Ambiguity fixing on geometry free like model using modernized GNSS signals

Ambiguity fixing on the geometry free combination presents some desirable characteristics. In particular, it does not require precise ephemeris, modelling of station displacement motion or tropospheric modelling or estimation. For such reasons, it can be particularly interesting in the case where such data and models are not available or if simpler processing is wanted. Such fixing procedure has been studied in the past for dual-frequency and triple frequency cases. Unfortunately, especially in the two frequency case, this procedure is not practical due to the long observation period needed to reliable fix a correct integer set. In this contribution, we review the fixing performances of the “geometry free” model using an undifferenced uncombined approach. Furthermore, we present the case to four and five frequency cases using Galileo and Beidou observations showing that reliable fixing in a reduced time span is possible. All analyses presented are performed using real GNSS data from the IGS permanent network. Finally, some possible applications are presented with a focus on ionospheric studies.