. Global Positioning System
For more GPS information: https://wendahere.github.io/GS5/GPS/ https://wendahere.github.io/GS5/GPS/
1. Introduction
This section builds upon the previously developed GPS subsystem by evaluating heading accuracy performance and baseline requirements for high-precision operation.
2. System Overview
A dual-antenna GNSS configuration was implemented to enable direct heading computation using relative positioning (UBX NAV-RELPOSNED). Detailed system architecture is provided in the Interim Report. Code is under appendix N.
3. Heading Accuracy Principle
The heading accuracy of a dual-antenna GNSS system is governed by the relationship:
σθ ≈ σb / L
Where:
- σθ = heading error (radians)
- σb = baseline error (meters)
- L = antenna separation (baseline length in meters)
This shows that heading accuracy improves inversely with increasing baseline length.
4. Baseline Requirement for 0.1° Accuracy
To achieve a target heading accuracy of:
0.1° = 0.001745 radians
Assuming a realistic baseline error of:
σb ≈ 0.01 m (10 mm)
The required baseline is:
L = 0.01 / 0.001745 ≈ 5.7 meters
Conclusion
To reliably achieve 0.1° heading accuracy, a baseline of approximately 5.7 meters is required under typical operating conditions.
This accounts for real-world factors such as:
- Multipath effects
- Antenna phase center variation
- Environmental interference
Shorter baselines (e.g., ~1 m) can achieve sub-degree accuracy (~0.2–0.3°), but are insufficient for consistent 0.1° performance.
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5. Experimental Observations
From system testing:
- Achieved heading accuracy: ~0.28°
- Satellites used: ~28 satellites
- Fix type: 3D GNSS fix
Testing of GPS with baselength of 5.33m
Experimental results showed that with a baseline length of 5.33 m, the dual-antenna GNSS system achieved a heading accuracy of ±0.10°. This agrees closely with the theoretical estimate that a baseline of about 5.7 m is required to reliably achieve 0.1° heading accuracy under conservative real-world conditions.
6. Satellite Monitoring Implementation
Building upon the GPS parsing framework developed in the Interim Report, additional functionality was implemented to display all satellites in view and identify those actively used in the navigation solution.
This enhancement provides improved visibility into satellite geometry and signal quality, enabling better system diagnostics and validation.
Outcome
The implemented code allows real-time monitoring of satellites used in the solution, supporting analysis of system performance and accuracy.
7. Key Factors Affecting Accuracy
The following factors were identified as critical in achieving high heading accuracy:
- Baseline Length (dominant factor)
- Multipath Interference
- Antenna Placement and Symmetry
8. Recommendations
To achieve and maintain 0.1° heading accuracy:
- Increase antenna baseline to ~5.7 m
- Ensure antennas are:
- Mounted symmetrically
- Away from metal structures (>20–30 cm clearance)
- Maintain clear sky visibility
- Ensure carrier-phase solution remains FIXED
- Use consistent and stable mounting platforms
9. Conclusion
The analysis shows that achieving 0.1° heading accuracy requires a baseline of approximately 5.7 m under conservative conditions. Experimental validation with a 5.33 m baseline achieved ±0.10° accuracy, confirming the theoretical estimation.
In addition, the implemented satellite monitoring functionality enhances system observability and supports performance optimisation.
10. Future Work
Future work will focus on reducing the required antenna baseline while maintaining high heading accuracy. One key improvement is the adoption of a higher precision GNSS antenna, which offers improved phase centre stability and reduced measurement noise. By lowering the effective baseline error, it becomes possible to achieve the same heading accuracy with a shorter antenna separation.
This would allow for a more compact system design while maintaining or improving performance, making the solution more practical for integration into space-constrained platforms.
To avoid duplication, detailed descriptions of the GPS subsystem design, specifications, and implementation are not repeated here and can be found in the Interim Report: