A Multi-Technique Approach for Characterizing the SVN49 Signal Anomaly - Part 2: Chip Shape Analysis

Abstract

Due to a satellite internal reflection at the L5 test payload, the SVN49 (PRN1) GPS satellite exhibits a static multipath on the L1 and L2 signals that results in elevation dependent tracking errors for terrestrial receivers. Using a 30m high-gain antenna, code and carrier phase measurements as well as raw in-phase and quadrature radio-frequency samples have been collected during a series of zenith passes in mid April 2010 to characterize the SVN49 multipath and its impact on common users. Following an analysis of the receiver tracking data and the IQ constellation provided in Part 1 of this study, the present Part 2 provides an in-depth investigation of chip shapes for the L1 and L2 signals. A single reflection model is found to be compatible with the observed chip shape distortions and key parameters for an elevation dependent multipath model are derived. A good agreement is found for multipath parameters derived independently from raw IQ-Samples and measurements of a so-called Vision Correlator. The chip shapes and their observed variation with elevation can be used to predict the multipath response of different correlator types within a tracking receiver. The multipath model itself is suitable for implementation in a signal simulator and thus enables laboratory testing of actual receiver hardware.