A General Model of Multipath Error for Coherently Tracked BOC Modulated Signals

Abstract

A new class of signals, modulated using a binary offset carrier (BOC), is being implemented and tested in multiple Global Navigation Satellite Systems (GNSSs). A receivers that tracks a BOC signal is considered more resistant to interference than tracking a signal modulated with a binary phase shift key (BPSK). In this study, that resistance is evaluated by analytically modeling the impact of multipath interference on signal tracking. Signal tracking error is then mapped to errors in the measurements produced by GNSS receivers, pseudorange and carrier phase. The model is general so that it can apply to measurements derived from any BOC modulated signal, including those from Galileo or modernized GLONASS systems. The model incorporates a single reflector and signal tracking that is coherent with signal phase. The timing between early and late correlation processes is left as a free parameter in order to emulate the design known as narrow correlation. The error models are applied to predict errors inserted into the GPS control segment ephemeris generation process, when control segment begins tracking the BOC modulated M-Code. First, conditions by which it is possible for M-Code receivers to exhibit more multipath error than P/Y-Code receivers are solved. Second, the mean multipath error is examined. For carrier phase, the condition for zero mean is proven to be uniformly true. In contrast, pseudorange exhibits zero mean only in certain tracking conditions.