# VQF-Based Decoupled Navigation Architecture for High-Curvature Maneuvering of Underwater Vehicles

## TL;DR

This paper introduces a new navigation system for underwater vehicles that improves accuracy during sharp turns by separating attitude and position calculations.

## Contribution

A decoupled navigation architecture using VQF is proposed to reduce position divergence in high-curvature maneuvers.

## Key findings

- The decoupled architecture significantly improves positioning accuracy in high-curvature scenarios.
- The proposed method suppresses extreme errors by compensating for attitude uncertainty.
- The system shows enhanced robustness compared to traditional fully coupled architectures.

## Abstract

To mitigate the position divergence resulting from attitude error amplification in conventional fully coupled architectures, this study proposes a decoupled navigation architecture based on the Versatile Quaternion-based Filter (VQF). This architecture removes attitude estimation from the state vector, forming a two-layer structure comprising an independent attitude module and a navigation filter. The VQF is integrated as a standalone attitude module via a standardized interface. An uncertainty quantification model is developed by extracting the VQF’s internal correction states, which maps deviations among intermediate quaternion values to a measurable uncertainty metric. To compensate for the loss of cross-covariance induced by decoupling, a dual-layer compensation mechanism is introduced: a base layer adjusts the overall uncertainty using innovation statistics, while a compensation layer explicitly propagates attitude uncertainty through parameterized noise matrices. Experimental results demonstrate that the proposed method achieves notable improvements in positioning accuracy and significantly suppresses extreme errors in high-curvature scenarios. The approach is particularly effective for high-curvature, high-dynamic applications where process noise modeling is inherently difficult. Compared to traditional fully coupled architectures, the decoupled architecture offers enhanced robustness. The complementary characteristics identified between the two architectures provide valuable insights for expanding the operational envelope of underwater navigation systems.