Signal Quality Monitoring through Analysis of Chip Shape Deformation for GNSS Signals

Abstract

Standalone Global Navigation Satellite System (GNSS) applications demand higher precision than is typically achieved using differential processing. While differential processing removes the effects of most common-mode error sources, it provides limited compensation for distortions caused by multipath or pseudorange measurement biases from dissimilar receiver hardware due to subtle space vehicle-borne signal deformations. These naturally occurring phenomena directly impact system integrity and lead to ranging error in the GNSS receiver solution. Signal Quality Monitoring (SQM) has the objective of providing confidence in the GNSS Positioning, Navigation, and Timing (PNT) solution, and aims to offer timely warning in the event that SV signal conditions degrade to unsafe levels. Several methods of SQM have been previously introduced and implemented to augment civilian Safety-of-Life (SoL) applications. The methods considered in this work focus on implementing effective SQM using low-cost Commercial Off-theShelf (COTS) equipment, a Software-Defined Radio (SDR), and a typical software GNSS receiver architecture that tracks the Galileo E1 signals and the Global Positioning System (GPS) L1 Coarse-Acquisition (C/A) signals. The techniques here are centered on acquiring and discriminating signal chip shapes with a goal of identifying both ‘clean’ and ‘deformed’ signals. The demonstrated identification method is relevant to the growing significance of SQM for SoL applications while providing benefit for confidently monitoring received GNSS signal integrity without requiring specialized receiver hardware.