ECE 4901 Fall 2012
Underwater Network Localization:
Final Written Proposal
Team 170
Tausif Shaikh (EE)
Johanna Thomas (EE)
Patrick Lazar (EE)
Kaleel Mahmood (EE)
Advisor:
Shengli Zhou
Introduction
Conventional localization is used on a daily basis to navigate to destinations, provide
directions in real time and discover nearby attractions. Localization is traditionally achieved
through Global Position System (GPS) technology. GPS works by using satellites to send out
electromagnetic signals to a receiver whose position is unknown. Based on the propagation
time required for the signal to reach the user, the user’s position can be computed
geometrically using a method known as triangulation. GPS can accurately give your location on
the surface of the Earth but implementing localization in aquatic environments comes with
significant challenges. In commercial GPS electromagnetic waves are transmitted with a center
frequency of 1575.42 MHz. Electromagnetic waves work well as a means of signal transmission
because the conductivity of air is low varying from 3×10−15 to 8×10−15 Siemens per meter so
signal degradation is negligible. Fresh water however has a conductivity of 2×10 −1 Siemens per
meter and salt water has a conductivity of 4 Siemens per meter so electromagnetic waves
quickly lose strength as they traverse through this type of medium. Additionally in water the
absorption coefficient of a signal is directly proportional to its frequency. At high frequency
such as those used by GPS, electromagnetic waves cannot propagate useful distances.
To circumvent the problems faced by electromagnetic signals acoustic signals can be
used as a means of transmission instead. Acoustic signal are better suited for use in aquatic
environments because their signal strength does not depend on the conductivity of the
medium that they propagate in. Using underwater sensor networks that transmit acoustic
signals various transmission schemes can be used to implement localization. There are four
main commercial based localization methods that have been developed for commercial use as
well as two research based methods. The goal of our project is to study the research based
localization topics and build working models so that they can be implemented for practical use
in the field such as on AUVs and for sea floor navigation. To create the best possible positioning
system we first studied all the localization set ups that are commercially available. In the next
section we will discuss the advantages and disadvantages of each commercial method as well
as the two research based methods.
Hardware
Our group needs six digital processing boards OMAP-L137 EVM, four anchor nodes, one tracking
node and one active node. We also need six hydrophones of type Hong Zhi ST 50 with an operating
frequency range: 100 Hz to 50 kHz and six transducers of type PT 25 Spherical with a resonance
frequency: 25 kHz our project requires underwater housing for all components. We also need four
GPS tracking devices.
Figure 1. DSP Boards in Waterproof Housing.
Research Based Underwater Localization
Synchronous
The synchronous localization system is one of the research methods which we will be testing in our
design project. In this system, we have nodes placed at the surface of the water which are equipped
with satellite-based GPS receivers. The clocks of the nodes are synchronized using the internal pulse
provide by the GPS device. Once the clocks are synchronized, the nodes send signal to the AUV which is
placed underneath the water surface. The nodes send the signals to the AUV after a certain delay. Figure
2 below shows the schematic of this system with its signal time diagram.
Figure 2. Synchronous Localization schematic and signal time diagram.
One of the biggest advantages of the synchronous localization system is that it is able to service multiple
AUVs at once and it also does not require a continuous GPS signal to synchronize the clocks on the
nodes. However, a disadvantage of this system is that the nodes must be on the surface of the water
initially to receive GPS signal. Any missed node signal means that position cannot be computed if
working with the minimum node schematic.
Asynchronous
The asynchronous localization system is other research method that we will be testing in our design
project. In this system, we have the nodes at the surface of the water and the AUV underneath the
water. Unlike the synchronous localization system, the GPS signal is not required in this system because
the clocks do not need to be synchronized. In this system, the AUV sends a pinger signal to the nodes.
Once all the nodes have received the signal, they send a signal back to the AUV which then computes
the position. Figure 3 shows the schematic of this system with its signal time diagram.
