%0 Journal Article
%T Galileo's Problem with PRS or What's in a Phase?
%A M. Stephen Hodgart
%J International Journal of Navigation and Observation
%D 2011
%I Hindawi Publishing Corporation
%R 10.1155/2011/247360
%X The upcoming Galileo global navigation satellite system has a design problem with the cosine-phased BOCc(15, 2.5) modulation of its Public Regulated Service (PRS A-code). This signal needs far more bandwidth than the available 40.92£¿MHz. The present signal and system specification cannot be expected to deliver design performance under practical operational conditions (noise, receiver phase distortion, and multipath). There would not have been this problem with sine-phased BOC(15, 2.5). 1. Introduction The Galileo global navigation satellite system has been more than a decade in the design and planning. The first two IOV satellites have been launched and at time of writing (January 2012) are being tested. The next two IOV satellites and FOC satellites are under construction but at present there is nothing in space to allow for a full check of their navigational capability. As is well known at least four satellites have to be up and running to attempt a full navigational solution. It is at that point this paper anticipates that some inherent problems will be confirmed because of an inherent design problem (not to say fault). It may seem surprising that after such a concerted effort and expert input that there could be any such a possibility. But if a system does not work properly, then it does not work. If the predictions of this paper turn out to be wrong, then there is of course no cause for concern. But if the predictions are right, then the reasons are fully explained here¡ªas is the necessary correction. The difficulty lies with the flag-ship PRS A-code (public regulated service): the wide-bandwidth signal transmitting on E1 channel (centred on 1575.42£¿MHz). It is predicted here that navigation receivers trying to track this signal and compute their location are likely to fail in any but the most ideal conditions. Low-strength signal (drop-outs), multipath, and all the contingent practical imperfections associated with real-world reception will make tracking and computations of the navigation solution unreliable. The same problem but less severe in its effect can be expected in reception of the other PRS -A code signal transmitting in the E6 channel centred on 1278.75£¿MHz. There are hints that responsible engineers already recognise the problem to come but are understandably reluctant to say so explicitly¡ªsee, for example, recent conference papers hosted by ESTEC [1, 2]. With the GATE test facility (Galileo Test Range) in Germany coming online experimental evidence ought to be forthcoming. These are however limited to a terrestrial test [3]. Such
%U http://www.hindawi.com/journals/ijno/2011/247360/