Carrier loop with multi-pulse coherent integration for tracking pulsed pseudolite signal.

Area of Science:

• Navigation Systems
• Signal Processing
• Control Systems

Background:

• Pseudolite systems offer centimeter-level positioning accuracy via carrier phase measurements, an alternative to satellite navigation.
• Carrier phase accuracy relies on phase-locked loop (PLL) tracking; cycle slips introduce measurement bias.
• Pulsed pseudolite signals, used to mitigate the near-far problem, are more susceptible to cycle slips in carrier tracking loops.

Purpose of the Study:

• To propose a novel phase-locked loop (PLL) with multi-pulse coherent integration (MPCI-PLL) for enhanced tracking of pulsed pseudolite signals.
• To improve the performance of carrier tracking loops under low carrier-to-noise ratios.
• To analyze the equivalent noise bandwidth of digital PLLs (DPLLs) and derive closed-form expressions.

Main Methods:

• Development of a PLL with multi-pulse coherent integration (MPCI-PLL).
• Derivation of closed-form expressions for the single-sided equivalent noise bandwidth of first-, second-, and third-order DPLLs using a discrete frequency domain approach.
• Testing the MPCI-PLL through simulations and a real-world experiment.

Main Results:

• The proposed MPCI-PLL significantly decreases the probability of cycle slips when tracking pulsed pseudolite signals at low signal-to-noise ratios.
• Performance improvements of approximately 3-4 dB were observed in both simulations and experimental results compared to conventional methods.
• Accurate closed-form expressions for DPLL equivalent noise bandwidth were derived.

Conclusions:

• The MPCI-PLL is an effective solution for improving carrier tracking performance in pulsed pseudolite systems, especially under challenging low signal-to-noise conditions.
• The derived noise bandwidth expressions provide a theoretical basis for digital PLL design in such systems.
• The enhanced tracking stability leads to more reliable and accurate positioning.