Challenge: Internet in the Ocean

1 - Introduction

Nowadays internet connection are becoming more and more inserted in society. Internet of Things brought connectivity to home appliances, and Industry 4.0 are using highly connected systems to improve efficiency and monitoring in large processes.

So what are the boundaries of the online world these days? Even at the International Space Station there is wi-fi connection. The response is: in the middle and deep of the oceans. The main reason is the low utilization rate of these resources, which makes conventional satellite transmission systems very expensive.

An alternative is to use underwater devices to extend the connection signals to users. However, radio waves do not travel well through salt water, because it is a good electrical conductor, and can become a Faraday cage.

So, it is impossible to communicate underwater at far distances? The answer can be obtained if we look more carefully at the animal kingdom: dolphins can use ultrasonic waves the detect objects at relatively long distances.

If we can have a technology which produces ultrasonic waves, similar to dolphins, we can communicate underwater? Yes, and it is already done by ships and submarines sonars.

However, these ultrasonic systems have limited range (between 10km and 500 km) depending on pressure and waves frequency.

The main idea of this project, is a communication network between a large number of underwater probes equipped with sonars, to cover a big area with internet connection.

For energy supply, photovoltaic solar panels protected from water by glass surfaces are used. A non-toxic and low-cost saltwater based battery is used for energy storage.

However, marine currents can displace and isolate probes from each other, interrupting internet connection. To solve this problem, a mesh network is used, which can grant connection between devices in a variable arrangement. This way, near ships can connect to probes and oper as an intermediate point between probes, and also uses the network if they don’t have internet connection.

This solution requires low adaptations of actual ships sonar systems, only the implementation of the communication protocols.

2 - Probe Project

The probe communication can by done through Massa TR-1055[1], a deep ocean transducer with nominal power of 1kW. To supply this transducer, 4 solar MPPT PV panels with 250kWp will be used.

To avoid interfering on wales and dolphins communication, an artificial intelligence will be used to detect these animals in the sea, through sonar captured signals. If there is animals near the probe, it will be offline temporaly.

Dependence on solar energy is very unpredictable and unreliable. However, if a probe reach a low energy state, they can be temporarily offline, and the Mesh Network will automatically change connections topology.

Two important values are used to determine how well a sound wave is going to be transmitted at approximately sea level in the ocean, which are absorption coefficient and spherical spreading. The spherical spreading is systematically used as a first approximation when evaluating the performance of underwater acoustics. Both parameters are then merged into a general equation, which are described by:

-TL=-20*log(R) -a*R (1)

where a is the absorption coefficient. In order to better illustrate how the propagation works, the following figure shows the relationship between the Range (R= distance between any place and the sonar) and TL (Transmission Loss) regarding several frequencies:

Figure 1

In Figure (1), a is calculated using T=10 ºC , S (salinity)= 35 p.s.u. , z (depth) = 10 m with respect to equation (1).

Although propagation loss is comprised of many factors, here we adopt a conventional propagation loss, in which the system may be well described by the transmission loss (TL) formula. The transducer specifications feature transmission response for voltages at 133 dB re 1 µPa @ 1 m @ 12kHz along with the receiving response, rated at -183 dBV / 1 µPa, that is, the maximum gain for probes to exchange signals are in the order of 133-(-183)= 316 dB. This value is used as a reference in further calculations to figure out what the greatest distance between probes will be. Using equation (1) and solving it for TL = 316 dB we have the transcendental equation:

-316=-20*log(R) -a*R

which is now to be analyzed using any numerical method, iterating so the value of R can be found. As a common choice we have used Newton’s method to find R:

R = 209.5 km

Once we have the greatest distance, the coverage area can also be calculated in order to map the ocean and correctly install the probes throughout the ocean.

Now we move to the buoyant force calculation, and thus the transducer shape has to be taken into account:

To calculate the volume the probe should be broken down into pieces and their values summed up. From the mounting dimensions we have that:

V_total = 2031 cm^3

Finally, the buoyant force is given by :

B=u*g*Vol = 1028.13*9.81*0.002031 = 20.48 N

where “u” is the water density at sea surface. For the weight force:

W = m*g = 4.535 * 9.81 = 44.48 N

From the values obtained, a floater will be required to prevent the probe from drowning.

3 - Mesh Network and Communication Protocols

Mesh network creates redundant communications paths throughout the network, each device can act as routers and forward traffic to others. If a device fails, the network automatically routes messages through alternate paths, being a proper system to transmit data between probe to probe, and probe to ship, which can have variable distance from each other.

Mesh networks are self-organizing and doesn't require system administrator, adding new devices or relocating existing ones is a simple task. The network discovers the new node and automatically incorporates it into the existing system.

Communication between probes can be done with a large number of application layer protocols. But, if a node of the network pretends to be an internet access point for users, they will need to send the message to a Gateway which will communicate with users through TCP/IP protocol.

Nasa's DTN protocol [3] is very suitable for probe to probe, and probe to ship communications. Even in the situation where a group of probes become isolated from main network, if a ship cross the location, the "stored for future transmission" concept from DTN can carry messages in the ship system until they reach the main network system.

4 - Alternative Applications

Developed system can be used for other purposes, such as real time ocean monitoring, through sonar technology, data acquisition (such as temperature, water pH and composition), sea life observation through installed cameras and national sea borders protection.

References

[1] https://www.massa.com/wp-content/uploads/2017/08/T...

[2] https://beckassets.blob.core.windows.net/product/readingsample/345611/9783540784807_excerpt_001.pdf

[3 ]https://www.nasa.gov/content/dtn