PI/4 DQPSK

Thanks for including my "cqpsk.py" decoder module in your distribution. That looks to be a very old version and there have been some further discoveries since that time which I wanted to pass along, FWIW... First, the Costas frequency lock loop in GR seems to work much better for PI/4 DQPSK signals if it's patched in phase_error_tracking() : #if ENABLE_COSTAS_CQPSK_HACK if (d_interp_counter & 1) // every other symbol sample = sample * PT_45; // rotate by +45 deg d_interp_counter++; #endif /* ENABLE_COSTAS_CQPSK_HACK */ The effect of adding this hack to the code can be seen in Fig. 10 at my page http://www.lightlink.com/mhp/lsm/ With the patch included, the time to achieve lock is much improved... Second, I've found that a Gardner symbol timing loop works much better in our application than the M&M loop used in GR gr_mpsk_receiver(). Both of these improvements are included in a new GR block which has been optimized for the particular flavor of "PI/4 CQPSK" (LSM). It's in our svn repo - see http://sedition.org.au/op25/wiki/BuildInstructionsPage Look for the block in the repeater/src/lib tree - see repeater_gardner_costas_cc.cc YMMV ;-) [update: Tues. morning] two more things... 1. There is also a new Polyphase Filter Bank receiver which has been added in the latest versions of GNU Radio. It would be interesting to test and compare the performance of that receiver with the current one... 2. Would it be possible to post complex sample files (preferably not encrypted) to permit evaluation of this signal type? Best Regards 73 de KA1RBI Max