Phase/frequency tracking in a GNSS software receiver

In the paper, a software-based technique for the tracking of frequency and phase of Global Navigation Satellite System (GNSS) signals is proposed. It is shown that a software-based receiver with precomputed, zero-phase carrier replicas for phase tracking is subject to phase jump in phase tracking and ambiguity problems in frequency estimation. A phase/frequency tracking architecture is proposed in which the frequency of the incoming signal is estimated based on a lead-lag structure which is similar to a traditional delay locked loop and the phase, after de-rotation, is estimated using a frequency-aiding phase locked loop. The effects of thermal noise and resolution-induced noise are analyzed and verified using simulation. The significance of frequency aiding in enhancing the phase tracking response is also described.