Steven- > I've made some improvements to the built-in GMSK demodulator, based mostly on > Simon > & Wang's "Differential Detection of Gaussian MSK in a Mobile Radio > Environment". > Also see "Differential Detection of GMSK Using Decision Feedback", Yongacoglu, > A. Makrakis, D. Feher, K. > > The intermediate steps I took were as follows: > > -Place a low-pass filter in front of the clock recovery block. Optimal > bandwidth is > a function of both Eb/N0 and xmitter BT product. > -Remove the quadrature demod (which was looking at change in phase over 1 > sample). > Replace with blocks to look at change in phase over 1 SYMBOL. (this is a true > 1 bit > differential detector) > -Instead of 1 bit differential detector, look at change in phase over 2 > symbols (2 > bit differential detector). (requires diff encode on xmit side). This > produces an > asymmetric eye diagram, so you have to bias it a little bit prior to clock > recovery. > > Initial Bit Error Rate results (just to get an idea of relative performance): > (xmit BT=0.25, 8 samp/sym, same input to all demods, at a certain Eb/N0) > > Original, unchanged GMSK demod: > BER=0.38 > > Original + pre CR filter: > BER=0.0090 > > True 1-bit diff detect + pre CR filter: > BER=0.0056 > > True 2-bit diff detect + pre CR filter: > BER=0.00076 > > Is this something that people would like to see checked in? If so, how's the > best > way to do so...via a developer branch?
The BER improvement looks outstanding. I would think this should be an excellent contribution. -Jeff _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
