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Design and Implementation of a Software-Based GPS Receiver

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Design and Implementation of a Software-Based GPS Receiver Powered By Docstoc
					Design and Implementation of a
Software-Based GPS Receiver


   Anthony J. Corbin
   Dr. In Soo Ahn

   Tuesday, June 28, 2011
Project Summary
 Software-Based Solution
   Advantages
     Size
     Cost
     Portability
   Implementation
     Sampling System
        Downconverter
        A/D Converter
     DSP System
        Simulates a microcontroller
Patents
 The table below lists relevant patents.
 Most of the patents are recent.
 Notably, two of the patents were granted to
  Denso and Toyota.

       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)
Referenced Work
 Kai Borre, Dennis M.
  Akos, Nicolaj
  Bertelsen, Peter
  Rinder, and Soren
  Holdt Jensent,
  Software-Defined GPS
  and Galileo Receiver :
  A Single-Frequency
  Approach. Birkhauser:
  Boston, 2007, pp. 29,
  83, 105.
Goals
 Implement a software GPS L1 signal model
 Develop a software-based GPS receiver model for
  processing a sample input dataset
 Implement the model in a high-level language such as
  C++
 Process the raw data using an embedded system or
  DSP kit using the model developed
 Connect the embedded system or DSP kit to a
  sampling device and perform satellite signal
  acquisition
 Compute position in real-time
High-Level Block Diagram

       GPS L1 Signal
       1575.42 MHz                Input:   GPS L1 Signal

                                  Outputs: Earth-Centered, Earth-Fixed Coordinates
          Antenna                          Latitude, Longitude, Altitude



Bandpass Filter - 1575.42 MHz




                                           Sampled Signal
            LNA                 SE4110L                     DSP     Display
                                             4.092 MHz



Antenna Stage
SE4110
 Functions
   LNA
   Downconverter
   A/D Converter
 Output
   Reference Clock
   Sign Bit
   Magnitude Bit
DSP Kit
 225 MHz
 2 MCBSPs
   Multi-Channel
    Buffered Serial
    Ports
 16 Megabytes of
  RAM
Software Processing                                                        [1]




                                               Raw GPS Sample Data




                                               °
                                              90




                                                      DFT




                                                                                 Update                Distance to
GPS Gold Code Generator   DFT     Delay             Correlator       Max                  Time Delay
                                                                                 Delay                  Satellite



                                Shift Early




                                Shift Late
Subsystem Requirements


  Error               Specification(s)
  Position Error      100 m
  Sampling Rate       4.092 MHz
  Time to First Fix   Cold Start : 36 seconds
                      Warm Start : 1 second
  Display             Earth-centered, Earth-fixed Coordinates
                      Latitude, Longitude, Altitude
                      UTC Time
                      Local Time
Position Error
 Estimated position is based on the sampling
  rate being 4 times the chipping rate.
 ¼ of the distance represented by a chip is
  therefore the approximate error.
                          m
                    3 10
                       8
              c           s  293.26m
       Chip  
               f 1.023 106 1
                            s
                   Chip 293.26m
       Precision                73.31m
                    4       4
Time to First Fix                    [1]




   A position fix requires that
    the ephemeris data is                   6 Seconds
    completely received.
   This requires a complete               Subframe 1
    frame of data, which takes
    30 s to transmit.
   However, it is unlikely that
    the receiver shall begin               Subframe 2
    collecting data at the
    beginning of a subframe
    indicating that an extra               Subframe 3   30 Seconds
    subframe lasting 6 s must be
    received.
   If the ephemeris data has
    already been received, the fix         Subframe 4
    time is minimal.

                                           Subframe 5
Display
 The display shall be relatively simple
  providing:
   Latitude, Longitude, and Altitude
   Earth-Centered, Earth-Fixed Coordinates
    (Relative)
   UTC Time
     Local time correction may be selected
L1 Signal Generation
 A generated L1
  sample is shown to
  the right.
 The signal
                         1

                       0.8

                       0.6




  generated is based
                       0.4

                       0.2

                         0




  on the
                       -0.2

                       -0.4

                       -0.6




  pseudorandom
                       -0.8

                        -1




  sequence
                              50   100   150   200   250   300




  generation shown
  on the next slide.
L1 Signal Generation                       [1]




                 Tap

       Tap




   1    2    3         4   5   6   7   8   9     10




                                                      GPS L1 Signal




   1    2    3         4   5   6   7   8   9     10
Cross-Correlation
 The cross-correlation
  characteristics of the
  L1 signal are what
  make it important.         1200



 Different L1 signals do
                             1000

                             800

  not correlate with each    600



  other!
                             400

                             200


 The figure to the right      0
                              10


  shows a graphical
                                                                10
                                                            8
                                    5                   6
                                                    4

  representation of the
                                                2
                                        0   0



  plane of all correlation
  possibilities.
Preliminary Measurements
 The GPS L1 signal
  is attenuated to a     -5
                              MHz   5 MHz   10 MHz   15 MHz   20 MHz


  level below the       -15



  noise floor.          -25



 The graph on the                                                     Magnitude Bit



  right shows the
                        -35
                                                                       Sign Bit




  result of an FFT of
                        -45




  the data from the     -55




  SE4110L device.       -65
Equipment List

Item              Description
SE4110L-EK1       Evaluation kit for receiving and sampling GPS
                  signals
F-female to       Adapter
BNC-male
BNC-female to     Adapter
MCX-male
GPS Antenna       Antenna on roof of Jobst Hall
TMS320C6713       Digital Signal Processing Kit
DSP Starter Kit
Preliminary Schedule
     Week        Activity
     1/23-1/26   Create a model to process sampled GPS signal data
     1/27-2/2    Continue developing GPS signal processing model
     2/3-2/9     Develop software to sample data from the SE4110L
                 using the DSP kit serial ports
     2/10-2/16   Process sampled data using the GPS signal processing
                 model
     2/17-2/23   Modify the GPS signal processing model to be run on the
                 DSP kit
     2/24-3/1    Continue modifying the GPS signal processing model to
                 be run on the DSP kit
     3/2-3/8     Debug the GPS signal processing model while running it
                 on the DSP kit
     3/9-3/15    Continue debugging the GPS signal processing model
                 while running it on the DSP kit
     3/16-3/22   Develop GPS data interpretation model
     3/23-3/29   Create coordinate conversion software
     3/30-4/5    Design display
     4/6-4/12    Develop and test display
     4/13-4/19   System debugging and documentation
     4/20-4/26   System debugging and documentation
     4/27-5/3    System debugging and documentation
References
 [1] Kai Borre, Dennis M. Akos, Nicolaj Bertelsen, Peter
  Rinder, and Soren Holdt Jensent, Software-Defined
  GPS and Galileo Receiver : A Single-Frequency
  Approach. Birkhauser: Boston, 2007, pp. 29, 83, 105.
 [2] SiGe, SE4110L-EK1 Evaluation Board User Guide.
 [3] SiGe, SE4110L Datasheet.
 [4] Wikipedia, “Global Positioning System” [online],
  available from World Wide Web:
  <http://en.wikipedia.org/wiki/Global_Positioning-
  _System>.
 [5] SiRF, “SiRFstarIII GSD3t” [online], available from
  World Wide Web: <
  http://www.sirf.com/products/gps_chip2e.html>.

				
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