Intelligent GPS receiver for robust carrier phase tracking in kinematic environments

Carrier phase measurement is essential for high accuracy positioning in mobile Global Positioning System (GPS) applications. For GPS receiver design, a narrow loop noise bandwidth is desirable to reduce the phase jitter due to thermal noise. However, it deteriorates the capability of tracking loops and may result in cycle slips. Based on an adaptive bandwidth criterion, a new design procedure for intelligent GPS receivers is presented to improve carrier phase tracking in the presence of highly kinematic environments. A fuzzy logic controller (FLC), which uses the carrier phase and frequency errors as input data, is first employed to provide rapid and accurate control of digital phase-locked loops (DPLL) in the transient and steady states. When the phase error or frequency error is large, the intelligent carrier loop increases the loop bandwidth adaptively and performs fast locking. Once the tracking errors are reduced, this tracking loop decreases the loop bandwidth and improves ranging accuracy. By utilising the highest dynamic stress information, the FLC loop is developed to offer several advantages over traditional methods in acquisition limitations, these being: wider lock range (150 Hz) and pull-in range (400 Hz); faster pull-in speed; and larger frequency ramp range (412 Hz/s). Simulation results demonstrate that the proposed fuzzy-based receiver does achieve a shorter settling time and broader acquisition range than conventional tracking loops while preventing the occurrence of cycle skipping.