GNSS Heading Determination with GRAFS Error Bounds
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Solution Overview
Problem
Current heading angle estimation methods for vehicles, such as aircraft, face challenges in providing sufficient accuracy and integrity for HUD approach guidance due to the high cost of inertial reference systems and the inaccuracy of magnetically referenced heading measurements, which are prone to magnetic field disturbances and drift issues.
Innovation Solution
A method and system utilizing Geometry Redundant Almost Fixed Solutions (GRAFS) or Geometry Extra Redundant Almost Fixed Solutions (GERAFS) to determine pitch or heading angles by receiving satellite signals on multiple antennas, enhancing integrity through vector determination and high confidence error bounds, allowing for accurate heading or pitch angle computation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If inertial reference systems (IRS) or gyrocompassing AHRS are used to provide accurate heading angle estimates, then heading accuracy and integrity are improved, but system cost increases significantly
Solution Approach 1:
The patent replaces mechanical inertial reference systems with a GNSS-based heading determination system that uses satellite signals and geometric redundancy algorithms (GRAFS/GERAFS) to compute heading angles, eliminating the need for expensive mechanical gyroscopes and accelerometers while maintaining high accuracy through mathematical processing of satellite position data
Solution Approach 2:
The patent creates a virtual model of the vehicle's orientation by computing baseline vectors from GNSS antenna positions and using these to derive heading angles, effectively copying the functionality of inertial systems through software-based geometric calculations rather than physical sensing
2Device complexity
If magnetically referenced heading measurement is used to reduce cost, then system cost decreases, but heading accuracy deteriorates due to magnetic field disturbances and drift
Solution Approach 1:
The patent replaces magnetic field-based heading measurement with a GNSS geometric calculation system that determines heading from satellite-derived antenna positions, eliminating susceptibility to magnetic disturbances from aircraft equipment or ferrous runway elements while maintaining low system cost
Solution Approach 2:
The patent introduces GNSS satellite signals as an intermediary reference frame to determine vehicle heading, using the known positions of satellites and the relative positions of antennas to compute baseline vectors that define the vehicle's orientation without relying on magnetic field measurements
3Reliability
If Directional Gyro (DG) AHRS is used as a backup when magnetic field measurement is inaccurate, then system reliability improves, but heading accuracy degrades over time due to DG drift rate
Solution Approach 1:
The patent replaces directional gyro mechanisms with a GNSS-based heading calculation system that continuously determines orientation from satellite positions, eliminating the time-dependent drift characteristic of mechanical gyroscopes while providing continuous, drift-free heading information
Solution Approach 2:
The patent implements a feedback mechanism where the GNSS receiver continuously receives satellite signals, updates antenna position calculations, and recomputes baseline vectors and heading angles in real-time, providing continuous correction and maintaining accuracy without the cumulative drift inherent in inertial integration systems
Data Source
AI summary
Systems and methods for use in navigating aircraft are provided. The systems can use Geometry Redundant Almost Fixed Solutions (GRAFS) or Geometry Extra Redundant Almost Fixed Solutions (GERAFS) to compute high confidence error bounds for a heading angle estimate or pitch angle derived using signals received on at least two antennas.