IEEE 802.15.7-Compliant Ultra-Low Latency Relaying VLC System for Safety-Critical ITS

Visible Light Communications (VLC) represents a very promising technology for the implementation of revolutionary Intelligent Transportation Systems (ITS) protocols. In cooperative ITS, where the interconnection of vehicular units will enable for revolutionary protocols such as car platooning, queue avoidance, and for many critical automatic and/or assisted driving applications, the capability of vehicles to relay safety-critical information to incoming units in a very fast and reliable way is a key factor. In this paper, we propose and test a novel infrastructure-To-vehicle-To-vehicle (I2V2V) VLC system for ITS, embedding a digital Active Decode-And-Relay (ADR) stage for decoding and relaying the information received from a regular LED traffic light, which is enabled for VLC, towards further incoming units. The experimental validation of the ADR VLC chain, as well as a thorough statistical analysis of packet error rate (PER) distribution in the transmission, has been performed for distances up to 50 meters. Our analysis shows that the VLC system reliably attains ultra-low, sub-ms latencies for distances up to 30 m, and still grants a latency below 10 ms even for distances of 50 m at 99.9% confidence level. Such latency values are far shorter than those reported in literature for RF-based technologies such as, e.g., those based on LTE or WiFi. Our results could boost the introduction of VLC technology in real cooperative ITS scenarios where very low latencies are essential. The demonstrated system prototype is compatible with IEEE 802.15.7 standard.