Multiple Carrier Ambiguity Resolution and Performance Benefits for RTK and PPP Positioning Services in Regional Areas

Yanming Feng, Chris Rizos, and Matt Higgings

Abstract:	Based on original code and phase measurements to three or more ranging signals offered by future GNSS systems, this paper outlines geometry-free and geometry-based ambiguity resolution (AR) strategies for DD phase measurements and introduces the algorithms that improve estimation of zero-differenced (ZD) phase biases using a network of GNSS reference stations. Given three L-band frequencies, AR strategies can generally identify two best Extra-widelane (EWL: ă.293cm, in this context) or Widelane (WL: 75cm .ă<293cm) virtual signals to allow for more reliable ambiguity resolution, thus supporting decimetre RTK positioning over baselines of hundreds of kilometres in length. Analysis shows that the success rates for these selected virtual signals, having minimal or near minimal ionospheric effects and low noise levels, can be easily over 90% with measurements from a signal epoch. The third virtual signal has to be a choice of Medium-lane (ML:19cm.ă<75cm) or Narrow-lane (NL: 10cm .ă<19cm) signals, whose integer ambiguity should be performed with refined widelane measurements, to support centimetre RTK positioning over distances of up to a hundred kilometres or so. When the doubledifferenced (DD) integer ambiguities between multiple stations are resolved and fixed, constraints can be imposed to ZD measurements from all the stations to improve the ZD phase bias of each receiver over a short span of observations. Precise ZD measurements are fundamental to enhanced Precise Point Positioning. Numerical experiments using 24-hour dual-frequency GPS data from four US CORS stations, with spacing 21, 56 and 74km, were performed in order to demonstrate the performance benefits of some of the key algorithms proposed in this paper. Results confirm that the AR with the ionosphere-reduced NL signals, instead of the original L1 and L2 signals, performs better over longer baselines. For instance, the AR success rate for the 74km data set is improved from 88% to 93%. Introducing DD constraints between four stations and eight satellites, the phase-bias estimates of ZD measurements are improved by a factor of 1.6, demonstrating the performance potential of the methods for precise point positioning using a short time span of observations.
Published in:	Proceedings of the 20th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2007) September 25 - 28, 2007 Fort Worth Convention Center Fort Worth, TX
Pages:	668 - 678
Cite this article:	Feng, Yanming, Rizos, Chris, Higgings, Matt, "Multiple Carrier Ambiguity Resolution and Performance Benefits for RTK and PPP Positioning Services in Regional Areas," Proceedings of the 20th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2007), Fort Worth, TX, September 2007, pp. 668-678.
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