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Three’s the Charm: Triple-Frequency Combinations in Future GNSS

by Dr. Andrew Simsky,
Septentrio, Belgium
With the advent of multi-frequency global navigation satellite systems, triple-frequency combinations of measurements shall become available that do not include information on receiver or satellite positions, velocities and clock biases (geometry-free), and no atmospheric delays as well (iono-free). These will offer important applications in future GNSS, in particular in multipath analysis and multi-frequency ambiguity resolution algorithms.

Geometry-free combinations of measurements from the same satellite, such as (Φ1 − Φ2) or (P1P2), are used in today’s two-frequency GNSS to estimate variations of inter-frequency ionosphere delays. These combinations also contain information on multipath, which cannot be separated from ionosphere delays if only two frequencies are used.

If the measurements on a third frequency are available, these dual-frequency geometry-free combinations can be combined together to form triple-frequency geometry-free/iono-free combinations, which contain the superposition of multipath and tracking errors for the three frequencies, while ionosphere delays are canceled out.

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