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

TL;DR

Wall-Street introduces a vehicle-mounted Huygens metasurface that can simultaneously steer a transmissive beam into a vehicle and a reflective beam between gNBs, enabling batched handovers and make-before-break operations for mmWave 5G roadside networking. The system offloads neighbor measurements from UEs to the surface and uses a two-slot bounding approach to decide HO for all UEs in a vehicle, triggering a single, efficient handover when beneficial. Implemented on the COSMOS testbed with real gNBs and multi-UE driving, Wall-Street demonstrates up to $78\%$ greater TCP throughput and up to $34\%$ lower RTT, along with a halving of unnecessary handovers. The work highlights practical benefits for reliable vehicular mmWave connectivity and outlines pathways to in-band control and faster beam alignment for scalable roadside networks, potentially enabling robust V2I/V2X services.

Abstract

5G mmWave roadside networks promise high bandwidth but face significant challenges in maintaining reliable connections for users moving at high speed. Frequent handovers, complex beam alignment, and signal blockage from car bodies lead to service interruptions and degraded performance. We present Wall-Street, a vehicle-mounted smart surface that enhances 5G mmWave connectivity for in-vehicle users. Wall-Street improves mobility management by (1) steering outdoor mmWave signals into the vehicle for shared coverage, enabling a single, collective handover decision for all users; (2) enabling neighbor-cell search without interrupting data transfer, allowing for seamless handovers; and (3) connecting users to a new cell before disconnecting from the old cell for reliable handovers. We have implemented and integrated Wall-Street in the COSMOS testbed and evaluated its real-time performance with multiple gNBs and users inside a surface-mounted vehicle, driving on a nearby road. In multi-UE scenarios, Wall-Street improves TCP throughput by up to 78% and reduces RTT by up to 34% over the standard 5G Standalone handover protocol.

Figures (23)

• Figure 1: Wall-Street's design innovations electronically split, shape, and steer mmWave transmissions in real time to enable seamless roadside 5G networks.
• Figure 2: 5G SA Xn handover:(1) Preparation phase; (2) Execution phase; (3) Completion phase. Data exchange is denoted with orange and yellow rectangles.
• Figure 3: (left) Wall-Street consists of over 4,000 paired electric and magnetic meta-atoms separated by a dielectric substrate. Biasing voltage on varactor diodes modulates current oscillation, creating EM field discontinuities; (right) VNA measured reflection and transmission response at 26 GHz, varying with biasing voltages ($u_m$, $u_e$).
• Figure 4: Wall-Street’s multi-beam operational modes: (a) dual-transflective steering for cell search and (b) dual-transmissive steering for make-before-break. Blue and red beams operate at different frequencies.
• Figure 5: System overview:(a) Initial UE-RAN attachment (\ref{['s:design:attach']}); (b) preparation using transflective surface power measurement (\ref{['s:design:ho:prep']}); (c) beam combining to enable make-before-break dual-cell connectivity (\ref{['s:design:ho:execute']}); (d) handover completion (\ref{['s:design:ho:complete']}). Each gNBs use different frequencies, and the source gNB controls the surface.