Connecting the Lost City of Atlantis

A broadband Internet connection has become almost a necessity in the modern world, and many have undertaken efforts to connect underserved areas. In that same vein, a new paper proposes a method that may be a boon to citizens of the lost city of Atlantis. Atlantean humor aside (you should hear their joke about the blushing lobster, but I digress), Aqua-Fi would also be useful for scuba divers to share real-time data, or to wirelessly control unmanned submersibles at a distance.

Aqua-Fi is a wireless optical data transmission method that has been adapted for use in aqueous environments. There are two variants — one using an LED, and the other a laser. The LED consumes less power, but is limited in range. Swapping the LED for a laser allows for significantly greater range, but at the expense of greater power consumption.

A pair of Raspberry Pis are used to modulate the optical signal. One Raspberry Pi is in a watertight case attached to the user. From there, it could either have wiring run to a device that it is to control, or it could use traditional WiFi to communicate with a device such as a smartphone. The second Raspberry Pi would sit above the water on a boat or buoy, and it handles the internet connection via traditional methods (e.g. cellular data, satellite). The two Raspberry Pis communicate via the optical link.

The astute reader may ask, “Why not use radio signals and skip the Aqua-Fi system entirely?” Radio waves are rapidly absorbed by salt water, so penetration is very limited. There is also another option in use for underwater data transmission, in the form of acoustic signals. However, while they can travel long distances, bandwidth is very limited. Real-time video streaming, for example, would not be reasonable with an acoustic solution.

The authors achieved reasonable performance under test conditions, clocking in at a 2.11 Mbps transfer rate with 1.03ms of latency. With refinement of the hardware and methods, those numbers should be able to improve.

As it currently stands, Aqua-Fi is not without flaws. The optical link requires very precise alignment to maintain communication. In the field this is difficult to maintain. Currents will continually shift the position of the underwater device, and wave action will similarly work to keep the above-water device out of alignment. The line of sight link can also be disrupted by water turbidity or other obstructions. Some of these obstacles may be difficult to overcome, but it will be interesting to see where this idea can go with a bit more refinement.