[time-nuts] Sinlge ADC multi-band receiver

Attila Kinali attila at kinali.ch
Sun Apr 9 16:29:16 EDT 2017

On Wed, 5 Apr 2017 08:27:58 -0400
Bob kb8tq <kb8tq at 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 "Equivalent Modulation Type"

[2] "On Generalized Signal Waveforms for Satellite Navigation",
by José Ángel Ávila Rodríguez, 2008
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

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