[time-nuts] GPS down converter question

Peter Monta pmonta at gmail.com
Wed Dec 2 16:26:57 EST 2015


Hi Attila,


>
> Galileo E1 and GPS L1C are not BOC(1,1). They both use a variant
> of the MBOC(6,1), CBOC(6,1,3/11) for E1 and TMBOC(6,1,4/33) for L1C.
> You can view those as a weighted combination of a BOC(1,1) signal with
> a BOC(6,1). This gives an additional peak at 7MHz offset, compared to
> a simple BOC(1,1) and helps to improve multipath.


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.)


> ... 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.

Cheers,
Peter



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