On Wed, 5 Apr 2017 08:27:58 -0400 Bob kb8tq <kb...@n1k.org> wrote: > Galileo E5 is a bit of a strange case. It’s really E5a and E5b. > You can either grab it all as one giant signal or as two separate signals. > You may (or may not) care about the data on E5a or b depending on what you > are trying to do. Getting the entire very wide signal likely has some > interesting benefits when it comes to working out very small differences > in location or … errr… time.
I wouldn't call it strange, but rather neat :-) The E5 signal is created as a single, 8-PSK signal(see [1]), which is modulated such, that the positive and negative frequency parts get a specific signal structure. This is done in order to allow an extremely wide band signal to be demodulated in parts. I guess they feared that a receiver for a 50MHz wide signal would be too expensive for the commercial market and made it possible to process the signal as two 20MHz wide pieces. There is a slight loss in correlation energy in this case, but for most applications it should not matter. The bigger issue is that the path delays for the two receiver channels would need to be calibrated and tracked during operation in order to make full use of the E5 signal. BTW: I have been told, that using the full E5 signal makes the use of any other signal kind of unnecessary as its extremely wide bandwidth allows a very fine tracking of the signal. Thus the use of any other signal (e.g. E1 OS) would actually degrade the receivers timing performance than improve it. > > One way to do the E5 signal would be a dual (duplicate) IF ISB downconverter. > How practical that turns out to be is an open question. The more conventional > approach is to take a monstrous chunk of L band down to a high speed sampler. As I have written above, to be able to do this is the reason for the E5's signal structure. And apparently the designers thought that this would be the way how most users would decode it. I am currently not aware of any commercial E5 receiver that is already on the market, so it is kind of moot to ask what the common way to decode E5 is. BTW: Rodriguez' PhD thesis[2] (which is the basis of navipedia) gives a very nice overview of the trade-off's that went into the Galileo signals and gives a few hints where future GNSS signals could further improve things. Attila Kinali [1] Galileo OS SIS ICD Issue 1 Revision 2, Section 2.3.1.3 "Equivalent Modulation Type" [2] "On Generalized Signal Waveforms for Satellite Navigation", by José Ángel Ávila Rodríguez, 2008 https://athene-forschung.unibw.de/node?id=86167 -- It is upon moral qualities that a society is ultimately founded. All the prosperity and technological sophistication in the world is of no use without that foundation. -- Miss Matheson, The Diamond Age, Neil Stephenson _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.