Optimal Pulsing Schemes for Galileo Pseudolite Signals

Tin Lian Abt, Francis Soualle, Sven Martin

EADS Astrium, Germany.

DOI:                 

Abstract

Galileo, the European Satellite Navigation System, is currently under development. Even before first satellites of the constellation are launched, Galileo signals will be provided through ground based Navigation Signal Generators for the investigation of signal performance and characteristics. Currently various projects are ongoing to develop these Galileo pseudolites (pseudo satellites). Since pseudolites are part of the Galileo system architecture namely as “Local Elements” it is expected that they will be used together with GNSS for position determination. The main characteristic of pseudolite navigation is the relatively small distance between the signal transmitter and the receiver, compared to the distances from the GNSS satellites to the receiver. This short distance causes the so-called “Near-Far-Problem”. Different attempts have been made in the past to overcome the near-far problem. A possible solution is to pulse the pseudolite transmitter signals, which has been proposed by many researchers and the success of pulsing has also been demonstrated. Basically these studies have been focused on the GPS pseudolites and the proposed pulsing schemes are optimised for the GPS signals (RTCM, RTCA). Due to major differences between the GPS and Galileo signal structures, these pulsing schemes cannot directly be adopted for use in the Galileo pseudolites. Thus new pulsing schemes and patterns have to be found and investigated. This paper summarises and assesses the existing GPS pulse patterns and pulsing techniques. The parameters which characterise a pulsing scheme are discussed and implemented. Simulations based on the Galileo signal structure (codes, chipping rates, cross correlation properties) have been performed and the results will be presented. These simulations form the basis for the proposal of a new optimised pulsing scheme for Galileo pseudolites w.r.t. pulse length, duty cycles and pulse patterns.

Keywords

Galileo, Pseudolites, Near-Far Problem

Conflicts of Interest

The authors declare no conflicts of interest.

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