Advanced Acquisition and Tracking Algorithms

TL;DR: This chapter focuses on the signal processing in the acquisition and tracking stages in a Galileo receiver, namely the unambiguous signal processing which takes into account the ambiguities of most of the proposed Galileo signals and tries to better cope with them.

Abstract: This chapter focuses on the signal processing in the acquisition and tracking stages in a Galileo receiver. The acquisition stage refers to the stage where the presence of one or several Galileo satellites is identified in the sky and some coarse estimates of the propagation delay (namely Line of Sight delay) and Doppler frequency shift corresponding to the identified satellites are obtained. The tracking stage refers to the block where fine estimates of LOS delay and carrier frequency and phase are obtained. We start this section with an overview of the challenges in acquiring and tracking a Galileo signal, by emphasizing the difference with GPS. We then present a compact overview of the acquisition methods used more widely, in any DS-SS system, and which can be directly applicable to Galileo signals, in the so called ‘ambiguous’ mode. Afterwards, we focus on the Galileo-specific processing in acquisition, namely the unambiguous signal processing which takes into account the ambiguities of most of the proposed Galileo signals and tries to better cope with them. The next parts are dedicated to tracking: first focusing on an overview of generic tracking methods valid for any DS-SS system, and then discussing unambiguous tracking methods and multipath impact on tracking. This chapter is not offering an exhaustive review of all possible algorithms and related challenges in acquisition and tracking, but it tries to cover some of the main aspects, in such a way that the reader becomes familiarized with the basic challenges and the available solutions. Many parts of this chapter illustrate the Author’s own understanding and own views on the problems addressed, and the notations may be sometimes different from what may be found in other GNSS-related books. The Author however tries to clarify these situations and gives references to other literature sources that can complement the Readers’ understanding.