Design and Experimental Validation of Short Range Underwater Li-Fi Communication System

Abstract

Underwater communication is a a big challenge. The Radio waves do not travel proper in underwater because water conducts electricity and absorbs them faster . Acoustic modems can work over longer distances, but they are quite expensive, bulky, and slow since sound travels slowly underwater .In this paper , a simple and low-cost underwater optical communication system is designed that avoids the above mentioned issues by visible light for transmission of short text messages. This setup has two parts: a transmitter and a receiver, both built and programmed with the Arduino IDE. The receiver compares the signal to a threshold to decode the binary data back into text. The Serial Monitors at the transmitter and receiver represents the process of data transmission in real time Increasing the feedback resistor from 220 k? to 1 M? significantly improved range from few centimeters to meters and reliability. Adding double convex lenses on both ends focus and collects the light better, boosting signal quality even more. Overall, this work shows that underwater optical communication can be built inexpensively with easy-to-find parts, making it a practical option for things like underwater sensor networks, diver communication etc

Introduction

The text presents a low-cost underwater optical communication system (LiFi) designed to overcome the limitations of traditional underwater communication methods.

Conventional technologies such as Wi-Fi, Bluetooth, and RF communication are ineffective underwater because water strongly absorbs radio waves. Acoustic communication is widely used instead, but it requires expensive and bulky equipment and has relatively high communication delays.

The proposed system uses visible light/optical communication as an alternative. It consists of two NodeMCU ESP8266 boards: one transmitter and one receiver. The transmitter converts text into binary data and sends it through a high-power LED using On-Off Keying (OOK). A BPW34 photodiode detects the light at the receiver, while an LM324 transimpedance amplifier strengthens the weak signal so the NodeMCU can process it. Convex lenses are used to focus the transmitted and received light.

The system follows these main steps:

1. Message input through the transmitter's Serial Monitor.
2. Binary encoding of the message.
3. LED-based optical transmission using OOK.
4. Photodiode detection of the light pulses.
5. Signal amplification using an LM324.
6. Threshold-based bit detection by the NodeMCU.
7. Error checking and decoding to reconstruct the original message.

Testing showed that increasing the feedback resistor from 220 kΩ to 1 MΩ and adding lenses significantly improved signal detection and communication range. However, the system still depends heavily on accurate alignment, stable power, and suitable underwater conditions. Ambient light and electrical noise can also cause errors.

Key advantages

• Low-cost and compact design
• Uses commercially available components
• Higher potential data rate than acoustic communication over short distances
• Lower latency
• Battery-powered and suitable for submerged operation
• Simple OOK modulation

Main challenges

• Shorter range compared with acoustic communication
• Strong dependence on transmitter-receiver alignment
• Light scattering and water turbidity
• Ambient light and electrical noise
• Stable power supply is required
• Limited automatic adaptation to changing underwater light conditions

Conclusion

Radio waves die almost instantly underwater, and sound takes its place but drags speed and complexity along with it. This paper takes a different route entirely: light. By pairing a high-power LED and IRLZ44N MOSFET transmitter with a BPW34 photodiode and LM324 transimpedance-amplifier receiver, the system sends typed text messages as binary data straight through air and water, encoding every character in a pattern of on-off light pulses and decoding it back, bit by bit, on the other side, with both the sent and received binary sequences visible in real time on the two Serial Monitors. Getting there meant real troubleshooting, not just wiring parts together. Reliable reception depended heavily on precise alignment and orientation between transmitter and receiver, and on adequate, stable power to both nodes — weak supply or poor alignment reliably showed up as noise, dropped bits, or an explicit \"no signal received\" report from the receiver. Increasing the receiver\'s feedback resistor from 220 k? to 1 M?, along with adding double convex lenses at both the transmitter and receiver ends to better focus and collect the light, meaningfully improved sensitivity and range, illustrating how much simple component and optical tuning can matter in a minimal analog front end. Under well-aligned, adequately powered conditions, the system consistently achieved accurate, error-free text transmission, as confirmed during testing. What emerged is a working, self-contained optical link — no acoustic transducers, no WiFi, no external infrastructure, just a transmitter and receiver talking to each other through water using light alone. It proves the core idea cleanly: visible light can reliably carry real data underwater when the circuit is designed carefully and every failure mode is chased down. Future work may extend this system through automatic ambient-light calibration, a hardware comparator stage, forward error correction, and higher-throughput modulation schemes, to bring it closer to real-world diver communication and underwater sensor network deployments.

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Copyright

Copyright © 2026 V Madhan Raj, Monish A, Mokesh A, Sakthivel Murugan S. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.