Tom Rondeau wrote:
stevie.glass wrote:
Your oscope signal of the baseband looks like good, clean QPSK,
though, so you're on the right track. The table you've posted is
definitely pi/4 DQPSK. What this does is shift the constellation by 45
degrees every symbol, which means that what used to be a 0 degree
phase shift (00) becomes a +45 degree phase shift. The idea here is to
minimize the phase transition between successive symbols so the
maximum is +135 degrees instead of +180. It's a minor change in the
modulator that helps lower the bandwidth of the signal.
And decrease the linearity demands on the amplifier as a result.
The big problem, though, is that the DQPSK block in GNU Radio doesn't
do the pi/4 coding scheme. You'll have to work on it to adjust the
rotation by +45 degrees each symbol. This should be fairly easy to do.
Tom
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