Array-Aided Multifrequency GNSS Ionospheric Sensing: Estimability and Precision Analysis

The dual-frequency Global Positioning System has proven to be an effective means of measuring the Earth's ionosphere and its total electron content (TEC). With the advent of multifrequency signals from more Global Navigation Satellite Systems (GNSSs), the opportunity arises to construct many more ionosphere-sensing combinations of GNSS data. With such diversity, various estimable ionospheric delays with differing interpretations (and of different precision) can be formed. How such estimable ionospheric delays should be interpreted, and the extent to which they contribute to the precision with which the unbiased TEC can be estimated, are the topics of this paper. Based on multifrequency GNSS code-only, phase-only, and phase-and-code data, we derive the closed-form solutions of different types of ionospheric observables that each can serve as input of an externally provided ionospheric model for TEC determination. Within such a general least-squares framework, we generalize the widely used phase-to-code levelling technique to its multifrequency version. We also show that only certain specific linear combinations of the observables contribute to the TEC solutions. As a further improvement of the multifrequency GNSS-derived TEC solution, we propose and study the usage of an array of GNSS antennas. Analytical solutions, supported by numerical examples, of this array-based concept are presented, together with a discussion on its relevance for TEC determination. This concerns the roles of time averaging and time differencing, of integer ambiguity resolution, and of the number of frequencies and number of array antennas in determining TEC

Galileo IOV RTK positioning: standalone and combined with GPS

Results are presented of real time kinematic (RTK) positioning based on carrier phase and code (pseudorange) observations of the four Galileo In-Orbit Validation (IOV) satellites, as they were in orbit and transmitting navigation data at the time of writing this article (2013). These Galileo data were collected by multi-GNSS receivers operated by Curtin University and as such this article is one of the first presenting results of short baseline ambiguity resolution and positioning based on Galileo IOV observations. The results demonstrate that integer ambiguity resolution based on the four IOV satellites needs fewer than three minutes when at least observables from three frequencies are used. Combined with data of four GPS satellites even instantaneous (single epoch) ambiguity resolution is demonstrated, using only two frequencies per constellation (i.e. E1+E5a & L1+L2). We also show that at locations with obstructed satellite visibility, such that positioning based on either GPS-only or Galileo-only becomes impossible or only in a very inaccurate way, combined Galileo&GPS positioning is feasible, within 10 min if one frequency of each constellation is used and only 2 min time-to-fix the ambiguities based on observations of two frequencies of each constellation. It is furthermore demonstrated that this results in positions with centimetre level accuracy in the horizontal plane and sub-decimetre accuracy in the vertical direction