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Re: [Discuss-gnuradio] BPSK to QPSK

From: Mattias Kjellsson
Subject: Re: [Discuss-gnuradio] BPSK to QPSK
Date: Wed, 03 Mar 2010 18:55:23 +0100
User-agent: Thunderbird (X11/20090817)

>>> Hum... I'm glad to hear that, although I thought that the pi- phase
>>> ambiguity of Costas- loops made them unsuitable for QPSK-
>>> constellations... But I guess there is something I'm missing in the code
>>> then?
>> You aren't missing anything, you just need to account for the possible
>> rotation.
>> The easy way to do this is with differential decoding, because the
>> instantaneous phase is irrelevant.
>> The harder-but-still-easy was is to transmit some know sequence at the
>> beginning to determine the phase offset and adjust your decoding
>> accordingly.
>> Jason
> Yes, what Jason said.
> I think of synchronization as making sure the constellation is
> aligned. The actual bit representations are the next step. Since we
> put a 64-bit access code on the front of every packet, it should be
> easy to add logic in the sink to determine what the rotation is, but
> we haven't done anything about that.
> Tom
Maybe I should have taken a few minutes to think about what was really
going on, before I started to write interleaved pilot- symbols in the
data- stream, and correcting the data on them at the rx- side then...
Anyway I got some more experience thinking in "gnuradio c++", and now a
new view upon things ;]


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