but also efficiency gains of multi-user (MU) multiplexing vs. serving one user at a time. While MU multiplexing is relatively well understood and widely deployed below 7 GHz, such solutions rely on the rich scattering environment of lower frequency channels. To date, beyond simple polarization multiplexing, there is no same-channel MU solution for line-of-sight channels that are often encountered at higher frequencies. In this paper, we introduce Multi-Spotlight, a novel system for sub-THz MU networking to generate multiple, finely concentrated spotlights, each precisely aligned with each user’s location. To do so, we exploit near-field wavefront engineering available due to small wavelengths relative to the aperture size and design high-resolution metasurfaces with phase profiles that combine linear and quadratic phase distributions, optimized to focus each user’s signal precisely at their location. We minimize inter-user interference by reducing overlap between the spatial footprints of the spotlights, thereby enabling the multiplexing of users even with the same angle of departure (AoD) at different distances from the transmitter. Our experimental results demonstrate Multi-Spotlight’s ability to multiplex users sharing the same AoD with inter-user separation as small as 50 wavelengths, and to deliver significant MU gains even under low SNR conditions, ensuring high aggregate network performance in challenging and dense environments.