# An Open-Source QAM MODEM for Visible Light Communication in FPGA for Real-Time Applications

## TL;DR

This paper introduces an open-source QAM MODEM for visible light communication in FPGA to enable low-latency, high-speed data transmission.

## Contribution

A resource-efficient, open-source QAM MODEM with synchronization for real-time visible light communication is developed and experimentally validated.

## Key findings

- The MODEM successfully achieved 2, 4, and 6 Mb/s data rates using 4-, 16-, and 64-QAM constellations.
- Latency was measured to be less than 1.3 μs, demonstrating low-latency performance.
- The open-source implementation provides a scalable foundation for real-time VLC research.

## Abstract

Visible Light Communication (VLC) is a transformative paradigm poised to revolutionize the automotive and numerous other sectors. As the demand for high data rates and low latency applications grows, the limited bandwidth of standard white LED-based lamps—typically restricted to a few MHz—presents a significant bottleneck. While high-order modulation schemes like Quadrature Amplitude Modulation (QAM) offer superior spectral efficiency, their computational complexity often hinders real-time implementation. Consequently, the existing literature lacks experimental validation of low-latency real-time VLC links. This work addresses this challenge by proposing a modified algorithm that is implemented in a resource-efficient QAM modulator/demodulator (MODEM) for an FPGA. The algorithm includes the synchronization loop. The proposed MODEM is available as open-source code and provides a scalable foundation for researchers to explore low-latency real-time VLC links. Experimental results demonstrate successful 2, 4, and 6 Mb/s links using 4-, 16-, and 64-QAM constellations, respectively, over a white-phosphor-power LED. We measured a latency of less than 1.3 μs.