By: Sam Price
Advisor: Dr. In Soo Ahn
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Overview of GPS
Overview of Receivers
Current Projects
Patents
Datasheet
Preliminary work
Schedule of tasks
L1 Carrier wave
1575.420 MHz
C/A code
1.023MHz
Satellite Identification
Navigation Message
50.000 Hz
Time of week
Ephemeris (Current position)
Almanac-Global data
Startup
Acquisition
Tracking
Loop
Position
Calculation
Acquisition
Uses C/A code to find satellites
Tracking
Performs phase lock loop to keep
track of satellites
3 satellites solve for X,Y,Z
Inaccurate receiver clock.
4 satellites solve for
receiver time bias.
Sampling frequency
Plays role in error.
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Process faster than sampling rate.
Solution must be accurate within 100m
◦ Implies sampling rate greater than or equal to 4Mhz
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For industry
◦ Minimum amount of Ram.
 Acquisition time will dictate this space.
 Hardware costs
◦ Minimum amount of processing power
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How fast you clean up Ram
Tracking loop efficiency
Acquisition algorithm efficiency
Dictate battery life & cost of processor.
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SoftOSGPS
12-7-2008
“It is able to process IF files or real time data from the GPS1A or SiGe with
various options for sub sampling and packing of the data. Please read the file
READMEFIRST for more detailed instructions.”
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GPS Toolkit
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GNU LGPL, Signal Tracking Simulation , Ionospheric modeling, Positioning
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GPS-SDR
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Uses FPGA board to supply computer with IF frequency.
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Pervious Project
Locates current position once.
Takes 4 minutes.
Patent Number
20060074554
20067046193
20067002515
2007213932
2005162313
Description
Software-defined GPS receivers and distributed
positioning system
Software GPS based integrated navigation
GPS receiver using software correlation for
acquisition and hardware correlation for tracking
Computer Programmed with GPS Signal
Processing Programs
GPS Receiver (Software)
•LNA (Low Noise Amp)
•IF frequency of 4MHz
•Sampling frequency of 16MHz
•Performs A/D conversion
•Outputs 1 byte signed value (-4 to 4) via USB.
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Acquisition
◦ Created chart of signal correlation strength.
◦ Used for future optimizations of acquisition stage.
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Tracking
◦ Performed timing analysis.
◦ Implemented optimizations.
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Structure
◦ Designing layout of new structure.
CA(t) Nav(t) Cos(IF)
Cos(IF) Cos(IF)
½Cos(IF+IF) + ½Cos(IF-IF)
½Cos (2IF) + ½Cos(0) = ½ CA(t)Nav(t)
CA(t)
XOR
0
CA(t)
XOR
XOR
Nav(t) = Nav(t)
Nav(t) = Nav(t)
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C/A code aligned.
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C/A code not aligned.
Tracking time (Seconds)
Last years code
210
Trig metric lookup table
126
Decimation 1
98
Decimation 2
82
Removed multiplication
60
Combined 3 for loops to 1
29
Switched to release build
12
Removed decimation
22
Total Optimization
Speed increase of 10x
Task
Refresh
Finish Date
Continuous importing of signal data
16MHz
1/27/09
Continuous deleting of signal data
3ms
2/10/09
Acquisition from data
20 sec
2/17/09
Continuous tracking of data
1ms
3/2/09
Continuous solution update
1 sec
3/16/09
Develop GUI
3/30/09
Optimize Acquisition(Optional)
4/13/09
Write final report
4/20/09
Prepare final presentation
4/27/09
Final Presentation
5/5/08
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Borre, Kai et.al. Software-Defined Gps and
Galileo Receiver. Basel: Birkhhäuser, 2007.
Tsui, James. Fundamentals of Global
Positioning System Receivers. Hoboken: John
Wiley & Sons Inc, 2005.
Hurn, Jeff. GPS A Guide to the Next Utility.
Wikipedia, “Global Positioning System”
[online], available from World Wide Web:
<http://en.wikipedia.org/wiki/Global_Positioning- _System>.
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