Ionosphere-Free Phase Combinations for Modernized GPS

In this contribution, optimal ionosphere-free combinations for a modernized triple-frequency global positioning system ~GPS! are derived. It is shown that these ionosphere-free combinations are directly related to the model based on carrier phase observations only, in which the ionospheric delays are estimated. For this model and thus for the ionosphere-free combinations, integer ambiguity estimation is possible, in contrast to what is often read in GPS positioning literature. In this article the estimable integer ambiguities are presented and the expected success rates when trying to resolve these ambiguities are given. In addition, the baseline precision is analyzed for both the ambiguity-float and ambiguity-fixed ionosphere-free cases. DOI: 10.1061/~ASCE!0733-9453~2003!129:4~165! CE Database subject headings: Global positioning; Data processing; Frequency.