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Session D3: GNSS Augmentation and Robustness for Autonomous Navigation

A Dual-frequency Dual-constellation Ground Based Augmentation System Prototype with GPS L5 and BDS B2a
Yi-Ting Sung, Shuo-Ju Yeh, and Shau-Shiun Jan, National Cheng Kung University
Alternate Number 3

The new modernized signals of the different constellations have been released for a period of time, such as GPS L5 and BDS B2a. They are also starting to be used in many commercial products. The objective of this paper is to analyze the performances of the dual-frequency dual-constellation ground based augmentation system (GBAS) with the addition of the new signals in the nominal condition and the anomalous ionosphere condition. A prototype of the dual-frequency dual-constellation GBAS has been developed to reduce the impacts of the ionosphere and increase the number of the satellites in view. In the previous work [1], we used the data collected at the Kaohsiung international airport (ICAO code: RCKH) in Taiwan to analyze the performance of the dual-frequency dual-constellation GBAS prototype with GPS L1/L2 and BDS B1I/B2I in the nominal condition by implementing the divergence-free smoothing method and the ionosphere-free smoothing method. The results showed that the availabilities of the dual-frequency dual-constellation GBAS with these two smoothing methods were over 99% under the nominal condition.
Since the characteristics of the new signals are different from those of the original signals, evaluating the modernized signals’ performance is the necessary work before we use them in the current prototype of the dual frequency dual constellation GBAS algorithm. The protection level is an indicator to show the integrity of the current estimated position solutions. The calculation of the protection level contains the uncertainties of the different residual errors which are be modeled, and the protection level should bound these residual errors. Among them, the residual error caused by multipath and noise might be different due to the characteristics of each signal. In order to make those models also applicable to new signals, the parameters in these models must be modified. The levels of noise and multipath are calculated by unsmoothed measurements with both of the new signals and the original ones and are compared to each other.
The use of two frequencies helps decrease the ionosphere effect. Besides, an anomalous ionosphere condition can also be detected by the ionosphere monitor in the dual-frequency dual-constellation GBAS prototype. However, the anomalous ionosphere condition is unpredictable. The worst case for the users is that either the users or the reference stations are suffered from the ionosphere storm. In this condition, the correction information provided from the reference stations may cause the position errors. In order to analyze the performance of the dual-frequency dual-constellation GBAS under the worst condition, we will simulate an ionosphere threat model based on the ionosphere storms happened before.
A field test with the new modernized signals of GPS and BDS would be hold near the Taichung international airport (ICAO code: RCMQ) to evaluate the performance of dual-frequency dual-constellation GBAS prototype with the requirements of GBAS approach service type (GAST) F defined in DO-253. The results of the GBAS prototype with the modernized signals including GPS L5 and BDS B2a will be presented in this paper.



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