Nice work Adrian. A good way to present this work is plots of BER against Eb/No for the various modulation schemes you are experimenting with. See my blog posts on FSK etc for examples.
It's useful to include the theoretical curves as comparisons to your real world implementations, these are well known for BPSK, FSK, and GMSK. You can also plot BER against SNR if the bit rate Rb and Noise BW N are equal. Eb/No is convenient as everything is normalised. Cheers, David On 05/07/16 08:16, Adrian Musceac wrote: > Hi, > > Some more news from the VHF modem front. First of all, I did some > performance comparisons between GMSK waveforms and regular AFSK as used > by a typical APRS modem. Obviously, there is a reason why Bell AFSK > was chosen: the Gaussian pulse shaping filter does introduce ISI as a > cost for reducing the signal bandwidth. > The next question was "how much". Luckily, using the excellent filter > design tool from Gnuradio, we can change the filter parameters and then > test the result against a channel with AWGN noise. The difference seems > to be around 2 dB in favour of AFSK. > > However, my earlier experiments showed that DBPSK will do even better. > Unfortunately, sending PSK over a narrow FM channel requires some tuning > of the modem parameters. 3 dB of improvement at the same BER is not > surprising, what was surprising to me though was the fact that adding a > pulse shaping filter immediately before the frequency conversion > improved the signal decoding by another 1-2 dB. A 9 dB SNR signal has > the same BER as a 14 dB SNR GMSK modem. At this point we are almost > doing better than analog voice already. > To add further gain we can always decrease the bitrate to 1200 bit/s. > > And since I was focused on filters, I had to take another look at the > data. What we want is a signal that can pass 1300 bit/s Codec2 through a > narrow mode FM transceiver (wide mode is beginning to be phased out at > this point). We still have bandwidth to spare, so it seemed to me that > using the same filter bandwidth for TX and RX is wasteful. Instead, the > TX filter is 20% wider than the RX filter for (very little) added > performance. > > The bad news is that the new modem is computationally about twice more > expensive. Using it on my phone will be a big stretch. We will see if I > can make it work on a 1.2 GHz CPU. > > Finally, there are some people out there who criticise Gnuradio for > being slow, bloated and too high level for this kind of stuff. I just > want to say that for me as a student, it is a very valuable tool for > learning. Maybe some day I will join the ranks of the Octave gurus, but > not today. > > A video and a screenshot of my flowgraph: > https://www.youtube.com/watch?v=YOX7H3Fcxe4 > > Cheers, > Adrian > > On Fri, Mar 25, 2016 at 10:17 AM, Adrian Musceac <kanto...@gmail.com > <mailto:kanto...@gmail.com>> wrote: > > Hi Brady, David, > > I have started transitioning my GRC flowgraphs to C++ and I have put > the code up on Github, just in case you might find it useful in your > tests for the 2400B mode. My choice of a modem is AFSK, 2000 bit/sec > (1200 bit voice or 1300 bit data). It has no FEC, no scrambling and > no interleaving (yet). The audio is framed for the standard 40 msec > Codec2. It works through a handheld FM transceiver and can be > decoded easily with Gqrx. > > The perfomance is 5 dB worse than analog FM, measured for 12 dB SNR. > I would be very curious to see a comparison with 2400B. My next step > is to transition the DBPSK modem which is 3 dB worse than analog FM > based on my USRP captured data. > > Link to the code repo: https://github.com/kantooon/gnuradio_audio_modems > Video of operation: https://www.youtube.com/watch?v=2FZBQvVm5Co > > Cheers, > Adrian (YO8RZZ) > > > On Thu, Mar 17, 2016 at 12:04 AM, Brady O'Brien > <brady.obrien...@gmail.com <mailto:brady.obrien...@gmail.com>> wrote: > > Hey Adrian, > > The gnuradio-companion pipelines I used for the test are > attached. These grc pipelines are only meant to get 16-bit 48k > samples in and out of the HackRF and rtlsdr for testing. The > meat of the FSK is done with the C fsk modem, used in freedv_rx, > freedv_tx, fsk_mod, and fsk_demod. We are also running our FSK > modem directly from SDR samples instead of through FM radios. We > will be running 2400B over legacy FM radios, but don't yet have > the same degree of test coverage. > > Thanks, > > Brady O'Brien > > On Wed, Mar 16, 2016 at 3:34 PM, Adrian Musceac > <kanto...@gmail.com <mailto:kanto...@gmail.com>> wrote: > > Hi David, > > Is it possible to get our hands on the Gnuradio code? I've > been trying > to optimize modems running at 1200 bits/second and the best > I could do > was 100% copy at 8 dB above analog FM for DBPSK and 12 dB > above for > GMSK. Your modem seems to be 16-20 dB better than that! If I > could see > the Gnuradio graph maybe I could figure out what I'm doing > wrong. > > Thanks, > Adrian > > On 3/16/16, Steve <coupaydevi...