Hi, What exactly does it mean to "look at change in phase over 1 SYMBOL"? Is it just measuring the phase difference of two samples (separated by the number of samples in one symbol) and then subtracting the phase rotation of the center frequency across one symbol? Or does your algorithm look at all the samples in-between too?
Can you please give a brief explanation? Thanks, Hans ----- Original Message ----- From: Steven Clark To: gnuradio mailing list Sent: Monday, October 15, 2007 1:28 PM Subject: [Discuss-gnuradio] Improvements made to GMSK demod All- 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? Tom Tsou- thanks for pointing the way to some of this stuff. -Steven -- This message has been scanned for viruses and dangerous content by MailScanner, and is believed to be clean. ------------------------------------------------------------------------------ _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio ------------------------------------------------------------------------------ No virus found in this incoming message. Checked by AVG Free Edition. Version: 7.5.488 / Virus Database: 269.14.11/1071 - Release Date: 10/15/2007 6:48 AM
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