“Besides downloading an app to their phone, the only thing people will need is a waterproof phone case rated for the depth of their dive.” Chen said.
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“The underwater scenario brings up new issues compared to aerial applications,” Chan explained. “For example, fluctuations in signal strength are compounded due to surface, ground and shoreline reflections. Movement caused by humans, waves and nearby objects may interfere with data transmission. Also, microphones and speakers have different characteristics in different smartphone models. We had to adapt in real time to these and other factors to ensure AquaApp would work in real-world conditions.
These other factors include the tendency of devices to change position and proximity quickly in the current and the different noise profiles the application may encounter due to the presence of ships, animals and even low-flying aircraft. altitude.
The team created an algorithm that allows AquaApp to optimize, in real time, the bit rate and acoustic frequencies of each transmission based on certain parameters, including distance, noise, and frequency response variations between devices. When a user wants to send a message to another device, their app first sends a quick note, called a preamble, to the other device. AquaApp on the second device runs the algorithm to determine the best conditions to receive the preamble; it then tells the first device to use those same conditions to send the actual message.
The researchers developed a networking protocol to share access to the underwater network, similar to how WiFi networks arbitrate Internet traffic, to support messaging between multiple devices. AquaApp can accommodate up to 60 unique users on its local network at the same time.
The team tested the real-world utility of the AquaApp system in half a dozen locations offering a variety of water conditions and activity levels, including under a bridge in calm water, at a popular waterfront park with strong currents, next to the fishing pier of a busy lake and in a bay with strong waves. In a series of experiments, they evaluated the performance of AquaApp at distances of up to 113 meters and at depths of up to 12 meters.
“Based on our experiences, up to 30 meters is the ideal range for sending and receiving messages underwater, and 100 meters for transmitting SoS beacons,” Chen said. “These capabilities should be sufficient for most recreational and professional scenarios.”