Wall-Street: Smart Surface-Enabled 5G mmWave for Roadside Networking

5G mmWave roadside networks promise high-speed wireless connectivity, but face significant challenges in maintaining reliable connections for users moving at high speed. Frequent handovers, complex beam alignment, and signal attenuation due to obstacles like car bodies lead to service interruptions and degraded performance. We present Wall-Street, a smart surface installed on vehicles to enhance 5G mmWave connectivity for users inside. Wall-Street improves mobility management by (1) steering outdoor mmWave signals into the vehicle, ensuring coverage for all users; (2) enabling simultaneous serving cell data transfer and candidate handover cell measurement, allowing seamless handovers without service interruption; and (3) combining beams from source and target cells during a handover to increase reliability. Through its flexible and diverse signal manipulation capabilities, Wall-Street provides uninterrupted high-speed connectivity for latency-sensitive applications in challenging mobile environments. We have implemented and integrated Wall-Street in the COSMOS testbed and evaluated its real-time performance with four gNBs and a mobile client inside a surface-enabled vehicle, driving on a nearby road. Wall-Street achieves a 2.5-3.4x TCP throughput improvement and a 0.4-0.8x reduction in delay over a baseline 5G Standalone handover protocol.