Aqua-Fi is a new technology for high-speed wireless internet underwater. Conventional Wi-Fi is powerless in these conditions.
Underwater telecommunications has always been a problem. Radio signals, the ubiquitous wireless standard, are unusable in this case because they are completely absorbed by the water. Acoustic transmitters (e.g. sonar) work better underwater, but they suffer from very low data rates. It wouldn’t be a bad idea to use Wi-Fi underwater, would it?
The Aqua-Fi system uses the Wi-Fi module of a Raspberry Pi computer, which converts the signal and transmits it to a laser. And the laser in turn transmits the signal to a repeater that sits on the surface of the water.
Researchers at King Abdullah University of Science and Technology (KAUST) in Tuvalu, Saudi Arabia, have developed underwater Wi-Fi. The system, which they call Aqua-Fi, uses a combination of lasers and some off-the-shelf components to create a bidirectional wireless connection for underwater devices. The system is fully compliant with IEEE 802.11 wireless standards, which means it can easily connect and function as part of a larger network.
Here’s how it works
Let’s say you have an underwater device that needs to transmit data (for the KAUST researchers, it was waterproof smartphones). They then used a regular Wi-Fi signal to connect that device to an underwater “modem.” They used a Raspberry Pi as the modem, which converted the wireless signal into an optical signal (in this case, a laser). The laser sent its signal to a receiver (relay) attached to a buoy on the surface of the water.
How did it all start?
Aqua-Fi is a continuation of work that KAUST researchers began in 2017, when they used a blue laser to transmit a 1.2-gigabit file underwater. But Bassem Shihada, an assistant professor of computer science at KAUST and one of the participants in the Aqua-Fi project, decided it wasn’t as large-scale as he would have liked: “Who cares about transferring just one file? Let’s do something bigger.”
And that’s when the team began exploring bi-directional communication to create a system capable of transmitting high-resolution video.
Shihada says it was important to him to use off-the-shelf components: “My first rule: I don’t want anything to be [made specifically for this].” The only exception was a circuit for the Raspberry Pi that converts a wireless signal into an optical signal and vice versa.
The team first used LEDs instead of lasers, but found that LEDs weren’t powerful enough for high data rates. With LEDs, the beam was limited to a distance of about 7 meters and a data rate of about 100 kilobits per second. When they switched to blue and green lasers, they achieved 2.11 megabits per second at a distance of 20 meters.
Two students at KAUST are talking on Skype using Aqua-Fi. Each phone on the edge of a black box is connected to an underwater Raspberry Pi, and the green laser is reflected several times (a multiple of the length of the box), traveling a distance of 20 meters.
Even with the limitations of the Raspberry Pi, the KAUST researchers were able to use Aqua-Fi for Skype calls and file transfers.
Shihada says the system is currently limited by the Raspberry Pi’s capabilities. The team twice burned the custom circuitry responsible for converting optical and wireless signals when they tried to use a laser that was too powerful. In order for this setup to include more powerful lasers that can transmit farther (in meters) and more (in megabits), the Raspberry Pi needs to be replaced with a special optical modem.
But there’s still a big problem that needs to be solved to make a system like Aqua-Fi commercially viable. No, it’s not a replacement for the Raspberry Pi. It’s not that simple: laser customization remains the biggest challenge. Because lasers are very precise, even slight water fluctuations can throw the beam off course.
The KAUST researchers are looking at two options to solve this problem. First, a technique similar to the “photon fence” developed to kill mosquitoes could be used. A low-power guiding laser would scan the relay. When a connection is established, it will tell another higher-power laser that it can start sending data. If the waves move the system again, the high-power laser will turn off, reactivate the auxiliary guiding laser, and begin a new search.
Another option is a MIMO-like solution that uses a small set of relays. If the laser transmitter shifts slightly due to waves, it will still maintain the connection.
MIMO is a method of spatial signal coding to increase the bandwidth of a channel in which data transmission and reception are performed by systems of multiple antennas.
Who needs it?
Why would anyone want the Internet underwater? First, there is a great need for storing and transmitting large files, such as in the field of remote observation of marine life and coral reefs. High-definition video collected and transmitted by wireless underwater cameras can be extremely useful to natural resource advocates. It’s also good for the high-tech industry. Companies like Microsoft are exploring the possibility of placing data centers at sea and underwater. Placing data centers on the ocean floor could conceivably save money on both equipment cooling and energy costs. Especially if the kinetic energy of the waves can be harvested and converted into electricity. And since the data centers will be located underwater, the Internet should also be there.