Downlink Multi-User Sub-THz Communication with a Programmable Metasurface

Among the many challenges in realizing wireless networks above 100 GHz, multi-user access remains one of the least explored. Traditionally, multi-user multiplexing at lower frequencies requires the implementation of one RF chain per data stream (user). Adapting such technology to higher frequencies above 100 GHz incurs prohibitively complex design and fabrication challenges, especially when scaling to many users. Here, we propose a fundamentally new approach that enables sub-terahertz multi-user access without any RF chains. Our design consists of a programmable, transmissive metasurface and a single monochromatic sub-terahertz source. We use the metasurface to modulate the phase and amplitude of the transmitted sub-THz wave using random voltage patterns, producing a high-entropy wavefront that has unique angular-dependent patterns. Generating these spatially diverse responses enables concurrent transmission of distinct information symbols to multiple users at different angular locations. We demonstrate the feasibility of this approach using both numerical simulations and exper-imental studies, showcasing the ability to serve multiple users simultaneously with distinctive data streams, even in scenarios with minimal angular separation between users. The study paves the way for a new architecture for sub-THz spatial multiplexing with no RF chains.