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Design and Implementation of a Software-Based GPS Receiver Anthony J. Corbin Dr. In Soo Ahn Friday, June 19, 2015
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Project Summary Software-Based Solution Advantages Size Cost Portability Implementation Sampling System Downconverter A/D Converter DSP System Simulates a microcontroller
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Patents The table below lists relevant patents. Most of the patents are recent. Notably, two of the patents were granted to Denso and Toyota.
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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.
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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
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High-Level Block Diagram
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SE4110 Functions LNA Downconverter A/D Converter Output Reference Clock Sign Bit Magnitude Bit
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DSP Kit 225 MHz 2 MCBSPs Multi-Channel Buffered Serial Ports 16 Megabytes of RAM
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Software Processing [1]
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Subsystem Requirements
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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.
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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.
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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
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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.
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L1 Signal Generation [1]
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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.
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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.
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Equipment List
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Preliminary Schedule
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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:.
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