Separating Receiver Noise and Multipath Effects in Time Series of GPS Baselines Using Harmonic Functions

AliReza Amiri-Simkooei

Abstract:	In GPS applications, the parameters of interest, as baseline coordinates, are estimated using the least-squares technique. The estimators obtained by this method are unbiased and of minimum variance. The unbiasedness property however is achieved only if unmodelled effects as multipath can be avoided. And on the other hand, a realistic description of the measurement noise characteristics through the observation variance-covariance matrix is required to yield minimum variance (best) estimators. Typically, receiver noise characteristics are assessed through zero baseline measurements. On an ordinary (short) baseline, these characteristics seem to be ’overruled’ by unmodelled systematic effects as multipath. Using the least-squares spectral analysis, it is possible, in part, to remove the periodic multipath effects using harmonic functions. This contribution proposes a method to separate multipath effects and receiver induced noise in GPS baseline measurements; thereby the optimal properties of the least-squares variance component estimators are guaranteed. Such an optimal stochastic model is of direct importance to guarantee optimality of the estimators for the unknown parameters of interest, for carrier phase ambiguity resolution and for GPS data quality control. Three receiver types, from the same manufacturer but of different age, are used to demonstrate the working and results of the proposedmethod. It is shown that carrier phase noise characteristics now obtained from-short baselinemeasurements are similar to those traditionally obtained from special zero baseline measurements. The procedure outlined in this paper is generally applicable and can be used to assess and compare, in an objective manner, the performance of different receivers, even from different manufacturers.
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:	1034 - 1045
Cite this article:	Amiri-Simkooei, AliReza, "Separating Receiver Noise and Multipath Effects in Time Series of GPS Baselines Using Harmonic Functions," 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. 1034-1045.
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