[Paper Review] IEEE 802.15.7-Compliant Ultra-Low Latency Relaying VLC System for Safety-Critical ITS

Tassadaq Nawaz, Marco Seminara+4 more|arXiv (Cornell University)|Jan 1, 2019

Optical Wireless Communication Technologies32 references75 citations

TL;DR

This paper presents an IEEE 802.15.7-compliant visible light communication (VLC) system for safety-critical intelligent transportation systems (ITS), using a standard traffic light as a transmitter and an active decode-and-relay (ADR) node in a vehicle to forward ultra-low-latency alerts. The system achieves sub-millisecond total latency (99.9% confidence) and packet error rates below 5×10⁻³ up to 50 m, enabling real-time applications like automatic braking and platooning.

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 $5 imes10^{-3}$, 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.

Motivation & Objective

• To enable ultra-low-latency, safety-critical vehicle-to-vehicle and infrastructure-to-vehicle communication in ITS using visible light.
• To implement a cost-effective, IEEE 802.15.7-compliant VLC system based on standard traffic lights and low-cost microcontrollers.
• To validate sub-millisecond end-to-end latency and low packet error rates (PER) in real-world outdoor conditions up to 50 m.
• To provide a statistical model for latency and error distribution to support protocol design in cooperative ITS.
• To demonstrate the feasibility of VLC for critical applications such as automatic braking and vehicle platooning.

Proposed method

• The system uses a standard LED traffic light as a transmitter, emitting modulated visible light using Manchester encoding at up to 230 kBd.
• A vehicle-mounted receiver decodes the signal using a photodiode and an Arduino DUE microcontroller, implementing an active decode-and-relay (ADR) function.
• The ADR stage re-encodes and retransmits the message to downstream vehicles, enabling I2V2V communication.
• Experimental validation was conducted over distances from 1 to 50 m using a regulated traffic light infrastructure.
• Statistical analysis of error distribution and latency was performed to derive a model for average latency (SAL) under varying PER conditions.
• A mathematical model of total latency was developed, accounting for propagation, processing, and inter-packet delay (IPD) times.

Experimental results

Research questions

• RQ1 Can a VLC system based on standard traffic lights achieve sub-millisecond end-to-end latency for safety-critical ITS applications?
• RQ2 What is the achievable packet error rate (PER) and latency performance of an ADR-based I2V2V VLC chain at distances up to 50 m?
• RQ3 How does the system performance vary with transmission rate and distance, particularly under high-speed conditions?
• RQ4 To what extent can VLC outperform RF-based IEEE 802.11p in terms of reaction and stopping distances in emergency braking scenarios?
• RQ5 Can a low-cost, open-source microcontroller platform like Arduino DUE support real-time ADR processing for vehicular VLC?

Key findings

• The system achieves sub-millisecond total latency (99.9% confidence) for PER ≤ 5×10⁻³, even at 50 m distance.
• At 230 kBd, the system achieves a PER as low as 10⁻⁵ under optimal conditions, with a statistically averaged latency (SAL) below 1 ms at 99.9% confidence.
• Even at 50 m, the total latency remains below 10 ms, significantly below the 100 ms maximum allowed by IEEE 802.11p.
• The model predicts that SAL remains below 10 ms for PER values up to 5×10⁻³ across all tested distances.
• The system enables a total stopping distance reduction of up to 24 m at 40 km/h and 79 m at 90 km/h compared to human reaction times.
• The results demonstrate that VLC can support critical applications like automatic braking and vehicle platooning with effective reaction distances below 0.1 m at high speeds.