ece290 final report

7/28/2019 Ece290 Final Report

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ECE 4902 Spring 2008

Prototyping and Real Time Testing of

Underwater Acoustic Modem

Final Report

Jason Thomas Electrical Engineering

Abbas Zaidi Electrical Engineering

Juny Thengumthyil Electrical Engineering

Advisor Shengli Zhou

Sponsor:

University of Connecticut, ECE Department


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Abstract:

The aim of our senior design project is to prototype and test a stand-alone underwater

acoustic modem, based on existing multicarrier modem designs tested mainly in a lab

environment. Important aspects are signal amplification and system modularization. With

signal amplification, we were able to transmit the signal for a range of almost 200 meters

as opposed to the previous tests of distance about 1 meter. With system modularization,

we were able to perform real time tests of the stand-alone modem in the lakes, rather than

in the tanks. In the demonstration, transmitter is implemented in two ways. The first one

uses a laptop with GUI interface and second one uses a DSP board which is programmed

to send data in every 20sec. There are two receivers to be demonstrated, the first one uses

Matlab programs on a laptop, while the second one is based on a DSP board containingall the system software. The DSP board, a power amplifier, batteries, and an underwater

transducer/hydrophone are placed in a waterproof casing.

Statement of need:

Electromagnetic waves do not propagate in an effective manner through water.

The use of acoustics for transmission provides an alternative method to efficiently

transmit data under water. Sound waves were chosen because they propagate well in

water and travel at a speed of about 1500m/s. Data transmission via waves also provides

isolation between portions of a data transmission system. Much like a transformer, a

failure on one side of the system would not have an effect on the other. This system also

allows for minimal hardware to be in contact with the water media, and also provides a

cost reduction by eliminating hard lines over large distances.

Previous work:

This is an ongoing project that has currently been implemented in two ways. The Fall

2006 groups method used code, programmed in Matlab, to transmit data between two

laptops: one laptop was used in conjunction with a transmitter to send the signal, and the

other laptop was connected to a receiver. The first laptop converted the digital data into

sound signals. The transmitted signals were then received by the second laptop which


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then converted the signal back into the original digital file. The system used Orthogonal

Frequency Division Multiplexing for the process. For underwater testing, a speaker and

hydrophone were placed in a water tank. Instructions were then fed to the transmitting

laptop, and the receiving laptop successfully acquired and decoded the data. This design

allowed for the transmission of data, but had a limited range of about one meter.

The Fall 2007 group modified the first project by implementing a three node

relay using the same principles as that of the first design. The three nodes acted like a

daisy chain, such that the communication between the end computers should be

through the middle one .This modification provided an increase in transmission distance

due to the middle computer acting as a relay unit. Another modification was the

incorporation of a motion sensor. Whenever motion occurred, the computer attached to

the sensor would wake up and record the data and send the data automatically to the

other nodes. Further modifications are currently being implemented to make a four node

relay/network.

Approach:

Our group had three major tasks: 1) Amplification of the transmitted signal

2) Build a transmitter module and a receiver module 3) Real time testing at Mansfield

Hollow Lake and Mirror Lake.

In order to amplify the signal, we had to purchase a power amplifier. Part of the

research involved determining which class of amplifier to use for our application. The

choices we looked at were class A, class B, class A/B, and class D. Class A required a lot

more power, was less efficient and produced more heat. We decided against class B since

it only amplifies 1800 of the signal. Class B amplifiers are also subjected to crossover

distortion if a complementary transistor is added to obtain the other half of the signal.

Class D amplifiers, though they are the most efficient, use pulse width modulation and

current technology limits this class of amplifier to low frequency applications. Since our

application uses a center band frequency of 12 KHz, this class cannot be used. Class A/B

amplifiers incorporate the benefits and minimize the limitations of class A and class B

amplifiers. Due to these findings, we decided to use a class A/B power amplifier.


