Frequency-Domain Characterization of GPS Multipath for Estimation and Mitigation

Chun Yang and Alec Porter

Abstract:	GPS multipath mitigation has been treated predominantly in the time domain for most GPS receivers. This paper presents a frequency-domain approach to reduce GPS multipath errors through direct manipulation of signal, replica, and correlation spectra. This approach is particularly suitable for a frequency-domain software GPS receiver where the signal and correlation spectra are available as a by-product of the FFT-implemented correlation process. The concept of a GPS signal channel transfer function is introduced. The time-domain superposition of multipath signals (i.e., the convolution of direct signal with the multipath channel impulse response) is equivalent to the frequency-domain multiplication of the direct signal spectrum and the multipath channel transfer function. It thus transforms a nonlinear functional operation to a linear parametric operation. The latter is relatively easy to work with. As a sum of complex exponentials, multipath estimation thus becomes determination of distinct “tones” from the noisy channel transfer function. The paper investigates such methods as frequency domain least square fitting, direct implementation of IFFT (impulse response), cepstral analysis, linear prediction methods, and subspace estimation to estimate the harmonic components. Additionally, the frequency-domain modeling of multipath in terms of channel transfer function affords alternative explanation of the effects of prefiltering bandwidth on multipath estimation and mitigation. Simulation results are provided to illustrate the concept and substantiate the findings.
Published in:	Proceedings of the 18th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2005) September 13 - 16, 2005 Long Beach Convention Center Long Beach, CA
Pages:	2104 - 2118
Cite this article:	Yang, Chun, Porter, Alec, "Frequency-Domain Characterization of GPS Multipath for Estimation and Mitigation," Proceedings of the 18th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2005), Long Beach, CA, September 2005, pp. 2104-2118.
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