The Use of Satellite Geometry for Prevention of Cycle Slips in a GPS Processor

Abstract

For kinematic survey and precise control of aviation, marine, and land vehicles, reliable GPS carrier phase tracking is critically important. In commercial GPS receivers, carrier phase tracking functions for individual satellites are carried out in a decoupled fashion, ignoring intersatellite path correlations seen at the receiver antenna. In contrast with traditional GPS signal processors, the performance of the new coupled tracker is geometry-dependent. Simulations for the complete tracking loop system illustrate how the coupled structure takes advantage of path correlations to greatly reduce phase tracking errors during periods of signal attenuation and blockage. The coupled processor is compared with a traditional processor during simulated aircraft turning maneuvers. Cycle tracking continuity is explored for overdetermined and minimal geometry scenarios. Differential correction options and computational load are also addressed.

A valid comparison of vector and scalar tracking loops

“…In the second method, the states of the central filter are the pseudoranges and pseudorange-rates of the available satellites. This type of filter design is referred to here as the pseudorange state formulation and is similar to the filter used in [3] [4]. The two formulations yield identical performance when used in identical scenarios [5].…”

Performance Comparison of Different Forms of Kalman Filter Approaches for a Vector-Based GNSS Signal Tracking Loop

“…First, a static user scenario in an open-sky environment without variation of visible satellites was simulated. The C/N 0 of three visible satellites (SV#24, 26, 27) was set to be linearly degraded down to 15 dB-Hz from 50 dB-Hz, while the other five visible satellites (SV#9, 10,15,18,21) were assumed to provide a high enough C/N 0 (%50 dB-Hz). For the assessment of the local filter performance without any influence from the navigation filter, the local KFs of interest (Options 2, 3, and 4) were implemented to operate in a scalartracking mode that has a loop closure in each local channel, and their performance is compared with the traditional approach in terms of carrier tracking.…”

“…The concept of vector-tracking was originally proposed in the early 1980s [7]. A GPS receiver with coupled signal tracking channels to achieve improved performance was presented in a series of papers [8][9][10][11]. The most commonly cited reference for vectortracking appeared in the mid-1990s [12,13].…”

Implementation of a Vector-based Tracking Loop Receiver in a Pseudolite Navigation System

“…It introduced a GPS/Inertial Navigation System (INS) composite filter utilizing the user’s navigation state to estimate tracking control input. Sennott proposed a combined tracker–navigator construction and presented simulation results showing improved tracking performance of an attenuated signal [ 6 ]. The term Vector Tracking Loop was first used by Spilker [ 7 ].…”