What are the main challenges and benefits of using GNSS/INS for autonomous vehicles?

1 GNSS/INS integration methods

There are different methods to integrate GNSS and INS data, depending on the level of coupling and the architecture of the system. The simplest method is loose coupling, where the GNSS and INS outputs are processed separately and then combined using a filter, such as a Kalman filter. The advantage of this method is that it is easy to implement and does not require access to the raw GNSS measurements or the INS error model. The disadvantage is that it cannot correct for the INS errors or the GNSS outages in real time. A more advanced method is tight coupling, where the raw GNSS measurements and the INS outputs are processed together using a single filter. The advantage of this method is that it can improve the accuracy and robustness of the PNT solution by exploiting the redundancy and correlation of the GNSS and INS data. The disadvantage is that it requires access to the raw GNSS measurements and the INS error model, which may not be available or compatible for some devices. A third method is ultra-tight coupling, where the GNSS and INS data are integrated at the signal level, using the INS outputs to aid the GNSS signal tracking and acquisition. The advantage of this method is that it can enhance the performance of the GNSS receiver in challenging environments, such as low signal-to-noise ratio (SNR), high dynamics, or jamming. The disadvantage is that it requires a high level of synchronization and communication between the GNSS and INS components, which may increase the complexity and cost of the system.

2 GNSS/INS challenges

Despite the potential benefits of GNSS/INS integration, there are still some challenges that need to be addressed to ensure the optimal performance of the system. One of the main challenges is the calibration and alignment of the GNSS and INS sensors, which involves determining their relative position, orientation, and timing offsets. These parameters affect the accuracy and consistency of the PNT solution and need to be estimated and updated regularly using external references or algorithms. Another challenge is the selection and configuration of the filter that fuses the GNSS and INS data, which involves choosing the appropriate model, parameters, and inputs for the system. The filter needs to account for the uncertainties and errors of the GNSS and INS data, as well as the dynamics and environment of the vehicle. The filter also needs to be adaptive and responsive to changes in the availability and quality of the GNSS and INS data, such as signal loss, degradation, or spoofing. A third challenge is the validation and verification of the GNSS/INS system, which involves testing and evaluating its performance under different scenarios and conditions. The validation and verification process needs to consider the accuracy, reliability, integrity, and availability of the PNT solution, as well as the safety and efficiency of the vehicle.

3 GNSS/INS benefits

Despite the challenges, GNSS/INS integration offers many benefits for autonomous vehicles, especially in terms of enhancing their PNT capabilities and enabling their operation in various environments. One of the main benefits is that GNSS/INS integration can improve the accuracy and precision of the PNT solution by combining the complementary strengths of GNSS and INS. GNSS provides absolute and global positioning and timing information, while INS provides relative and local motion and orientation information. By integrating these data, the system can reduce the errors and biases of each sensor and provide a more accurate and consistent PNT solution. Another benefit is that GNSS/INS integration can increase the robustness and resilience of the PNT solution by mitigating the weaknesses and vulnerabilities of GNSS and INS. GNSS is susceptible to signal interference, jamming, spoofing, and multipath effects, while INS suffers from drift and noise accumulation over time. By integrating these data, the system can detect and correct for these anomalies and provide a more reliable and trustworthy PNT solution. A third benefit is that GNSS/INS integration can expand the coverage and continuity of the PNT solution by compensating for the gaps and outages of GNSS and INS. GNSS may not be available or sufficient in some environments, such as urban canyons, tunnels, bridges, or forests, while INS may not be able to provide long-term PNT information without external references. By integrating these data, the system can maintain and update the PNT solution using the available and valid data and provide a more continuous and seamless PNT solution.

4 Here’s what else to consider

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