Effect of Inter-system Biases Estimation for Mixed GPS-BeiDou on Ambiguity Resolution

Nobuaki Kubo, Hiroko Tokura, Sam Pullen

Peer Reviewed

Abstract:	Recently, the use of multi-GNSS has become very active in the field of precise positioning. Many BeiDou satellites operated by China are available in the Asian region. If both GPS and BeiDou satellites are used for positioning, a variety of biases should be considered from different satellite systems and different transmitted frequencies. To avoid the impact of their biases, separating the double-difference for each satellite system in RTK-GNSS has become mainstream. However, to enhance the effectiveness of the increased number of satellites, we do not wish to separate the double-difference for each satellite system because each primary satellite in each satellite system is required in RTK-GNSS. In this paper, a mixed GPS + BeiDou model with inter-system biases is developed by differencing the BeiDou carrier-phase and the code-phase observations relative to those corresponding to the primary GPS satellites. The proposed mixed GPS + BeiDou RTK method was evaluated using static data and kinematic data. Inter-system bias estimation was conducted using 12 h of data from both the high-grade GNSS receiver and the low-cost GNSS receiver. The data were compared with the results using shorter periods based on practical use, and the difference was found to be small. The kinematic data was collected in normal urban areas in Tokyo using the car. The bias estimation was conducted using the first 5 min of data while the car stopped under open sky conditions. Through this kinematic test, we found that the accuracy of the receiver clock estimation was essential to improve the mixed GPS + BeiDou RTK because frequency differences between GPS and BeiDou directly affect the accuracy of bias estimation. Therefore, the kinematic test was conducted using the external chip-scale atomic clock (CSAC). The behavior of the estimated receiver clock using CSAC was very smooth and easy to estimate. By estimating the receiver clock error as accurately as possible using the least squares method, the fix rate of mixed GPS + BeiDou RTK was better than the result of normal RTK. Specifically, the fix rate (number of fixed solutions / number of total epochs) was improved by approximately 10%, as compared with normal RTK.
Published in:	Proceedings of the 2017 International Technical Meeting of The Institute of Navigation January 30 - 2, 2017 Hyatt Regency Monterey Monterey, California
Pages:	730 - 744
Cite this article:	Kubo, Nobuaki, Tokura, Hiroko, Pullen, Sam, "Effect of Inter-system Biases Estimation for Mixed GPS-BeiDou on Ambiguity Resolution," Proceedings of the 2017 International Technical Meeting of The Institute of Navigation, Monterey, California, January 2017, pp. 730-744. https://doi.org/10.33012/2017.14916
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