Underwater Wireless Communication

Hello all,

I am right now doing my final year project. We have decided to work on Underwater Wireless Sensor Communication. In this project, we deploy a wireless sensor node inside the water. It has to communicate with that of the buoy like thing (a trans receiver) placed at surface of the water. The trans receiver then communicates with that of Laptop. We want to use 2.4 GHz band for this communication.

Our idea

We have planned to use an Arduino board connected to a pH sensor and a temperature along. The board will be interfaced with a WiFi transmitter. The data collected by the sensors must be transmitted yo buoy floating on the surface. We will enclose this inside a water proof case and immerse that inside the water 15 to 20 cm deep. We will place a WiFi receiver at the surface of the water. This receiver will receive the signals from underwater and re-transmit it to Laptop.

Now here are my following question:

  1. What is the best way to implement this project?
  2. Can we enclose Arduino kit and WiFi transmitter in a water proof box and leave it into water? Will WiFi work under the water for short distances?
  3. Are there any kits readily avaiable to implement this?
  4. If not, please suggest me which of the Arduino kits are best for the purpose and other components to be bought.

With regards, NPB

Will 2.4GHz work in water?

Yes, many IEEE papers show that it works.

For such a short distance, I'd be inclined to go for optical. If the water is too dirty for optical, then it's probably too conductive for radio too.

We are testing this in pure water. But I want to know whether Bluetooth and WiFi work in water at least for some feet.

I thought you wrote that IEEE papers said it would?

If the water is pure, why are you measuring the pH?

This might be of some interest: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3355409/

Can you suggest me a good Arduino processor with WiFi transmitter and receiver? I must be able to interface a temperature of pH sensor with this. The data from these sensors must be transmitted over WiFi for another receiver. Give some suggestions with respect to this.

NPB777: Yes, many IEEE papers show that it works.

Got any links to those papers?

bperrybap: This might be of some interest: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3355409/

Yes interesting, especially:-

Therefore, our underwater communication system has an optimum behavior at 16 cm, working at frequency of 2,432 GHz, with the BPSK and QPSK modulations.

For 16cm are you not best to just have a piece of wire?

One thing I noticed about that paper is that they didn't adjust the antenna to compensate for the wavelength stretching that goes on with a transmission in water.

I would suggest that no Arduino product is suitable for this project.

NPB777: We are testing this in pure water. But I want to know whether Bluetooth and WiFi work in water at least for some feet.

So acording to that paper that would be a NO then.

First we need to make sure we are not being sucked down into an "XY problem". (Google it if not familiar). But it sounds like we are headed down this path....

From my reading of your project description, I can't fully grasp what you wanting/needing to do. (BTW, want vs need are two very different things)

What isn't clear to me is the relationship between the sensor and the buoy. i.e. where is the "sensor node" and how far away is it from the buoy?

The description is unclear; particularly this sentence:

We will enclose this inside a water proof case and immerse that inside the water 15 to 20 cm deep

What is this referring to? The previous sentence talked about the buoy but I'm assuming you really meant the sensor?

And if the sensor is only 15-20 cm away from the buoy, why use wireless? Why not just hang the sensor from the bouy and use wire(s)?

If the distance between the sensor and the surface is so small, why use a buoy?

Why use Wifi from the sensor? Why not use a lower frequency transceiver?

Is your setup actually more complex and we haven't been told the full scope? (like are there multiple senders on the bottom that constantly collect information and the buoy is dropped at the surface to capture measurements?)

Clarification on details is needed so we don't go too far down the XY problem path.

--- bill

Ultra pure water is non-conductive other water is not. High frequency will not work. Submarines use ultra low frequencies and require massive amounts of power to transmit. A lot of down hole tools use a baud rate of 1. Just a series of audible clicks for their telemetry. Laser would be difficult if the buoy is floating in keeping the alignment.

Nasa: Ultra pure water is non-conductive other water is not. High frequency will not work. Submarines use ultra low frequencies and require massive amounts of power to transmit. A lot of down hole tools use a baud rate of 1. Just a series of audible clicks for their telemetry. Laser would be difficult if the buoy is floating in keeping the alignment.

For RF, the conductivity of water isn't the issue. It is the signal attenuation. And at least from the initial description, we are talking very sort distances. So the communication problem is much more limited in scope.

I think we are slowly falling down the XY problem rabbit hole....

--- bill

Bill,

The sensor node is under the water. The buoy is floating at the surface of the water. Practically, the sensor node consists of two sensors interfaced to a processor and they are closed in water proof case. The case will have two or three tiny opening through which the sensors touch the water surface. Now the challenge is to establish a secured wireless communication between the buoy and this sensor node which is inside the water. We want to achieve this communication using the ISM band.

Now the challenge is to establish a secured wireless communication between the buoy and this sensor node which is inside the water.

According to this paper http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3355409/ you can probably do that, if the distance between the buoy and the sensor is [u]15 cm or less[/u]. Security is hardly an issue, unless your eavesdropper is within 15 cm.

Any sensible person would use 15 cm of wire for that purpose.

Microwaves are severely attenuated by water. That is why you can boil a cup of water in the microwave oven. Unless the distance is only a few centimeters, it won't work. Quoting the paper above,

Therefore, our underwater communication system has an optimum behavior at 16 cm, working at frequency of 2,432 GHz, with the BPSK and QPSK modulations. These modulations had also good performance at distances of 17 cm, working at 2.422 and 2.427 GHz, with a percentage of lost packets slightly above 30%.

For the metric challenged, that is about 7 inches.

IMO, the information provided so far still does not fully describe the project and problem set. We still don't know why there is a need to have wireless communication between the sensor and the Buoy and if the sensor node is physically attached in any way to the Buoy.

For example, is this "sensor node" something that is pre-made and you have to live with its design or is it something that you are also building and/or have flexibility in its design or can choose other pre-made alternatives? Or if the sensor node is attached to the Buoy, why use wireless?

And if wireless is desirable because it makes some things easier, then why use 2.4Ghz WiFi between the sensor node and the Buoy?

And now you have just tossed in "secured wireless communication between the buoy and this sensor node". To me that means something very different than it may mean to you, as to me it means creating an encrypted data session using asymmetric keys, which brings up all sorts of new questions, like why does this type of data need to be secured?

ISM bands seem to include quite a variety of spectrum regions/ranges, including the popular 433 Mhz region.

At this point, I'm still trying to understand what you are wanting to do.

Can you please fully describe your project in terms of what is the overall problem to be solved and include what components you have to use that can't be swapped out vs what you have the freedom to select, purchase, design, use anyway you wish.

--- bill