Figure 3. Asynchronous Localization schematic and signal time diagram
The advantages of asynchronous localization system is that the clocks on the nodes do not need to be
synchronized together and extra timing measurements sent from other nodes can be factored into
calculations to provide better position accuracy. On the other hand, this system also has some
disadvantages. The initiator signal must send out a delay factor long enough so no nodes send out
signals at the same time. This system has also never been field tested so the actual accuracy
improvement is unknown.
Programming of Asynchronous
Localization
To start our programing we created a basic flow chart of how the system is going to be created. Each
node as well as the AUV will have their own code. For the nodes when the scenario starts the modem
code provided by the UWSN lab at UConn will be initialized. The purpose of this code is to set up the
communication between the nodes and the AUV. For the Asynchronous localization method each node
will then wait for a specific call from the AUV, when the call is received it will record the time it received
the call and send a response. At the moment that is all the code for the nodes is going to do, later on we
will look into the second half of the asynchronous localization which uses each nodes measurement to
also calculate the position.
In theory the extra calculations will yield a more accurate positioning.
Figure 4 shows the flow charts for both the nodes and the AUV.
Figure 4. The flow chart to be used for the node and AUV code implementation.
The code for the AUV starts out similar to the node in that the first thing after the scenario starts is the
initialization of the modem code to allow for communication throughout the Asynchronous localization
system. After this we go into the localize block which consists of a series of call statements. Each call
statement represents an (if) argument which goes through a list of the nodes. At each nodes call, the
AUV will send its’ transmission and be prompt for a response. When the response is received by the
AUV the (if) statement shifts to the next node and continues on in series. After all these responses are
received and cataloged the localize block moves to the position algorithm. In this phase the times
recorded by the AUV are used to calculate the position of the AUV.
Programming of Synchronous
Localization
To start the programming we created a simple flow chart of how the system is going to be created.
When the scenario starts, just as in Asynchronous the modem code is initiated allowing for
communication between the nodes and the AUV. In Synchronous localization the node code is rather
simple in that they are set up as pingers. Where each node (synched through GPS) will send its signal at
a predetermined time, after sending its signal it will wait for the full rotation of the other nodes and
send again. Figure 5 shows the flow diagrams for both the nodes and the AUV in this method.
Figure 5. The flow diagrams for Synchronous localization.
The code for the AUV starts out similar to the node in that the first thing after the scenario starts is the
initialization of the modem code to allow for communication throughout the Synchronous localization
system. In this scenario, the nodes are set up as pingers, constantly sending pulses at a known time
interval. The code for the AUV just has to listen for the node calls, when this loop receives 4 node calls
(one for each node) it can then take the information it receives and move it to the positioning algorithm.
Range Test
Our team will be implementing a range test to determine how fast the signal travels in the water. In
order to determine the speed of the signal, we need to first solve for the speed of sound in water. The
speed of sound travels at a faster rate in water than in air and it depends on water properties such as
temperature, salinity, and pressure. On average, the speed of sound travels at approximately 1500 m/s
under water. Below is a diagram of our set-up of the range test in the swimming pool with a graph which
shows the speed of sound versus temperature and pressure.
Figure 6. set-up of range test and graph showing sound of speed versus temperature and pressure
If you observe the graph on the right side in figure 6, you can see that it shows the speed of sound
versus the temperature and pressure. As the temperature of the water increases, the speed of sound
also increases. The graph shows us this is the case in the shallow parts of the water because the
temperature of the water has a higher effect on the speed of sound. On the other hand, as you go
deeper, the pressure of the water starts to have a higher effect on the speed of sound which increases
the speed of sound.
Noise Test
We will also implement a noise test to see how disturbance the signal will receive in the swimming pool.
