Triple-frequency Ionosphere-free Phase Combinations for Ambiguity Resolution

Linear combinations of the carrier phase data which are independent of the ionospheric delays are referred to as ionosphere-free linear phase combinations. In the dual frequency case there exists only one such combination which at the same time ensures the integer estimability of the ambiguities. In the triple-frequency case there is a whole class of such linear combinations. We identify this class of linear combinations and determine their phase-only ambiguity resolution performance. The advantage of using carrier phase-only data is that ambiguity resolution will be freed from the potential presence of pseudorange multipath. We also identify an important pitfall when using ionosphere-free linear phase combinations. It is shown that not all such triple-frequency combinations permit a parametrization that retains the integer nature of the ambiguities. Results will be shown for triple-frequency Galileo as well as for modernized GPS.