Real-time underwater wireless communication using an LED array
By: Anuj Prakash Gupta
Tags: Wireless, Led, Underwater, Communication, IoT

As far as humanity can recall, one thing has always been very evident, that from time-to-time we humans have invented or discovered things that then went on to make our lives simpler and more productive. Be it the discovery of fire, setting up currencies or something as natural as methods of efficient communication. Particularly in terms of communication has evolved beyond belief, who knew that we humans will progress from a point where we used to paint cave walls to the present day where we have 7,117 languages to express ourselves. Our bucket of literary languages is already brimming enough, but scientific methods of communication have an implausible scope, with newer and newer methods being devised each day by the ingenious minds of our country!

One such proposed and well accepted and acknowledged methodology is “Real-Time Text Transmission Implemented for Underwater Wireless Communication Using a LED Array”

This is a very important and trending technology, primarily because of its applications such as environment monitoring of difficult terrains, gathering of widely varying oceanographic data, search and rescue missions especially underwater. Underwater communication is a trending field of interest and approaches are under development for achieving low power consumption, compact size and better range. Use of optical waves for underwater communication is an effective approach for secured communication at faster data transfer rates.

The majority of Earth’s surface is covered by water bodies and hence with the advancements in the field of communication technology researchers are eagerly in attempts to utilise what is known as underwater communication. Today underwater communication is implemented by the optical fibres underlaid to allow communication across the globe. Various approaches have been implemented across the past to achieve successful communication in underwater terrains.

The proposed system deals with the implementation of a Li-Fi (Light Fidelity is a bidirectional wireless system that transmits data via LED or infrared light) based module for underwater communication. The system is designed and implemented on the principle of transmission through LED array and reception using a solar panel. The experimental observations analyses the distance versus power relationship for the transfer of textual data. The data transfer is very encouraging and found to be applicable for underwater communication.

Now let us take a closer look at the project and its working.

The conventional communication technologies that have been in usage for terrestrial communication, provide a few limitations because of which they cannot be applied for underwater communication. For example,

1. Acoustic approach: Slow data transfer speed.

2. Radio wave propagation: Design of antennas for tolerable noise.

3. Optical wave propagation: Consideration of scattering effects, absorption and interference effects as limiting factors.

LEDs due to inherent low thermal resistance are a better option. The concept of Li-Fi which is successfully being implemented in terrestrial terrains is among the best alternatives for underwater communication systems. The technique of utilization of very rapid flickering ability of LEDs for transmitting binary data serially is termed as “Light-Fidelity”. When the LED is OFF it represents a logic ‘0’ transmission and similarly, a logic ‘1’ is represented by LED when ON. The digital data rate is fast and is modulated at such a rapid rate that LEDs appear to be a constant source of illumination for human eyes.

In the designed module Manchester encoding has been implemented. Manchester encoding is a data modulation technique that can be used in many situations but which is particularly helpful in binary data transfer based on analogue, RF, optical, high-speed-digital, or long-distance-digital signals. Manchester code is also known as phase encoding is a line coding scheme in which the encoding of each data bit is either low then high, or high then low, for an equal interval of time. It is a self-clocking signal with no DC component. It is a simple digital modulation scheme that does two things:

1. Ensures that the signal never remains at logic low or logic high for an extended period of time

2. Converts the data signal into a data-plus-synchronization signal.

Manchester encoding can be implemented as per the user for example — A logic-high bit of data corresponding to a high-to-low transition, and a logic-low bit corresponding to a low-to-high transition or vice versa with a prerequisite knowledge at the receiver end to expect what to decode.

The Designed System:

The designed system is partitioned into two independent units — a transmitter module and a receiver module. Inside the transmitting unit, the data is first converted to binary form using an ADC and then further fed into a LED driver circuit which is controlled by a signal processor. The LED driver works on the principle of On-Off Keying modulation (Manchester encoding). After this, the high illumination LED fluctuates at high frequency and transmits the data as optical pulses through the wireless medium. At the receiving unit, these optical pulses are sensed by a photodetector and interpreted into an electrical signal which is amplified by a transimpedance amplifier and then converted back to binary data using a comparator.

FIG 1. Transmitter Section

FIG 2. Receiver Section

The transmitter module: In the transmitter module, an array of blue LEDs is used to transmit light, which would be used to transmit data. The array pattern implementation has the advantage of better range and higher performance as compared to a single LED. The source of the data that would be sent to the LEDs would be though the MCU of the transmitter circuit. The amount of power being sent to the LEDs from the MCU was low so the number of LEDs in the arrays were increased to improve the amount of power.

The receiver module: The receiver module aims to achieve a reasonably strong photocurrent that would only intake the signal from the transmitter LEDs and output that signal to the receiver MCU. To get a strong photocurrent at up to a range of few meters away, a sizeable array of photodiodes or a solar panel is required. “Solar cells” or “Photovoltaic devices” can also be used as a photodetector, i.e., to convert light into power which is the ultimate goal.

Results: The data is transmitted and received in the form of light intensity or optical waves. At the transmitter module, the binary data is processed from user-readable form to electrical equivalent and then consequently in the form of pulses of light. Similarly, at the receiver end, the optical pulses are first converted into electrical equivalent quantity and then back to the original format.

Future scope of the proposed project: The designed system has a manifold scope of betterment. To begin with the hardware components basically, the LEDs can be replaced with high power LEDs to achieve better range. The synchronization between receiver and transmitter parts before data transfer is another area of improvement. The designed system is on the Arduino with the Serial Monitor test for synchronization which can be improved upon with better controllers and algorithms.