It's already a separate block, so yes.
On Fri, Feb 28, 2014 at 9:15 AM, Dan CaJacob <dan.caja...@gmail.com> wrote: > Nick, > > Are you going to release the non-coherent timing recovery improvement as a > separate block too (not baked into a GMSK hier block)? Thanks! > > Very Respectfully, > > Dan CaJacob > > > On Fri, Feb 28, 2014 at 11:51 AM, Nick Foster <bistrom...@gmail.com>wrote: > >> I'm working on a generalized CPM demod based on Achilleas's previous work >> in gr-trellis/src/examples/test_cpm.py, and I have it more or less working >> although there are plenty of little bugs to work out. Since the Viterbi >> part was more or less worked out for me, synchronization is the hard part; >> my application isn't GSM, and I'd like the solution in Gnuradio to be >> applicable to a wide range of systems -- this means closed-loop timing and >> freq synchronization instead of just doing data-aided estimates from the >> preamble. I've implemented a timing synchronizer based on the D'andrea, >> Mengali, Reggiannini paper following MATLAB's example, and I'm using an >> adaptation of the correlate_and_sync block to synchronize to (G)MSK >> preambles. >> >> Don't know when I'll have it ready to release (i.e. when the code isn't >> an embarrassment to look at) but it's Working In The Lab (TM). It also >> takes quite a bit of setup to apply to each use case. >> >> If you don't need those extra few dB, it's a whole heck of a lot simpler >> both in implementation complexity and CPU cycles to just stick with the >> existing noncoherent GMSK block. When I release code I'll also release an >> updated noncoherent GMSK receiver block which uses the new timing >> estimator, as the primary weakness of the existing GMSK block is timing >> recovery. >> >> --n >> >> >> On Fri, Feb 28, 2014 at 7:31 AM, Sylvain Munaut <246...@gmail.com> wrote: >> >>> Also as a side note, you can't demod GSM and then slice it. You have >>> to demod it burst by burst so that you can lock to the training >>> sequence of each. So the demod block of GR is pretty much useless >>> here. >>> >>> airprobe has a viterbi demod (which is probably one of the few good >>> part of airprobe to re-use). >>> >>> Cheers, >>> >>> Sylvain >>> >>> >>> On Fri, Feb 28, 2014 at 4:27 PM, Tom Rondeau <t...@trondeau.com> wrote: >>> > On Fri, Feb 28, 2014 at 10:12 AM, Marcus Müller <mar...@hostalia.de> >>> wrote: >>> >> Hi Zhenhua, >>> >> as Aditya pointed out: Viterby is /not/ a demodulator. >>> >> You should read something on digital communication that explains the >>> >> difference between channel coding and modulation, then everything >>> will be >>> >> clearer to you. >>> >> >>> >> Greetings, >>> >> Marcus >>> >> >>> >> On 02/28/2014 04:04 PM, zhenhua han wrote: >>> >> >>> >> What confused me is the Viterbi algorithm. I saw it can be used to >>> >> demodulate GMSK in more than one place (such as here: >>> >> >>> http://www.mathworks.cn/cn/help/comm/ref/comm.gmskdemodulatorclass.html) >>> >> >>> >> I think it's better for me to read some materials of Viterbi and find >>> out >>> >> what really it is. >>> >> >>> >> Cheers >>> >> Zhenhua >>> >> >>> >> 2014-2-28 下午10:40于 "Aditya Dhananjay" <adi...@cs.nyu.edu> 写道： >>> >>>> >>> >>>> >>> >>>> As I have known, GSM uses GMSK modulation which BT = 0.3 and it uses >>> >>>> Viterbi algorithm for demodulation. And I took a look at the code >>> of GMSK >>> >>>> demod code in GNU Radio, it use quadrature_demod but not Viterbi as >>> >>>> demodulation method. So which one is better in doing demodulating >>> GMSK? >>> >>>> >>> >>>> Moreover, GSM uses Viterbi algorithm to decode the convolution >>> encoding. >>> >>>> Would it be possible to use quadrature_demod to demodulate GSM >>> signal >>> >>>> instead of Viterbi? What about the convolution decoding part (maybe >>> by some >>> >>>> other method)? >>> >>>> >>> >>> >>> >>> I think you are mixing up the modulation and coding components. >>> >>> >>> >>> At the transmitter, you first code (convolutional code), and then you >>> >>> modulate (GMSK). >>> >>> >>> >>> At the receiver, you first demodulate (quadrature demodulate) and >>> then you >>> >>> decode (Viterbi). >>> >>> >>> >>> Coding takes a stream of bits and converts it to another stream of >>> bits. >>> >>> Modulation refers to the process of converting the post-coded bits >>> into >>> >>> "symbols" that you will then send over-the-air. >>> >>> >>> >>> best, >>> >>> aditya >>> > >>> > >>> > Actually, guys.... >>> > >>> > http://www.ittc.ku.edu/~prescott/kcp/HPRC-GMSK-Demod.pdf >>> > >>> > You can demodulate GMSK using the Viterbi algorithm. >>> > >>> > Zhenhua, >>> > >>> > We don't implement this method in our GMSK demodulator, though I have >>> > wanted to see someone do it. The Viterbi is the maximum likelihood >>> > detector for GMSK, but it's more complicated to implement. The >>> > quadrature method we use is simple and intuitive but suboptimal. >>> > >>> > Tom >>> > >>> > _______________________________________________ >>> > Discuss-gnuradio mailing list >>> > Discuss-gnuradio@gnu.org >>> > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >>> >>> _______________________________________________ >>> Discuss-gnuradio mailing list >>> Discuss-gnuradio@gnu.org >>> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >>> >> >> >> _______________________________________________ >> Discuss-gnuradio mailing list >> Discuss-gnuradio@gnu.org >> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >> >> >
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