Split Vertical ARAIM for Lower-Altitude Aircraft Integrity Monitoring
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Solution Overview
Problem
Current GNSS systems face challenges in providing sufficient integrity for aircraft to operate at Category II minima, especially in difficult weather conditions, due to the need for expensive ground infrastructure and limitations in existing integrity monitoring algorithms.
Innovation Solution
The implementation of an optimized split vertical protection level (VPL) technique, which alters the standard ARAIM algorithm to allocate integrity budget asymetrically between upward and downward VPL components, utilizing radar altimeter and satellite measurements to enhance navigation system integrity and availability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If expensive ground infrastructure is installed to provide sufficient integrity for Category II minima, then navigation system integrity is improved, but system cost and complexity increase
Solution Approach 1:
The system performs autonomous integrity monitoring using onboard sensors (GNSS receiver, radar altimeter, inertial measurement unit) without requiring external ground infrastructure. The integrity monitoring is self-contained within the aircraft, eliminating the need for expensive ground-based augmentation systems while maintaining Category II minima capability
Solution Approach 2:
The integrity monitoring system uses multiple sensors that serve dual purposes: the radar altimeter provides both altitude measurement and integrity monitoring data, the GNSS receiver provides both positioning and integrity information, and the inertial measurement unit contributes to both navigation and integrity assessment. This multi-functionality reduces the need for dedicated ground infrastructure
2Ease of operation
If integrity budget is allocated symmetrically to upward and downward VPL components, then calculation simplicity is maintained, but navigation system availability decreases at lower decision heights
Solution Approach 1:
The integrity budget is allocated asymmetrically between upward and downward vertical protection level components. The downward VPL component is assigned a larger portion of the integrity budget because downward position errors are more critical for safety during approach and landing operations. This asymmetric allocation allows the system to maintain Category II minima capability at lower decision heights where symmetric allocation would fail
Solution Approach 2:
The system dynamically adjusts the integrity budget allocation parameters based on flight phase and decision height. By changing the allocation ratio between upward and downward VPL components according to operational requirements, the system optimizes both availability and safety margins without requiring complex ground infrastructure
Data Source
AI summary
A method comprises computing position information from a global navigation satellite system (GNSS); computing an altitude measurement based on retrieved information from a vertical position sensor; determining a vertical protection level (VPL) associated with the position information; splitting the VPL into an upward VPL component and a downward VPL component; determining a vertical alert limit (VAL) associated with the altitude measurement; and splitting the VAL into an upward VAL component and a downward VAL component. The method optimizes an integrity budget allocation between the upward and downward VPL components. The method then recomputes the upward and downward VPL components given the optimized integrity budget allocation.