An Advanced Multipath Model for DGPS Reference Site Analysis

Joseph M. Kelly, J. Curtis Cohenour, Michael F. DiBenedetto and Dave Lamb

Abstract:	A three-dimensional computer model of GPS multipath interference is currently under development by the Ohio University Avionics Engineering Center. Funded by the FAA, this work is intended to aid in site analysis, multipath threat assessment, and siting criteria development for the GPS Local Area Augmentation System. The FAA William J. Hughes Technical Center is responsible for overseeing this effort and for providing field data for model validation. This paper contains a comparison between model predictions and preliminary field data for several contrived multipath scenarios, and aims to verify the feasibility of the approach taken to produce a high-fidelity model of the multipath phenomenon. Analysis will focus on predictable, repeatable, and deterministic instances of multipath, and will include cases of large scattering objects, small scattering objects, direct signal blockage, and polarization effects. Field data include cases designed to validate initial two-dimensional assumptions and modeling techniques, as well as data collected to aid in the development of a more complex three-dimensional model. Current capabilities of the three-dimensional model to date include consideration of: signal scattering from surfaces, edges, corners, curved surfaces, and wires; polarization of the propagating electromagnetic fields; gain, phase and group delay characteristics of the reception antenna; time-dependent feedback processes in the GPS processing equipment; and signal distortion in the receiver due to bandwidth, thermal noise, and C/A code properties. Multipath is isolated from field data by applying code-minus-carrier differencing, and code/carrier tracking loops in the model allow comparison with equivalent data. Further, time-series outputs of the model are expected to directly correspond with collected data, as satellite almanac data are used to generate inputs to the model for the specific period of each data collection, and processing rates in the model are designed to match those typical of commercial hardware.
Published in:	Proceedings of the 60th Annual Meeting of The Institute of Navigation (2004) June 7 - 9, 2004 Dayton Marriott Hotel Dayton, OH
Pages:	315 - 327
Cite this article:	Kelly, Joseph M., Cohenour, J. Curtis, DiBenedetto, Michael F., Lamb, Dave, "An Advanced Multipath Model for DGPS Reference Site Analysis," Proceedings of the 60th Annual Meeting of The Institute of Navigation (2004), Dayton, OH, June 2004, pp. 315-327.
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