AquaFi or Wi-Fi underwater

Researchers from King Abdullah University of Science and Technology in Saudi Arabia have developed an underwater Wi-Fi system based on light signals, either by LED or laser. During their tests with divers, these scientists obtained a transfer speed of around 2 MB per second.

On land , in the air and soon under the sea? Wireless technology essential for everyday life, Wi-Fi could very soon take on water, and allow divers and scientists to communicate with each other during explorations and underwater work. This is the challenge launched by King Abdullah University of Science and Technology in Saudi Arabia.

By combining classic Wi-Fi and Aqua-Fi, the diver can almost instantly share videos and photos with the boat.  © Kaust

Currently, underwater communication is possible with radio , acoustic and light signals . In 2013, a first experiment in underwater Wi-Fi had also been tested with acoustic waves  , but this time, the researchers opted for light signals. According to these scientists, including Basem Shihada, the radio signal can only carry data over short distances, while acoustic signals support long distances but with a limited data rate . As for light , if it combines speed and distance, it needs its beam to be as little obstructed as possible between transmitters and receivers.

LED or laser depending on the depth of the diver

Inexpensive and simple to set up, Aqua-Fi is an underwater wireless system that uses LEDs or lasers to transmit data from the diver to the boat. The prototype presented by the university uses green LEDs or a 520 nm laser to send data from a simple computer to a light detector connected to another computer. The technology differs depending on the distance. LEDs consume very little energy and are ideal for short distance communication (10 meters and less), while lasers are more energy intensive but they can double the signal strength and the distance (20 meters).

In their demonstration, the scientists equipped each diver with a smartphone placed in an airtight case and a mini-computer. After taking a photo or an underwater video, the diver transfers the photo to his computer via Wi-Fi, in this case a Raspberry Pi  that weighs less than 50 grams. This first computer converts photos and videos into a series of 1s and 0s, which are translated into flashing light beams at high speed. The light detector, placed under the boat, detects this variation and transforms it back into 1 and 0, which the receiving computer converts back into original images.

10MB photo sent in five seconds

For their tests, the researchers transferred files between two divers a few meters underwater, each with a computer. It was both a download and data transfer test, and they recorded a maximum data transfer speed of around 2 MB per second with an average delay of one millisecond for a round trip. . Then, the connection to the mainland is  via satellite.

This test was carried out in static water and under optimal conditions. In order for Aqua-Fi to generalize in the long term, there are still some obstacles to overcome and optimizations to implement. This is essentially to ensure the alignment of the light beam in agitated water, but also to be able to allow divers to send the data without necessarily being in the axis of the receiver. For this, the team is thinking about choosing a spherical receiver capable of receiving beams of light from all angles.