The noise interfering with the signal may reduce the strength of the signal and that is why we have to
take into account the noise in our design. The signal may be affected by two types of noises; the
ambient and man-made noises. The ambient noises are from the natural surrounding such as waves,
tides, or marine animals. The man-made noises occur from disturbances by human beings such as
construction or drillings. We calculate the variance from the noise test and use it to calculated the Time
of Arrival (TOA) of the signal. The set-up for the noise test is the same as the set-up of the range test
shown in figure 6.
Future Work
We still have a long way to go on our project, one of the first things we need to do is implement our
pool test. Here we will test the nodes in hope to find the range of the equipment, determine the delay
time we will need to prevent the signals from interfering with each other, and to determine if the pool
will create interference due to its reflective siding and small size. We then will look at the modem
initializing code supplied by the UWSN lab in hopes to understand and manipulate it as needed later in
our project. Another task is to create the Algorithm code for both system methods (Asynchronous and
Synchronous). Using the basic math required for these calculations we will try and find the best way of
calculating the position in the fastest manner. Once all these goals are met, we will look deeper into the
localization method and try and develop a way to speed up the system and make it useful for a moving
object. At this stage in our project we are using a system that requires a minimum wait of 8 seconds
between the first node’s call and the last nodes call being received by the AUV. In this scenario if the
AUV is moving it will be 6 seconds farther from where it previously was when the final node sends its’
signal. When we do our testing we will look at how this impacts our results and if the lost accuracy can
be compensated.
Budget
The Department of Electrical and Computer Engineering (ECE) at the University of Connecticut has
provided us with a budget of $1000. We will be obtaining all hardware from the University of
Connecticut Underwater Sensor Network Laboratory for designing and testing. In terms of software the
version of Code Composer studio we use is a license free version provided by the company. At this time
we have no plans to use the $1000 budget but in the future we may consider using funding to buy
additional digital signal processing boards from Spectrum Digital if necessary.
Timeline of Events
September
October
• Project
Statement.
•Background
research in
existing
Localization
methods.
January
•Ranging and
pool tests using
two nodes.
•Hardware setup
of remaining
nodes.
•Field testing of
algorithms .
November
•Project
specifications.
•Additional
localization
research.
•Coding DSP C
February
•Field testing of
algorithms.
•Algorithm
comparison
analysis.
December
•Code composer
studio setup and
completion of
tutorial on coding
in DSP C.
•Finalize
implementation
plans.
March
•Field testing of
algorithms.
•Algorithm
comparison
analysis.
April
•Integration of
localization with
other groups.
•Algorithm
comparison
analysis.
•Ranging and
noise pool tests
using two nodes.
•Coding DSP C
algorithms.
May
•Complete
integration of
localization
with an AUV.
Shown above is an overview of our progress so far and our future objectives for the project. We have
already conducted extensive research on the commerical and research localization methods. This
November we plan to learn how to code the main component of the sensor nodes, the digital signal
processing board. In December and January we will conduct pool testing to establish the sound speed of
the acoustic signal in the pool water and get variance measurements corresponding to the water
conditions of the pool. In Jaunary we will set up the required nodes for testing and begin field testing in
the pool and if results are favorable, possiblly in the lake. Finally at the end of our timeline we plan to
have a working accurate localization solution that can be integrated with an AUV.
Team Roles
Our group is tasked with creating an underwater localization system. Based on this objective we have
divided up the work and roles as follows. Tausif Shaikh and Johanna Thomas will be coding the
synchronous and asynchronous localization algorithms in C based on the data delivered by the acoustic
modems. Patrick Lazar and Tausif Shaikh will both be responsible for updating the senior design website
with our current progress. Patrick Lazar and Kaleel Mahmood will study the existing acoustic modem
code developed by the Underwater Sensor Network Laboratory and make modifications corresponding
to the transmission schemes used in the different localization setups. Together all members will conduct
range and noise tests. Kaleel Mahmood and Patrick Lazar will be responsible for hardware setup in these
tests and Johanna Thomas and Tausif Shaikh will be responsible for the data analysis from the tests.