Wireless communication under water

Question

I am looking for a under water wireless communication, distance up to 3000 meters. For this I quickly did some research on it and found out that Acoustic communication would be the best solution since they travel longer distance under water. I found these modems from EvoLogics (link)

I would like to know what are the things I need to keep in mind before I start making such communications. What can be the major problems on these type of communication or during the communication setup? I can already imagine of something that can cause problem which is the wave of the water if the water is not still, this can carry away the wireless modem which will result in lost of communication. Is there more things that can make the communication difficult?

Answer 1

Any of the underwater acoustics companies would be able to advise on likely performance and potential problems with a bit of detail about your application, typical considerations (as others have noted) include:

• There is a trade off between range and data rates (low frequencies allow longer range but lower data rates)
• Power supplies can be a limitation, energy per bit for acoustic communications underwater is substantially higher than RF communications in air, and usually there is no power supply network nearby
• Environmental issues need to be taken into account (frequencies used by marine life for communications and 'sonar' are well known, equipment can be selected to avoid interference)
• Size and weight of equipment (again, usually led by battery pack limitations)
• Efficiency (e.g. a directional transducer will increase power efficiency and/or remove some noise off axis, but require some alignment between transmitter and receiver)
• Physical effects (refraction, reflections, propagation delay) typically limit maximum performance (e.g. thermal gradients in deep water typically refract signals upwards, limiting maximum range)

If you add more details about your application, you might get more specific advice about the real-world problems you might face, for example can you give a little bit more information on:

• Water depth
• Position of the modems (surface or sea-bed)
• Location (open seas have different acoustic effects to harbours, narrow channels, or areas where fresh water flows into the sea)
• Noise sources in the area (are the modems attached to vessels with engines, or remote from man-made noise)
• Data transfer rates that you are aiming for

There are a number of suppliers of equipment, targeted at a range of applications, from modem suppliers through to acoustic positioning and control (off the top of my head, these include Kongsberg, Nautronix, Sonardyne, Linkquest, Evologics (in no particular order!)). Each optimises performance for their application area so there isn't a list of 'major problems' that you can consider, each trades off one limitation for another.

[Disclosure, I work for one of the above companies, but I'm confident there's nothing in this answer which any of the others would disagree with]

Answer 2

As noted there are many considerations. Sound can be heard thousands of miles away with the right equipment/conditions (I rode sumarines for nearly 8 years). Our job was to hide and produce as little sound as pssible. We also used ELF technology as a backup way to communicate directly underwater. I suspect it takes huge amopunts of power to do it that way. You also need to consider the layers of the ocean. Some layers rapidly attenuate sound and others carry sound very far. How deep will you need to communicate? It is not easy but possible for a submarine (very big) to hear with its passive sonar in a conducting layer and hide most of its own noise in a nonconducting layer for short periods of time. I doubt any communication system will perform the same every day and in every situation, so I would have a very high margin of overkill if the communication is vital. Also frequency plays a big role, not to mention the salinity and temperature of the exact location you are using. Will yoU use the same locatoin or different locations? We dropped sensors to record temperature layers. When looking for submarines they use varying frequency sonar bouys to ping. As always signal to noise ratios are very important. The background noise (especially close to shore where the bottom reflects sound) can be very bad in some locations, like in a harbor with many pieces of equipment running. Newer submarines designed to operate close in need to be even quieter than the super quiet Tridents I rode. Hope this helped in some way. If not ask some more questions.