Re: [Discuss-gnuradio] Why no phase ambiguity in digital-bert...

[Johnathan Corgan]

On Wed, Apr 14, 2010 at 06:48, Tom Rondeau <address@hidden> wrote:

> Another point of clarification for the way benchmark_rx works. We use
> differential modulation to account for the phase ambiguity. For BPSK,
> there would indeed be a 180 degree ambiguity, but we use DBPSK, which
> is insensitive to that. For anyone wanting to use non-differential
> BPSK, you would have to use information in the preamble to account for
> that.

There seems to be confusion about which script the original poster is
referring to.  Both the digital packet modem ("digital") and the
digital bit error rate tester ("digital-bert") have scripts called
benchmark_rx.py.  The original question was how the digital-bert
example was avoiding phase ambiguity while using straight BPSK and not
differential BPSK.  This is due to the use of a self-synchronizing
digital scrambler prior to modulation.

As you point out above, the receive chain in the digital packet modem
is indeed using DBPSK to avoid the phase lock ambiguity, but that's
not what the OP was referring to, unless I am mistaken.  Either way
it's important to distinguish between these two applications, as they
work differently.

Johnathan