Design and Implementation of a Software-Based GPS Receiver Anthony J. Corbin Dr. In Soo Ahn Friday, June 19, 2015

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.

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

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]

Subsystem Requirements

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.

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

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 generated is based on the pseudorandom sequence generation shown on the next slide.

L1 Signal Generation [1]

Cross-Correlation  The cross-correlation characteristics of the L1 signal are what make it important.  Different L1 signals do not correlate with each other!  The figure to the right shows a graphical representation of the plane of all correlation possibilities.

Preliminary Measurements  The GPS L1 signal is attenuated to a level below the noise floor.  The graph on the right shows the result of an FFT of the data from the SE4110L device.

Equipment List

Preliminary Schedule

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:.  [5] SiRF, “SiRFstarIII GSD3t” [online], available from World Wide Web:.