Doppler Aided Navigation Voting System for GPS Loss
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Solution Overview
Problem
Conventional aircraft navigation systems face challenges in maintaining accurate navigation performance after GPS signal loss due to erroneous GPS receiver failures and uncorrected inertial system drift, which can compromise safety within tight Required Navigation Performance (RNP) limits.
Innovation Solution
A method and system utilizing data from multiple absolute navigation systems and a relative navigation system to generate high-integrity corrections, compare outputs, and isolate erroneous data, thereby providing accurate and reliable navigation even after GPS loss, using Doppler measurements from weather radar to correct inertial system errors and reduce drift.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional aircraft rely on GPS and INS for navigation, then navigation performance can be maintained during normal operation, but navigation accuracy deteriorates after GPS signal loss due to INS drift
Solution Approach 1:
The system continuously compares GPS position data with INS position data and uses the differences (drift) to generate correction signals that feed back to the INS. This feedback mechanism allows the INS to be corrected periodically, maintaining navigation accuracy over time even during GPS signal loss.
Solution Approach 2:
The system performs preliminary actions by continuously monitoring and comparing GPS and INS data during normal operation, preparing correction information in advance. When GPS signal is lost, the system has already been tracking the drift characteristics and can immediately apply corrections based on pre-established patterns and relationships between the two systems.
2Reliability
If redundant navigation sources are added to handle GPS failure, then navigation reliability improves, but system cost and weight increase
Solution Approach 1:
The patent merges the GPS and INS systems into a unified navigation architecture where both systems work together through data fusion. Instead of adding completely separate redundant systems, the invention combines GPS and INS to create a complementary system that leverages the strengths of both: GPS provides absolute position reference while INS provides continuous relative navigation, reducing the need for additional separate redundant systems.
Solution Approach 2:
The navigation system is designed with multi-functionality where the same hardware components serve multiple purposes. The GPS receiver not only provides position data during normal operation but also serves as a reference for calibrating INS drift characteristics. The INS serves both as the primary navigation system during GPS availability and as the backup system during GPS failure, eliminating the need for separate dedicated backup hardware.
3Device complexity
If FMS calculates only position offset in IRS solution, then system complexity is reduced, but navigation accuracy deteriorates due to uncorrected sensor error drift
Solution Approach 1:
The system implements feedback by continuously monitoring the relationship between GPS and INS outputs and using this information to dynamically adjust and correct INS sensor error parameters. This allows the system to maintain navigation accuracy without requiring overly complex processing, as the corrections are applied through straightforward parameter updates in the navigation solution.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances navigation accuracy and integrity by quickly identifying and correcting errors, extending the time aircraft can maintain RNP limits after GPS loss, ensuring safer operations within tight navigation constraints.
Implementation Method 1
A doppler measurement system provides ground speed and drift angle parameters to the integration function by analyzing doppler shifts in weather radar returns
Data Source
AI summary
A position determining voting system that uses Doppler information from an on-board weather radar to improve the system's accuracy and/or fault tolerance includes a comparison function and an error integration function. The comparison function is used to monitor the independent position sources for correct operation, comparing and identifying a position source that should not be used based on its relative error compared with the other position sources and their characteristics. The integration function provides corrections to relative position sources by integrating the data from multiple absolute position sources when they are mutually consistent.