A High Performance Code and Carrier Tracking Architecture For Ground-Based Mobile GNSS Receivers

Abstract

It is well-known that vector delay and frequency locked loops (VDFLLs) have several advantages over traditional scalar tracking loops in GNSS receivers, especially in mobile platforms subject to poor signal environments and accelerations. This paper presents an approach to further VDFLL performance improvement for ground-based mobile receivers which apparently has not yet been exploited. The performance improvement results from using the dynamics limitations of typical ground-based vehicles, long-term premeasurement integration, and the weak-signal advantages of direct maximum-likelihood (ML) estimation of position and velocity to materially improve weak-signal tracking capability. In the new VDFLL design, which will be denoted by MLVTL (Maximum Likelihood Vector Tracking Loop), a Kalman filter for the navigation processor is not required. Additionally, map aiding can be incorporated directly in the tracking loop to reduce position and velocity errors, lower the tracking threshold, and reduce the minimum number of satellites required to maintain tracking.