Airport Surface Movement - Performance Requirements, Architecture Considerations & Integrity Algorithms

Satellite Navigation has become increasingly important in the optimisation of efficiency and safety within the aviation industry. ANASTASIA (Airborne New and Advanced Satellite techniques and Technologies in A System Integrated Approach) is a European Commission project within the Sixth Framework Program, with the basic objectives to define and implement future (beyond 2010) communication and navigation avionics based on satellite services. The objectives are to be achieved by exploiting the multi-constellation and multi-frequency architectures in combination with multiple onboard sensors, to provide a worldwide gate-to-gate service. Included in the objectives is a study of the most stringent navigation system performance requirements for a surface movement functionality under zero visibility conditions. This paper reviews existing navigation system performance requirements and compares them with those derived in this paper based on operational requirements, for each airport category. The stringency of the performance requirements suggests that the code-based GBAS architecture currently under development for CAT III landings may not be able to meet all the requirements of surface movement, and that carrier-phase based techniques may be required. In order to address the very stringent integrity requirements of surface movement, this paper uses a novel carrier-phase RAIM (C-RAIM) algorithm developed at Imperial College London, based upon a multiple set separation method with a multiple failure detection and exclusion capability [1]. The C-RAIM algorithm performance is dependent upon the range measurement uncertainties. For relative or differential measurements (e.g. GNSS augmented by GBAS), uncertainties in the measurements by the reference station and the user, as well as the error decorrelation between these measurements contribute to the overall measurement uncertainty at user level. The principal sources of uncertainty are noise, multipath, the troposphere and the ionosphere, the latter being of particular concern for surface movement. In order to accurately determine the ionosphere error residuals in real-time, and hence mitigate integrity risks and optimise availability, this paper develops a ground-based monitoring architecture, which we have called Extended GBAS (E-GBAS), based upon a modified GBAS CAT III architecture. The performance of the C-RAIM algorithm is analysed, using as input the ionosphere uncertainty provided by the E-GBAS, taking into account the specificities of the airport environment. Initial results suggest that the CRAIM algorithm, in combination with the E-GBAS architecture, will be able to meet the surface movement performance requirements. A value added outcome is that when used in combination with a state-of-the-art codebased architecture, the E-GBAS monitoring architecture has the potential to meet the navigation system performance requirements for CAT III landings.