Near Real-Time Carrier-Phase Multipath Mitigation in Kinematic Applications, Using a Dual-Antenna System and Effective Close Range Reflectors

L. Serrano, D. Kim, R.B. Langley

Abstract:	At UNB we have been developing multipath-mitigation procedures using single-difference multipath observables with a dual-antenna system. These observables are obtained from the higher-order range-dynamic observations coming from the antenna pseudo-random motions. To examine this very interesting system, we apply it using a motion table in a static scenario, since it is possible to understand the relationship between several factors: the satellite geometry and its effect on the multipath spectra (mainly the specular component) in one or more antennas, as the satellite moves along its trajectory; the reflector positioning and its influence on several closely spaced antennas; and other systematic errors affecting the carrier-phase observable, besides multipath. These errors have their own periodic or quasi-periodic effects, and include phase wind-up (due to the circular motion of the antennas) and antenna phase-center variation. But in practice, an applicable system has to be adapted to the requirements of any GPS carrier-phase real-time application, i.e., we should calibrate the multipath effects in (near) real-time and in the shortest elapsed time, whilst the platform continuously changes its position and orientation. Machine guidance is a good example, where in some scenarios it is important to have two rover antennas positioned on the platform providing both very accurate positions and between-antenna relative platform heading. Other examples include precise and automatic farming, intelligent transportations systems, etc. In these kinds of real-life situations, our approach to obtain (near) real-time between-antenna multipath observables, parameterize them and estimate effective reflectors is considerably more complex when compared with the testing scenario described. However, these are the applications that have a considerable interest in the industrial and scientific community. Therefore, this paper addresses mainly the studies being currently performed to assess if our multipath mitigation approach will be feasible or not when applied in these applications. This approach relates to the randomization and treatment of the ensemble of differenced-in-time, single-differenced measurements (containing the multipath to be separated) as a random stochastic process. Using a motion table or robot, it is possible to treat these measurements as such due to the decorrelation introduced by the pseudo-random motion of the antennas and the knowledge of the positions of the fixed reflectors. In a real scenario, one way to obtain this kind of decorrelation is to use the between rover-antenna relative motion (which can approximate a random distribution after a certain period of time), the changing reflectors and their physical behavior. During such a scenario, this ensemble of data can be modeled as an oscillatory random process, for which second or higher order Gauss-Markov models can provide good modeling. In this paper, we address the proper order based on a cost function. To determine the viability of our approach, we processed data from a GNSS hardware signal simulator with which it is possible to assess these issues in a multitude of known and controlled environments.
Published in:	Proceedings of the 19th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2006) September 26 - 29, 2006 Fort Worth Convention Center Fort Worth, TX
Pages:	863 - 872
Cite this article:	Serrano, L., Kim, D., Langley, R.B., "Near Real-Time Carrier-Phase Multipath Mitigation in Kinematic Applications, Using a Dual-Antenna System and Effective Close Range Reflectors," Proceedings of the 19th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2006), Fort Worth, TX, September 2006, pp. 863-872.
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