Multipath-Desensitized Delay Estimation with GPS Signal Channel Transfer Function Filtering

Chun Yang, Alec Porter

Abstract:	"This paper presents a frequency-domain multipathdesensitized delay estimation (MDDE) technique which is less sensitive to the detrimental effects of multipath in GPS code delay estimation than conventional code error discriminators. The technique is based on the frequencydomain estimation of the GPS signal channel transfer function with FFT/IFFT rather than the correlation function. The correlation function of most GPS codes (BPSK-type) has a chip duration of ±Tc. For correlation spacing of d chips, any multipath with a delay t < (1+d)Tc can superimpose its correlation onto the direct signalÕs correlation resulting in a distortion of the composite correlation function thus moving the zero crossing of the early-minus-late correlation type delay error discriminator away from the true timing. This multipath-induced timing error is translated into the GPS ranging errors. One way to reduce multipath errors is to increase the chipping rate fc (equivalent to 1/Tc) and to reduce the correlator spacing d. This can exclude multipath signals of relatively large delays from influencing the direct signal correlation while tolerating close-in multipath signals of relatively small delays that do not introduce large ranging errors. This explains why P(Y)-code has better multipath performance than C/A-code as well as the performance advantages of narrow correlator receivers. After presenting the multipath model in the frequency domain, the paper introduces the GPS signal channel transfer function. For BPSK-type codes, spectral filtering is required to remove excess noise dominant around mfc, m = 1. The resulting impulse response is then used for signal detection and delay estimation with interpolation. Simulation results are presented to show the functionality and performance of the approach as compared to the theoretical multipath error envelope under different SNR and with complex multipath coefficients."
Published in:	Proceedings of the 61st Annual Meeting of The Institute of Navigation (2005) June 27 - 29, 2005 Royal Sonesta Hotel Cambridge, MA
Pages:	508 - 515
Cite this article:	Yang, Chun, Porter, Alec, "Multipath-Desensitized Delay Estimation with GPS Signal Channel Transfer Function Filtering," Proceedings of the 61st Annual Meeting of The Institute of Navigation (2005), Cambridge, MA, June 2005, pp. 508-515.
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