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

## TL;DR

This paper presents an IEEE 802.15.7-compliant VLC system for ITS that achieves ultra-low latency communication over 50 meters, suitable for safety-critical automatic driving applications.

## Contribution

It introduces a novel I2V2V VLC system with active decode-and-relay, validated experimentally for ultra-low latency transmission in ITS environments.

## Key findings

- Achieves sub-millisecond latency at 99.9% confidence level.
- Maintains latency below 10 ms at 50 meters distance.
- Compatible with IEEE 802.15.7 standard.

## Abstract

The integration of Visible-Light Communications technology (VLC) in Intelligent Transportation Systems (ITS) is a very promising platform for a cost-effective implementation of revolutionary ITS and cooperative ITS protocols. In this paper, we propose an infrastructure-to-vehicle-to-vehicle (I2V2V) VLC system for ITS, implementing it through a regular LED traffic light serving as a transmitter and a digital Active Decode-and-Relay (ADR) stage for decoding and relaying the received information towards further incoming units. The proposed VLC system targets the challenging and important case of ultra-low latency ADR transmission of short packets, as this is needed for emerging applications of automatic braking, car platooning and other critical automatic and/or assisted driving applications. The experimental validation of the ADR VLC chain, as well as a thorough statistical analysis of errors distribution in the transmission, has been performed for short to medium distances, up to 50 meters. The performances of the designed system are evaluated by measuring the packet error rate (PER) and latency in the whole ADR transmission chain. Our analysis shows that our system attains ultra-low, sub-ms latencies at 99.9\% confidence level for PER as high as $5\times10^{-3}$, yet granting a latency below 10 ms even for distances of 50 m. The demonstrated system prototype is compatible with IEEE 802.15.7 standard.