GNSS/eLoran Fusion-Based RAIM for Satellite-Deficient Environments.

Area of Science:

• Navigation Systems Engineering
• Geomatics Engineering
• Signal Processing

Background:

• Global Navigation Satellite Systems (GNSS) are crucial for positioning, navigation, and timing (PNT) but degrade in poor signal environments.
• Existing Receiver Autonomous Integrity Monitoring (RAIM) struggles with limited satellite availability and interference.
• Enhanced Loran (eLoran) offers a complementary terrestrial PNT source.

Purpose of the Study:

• To develop and evaluate a hybrid GNSS/eLoran integrity monitoring framework.
• To enhance the redundancy and fault detection capabilities of positioning systems.
• To ensure reliable PNT services in satellite-deficient or interference-prone conditions.

Main Methods:

• A simplified Receiver Autonomous Integrity Monitoring (RAIM) architecture is adapted for hybrid GNSS/eLoran data fusion.
• Weighted least-squares estimation combines GNSS and eLoran measurements.
• A global chi-square test and solution separation strategy are used for fault detection and exclusion.
• Horizontal Protection Level (HPL) calculation ensures bounded positioning error.

Main Results:

• The hybrid framework demonstrated improved redundancy and fault observability compared to GNSS-only RAIM.
• Reliable fault detection was maintained even with simulated satellite faults and eLoran disturbances.
• Positioning errors were consistently bounded by the calculated Horizontal Protection Level across all tested scenarios.

Conclusions:

• The proposed hybrid GNSS/eLoran integrity monitoring framework effectively enhances positioning reliability.
• Integrating terrestrial eLoran measurements significantly improves robustness in challenging GNSS environments.
• The method provides a viable solution for safety-critical applications requiring dependable PNT services.