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Re: [Discuss-gnuradio] Improvements made to GMSK demod
From: |
Jeff Brower |
Subject: |
Re: [Discuss-gnuradio] Improvements made to GMSK demod |
Date: |
Mon, 15 Oct 2007 16:27:52 -0500 |
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