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Implementation of a Software-based GPS Receiver

Implementation of a Software-based GPS Receiver. Anthony J. Corbin Dr. In Soo Ahn Friday, June 6, 2014. Overview. Progress Flowcharts Acquisition Tracking Position Calculation Software Organization Changes to Project Objectives Results DLL/PLL Tracking Position Updated Schedule.

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Implementation of a Software-based GPS Receiver

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  1. Implementation of a Software-based GPS Receiver Anthony J. Corbin Dr. In Soo Ahn Friday, June 6, 2014

  2. Overview • Progress • Flowcharts • Acquisition • Tracking • Position Calculation • Software Organization • Changes to Project Objectives • Results • DLL/PLL Tracking • Position • Updated Schedule

  3. Progress • MATLAB GPS software [1] has been ported to C++ • This includes: • Coordinate conversion • Tracking loop • Acquisition algorithms • DSP design approach was abandoned due to technical issues which will be discussed later. • C++ code can accurately find a position from stored sample data.

  4. Coarse Acquisition • Coarse acquisition searches around the intermediate frequency in the range +/- 10 KHz with a step of 500 Hz • Frequency Domain Correlation

  5. Fine Acquisition • Uses the frequency estimate from Coarse Acquisition to obtain a better estimate • The overall functionality is very similar to Coarse Acquisition

  6. Tracking

  7. Delay-Locked Loop [1]

  8. Position Calculation

  9. Functional Software Diagram

  10. Changes to Project Objectives • Finding the satellite positions requires an accurate time…requiring collection of at least subframes 1-3 of the ephemeris data • The equation below shows the number of multiplications per second required to track one satellite. This does not include C/A code generation, carrier demodulation, or the overhead involved with sampling. • The DSP considered is clocked at 225 MHz which is simply not fast enough.

  11. USB GPS Dongle • USB 2.0 Interface • Simple software interface

  12. C/A Code Tracking • The graphs to the right show the code error output from the delay-locked loop. • The parameters have been selected in such a way that the loop converges very quickly.

  13. Carrier Tracking • Carrier error is shown on the right with respect. • In this example, the frequency of the carrier appears to be drifting further below the intermediate frequency. • This is an illustration of the Doppler Effect.

  14. Navigation Data • The figures to the right show resolved 50 Hz navigation data. • The top graph shows 32s of data, while the bottom graph shows 3s.

  15. Position Results 51.81 m

  16. Position Results 104.4 m

  17. Current Display • The display currently uses a console window. • A GUI could be written in any language.

  18. Speed • Currently the C++ code requires under a minute (per satellite) to read a full 36 s of satellite data. • Compare this with the Matlab code which takes 6 minutes per satellite.

  19. Intel Threading Building Blocks • Intel’s TBB is a library for creating threaded programs • Platform independent • Relatively easy to use

  20. Real-time Functionality • Taking a direct approach to implementing real-time functionality appears to be extremely difficult (possibly impossible) given current hardware limitations. • However, a possibility exists, which may feasibly yield results.

  21. Real-time Functionality

  22. Updated Schedule

  23. 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.

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