Thank you very much guys for your responses. I will continue to play with Gnuradio and try to test various modulation schemes over the air as this is an interesting exercise.
Cheers, Adrian On 3/7/16, glen english <g...@cortexrf.com.au> wrote: > Hi Brady > ahh yes > > I think I know where you numbers were- assumption I think is in correct for > dmr radio sensitivity. > They can do quite alot better than your assumption. > > But, it is a reasonable start. > Remember also the coding performance on DMR is strong. (Your green line does > not take this into account- (it is pretty much like a vertical cliff due to > the Iterative Turbo block product code) > > The noise figure for a 'good' DMR radio will be about 4dB to 5dB approx. > The better ones will do about -123dBm for quasi error free, and 12dB SINAD > in narrow band of about -125dBm (~ 7dB CNR) I think about 9dB CNR is quasi > error free in the turbo radios. > > On 7/03/2016 5:21 PM, Brady O'Brien wrote: >> >> Glen, >> >> I think the extra perf we're expecting comes from the tone spacing and RRC >> filtering in DMR. For ideal non-coherent 4FSK, the tones should be spaced >> Rs apart. The tone spacing of DMR is 1296 Hz, as you've said above. David >> wrote it up here: http://www.rowetel.com/blog/?p=4650 . >> >> Thanks, >> >> Brady O'Brien >> >> On Sun, Mar 6, 2016 at 10:29 PM, glen english <g...@cortexrf.com.au> >> wrote: >>> >>> Hi David >>> >>> I too am a fan of 4FSK. Just the right amount of complexity/ tradeoffs. >>> >>> How are you doing 10dB better than DMR (which also uses 4FSK) when the >>> symbol rate is 1/4 that of DMR (implying 6dB would be more like it) ? >>> different rolloff ? >>> >>> Peak deviation of DMR is ± 1.944kHz. "half" deviation is ± 648 Hz. >>> >>> or D = 3h/2T >>> >>> regards >>> >>> On 7/03/2016 10:08 AM, David Rowe wrote: >>> > Hi Adrian, >>> > >>> > Modem performance and trade offs like RF bandwidth is something I have >>> > been studying, e.g. this one compares various modulation schemes for >>> > digital voice: >>> > >>> > http://www.rowetel.com/blog/?p=4663 >>> > >>> > and many other posts. There seems to be a lot of "low hanging fruit" >>> > in >>> > the area of modems - opportunities to significantly improve our >>> > communications systems with a small amount of effort. >>> > >>> > Yes for FSK you need Rs Hz (symbol rate) between the tones to get the >>> > best BER performance at a given SNR. Many services, such a C4FM, DMR, >>> > use a smaller spacing and cop the performance hit, presumably to save >>> > bandwidth. >>> > >>> > Yes mPSK can be very bandwidth efficient, especially with high order >>> > constellations. However it's hard to get the theoretical performance >>> > of >>> > PSK in practical implementations. For example to avoid phase >>> > estimation >>> > using DQPSK means double the bit error rate of coherent PSK. >>> > >>> > I've found it's very easy to get "ideal" (bang on theoretical) >>> > performance from FSK modems. They go through crappy PAs. The >>> > receivers >>> > don't need a linear signal path or AGC. For the VHF FreeDV modem and >>> > SM2000 I've settled on non-coherent 4FSK at 1200 symbols (2400 bits) >>> > per >>> > second. It's 5kHz bandwidth, and performance is just 2dB off coherent >>> > PSK. The combination outperforms analog FM and DMR by > 10dB. >>> > >>> > You can actually put unfiltered BPSK through a non linear amplifier, >>> > for >>> > example use an XOR gate for the "mixer" to reverse the phase of the >>> > carrier. This can be friendly to other users of spectrum if you >>> > broadly >>> > filter say 10Rs wide to reduce way out of band emissions. >>> > >>> > I've found this PDF from Atlanta Signal Processing to be a great >>> > overview: >>> > >>> > http://www.atlantarf.com/FSK_Modulation.php >>> > >>> > Cheers, >>> > >>> > David >>> > >>> > On 07/03/16 07:37, Adrian Musceac wrote: >>> >> Hi David, >>> >> >>> >> Since you mentioned working on a 4FSK modem, I have started to model >>> >> one using Gnuradio and test it over a noisy channel. >>> >> My question is: since to maintain a reasonable bandwidth of the signal >>> >> you have to do heavy pulse shaping and not use orthogonal freqencies, >>> >> how do you manage a reasonable BER? >>> >> By my simulations, 4FSK requires orthogonal tones in order to still >>> >> get a reasonable decode error with a noisy channel. That creates a >>> >> signal with a huge bandwidth, especially compared with DQPSK which for >>> >> less bandwidth handles noise a lot better. Of course QPSK requires >>> >> high linearity of the amplifier, which is why my next step is to >>> >> investigate PI/4 DQPSK which is used as modulation scheme by the Tetra >>> >> standard. >>> >> >>> >> >From my experiments so far, given a fixed bandwidth and a noise >>> >> spectrum with the same power, the ranking from best to worst in BER >>> >> is: DBPSK > DQPSK > 2FSK, GMSK, 4FSK >>> >> >>> >> Can you confirm this using you mathematical knowledge? >>> >> >>> >> Cheers, >>> >> Adrian >>> >> >>> >> ------------------------------------------------------------------------------ >>> >> _______________________________________________ >>> >> Freetel-codec2 mailing list >>> >> Freetel-codec2@lists.sourceforge.net >>> >> https://lists.sourceforge.net/lists/listinfo/freetel-codec2 >>> >> >>> > ------------------------------------------------------------------------------ >>> > _______________________________________________ >>> > Freetel-codec2 mailing list >>> > Freetel-codec2@lists.sourceforge.net >>> > https://lists.sourceforge.net/lists/listinfo/freetel-codec2 >>> > >>> >>> -- >>> - >>> Glen English >>> RF Communications and Electronics Engineer >>> >>> CORTEX RF >>> & >>> Pacific Media Technologies Pty Ltd >>> >>> ABN 40 075 532 008 >>> >>> PO Box 5231 Lyneham ACT 2602, Australia. >>> au mobile : +61 (0)418 975077 >>> >>> >>> >>> ------------------------------------------------------------------------------ >>> Transform Data into Opportunity. >>> Accelerate data analysis in your applications with >>> Intel Data Analytics Acceleration Library. >>> Click to learn more. >>> http://makebettercode.com/inteldaal-eval >>> _______________________________________________ >>> Freetel-codec2 mailing list >>> 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://makebettercode.com/inteldaal-eval >> >> >> >> _______________________________________________ >> Freetel-codec2 mailing list >> Freetel-codec2@lists.sourceforge.net >> https://lists.sourceforge.net/lists/listinfo/freetel-codec2 > > > -- > - > Glen English > RF Communications and Electronics Engineer > > CORTEX RF > & > Pacific Media Technologies Pty Ltd > > ABN 40 075 532 008 > > PO Box 5231 Lyneham ACT 2602, Australia. > au mobile : +61 (0)418 975077 > > ------------------------------------------------------------------------------ Transform Data into Opportunity. 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