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There were two versions of the transmitter module as shown in phase two and

phase three figures. The first version consisted of a transducer connected to a power

amplifier which was connected to both to a 12V DC battery as a power supply, and a

laptop which provided the input data for our system. The second version consisted of the

same components, but used a programmed DSP board to provide the system input. These

components were then placed in a water proof case, with the transducer placed in the

water.

Project Plan:

Our project plan was divided into three phases

Phase 1 Interface/ Testing Housing

Battery Testing

Real Time Tests

Phase 2 PC based tests Amplification

Signal Acquirement / Processing

Phase 3 DSP based tests Amplification

Signal Acquirement / Processing


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Phase 2 schematic:

In this phase we used laptop sound cards to send and receive the data.

Phase 3 schematic:

In phase 3, we assembled the prototypes using the DSP boards as the transmitter and

receiver data encoders/decoders.

Components:


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The following are the components used, with specifications given below each figure.

DSP Board TMS320C6713 (Used in phase 3)

Stand Alone Product

Includes Audio Encoder and Decoder

Includes Stereo IO

Presonus TUBE Pre Mono Tube Pre Amplifier (DSP Pre Amp, used in phase 3)

Switchable phantom power

80 Hz low cut filter

Up to 20 dB of tube drive48V Phantom power

Pelican 1650 Waterproof Case


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Outside Dimensions: 32.50"L x 20.50"W x 11.31"D

Inside Dimensions: 29.00"L x 17.88"W x 10.50"D

Weight: 37 lbs

Valve regulated- Gelled Electrolyte Battery

Dimensions: 8.31 x 5.13 x 7.25

Nominal Voltage: 12V

Capacity: 36.5Ah

Weight: 23.4 Lbs.

Deepwater Omni directional Transducer


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Freq Range: 1.00 Hz 45KHZ

Input Power: 800 watts

Resonance Freq: 33 kHz

Oceanears DRS-8 Transducer

Freq Range: 200 Hz 32 kHz

Input Power: 200 Watts (max)

MOSFET Bridgeable Power Amplifier


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Peak Power: 200 W 2 channel

THD @ 4: 0.01%

S/N ratio : 102 dB

High pass crossover

Variable Low Pass Crossover

Dimensions: 11.8 x 7.2 x 2.8

Weight: 7.8 pounds

Miniature Reference Hydrophone

Freq Range: 1Hz to 170KHZ

Sensitivity(dB re V/Pa): 211

High sensitivity, broad banded, and Omni directional

Aquarian AQ-3 Hydrophone


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Freq Range: 20Hz - 100 kHz

Low self noise

Power Output: 300 mWatts

Input Voltage: 6 15 Vdc

VP 1000 Voltage Preamp

VP 1000 Voltage Preamp

Input Impedance : 100MOhm

Output Impedance: 10Ohm

Operating Freq Range:

0.5 Hz to 1 MHz

Preliminary Experimental results:


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We used a Sony Xplode 300 Watt 2 channel car audio amplifier to amplify a

signal sent to a transducer. The input to the amplifier was music from a laptop. We did

this preliminary testing out of water to test whether our wiring and amplification idea

would qualitatively work. The results of the experiment showed that the sound was in

fact amplified using the car audio amplifier. But due to the high power of the amplifier

(the transducer was rated for 200 Watt maximum input) the sound coming out of the

transducer was distorted. Lowering the gain of the amplifier did correct the problem

however. Taking this into account, we have concluded that we can use a smaller

amplifier, which will also be a cost reduction, to begin testing of our project.

Final Results (Phase 2):

The following plots give the results obtained via laptop using Matlab coding. The top left

graph gives the received data. The first packet is used to ensure proper signal

synchronization and the second packet contains the actual transmitted data. The top right

graph gives the impulse response of the channel. The bottom left graph is the Correlation

Plateau, which shows an analysis of the first packet. It checks the first half of the packet

against the second half. Both halves should be identical which would be indicated by a

plateau equal to one. The code searches for the best correlation which is shown by the red

line in the graph. The bottom right graph shows the data point acquisition. This graph is

separated into four quadrants. The blue circles represent two bits of data:

Quadrant 1: 00

Quadrant 2: 01

Quadrant 3: 10

Quadrant 4: 11

Deviation from the centre of the quadrants is due to noise interference. If the noise is

high, it may cause the transferred two bits to appear in the wrong quadrant giving

erroneous data, causing the signal to not decode properly.

