Long Distance Kinematic Carrier-Phase Ambiguity Resolution Using a Simulated Reference Receiver Network

J. Raquet and G. Lachapelle

Abstract:	In order to perform the most precise relative positioning using GPS, it is necessary to determine the correct carrier-phase integer ambiguities. Unfortunately, this process be-comes increasingly difficult as the distance between the mobile and reference GPS receivers increases, due to the decorrelation of some of the GPS errors with distance. This results in a practical limit on the distance over which carrier-phase ambiguity resolution can be performed. This is especially limiting in the case of single frequency carrier-phase ambiguity resolution, due to the short wavelength of the phase measurement, relative to dual frequency (wide-lane) ambiguity resolution. An algorithm has been developed whereby a network of reference receivers is used to significantly increase the dis-tance over which kinematic single-frequency carrier-phase ambiguity resolution can be performed without sacrificing accuracy or increasing the time to resolve the ambiguities. In previous work by the first author, this NetAdjust method has been applied to both the single and dual frequency (widelane) cases for a network obtained at Holloman Air Force Base, resulting in substantial reductions in the time to reduce the ambiguities. The NetAdjust method is based upon a least-squares condition adjustment of the measure-ments from the network of reference receivers, and the cor-rections are parameterized by the mobile receiver position, so that they can be used by any number of receivers at un-specified locations within the reference receiver network. Also, information from the reference receiver network is “encapsulated” into the measurements from a single refer-ence receiver, so standard ambiguity resolution techniques can be used between that reference receiver and a mobile receiver. This paper describes a GPS measurement simulator, called NetSim, which is capable of generating simulated mea-surement data for a network of fixed and mobile GPS re-ceivers. NetSim models multipath, measurement noise, ionospheric, tropospheric, and satellite position errors. It is validated by comparing various aspects of the data be-tween a real network and a simulation of that network. In order to test the NetAdjust concept, NetSim was used to simulate eight different reference receiver networks of varying size. All processing is performed using single fre-quency (L1) measurements in kinematic mode. A large number of test cases are used in order to obtain statistically significant results showing the time to resolve the ambigui-ties (and the correctness of the ambiguities) as a function of the distance to the reference station. These results clearly show that the ability to resolve the integer ambiguities is significantly extended by using the reference receiver net-works.
Published in:	Proceedings of the 10th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1997) September 16 - 19, 1997 Kansas City, MO
Pages:	1747 - 1756
Cite this article:	Raquet, J., Lachapelle, G., "Long Distance Kinematic Carrier-Phase Ambiguity Resolution Using a Simulated Reference Receiver Network," Proceedings of the 10th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1997), Kansas City, MO, September 1997, pp. 1747-1756.
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