A Study of Linear Phase Combinations in Considering Future Civil GPS Frequencies

Swen Ericson

Abstract:	Linear combinations of GPS carrier phase measurements have been strategically used to solve precise relative po-sitioning problems. A commonly used combination of the existing signals is the wide lane, which subtracts L2 from L1. This creates a signal with a wavelength more than four times larger than L1, which helps in ambiguity resolution techniques. Depending on the desired proper-ties, other combinations can be made, but those meeting the following criteria are of most interest: integer coeffi-cients to produce integer ambiguities, reasonably large wavelength to help ambiguity fixing, low ionospheric in-fluence and limited observation noise. [1] These criteria should be kept in mind when planning new civil GPS frequencies. While there are restrictions as to which bands a new signal can occupy, there is usually a range of possibilities. Therefore, a search of frequencies can be made to optimize possible linear combinations of phase measurements while retaining other objectives for new signals. One type of phase combination that can be made is one that provides, with a reasonably large wavelength and limited noise, an integer-ambiguity ionosphere-free sig-nal. An example of how this type of combination can used for ionosphere-free positioning is shown. Another modernization opportunity discussed is the optimization of wavelength diversity to reduce the number of possible ambiguity candidates in a solution search. Wide lane combinations of sets of three and four frequencies are also evaluated for their ability to determine the ambiguity of a single-frequency phase measurement in one epoch. While the currently proposed set of three frequencies will lead to significant enhancements to GPS positioning, it found that adding a suitably placed fourth would provide greater benefit, especially in ionospheric estimation for precise long baseline solutions. With careful selection a fourth GPS frequency, instantaneous ambiguity resolu-tion and long-range precise surveying and navigation will advance to levels of capability that would not be pro-vided by the proposed set of three.
Published in:	Proceedings of the 1999 National Technical Meeting of The Institute of Navigation January 25 - 27, 1999 Catamaran Resort Hotel San Diego, CA
Pages:	677 - 686
Cite this article:	Ericson, Swen, "A Study of Linear Phase Combinations in Considering Future Civil GPS Frequencies," Proceedings of the 1999 National Technical Meeting of The Institute of Navigation, San Diego, CA, January 1999, pp. 677-686.
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