Article,
Spreading Code Selection Criteria for the future GNSS Galileo
Proc. of the European Navigation Conf. GNSS, (2005)
Abstract
The significant changes of the GALILEO signal structure have lead
to the need of designing new spreading codes for the different open
signals. In order to compare different candidate of code sets, selection
criteria have been set up in the frame of an ESA contract (Phase
C0). These criteria model the impact of the spreading code characteristics,
and in particular of their auto- and cross-correlation functions
onto the receiver performance. For this purpose three main aspects
have been considered, namely the performance in the acquisition mode,
in the tracking mode and the robustness against interfering narrow-band
signals. This paper pretends to explain the way the different criteria
were derived and the driver behind each of them. As it can be imagined,
not always the best criterion from a purely theoretical point of
view is the best, since the required computational effort that would
be required would make the whole optimization process nearly unaffordable.
We must keep in mind that the performance of a set of codes depends
on a wide range of parameters such as the code combinations, relative
delays, Doppler effects or data modulation. Additionally it must
be noted that when we optimize the codes, we must find the optimum
for all the potential environments Galileo is expected to play an
important role in the future. This means that for a particular environment,
different codes would result from the optimization. All these important
constraints show very clearly the enormous difficulties that the
code group had to deal with.
