[time-nuts] GPS down converter question

Attila Kinali attila at kinali.ch
Fri Dec 4 04:56:24 EST 2015


Moin Peter,

On Wed, 2 Dec 2015 13:26:57 -0800
Peter Monta <pmonta at gmail.com> wrote:

> Yes, but I suspect some receivers will implement just the BOC(1,1) for cost
> reasons.  (Spectral peak is at 6 MHz actually, or rather 6*1.023.)

Right, 6MHz. I shouldn't write highly technical mails when it's late :-)

Yes, I think a lot of the receivers that claim Galileo compatibility
these days are still BOC(1,1) receivers. But i'm not sure whether the
price impact is actually that high. Most ADCs for GNSS applications
are still of the sign-magnitude style (aka 2bit) and thus pretty cheap
to manufacture (4 comparator are enough), even at "high speed". The use
of higher BW low pass filters might actually make things cheaper
(smaller components). The bigger question is the availability of
wide band SAW filters. Unless the consumer (aka phone) market orders
SAW filters wide enough for full MBOC(6,1) use, there will not be
any cheap filters available for anyone else (SAW filters might be
cheap to manufacture, but initial costs are relatively high).
 
> > ... Although it's possible to track both
> > of these signals with just a BOC(1,1) decoder (and thus a narrower
> > bandwidth),
> > this will induce a slight bias into the tracking loop and thus an error
> > in the PVT solution.
> >
> 
> But BOC(6,1) is orthogonal to BOC(1,1), so I'm not seeing the bias.  I
> could be wrong, though; some of these things are subtle.  If you have a
> reference I'd be curious to read about it.

Apparently the cross correlation function of an MBOC with its BOC is not
exactly symmetric. I haven't understood the details yet (still reading)
but this popped up a couple of times in different papers.

BTW: how is the work on the GNSS Firehose going?

			Attila Kinali

-- 
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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