hi Max: Thank you for your help. I will look at the op25 to see if it can help me.
inter. > Date: Thu, 12 May 2011 13:51:14 -0700 > From: ikj12...@yahoo.com > To: discuss-gnuradio@gnu.org > Subject: Re: [Discuss-gnuradio] how to use the gr_mpsk_receiver_cc > > > > Did anyone use it to receive pi/4 DQPSK signal before? > > In the op25-dev project <http://sedition.org.au/op25/> we see a > very common variant of PI/4 DQPSK, so-called CQPSK/LSM. > > Experimentation has shown that the gr_mpsk_receiver_cc() is not > optimal for CQPSK. There seem to be multiple causes, e.g.,: > > 1) PI/4 (D)QPSK apparently looks enough like 8-PSK that the standard > GR QPSK phase detector has difficulty achieving phase lock. There's > a hack to rotate the second of every two symbols by 45 degress which > seems to give a large improvement [see Fig 10. of my LSM page > at http://www.lightlink.com/mhp/lsm/ ] > > 2) At least for the specific case of LSM/CQPSK, it was found that a > Gardner symbol timing loop was superior to the M&M loop (and to the > GR PFB clock sync block) as used in the GR receivers. > > The op25 site has example code for using both the gr_mpsk_receiver_cc > as well as a complete working example using Gardner's method, including > the PI/4 hack mentioned above. > > Finally, you should also take a look at the new "magic" PFB receiver > (dqpsk2.py in GR) for your application... > > Max > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
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