FPGA Implementation of a Vector Tracking GPS Receiver using Model-Based Tools

W.L. Edwards, M. Lashley, D.M. Bevly

Abstract:	This paper seeks to introduce the reader to field-programmable gate arrays (FPGAs), vector tracking GNSS algorithms, and to discuss the implementation details of a real-time vector tracking platform on an FPGA. In the navigation community, researchers have utilized the FPGA as a realtime platform for the implementation of GPS receiver algorithms [1–3]. Researchers have also separately analyzed the efficacy of vector tracking algorithms [4–7]. Real-time vector tracking systems have been previously designed, but there are no documented attempts of achieving real-time performance using an FPGA. A traditional receiver architecture uses scalar tracking loops that operate independently in order to estimate the parameters of received satellite signals. In a vector based architecture, these scalar tracking loops are replaced by an extended Kalman filter (EKF) which tracks received signals and estimates the receiver’s position, velocity, and time states simultaneously. Some of the advantages of using vector tracking algorithms include increased interference and jamming immunity and the ability to function in very low signal to noise ratios. These advantages come, however, at a significant increase in computational cost and algorithm complexity, which poses an obstacle for a realtime vector tracking solution. An FPGA contains many inherent qualities that make it an ideal platform for achieving this real-time performance. It offers the possibility of high parallelism, speed comparable to an ASIC, a large number of input/output (I/O), reprogrammability, and a great deal of design flexibility. Recently, FPGA vendors have recognized that many of their clients use FPGAs to perform digital signal processing (DSP) and have therefore created software suites especially suited for DSP applications. These model-based tools are part of the integral framework for implementing the vector tracking algorithms at a significantly reduced development time. This paper discusses an actual vector tracking system that is currently in development using these model-based DSP tools where some of the methods in which the difficulties of vector tracking have been mitigated.
Published in:	Proceedings of the 22nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2009) September 22 - 25, 2009 Savannah International Convention Center Savannah, GA
Pages:	273 - 280
Cite this article:	Edwards, W.L., Lashley, M., Bevly, D.M., "FPGA Implementation of a Vector Tracking GPS Receiver using Model-Based Tools," Proceedings of the 22nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2009), Savannah, GA, September 2009, pp. 273-280.
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