Conventional road signs convey very concise and static visual information to human drivers, and bear retroreflective coating for better visibility at night. This paper introduces RetroI2V - a novel infrastructure-to-vehicle (I2V) communication and networking system that renovates conventional road signs to convey additional and dynamic information to vehicles while keeping intact their original functionality. In particular, RetroI2V exploits the retroreflective coating of road signs and establishes visible light backscattering communication (VLBC), and further coordinates multiple concurrent VLBC sessions among road signs and approaching vehicles. RetroI2V features a suite of novel VLBC designs including late-polarization, complementary optical signaling and polarization-based differential reception which are crucial to avoid flickering and achieve long VLBC range, as well as a decentralized MAC protocol that make practical multiple access in highly mobile and transient I2V settings. Experimental results from our prototyped system show that RetroI2V supports up to 101 m communication range and efficient multiple access at scale.

Visible light backscatter communication (VLBC) presents an emerging low power IoT connectivity solution with spatial reuse and interference immunity advantages over RF-based (backscatter) technologies. State-of-the-art VLBC systems employ COTS LCD shutter as optical modulator, whose slow response fundamentally throttles its data rate to sub-Kbps, and limits its deployment at scale for use cases where higher rate and/or low latency is a necessity.

We introduce PassiveVLN, a flexible, modular and software-defined platform for visible light backscatter networks. PassiveVLN incorporates a modular hardware design and a full-stack software implementation, enabling convenient and scalable deployment as well as rapid prototyping for testing new protocols and applications.

Vehicle-to-anything (V2X) communications technology is an essential substrate to realize future road intelligence and autonomous driving, especially in the areas where there are no existing (radio) network infrastructure. The emerging visible light backscatter communication technique shows great potentials in enabling the massive on-road retroreflective objects to delivery dynamic information to host vehicles. In this work, we design a polarization-based differential reception scheme to suppress ambient noise and realize long range retroreflective V2X communications.