Satellite and Receiver Phase Bias Calibration for Undifferenced Ambiguity Resolution

Simon Banville, Rock Santerre, Marc Cocard and Richard B. Langley

Abstract:	Precise point positioning (PPP), considered an alternative to differential positioning, is used in a significantly increased number of applications. Its integration into many practical areas is, however, slowed down by the long convergence time required in order to obtain cmlevel accuracy. This drawback is caused by the difficulty in fixing carrier-phase ambiguities to integers. As opposed to the differential mode, where many error sources are eliminated or greatly reduced, PPP has to properly account for all of them. Some of these error sources, such as code and phase biases, are complex to model as they tend to merge with the ambiguity parameters during the estimation process, leading to unsuccessful ambiguity resolution. This paper focuses on the receiver and satellite phase bias calibration required to recover the integer nature of carrier-phase ambiguities. A proper estimation of these biases would allow correcting the measurements and using the ambiguity resolution techniques developed for differential positioning. In this way, instantaneous cmlevel accuracy could be something conceivable even with a single GPS receiver, considering that the other error sources have been reduced to a significant level. The first step taken to achieve this objective is to clearly understand PPP’s functional model representing the code and phase measurements made by the GPS receiver. Special attention is paid to hardware delays, such as code and phase biases, which play a crucial role in the estimation process using undifferenced measurements. The impact of these quantities on some estimated parameters is described in order to have a better understanding of the concepts presented throughout this paper. In the second step, a receiver phase-bias calibration technique using a GPS signal simulator is introduced. A simulator has been used to generate errorless signals which are ideal to isolate the biases inherent to the receiver. Results show that this calibration process is complex due mainly to the correlation between the receiver clock and the ambiguity parameters. As such, between-satellite single differencing still seems to be the best way to eliminate receiver phase biases. The last part of this paper concerns satellite phase-bias calibration. To properly calibrate the satellite phase biases, the impact of code biases has to be carefully taken into consideration. For this purpose, an alternate widelane phase-bias calibration method is proposed and is shown to be coherent with PPP’s functional model.
Published in:	Proceedings of the 2008 National Technical Meeting of The Institute of Navigation January 28 - 30, 2008 The Catamaran Resort Hotel San Diego, CA
Pages:	711 - 719
Cite this article:	Banville, Simon, Santerre, Rock, Cocard, Marc, Langley, Richard B., "Satellite and Receiver Phase Bias Calibration for Undifferenced Ambiguity Resolution," Proceedings of the 2008 National Technical Meeting of The Institute of Navigation, San Diego, CA, January 2008, pp. 711-719.
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