Quasi-Tightly Coupled GNSS-INS Integration for Partial Satellite Outages
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Solution Overview
Problem
Current GNSS-aided INS systems face challenges in maintaining accuracy during partial satellite outages, as they require at least four satellites for a fully constrained position fix, and existing integration methods do not effectively manage errors when fewer satellites are available.
Innovation Solution
The quasi-tightly-coupled (QTC) integration process, which includes INS position seeding and an observable subspace constraint, allows for continued aiding and error regulation with fewer than four satellites by using INS-derived data to constrain the GNSS positioning algorithm and applying a transformation to the INS-GNSS position measurement, ensuring consistency with available satellite data.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a loosely-coupled integration is used, then the GNSS positioning algorithm can be implemented with minimal modifications, but the system cannot compute a position fix with fewer than 4 satellites and AINS errors grow without constraint
Solution Approach 1:
The system dynamically adapts its operation mode based on the number of available satellites. When 4 or more satellites are available, it operates in standard loosely-coupled mode. When fewer than 4 satellites are available, it automatically transitions to using INS position seeding to maintain continuous positioning capability, thus adapting to changing environmental conditions to ensure reliability.
Solution Approach 2:
The INS position seeding acts as an intermediary mechanism that bridges the gap between GNSS observations and position solution when satellite availability is insufficient. By seeding the GNSS positioning algorithm with INS-derived position and covariance information, the system maintains positioning continuity without requiring complete loss of GNSS functionality.
2Reliability
If a tightly-coupled integration is used, then the system can process pseudoranges and carrier phases with fewer than 4 satellites, but the GNSS positioning algorithm requires significant modifications
Solution Approach 1:
Instead of implementing the full tightly-coupled integration which processes all GNSS observables (pseudoranges and carrier phases) through the AINS Kalman filter, the patent applies a partial approach by only seeding the GNSS positioning algorithm with INS position and covariance. This partial action achieves the essential benefit of continued positioning with fewer than 4 satellites while avoiding the excessive complexity of complete tightly-coupled implementation.
3Device complexity
If standard LC integration is used during partial satellite outage, then the system structure remains simple, but AINS errors grow without constraint
Solution Approach 1:
The system implements feedback by continuously using INS position estimates to seed the GNSS positioning algorithm. This feedback loop ensures that even when satellite availability is reduced, the position solution remains constrained and accurate by leveraging the complementary strengths of both INS and GNSS systems, preventing error growth without complicating the overall system structure.
Data Source
AI summary
A quasi tightly coupled (QTC) aided INS (AINS) process has an inertial navigator system with a loosely-coupled AINS Kalman filter that constructs INS-GNSS position measurements, a GNSS position engine that computes a position fix from observables and an externally provided a priori position and position VCV matrix. An INS position seeding process in which the externally provided a priori position to the GNSS position engine is an antenna position computed from the INS position and attitude solution. An observable subspace constraint (OSC) process computes an OCS matrix that suppress the components of the GNSS position error due to a poor geometry in the GNSS position solution in the IG position measurement constructed by the AINS Kalman filter and that multiplies the OSC matrix and the IG position measurement and measurement model matrix to suppress uncorrected component of the GNSS position error in the IG position measurement and measurement model.