Ham modes/implementations that are not bandwidth critical should always do better than bandwidth constrained modes like DMR.
consider the low deviation that DMR operates with... a symbol rate of 4800 sps and a maximum deviation of 1944 Hz, This is a comparatively low modulation index. This low modulation index REALLY hurts a FM-discriminator(non linear) demodulator implementation. There is a square root raised cosine filter in there, and post TX filter, the peak dev is only 2749 Hz. So, the modulation is highly constrained. This is reasonable because the FM demodulation operating in that IF bandwidth cannot USEFULLY work down in the threshold region because of FM clicks, so if you cannot work in the threshold region, you might as well not even try ! Hence the designed operation post threshold and bandwidth constrained. If WE operated the same demodulator chain (FM discriminator, similar IF) we are not going to do any better either, again because the threshold region is death. And, as we already know here , we can do MUCH better with a linear demodulator. On 13/09/2017 10:40 PM, Adrian Musceac wrote: > On 9/12/17, David Rowe <da...@rowetel.com> wrote: >> Have you performed any BER tests to conform the BER versus Eb/No >> performance of the DMR waveform over ideal FSK? >> >> Cheers, >> >> David >> > Hi David, > > No I haven't done any BER tests yet. The code for BER is partly in > place, but the 4FSK demodulator is WIP (currently only a "dumb" > quadrature demodulator followed by a symbol filter and clock sync). > This is why my 4FSK demodulator performance is worse than the QPSK > demodulator. I've done some over the air tests and I'm currently happy > with the RF performance / CPU load balance on my Android phone. > Any help here much appreciated from people familiar with Gnuradio as > this is a full SDR implementation which will be used in the future > with wideband signals (think H264 video streaming). > > Cheers, > Adrian > > ------------------------------------------------------------------------------ > Check out the vibrant tech community on one of the world's most > engaging tech sites, Slashdot.org! http://sdm.link/slashdot > _______________________________________________ > Freetel-codec2 mailing list > Freetel-codec2@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/freetel-codec2 > ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Freetel-codec2 mailing list Freetel-codec2@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/freetel-codec2
