Novel Satellite Fault Isolation Method for Real-Time Advanced RAIM Algorithms

Kurzfassung

An increased number of Global Navigation Satellite System (GNSS) satellites, broadcasting at multiple civilian frequencies, are expected to become operational over the next decade. Consequently, each user will be able to independently conduct an integrity check for their estimated position. This research seeks to enhance the Advanced Receiver Autonomous Integrity Monitoring (ARAIM), described in [Ene 2009], as an alternate way to bring airplanes within 200 ft (60 m) of the ground even in poor visibility conditions, and at terrain-constrained airports. In traditional aviation, ground equipment plays a major role in providing assistance to aircraft for maintaining the desired trajectory during both terminal and en-route phases of flight. However, ground navigational aids owned by the national aviation administrations involve large costs which scale with the total number of airports and the overall air traffic capacity. These operational costs can be reduced by equipping airplanes with GNSS-enabled instrumentation. The integrity requirement of having at most one failure to bound the user position errors over 10^-7 approaches is seen here as the most stringent operational constraint. If the ARAIM algorithm includes an existing fault in the integrity calculation, for which a significantly lower prior probability is assumed, the risk of Hazardously Misleading Information (HMI) being passed onto the aviation user may become higher than the value stated in the integrity requirement. Previously developed fault detection methods for ARAIM in [Ene at al 2007] were validated for removing single faults from each snapshot measurement, but the riskiest conditions may actually ensue from developing multiple-satellite faults. The current paper proposes additional detection criteria for isolating potentially faulty satellites, whose range measurements will then be excluded from the position solution for a longer term, until the health of their signals is reevaluated. Then, a procedure is proposed for the reinclusion of a previously removed ranging source, based either on an autonomous health check or on trusted new external information (e.g. an ISM update). Finally, the proposed fault isolation and reinclusion methods will be implemented within the Multiple Hypothesis Solution Separation (MHSS) ARAIM algorithm framework and validated by running tests under different faulted and fault-free scenarios. The purpose of this work is to propose an enhancement to the ARAIM algorithm, which will help further protect the user against single and multiple potential faults that could invalidate a static set of algorithmic assumptions. This technique will help increase the potential latency period of an external Integrity Support Message (ISM), effectively lowering the constraints on the ground monitoring network and helping reduce its required setup and maintenance costs. Computer simulations and real-time measurements will be used to demonstrate the ability of the new method to increase the robustness of ARAIM to satellite fault latency, while maintaining the previously demonstrated levels of performance, corresponding to the ICAO requirements for LPV-200 approaches.