Using Optimal GNSS Multi-Frequency Carrier Phase Combinations for Precise Kinematic Positioning

Robert S. Radovanovic and Naser El-Sheimy

Abstract:	Traditional combinations of dual-frequency GPS carrier phase data have focused on three combinations, namely the widelane (WL), the narrowlane (NL), and the ionospheric-free (IF) combination. All of these combinations suffer from limitations, which affect the overall accuracy of precise positioning. For example, the ambiguities resolved by using the IF combination are not integer. Although resolving ambiguities using the WL combination is easier than resolving ambiguities of the component frequencies, the resulting positioning accuracy is degraded somewhat from the inherent amplification of the noise. Furthermore, previous studies of phase combinations have regarded errors on both frequencies as independent. In reality, errors such as tropospheric and ionospheric delays are correlated between frequencies. Thus, combinations of phase measurements may actually have reduced error magnitudes than the original measurements. Previous work by the authors has established a procedure for determining the optimal linear combination of dualfrequency measurements observed at receivers in a reference network. This optimal combination minimizes the ionospheric, tropospheric, and multipath variances in terms of distance, resulting in a very high accuracy pseudo-observable. A case study using a high static platform shows that the optimal combination results in positioning accuracies equal to that of using both frequencies simultaneously, and greatly outperforms both the L1-only and widelane cases. In addition, the performance of the optimal combination is very insensitive to the stochastic model used, which is of great use when such information is unavailable.
Published in:	Proceedings of the 58th Annual Meeting of The Institute of Navigation and CIGTF 21st Guidance Test Symposium (2002) June 24 - 26, 2002 Hyatt Regency Hotel Albuquerque, NM
Pages:	223 - 230
Cite this article:	Radovanovic, Robert S., El-Sheimy, Naser, "Using Optimal GNSS Multi-Frequency Carrier Phase Combinations for Precise Kinematic Positioning," Proceedings of the 58th Annual Meeting of The Institute of Navigation and CIGTF 21st Guidance Test Symposium (2002), Albuquerque, NM, June 2002, pp. 223-230.
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