Plot at 10m

SNR: 15 dB


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Plot at 20 m

SNR: 12dB

Plot at 30m

SNR: 16.7 dB


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Plot at 50m

SNR: 19.7dB

Plot at 100m

SNR: 25dB


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Plot at 150m

SNR: 21.6

Timeline


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Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Research

Purchasing

Construction

Testing

Demo

Budget:

Product Quantity Price

MOSFET Bridgeable

Power Amplifier

1 62

Valve regulated-

Gelled Electrolyte

Battery

2 170

12 Volt BatteryCharger

1 100

Pelican 1650

Waterproof case

2 380

Miscellaneous

Expenses

200

Total 912

Problems Encountered:

One of the problems we encountered was extraneous noise. When we first went

out for testing we used the Aquarian AQ-3 hydrophone which did not have a signal filter.


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This lead to triggering by any noise present in the water. To counter this problem, we

had to turn up our trigger value which lowered the transmission distance. This happened

because our signal had to be sent at higher gain values. At larger distances this lead to

being at the saturation level of the speaker. As a solution to this problem, our advisor

ordered the Miniature Reference hydrophone which included a high-pass filter and built

in pre-amp. This hydrophone eliminated the motor boat noise and wildlife noise present

in the lake. This dramatically increased our transmission distance. We did note that on a

windy day the choppy water still caused some false triggers. But most of the other

interference was eliminated.

Another problem we encountered was the power supplies of the DSP boards.

While reading the product manual in the first semester, we understood that a part could

be ordered providing a 5V input to the DSP board from a 12V DC source. When we

ordered this part, we realized that this connector was only to be used with a desktop

computers power supply, so we could not use our original plan of using it with our 12V

battery. To remedy this, we made 4.5V battery packs using battery holders and AA

batteries, but their life span was approximately 30 minutes.

Another issue was the power supply of the Presonus TUBE Pre Mono Tube Pre

Amplifier used for the DSP board. It required a 16V AC input, which we were unable to

provide in time for project completion deadline. We ordered a 12V DC pre-amp but its

limitations proved inadequate for proper system operation. This was mainly due to this

pre-amps inability to control its gain level. This was proved when we took this

configuration out for testing in the lake. We were unable to receive any successful

messages using this configuration.

Conclusion:

We met our goal of increasing the transmission distance from 1m to 100m. We

got reliable transmission and reception from up to 200m. In fact we were able to get a

successful decoded message from 700m using the phase 2 setup with the Oceanears

DRS-8 Transducer and the Miniature Reference Hydrophone. But at this distance the

reception is unreliable using our components because only about 1 in 10 messages get

decoded correctly. We desired to do further testing with the Deepwater Omni directional

Transducer, but weather and time constraints did not allow us to do so. From our


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observation of using the higher quality hydrophone and in lab testing of using the

superior DSP board, we believe that the higher quality transducer will significantly

improve our results.

Our other goal was to provide an independent prototype using off the shelf

components. We were semi-successful in this case. Our phase 2 setup was implemented

and provided the majority of our testing. But the phase 3 setup had power supply

problems. The 12V DC DSP board pre-amp we purchased was inadequate. The phase 3

setup worked in the lab trials in the water tank. But data could not be properly received

and decoded in the real time testing environment on the lake. We believe this is due to

the pre amplifier.

We think this was an excellent project and could be used in many applications

including wireless unmanned submersible communication. We would like to thank Janny

Liao and Sean Mason for helping us in the underwater acoustic modem lab. They

provided all the code changes and DSP programming and helped us understand the

system and designs of previous teams. We would also like to thank our advisor Dr.

Shengli Zhou for the support of providing us with all the high-end components and

helping us organize our research and testing efforts.

ece290 final report

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