New standard for Underwater Communications

New NATO standard protocol for underwater communications

JANUS could really revolutionize the diving industry with devices able to communicate and share information that is never a bad thing (He recalls how the Internet has impacted on life with the availability of free information?). The JANUS protocol could allow an IoT underwater and mesh networks that could potentially increase the data transmission speed if a data block is divided and sent on different frequencies from different sources.

The underwater transmission protocols may eventually be unified as NATO adopts a new standard, JANUS.

NATO has announced recently that it is adopting a standard for underwater communications protocol. What JANUS and how the submarine communication differs from the transmission of broadcast data?

Because it was necessary JANUS

Thanks to its standard communication protocols, the devices can communicate effectively. Wi-Fi, 4G and Li-Fi are all examples of protocols that allow for reliable data transmission, allowing mobile industry growth and the ubiquitous Internet of Things.

The electronics industry is also involved in facilitating the maritime industry it includes buoys, submarines and other autonomous underwater devices, dependent largely on wireless communication. This is partly due to the vastness of our oceans. Eg, a submarine that has to map the ocean floor at a depth of 8 km and then explore crevices and caverns can not reliably use a cable. In this scenario, wireless communication would be ideal as it would allow complete freedom of movement and would not require host (a ship, for example,) to transport 10 km of cable.

However, there is a serious problem with conventional wireless communication technologies: They are based on electromagnetic waves to transmit data. We tend to assume that electromagnetic radiation works very well in the atmosphere (mainly due to the fact that the air is mostly an almost empty space) e, Consequently, we can get radio signals that propagate over large distances with decent reliability. As a matter of perspective, ESP8266 the module can transmit a Wi-Fi signal up to 5 km (with the aid of a telescopic aerial) while traditional radio stations can transmit their signals up to 100 km and beyond, someone at night listening to AM broadcasts from overseas. The radio equipment on board voiager probes 1 e 2 They are sending their data over a distance greater than the size of the solar system!

Then, Electro Magetiche if the waves can travel these distances, because they can not be used for underwater communication?

Light and sound and water

It was established that electromagnetic waves can travel quite a distance in the atmosphere. But how far they can travel underwater?

The water molecules are actually much closer of the molecules in the gaseous state. This small distance is one of the reasons why the water is very effective in absorbing radiation and also one of the reasons why a bright light will struggle to exceed 100 meters underwater. In fact, sunlight arrives no more than 200 m in the ocean, making it impossible photosynthesis at greater depths.

The light can not penetrate very far into the water. Image taken from NOAA

The density of water makes it ideal a different type of wireless transmission: that acoustic. The more dense material is a, the better the sound transmission. Who has not played as a child with two cans and a tightrope between the two to talk to each other at a distance. Not only the sound travels farther in a denser medium but also travels at a faster rate (eg, the speed of sound in air is 343 m / s while the speed of sound in water is 1.500 m /s).

The audio communication is so practical in water than the blue whale, the largest mammal and noisier (180dB a 14Hz), It can communicate to thousands of km with other whales just by low frequency noise. The sound is currently used in many applications under water with one of the most famous is the SONAR (Sound Navigation And Ranging), in which a sound pulse is emitted by a source and the reflected pulse is received by underwater objects. Using multiple receivers, you can determine the size and distance of objects, which can be of great help in generating an image of the environment when there is low light.

The data transmission is possible in a manner almost identical to the normal wireless communication that includes error correction and parity bits.

Acoustic Data Transmission

The underwater acoustic digital data currently does not follow one specific protocol. Although each specific protocol has its own frequency and / or unique message structure, usually use one of the following encryption methods to actually define a 1 O 0:

Frequency shift keying

Phase shift keying

Frequency hopped spread spectrum

Orthogonal frequency-division multiplexing

The use of more different protocols brought the devices to be able to communicate and share information.

In the underwater world we have a very similar situation similar to that which they were to manage before you were using the IBM standard for computers when there were many different manufacturers that specify their data protocols and file structures.

JANUS could be the solution, underwater a unified protocol that will allow all devices to communicate.

The unified protocol

JANUS is a diver protocol developed by the Center for Research and NATO Maritime Organization experimentation for science and technology. It was recently adopted by NATO to help unify all underwater communications and enable cross communication between devices made by different manufacturers. JANUS is an open source robust signaling method for underwater communications, freely distributed under the GNU General Public License, and this is its strength

What makes JANUS a unified protocol is its ability to allow devices to advertise itself on a standard frequency and commonly used 11,5KHz. Then, when two devices have decided to connect, They can switch to a different frequency or a transmission method for speed faster transmission. This is incredibly important because the data transmitted using sound waves have a seriously limited speed of transmission in which the transmission rate is affected by the carrier wave frequency, by reflections of nearby objects, from the sound-noise ratio and more.

Joao Alves, one of the key researchers, It used an analogy to explain JANUS: Imagine two people who meet in a foreign country and want to communicate with each other. It is likely that both would speak English to establish a common universal language. However, they discover that they both speak Spanish fluently and then change language for ease and speed. In this case, JANUS provides a common platform for people to announce who they are and how fast they can communicate.

The JANUS protocol also defines how the sound should be encoded in a carrier wave (specifying the use of FH-BSK), as well as the correction of errors and redundancies. Some of the specifications of the protocol follow some key points:

  • Three pulses are used as ad “wake-up” to allow other devices to start listening. The time between the pulses must not be less than 0,4 seconds, since the reverberant energy must be dissipated (that is, reflections of objects and average limits).

  • four inputs are required for the first 64 Bit of a JANUS message, including sample rate, name of the output file, output format and name of an external file.

  • You can broadcast up to 4096 bits as payload for data transmission.

The rest of the specifications is easily retrievable on the net having regard to its GNU General Public License


2 replies
  1. mau22
    mau22 says:

    Amilcare, you're always a source of interesting information

    With this article you've greatly intrigued, and the result of my insights write here.
    I spent several hours searching the internet, and I found in various free information effects.
    There is even a Janus Wiki, complete with a forum, and the possibility to download software examples.
    So I made me want to see what might be complicated by a hobbyist / small company to build a device compatible with this standard.
    I found the brief description of small appliances to be put inside a metal tube, but nothing detailed.
    In particular, there is no information about the network to be used trasduttre.
    The first frequency to use, that of communication ad, is 11,5 kHz, and I have not found any network that produces this frequency transducers, so I think it's homebuilt.
    Put me to calculate it from scratch is a company that takes a long time, since I have never done anything in this area.
    Someone in the forum has experience ?



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