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Software Defined GPS Receiver

Software Defined GPS Receiver. By: Sam Price Advisor: Dr. In Soo Ahn. Outline of Presentation. Overview of GPS Overview of Receivers Current Projects Patents Datasheet Preliminary work Schedule of tasks. Overview of GPS. L1 Carrier wave 1575.420 MHz C/A code 1.023 MHz

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Software Defined GPS Receiver

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  1. Software Defined GPS Receiver By: Sam Price Advisor: Dr. In Soo Ahn

  2. Outline of Presentation • Overview of GPS • Overview of Receivers • Current Projects • Patents • Datasheet • Preliminary work • Schedule of tasks

  3. Overview of GPS L1 Carrier wave 1575.420 MHz C/A code 1.023 MHz Satellite Identification Navigation Message 50 .000 Hz Time of week Ephemeris (Current position) Almanac-Global data

  4. Overview of GPS Receiver Acquisition Uses C/A code to find satellites Tracking Performs phase lock loop to keep track of satellites

  5. Position Calculation 3 satellites solve for X,Y,Z Inaccurate receiver clock. 4 satellites solve for receiver time bias. Sampling frequency Plays role in error.

  6. Real time Requirements • 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.

  7. Current Projects • 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  • GPS-SDR • Uses FPGA board to supply computer with IF frequency. • Pervious Project • Locates current position once. • Takes 4 minutes.

  8. Patents

  9. GN3S Sampler V1 • 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.

  10. Preliminary work • 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.

  11. Signal Processing Overview 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) XORNav(t) = Nav(t) 0 XORNav(t) = Nav(t)

  12. Correlation results • C/A code aligned. • C/A code not aligned.

  13. Acquisition Chart

  14. Tracking Optimizations

  15. Future Program Structure

  16. Schedule of tasks

  17. References • 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>.

  18. Questions • ?

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