The carrier tracking loop in a GPS receiver is considered to be an important process but also a weak link since loss of signal lock can occur in a variety of situations. Low carrier-to-noise ratios (CNR) and highly dynamic environments are common scenarios for a vehicular communication channel when random phase fluctuations in a dynamic environment are common. We propose a novel and robust carrier tracking approach by dynamically integrating an adaptive unscented Kalman filter assisted by a third-order phase lock loop in order to improve the robustness of tracking capability and accuracy in dense and dynamic environments. Experiments are conducted to investigate the tracking performance of the proposed carrier tracking approach and compare it with existing algorithms for generic GPS receiver. Results indicate that the proposed approach has a better performance in tracking capability and tracking accuracy in highly dynamic environments, and the proposed method achieves a better performance on vehicular communication channels.

The demand for reliable Positioning, Navigation, and Timing (PNT) solutions is rapidly increasing due to the growing need for precision, efficiency, and safety in unmanned systems. As operations become more autonomous, the reliance on accurate and continuous PNT data becomes critical for maintaining system integrity. The Global Navigation Satellite System (GNSS), while serving as the primary global PNT service, is vulnerable to interference, jamming, and spoofing attacks. This raises serious concerns, particularly for safety-critical applications, and urgently requires resilient Alternative PNT (A-PNT) solutions. An existing worldwide infrastructure, the Distance Measuring Equipment (DME) system, is considered one of the most promising candidates for A-PNT to address GNSS vulnerabilities. Utilising the carrier phase of the DME signal enables distance measurements with centimetre-level accuracy. However, due to the pulse system nature of DME transmissions and the sparsity of phase observations, conventional carrier tracking loops such as PLLs and FLLs struggle to maintain a reliable phase lock. To address these challenges, this work proposes a zero-crossing-integrated Kalman filter-based approach to track the DME carrier signal at an irregular rate. The performance of the proposed algorithm is validated through a series of drone tests at Cranfield University, UK. The validation results demonstrate that the proposed enhanced carrier tracking approach consistently delivers stable and accurate performance.