GBAS Testbed Development in Taiwan with A Prototype GPS/GBAS Software Receiver

He-Sheng Wang, Jimmy Huang, Szu-Kai Wang, Yuan-Chyi Chuang, Ann Kao, Yuh-Jou Tsen,Yeou- Jyh Tsai, Fan-Ren Chang and Wen-Chieh Yang

Abstract:	In this paper, we present the development of a local area differential GPS test bed of the ground-based augmentation system (GBAS) as the future airport navigation facility in the Taipei Flight Information Region (FIR) in Taiwan. The testbed is mainly a GBAS ground facility. The ground system, which is consisted of a ground station, three GBAS receivers and a VDL broadcast antenna, will generate the differential corrections and broadcast the SCAT-I correction messages as specified in the RTCA DO-217. These differential corrections are calculated on the ground station differential correction processor by collecting the in-view satellite observations and navigation data. The differential corrections are generated once per second, and are then encoded and broadcast via the VDL antenna to the airborne users. A potential GBAS ground facility deployment will be proposed in this paper. It will be shown that the whole Taipei FIR can be covered with GBAS precision guidance services with at most four ground facilities. On the other hand, we will also present an airborne GPS/GBAS prototype receiver in this paper. As mentioned above, the airborne subsystem (a GPS/GBAS receiver) will receive the correction messages from the ground subsystem. After that, it will computes appropriate protection levels to provide the required accuracy for the approach phase of flight. On the airborne side, the weighted least square method is used to calculate the position fix, while the carrier smoothing technique is incorporated in the estimation algorithm. The weighting matrix consists of the user-defined range accuracy (UDRE), which is broadcasted by the GBAS ground station in the SCAT-I message type 1. The airborne subsystem also receives the SCAT-I message type 4, which contains the airport runway information. After computing the position of the aircraft and the location of the glidepath, the airborne receiver then generates the vertical and lateral deviations to the existing navaid equipment on the aircraft (such as EFIS). In order to provide an ILS-look-alike approach and landing, the output messages of the airborne receiver are packed in an ARINC 429 format. The proposed airborne system has a software-based GNSS receiver structure. Two separated DSPs (digital-signal processors) are used to process the navigation core functions and receive the VHF data broadcast, respectively. Simulations will be done in the laboratory at CAST/ITRI. The equipments used in the experiment include an Ashtech G12 receiver, a 12-channel GPS/WAAS simulator, and a SCAT-I ground station SLS2000 jointly manufactured by Honeywell, Inc. and Pelorus. We will use the GPS simulator to emulate flight dynamics so as to perform GNSS approaches and evaluate the results. A fast integrity algorithm called EWMA(exponentially weighted moving average) filter will be incorporated in the near future. The main difference between the traditional snapshot integrity algorithm and the EWMA method is that the EWMA method uses also the old information of the residual errors, so that the fault detection time and the alert limit can be reduced.
Published in:	Proceedings of the 14th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2001) September 11 - 14, 2001 Salt Palace Convention Center Salt Lake City, UT
Pages:	1796 - 1804
Cite this article:	Wang, He-Sheng, Huang, Jimmy, Wang, Szu-Kai, Chuang, Yuan-Chyi, Kao, Ann, Tsen, Yuh-Jou, Tsai, Yeou- Jyh, Chang, Fan-Ren, Yang, Wen-Chieh, "GBAS Testbed Development in Taiwan with A Prototype GPS/GBAS Software Receiver," Proceedings of the 14th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2001), Salt Lake City, UT, September 2001, pp. 1796-1804.
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In