@gmail.com > <mailto:coupaydevi...@gmail.com>> wrote: > > Ha, I wish it was through a radio! > > > > I'm trying to think what I have laying around here that > might make a good > > transmitter for it. > > > > On Wed, Mar 16, 2016 at 4:02 AM, glen english > <g...@cortexrf.com.au <mailto:g...@cortexrf.com.au>> wrote: > > > >> ah. good stuff. nice progress. > >> > >> > >> On 16/03/2016 7:50 PM, Steve wrote: > >> > >> Just using the script: > >> > >> freedv_tx 2400A ve9qrp_10s.raw modem.raw > >> > >> Which produces a RAW audio file sampled at 48 kHz and > importing that into > >> audacity. > >> > >> On Wed, Mar 16, 2016 at 3:46 AM, glen english > <g...@cortexrf.com.au <mailto:g...@cortexrf.com.au>> > >> wrote: > >> > >>> Hi Steve > >>> > >>> Nice > >>> > >>> is that through a PA- if so, linear or linear in say > 3dB compression? > >>> > >>> > >>> On 16/03/2016 7:42 PM, Steve wrote: > >>> > >>> Thought I'd upload a spectrum snapshot. You can't > really see the > >>> carriers > >>> until you drop the number of samples to about 256, but > this shows how > >>> wide > >>> it is. > >>> > >>> I noticed that the freedv_tx was outputting +/- 1.0 > signals and a couple > >>> of clips going on. Maybe need to knock it down to +/- > .5 like the old > >>> FDM > >>> modes. > >>> > >>> FYI > >>> > >>> Steve > >>> > >>> > >>> > >>> > > ------------------------------------------------------------------------------ > >>> Transform Data into Opportunity. > >>> Accelerate data analysis in your applications with > >>> Intel Data Analytics Acceleration Library. > >>> Click to learn > >>> > > more.http://pubads.g.doubleclick.net/gampad/clk?id=278785231&iu=/4140 > >>> > >>> > >>> > >>> _______________________________________________ > >>> Freetel-codec2 mailing > >>> > > listFreetel-codec2@lists.sourceforge.nethttps://lists.sourceforge.net/lists/listinfo/freetel-codec2 > <http://lists.sourceforge.net/lists/listinfo/freetel-codec2> > >>> > >>> > >>> > >>> > >>> > ------------------------------------------------------------------------------ > >>> Transform Data into Opportunity. > >>> Accelerate data analysis in your applications with > >>> Intel Data Analytics Acceleration Library. > >>> Click to learn more. > > >>>http://pubads.g.doubleclick.net/gampad/clk?id=278785231&iu=/4140 > >>> _______________________________________________ > >>> Freetel-codec2 mailing list > >>>Freetel-codec2@lists.sourceforge.net > <mailto:Freetel-codec2@lists.sourceforge.net> > >>>https://lists.sourceforge.net/lists/listinfo/freetel-codec2 > >>> > >>> > >> > >> > >> > ------------------------------------------------------------------------------ > >> Transform Data into Opportunity. > >> Accelerate data analysis in your applications with > >> Intel Data Analytics Acceleration Library. > >> Click to learn > >> > more.http://pubads.g.doubleclick.net/gampad/clk?id=278785231&iu=/4140 > >> > >> > >> > >> _______________________________________________ > >> Freetel-codec2 mailing > >> > > listFreetel-codec2@lists.sourceforge.nethttps://lists.sourceforge.net/lists/listinfo/freetel-codec2 > <http://lists.sourceforge.net/lists/listinfo/freetel-codec2> > >> > >> > >> > >> > >> > > ------------------------------------------------------------------------------ > >> Transform Data into Opportunity. > >> Accelerate data analysis in your applications with > >> Intel Data Analytics Acceleration Library. > >> Click to learn more. > >> > http://pubads.g.doubleclick.net/gampad/clk?id=278785231&iu=/4140 > >> _______________________________________________ > >> Freetel-codec2 mailing list > >> Freetel-codec2@lists.sourceforge.net > <mailto:Freetel-codec2@lists.sourceforge.net> > >> https://lists.sourceforge.net/lists/listinfo/freetel-codec2 > >> > >> > > > > > ------------------------------------------------------------------------------ > Transform Data into Opportunity. > Accelerate data analysis in your applications with > Intel Data Analytics Acceleration Library. > Click to learn more. > http://pubads.g.doubleclick.net/gampad/clk?id=278785231&iu=/4140 > _______________________________________________ > Freetel-codec2 mailing list > Freetel-codec2@lists.sourceforge.net > <mailto:Freetel-codec2@lists.sourceforge.net> > https://lists.sourceforge.net/lists/listinfo/freetel-codec2 > > > > > ------------------------------------------------------------------------------ > Transform Data into Opportunity. > Accelerate data analysis in your applications with > Intel Data Analytics Acceleration Library. > Click to learn more. > http://pubads.g.doubleclick.net/gampad/clk?id=278785231&iu=/4140 > _______________________________________________ > Freetel-codec2 mailing list > Freetel-codec2@lists.sourceforge.net > <mailto:Freetel-codec2@lists.sourceforge.net> > https://lists.sourceforge.net/lists/listinfo/freetel-codec2 > > > > > > ------------------------------------------------------------------------------ > Attend Shape: An AT&T Tech Expo July 15-16. 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