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

[Tom Rondeau]

On Tue, Apr 13, 2010 at 1:11 AM, Ian Holland
<address@hidden> wrote:
>
> Hi All
>
> I have been studying up on the Costas loop, and have a couple of queries as
> to the benchmark_tx.py and benchmark_rx.py as a result.
>
> Firstly, for BPSK, there should in theory be a 180 deg. phase ambiguity when
> using a Costas loop. Why does this not seem to occur with the
> benchmark_rx.py example? Is this related somehow to the PN code introduced
> by the scrambler.

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.

Tom