On 07/14/2012 01:49 AM, David I. Emery wrote:
On Wed, Jul 11, 2012 at 03:48:52PM -0400, paul swed wrote:
David
Read your comments and have been traveling. So finally a chance to email.
I read the document also and walked away with what I shared.
In your reading would you believe the following.
Its an absolute phase and that when it switches to 0 there is 1 transition
at the beginning of the second to 180 degrees staying that way to the next
bit or flipping again to 0 degrees if its a 1 at the 1 sec tic???
What I mean by absolute phase is that a 1 is always 180 degrees
and a zero always 0 degrees. In your example this would imply that the
two ones in a row would result in two seconds of 180 degree phase
without a flip after the first 1.
The document is confusing, but the best I can do with its
language is to conclude they are talking about absolute phase. Normally
when one talks about baseband waveforms one is referring to absolute I
and Q components relative to an unchanging carrier phase, not relative I
and Q with respect to the last bit phase. So I take their language to
mean a zero is 0 degrees and a 1 180 degrees relative to an unchanging
carrier.
I think the PTTI article isn't as much documentation as presentation of
general principle, showing details more as to present how it can be
done, but not necessarily guarantee it will be done that way. Knowing
the synchronisation sequence, polarity should not be ambiguous. Also
note that other data such as hours would be known from the AM signal, so
we can reverse engineer it. A receiver knowing this sequence will either
bootstrap from the AM or attempt straight lock. It's not too hard to
build a maximum likelihood receiver for it.
Cheers,
Magnus
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