Design of airport surface movement using single-frequency GPS [electronic resource]
Keywords: Aeronautics and Astronautics.

Ground Based Augmentation Systems (GBAS), such as the U.S. Local Area Augmentation System (LAAS), augment satellite navigation systems by providing differential corrections and integrity information to aviation users within several tens of kilometers of GBAS-equipped airports. GBAS can be used for both precision approach and Differentially Corrected Positioning Service (DCPS) applications. DCPS is broadly composed of (but is not limited to) three operations. The first operation is terminal-area navigation for aircraft in the area from the precision approach region to 45 kilometers away from the GBAS Ground Facility. The second operation is en route navigation for aircraft passing over the airport that can receive and make use of the GBAS VHS Data Broadcast receiver (VDB). The third operation is airport surface movement for aircraft on airport taxiways (and thus quite close to the GBAS Ground Facility centroid). This last operation is the subject of this research. One of the residual errors that can build up for the user of a differential GPS system like GBAS is ionospheric spatial decorrelation error. This error is caused by the fact that two GPS signals are passing through different regions of the atmosphere, and the resulting ionospheric delays cannot be completely canceled out even after applying differential corrections. Under severe ionospheric storm conditions, these errors can grow large enough to pose a threat to user integrity. In addition, since an aircraft undergoing airport surface movement is on the ground, it suffers from higher multipath errors than while in flight, as additional signal reflections come from the ground, other aircraft or vehicles, and nearby buildings. In order to cover higher multipath errors in the surface movement and represent anomalous ionospheric errors, Jahn's Multipath Model for Urban and Suburban Environments [Jahn, 1996] and the CAT-I Conterminous United States (CONUS) Anomalous Ionospheric Threat Model [Pullen, 2009], respectively, are used for horizontal position errors. Because, for certain scenarios, GBAS Ground Facility geometry screening and new values of multipath errors for the suburban-optimistic environment are not sufficient by themselves, the proposed additional airborne geometry screening is performed to meet the requirements and lower the acceptable error to a beneficial level while maintaining useful availability. The results show the sensitivity of availability to the multipath model and the ionospheric threat impact model for several Maximum Acceptable Error (MAE) levels. The multipath models considered are no multipath, suburban-conservative, urban-optimistic, and urban-conservative multipath models. The 0-satellite (no ionosphere), 1-satellite, and 2-satellites impact models of ionospheric threat are studied. In conclusion, the proposed approach to GBAS airport surface movement is feasible for surveillance applications, which are used to detect and display the position of aircraft in the terminal area, with an error bound of 20 meters. Guidance applications, which are used to guide aircraft from runway to the gate or vice versa, with an error bound of 10 meters are also feasible if multipath models less extreme than urban-conservative are used.