GPS Block IIF Research Articles

Low-Noise Linear Combinations of Triple-Frequency Carrier Phase Measurements

: With the introduction of a third frequency on GPS Block IIF satellites and the implementation of Galileo, there will be three freely available carrier phase measurements transmitted from each system. This article provides the mathematical equations needed to understand the effect of linear combinations of GNSS data. The article focuses on short baselines where the effect of the ionosphere and troposphere are negligible and the dominant error sources are thermal noise and multipath. Assuming base ambiguities can be reliably resolved to integer values, a set of combination coefficients is established that can provide a combined signal with the absolute minimum of noise. It is shown that the third frequency will enable linear combinations that reduce the effect of the noise and multipath marginally better than the currently available dual frequency systems: 54 percent for GPS and 53 percent for Galileo, as compared to 48 and 46 percent, respectively, using two frequencies.