Increasing Vehicular Visible Light Communications Range Based on LED Current Overdriving and Variable Pulse Position Modulation: Concept and Experimental Validation

Beguni, Cătălin; Căilean, Alin-Mihai; Avătămăniței, Sebastian-Andrei; Potorac, Alin-Dan; Zadobrischi, Eduard; Dimian, Mihai · 2023 · Crossref

DOI: 10.3390/s23073656

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Summary

This paper addresses the critical challenge of extending the communication range of Visible Light Communications (VLC) systems in vehicular environments, a key requirement for Vehicle-to-Vehicle (V2V) and Vehicle-to-Infrastructure (V2I) safety applications. While VLC offers advantages such as unlicensed spectrum usage and compatibility with existing LED lighting, its effectiveness is often limited by short transmission distances and susceptibility to atmospheric interference. The authors identify that most existing research focuses on enhancing receiver sensitivity, whereas transmitter improvements are constrained by strict lighting regulations regarding glare and maximum optical irradiance. To overcome this, the study proposes a novel transmitter-side approach that increases instantaneous optical power without violating average irradiance limits. The proposed method combines LED current overdriving with a modified Variable Pulse Position Modulation (VPPM). By significantly increasing the forward current through the LED during short pulse intervals, the system achieves higher instantaneous optical power, which improves the Signal-to-Noise Ratio (SNR) at the receiver. To compensate for this power spike and maintain compliance with eye safety regulations and prevent LED overheating, the duty cycle is proportionally reduced. This ensures that the average optical irradiance remains within standard limits, even though the peak brightness is substantially higher. The authors detail the theoretical framework, including equations relating nominal current, pulsed current, and duty cycles, demonstrating how n-ary PPM schemes allow for current overdrive factors proportional to the modulation order. Experimental validation was conducted in laboratory conditions to test the viability of this concept. The results confirmed that the proposed technique significantly enhances communication distance. Specifically, the study demonstrated an increase in communication range of up to 370% compared to standard configurations, while maintaining the same overall optical irradiance at the transmitter level. The experiments utilized a setup with a single cell of three LEDs, noting that future outdoor tests with complete vehicular light systems are planned. The findings indicate that this approach allows for robust long-range links necessary for highway safety applications, such as timely signaling of road events. The significance of this work lies in its shift in paradigm from receiver-centric to transmitter-centric range enhancement. By exploiting the temporal characteristics of LED modulation, the method achieves substantial range improvements without requiring complex receiver modifications or violating regulatory standards. This approach offers a practical solution for integrating VLC into smart mobility frameworks, enabling reliable inter-vehicle communications that complement Radio Frequency technologies. The study concludes that LED current overdriving combined with VPPM is a viable and effective strategy for meeting the stringent distance requirements of vehicular safety systems.

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• v2x connected vehicle