Software Defined GPS Receiver

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					By: Sam Price
Advisor: Dr. In Soo Ahn
   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
                          Tracking    Position
  Startup   Acquisition
                            Loop     Calculation

    Uses C/A code to find satellites
    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.
   Process faster than sampling rate.
   Solution must be accurate within 100m
    ◦ Implies sampling rate greater than or equal to 4Mhz
   For industry
    ◦ Minimum amount of Ram.
      Acquisition time will dictate this space.
      Hardware costs
    ◦ Minimum amount of processing power
        How fast you clean up Ram
        Tracking loop efficiency
        Acquisition algorithm efficiency
        Dictate battery life & cost of processor.
   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.”

   GPS Toolkit
   GNU LGPL, Signal Tracking Simulation , Ionospheric modeling, Positioning

   Uses FPGA board to supply computer with IF frequency.

   Pervious Project
   Locates current position once.
   Takes 4 minutes.
Patent Number   Description
20060074554     Software-defined GPS receivers and distributed
                positioning system
20067046193     Software GPS based integrated navigation
20067002515     GPS receiver using software correlation for
                acquisition and hardware correlation for tracking
2007213932      Computer Programmed with GPS Signal
                Processing Programs
2005162313      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.
   Acquisition
    ◦ Created chart of signal correlation strength.
    ◦ Used for future optimizations of acquisition stage.

   Tracking
    ◦ Performed timing analysis.
    ◦ Implemented optimizations.

   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   CA(t)   XOR   Nav(t) = Nav(t)
           0   XOR   Nav(t) = Nav(t)
   C/A code aligned.

   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
   Borre, Kai 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:
    < _System>.
   ?