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Data-Bits Asynchronous Tracking Loop Scheme for High Performance Real-Time GNSS Receivers

Authors:
Pedro Roncagliolo
Javier Garcia
Carlos Muravchik

Keywords: GNSS; Real-Time Receivers; Phase Locked Loops; Vector Tracking Loops.

Abstract:
Tracking loops are very often chosen for code and carrier phase estimation in real-time Global Navigation Satellite System receivers due to their low computational complexity. The inputs to these loops are obtained from correlations of the received signal with locally generated replicas. Usually, correlation intervals are chosen synchronously with the data-bits sent with each satellite signal. As a consequence, each loop operates at its own time and the navigation task must extrapolate loop measurements to a common instant. We propose to change this philosophy using a common correlation interval for every satellite signal. In this way, the tracking loops work in synchronism with the navigation process, rather than with the data bits. We show how to account for the occurrence of bit transitions inside a correlation interval and how to derive a suitable discriminator for phase and code errors. The performance of this discriminator is very close to that obtained with the usual bit-synchronous correlations. The proposed scheme was applied to a scalar phase lock loop structure intended for high dynamics Global Navigation Satellite System receivers. The loop is shown to have almost the same tracking threshold and phase estimation quality than those working bit-synchronously. However, control of the measurement instant can produce significant improvements in phase estimation. Moreover, the main contribution of this scheme is for the implementation of real-time vector tracking loops, since it naturally generates a vector of simultaneous measurements in real-time.

Pages: 108 to 113

Copyright: Copyright (c) IARIA, 2012

Publication date: April 29, 2012

Published in: conference

ISSN: 2308-4480

ISBN: 978-1-61208-194-6

Location: Chamonix, France

Dates: from April 29, 2012 to May 4, 2012