  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.
