Advances in Time and Frequency Transfer From Dual-Frequency GPS Pseudorange and Carrier-Phase Observations
NATURAL RESOURCES CANADA OTTAWA (ONTARIO)
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Although carrier-phase observations are thought to drive the accuracy of time and frequency transfer accuracy obtainable using geodetic GPS receivers, there has been evidence of how colored noise on the pseudorange observations reduces the effectiveness of the technique. We present a new parameterization of the GPS pseudorange and carrier-phase observations, called the decoupled-clock model, where a pseudorange bias is estimated for each clock in the system as a white noise parameter. The new parameterization separates the pseudorange observation colored noise from the carrier-phase parameters ambiguities and clock, and also isolates the ambiguities as integer-valued parameters. While ambiguous, the carrier-phase clock estimates yield continuous frequency estimates at carrier-phase precision over carrier-phase continuous periods. The obtained frequencies are consistent with those implied by the International GNSS Service Rapid clock products without solution-boundary discontinuities. The supporting rationale for the decoupled-clock model is presented from recently published literature and actual processing examples. The carrier-phase clock solutions are compared to the IGS Rapid solutions and common clock parameterization. Combination methods are considered, including the re-introduction of observed pseudoranges through functions of the estimated pseudorange biases, with the goal of bridging losses of lock on the constellations, and removal of the ambiguity in the carrier-phase clocks to yield time transfer capability.
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