Gullik Webjörn wrote on 2012-07-15 16:59:
>> *) The modulation is a phase modulation, that is primarily not working >> with amplitude shifts. That makes it more robust against amplitude >> noise. It's quite the same with the difference between AM an FM, where >> AM is very sensitive to atmospheric noise. The downside of FM is >> bandwidth usage, with a phase modulation it is kind of the minimum >> sampling rate. > > Hmm, I would agree with you provided it was ONE carrier, but now we have > 15, summed, and with 13.5 periods up to 34.5 / symbol. Still, it's phase modulation. Try this with some QAM scheme, you will see the difference. >> *) SNR to bits resolution has a know relation: >> SNR = (1.76 + n*6.02) dB >> where n is the number of bits. For 8 bits you should get 749.92 dB SNR. >> ADCs are never perfect and add some noise, which lowers your SNR. Thus >> you get a certain effective SNR, which corresponds to certain effective >> (non-integer) bits resolution. Even good ADCs loose some 1 bit resolution. > > That sounds a bit big, I get 20*log(1/256) = -48 dB or 20 * log(256) = > 48 dB. Your formula gives 49.92 i guess a keyboard slip. Where does the > 1.76 come from? 49.92 of course. Usually, I'd just say n*6, that's fine enough, the complete formula just for the records. Have to lookup in my textbooks... Seems like 1.76 is accounting for quantization noise, wich is assumed to have sawtooth shape, with mean amplitude sqrt(2/3). Anyway, n*6 is fine enough. > Anyway, the experiment was simple, and sets the limits for a noisefree > channel, and *seems* to indicate that even with 8 bits there is a small > margin. Anyway, my first real attempt at this will be a test generator, > and in the "lab" with control over noise and other simulations. Lab experiments are fine, in theory. The difference between theory and practice is much bigger in practice than in theory. We are dealing here with real channels, real radios, and they are not that ideal as we like to think. You will always get some noise that corrupts your signal, sooner or later... In the end with digital communication systems it boils down to energy per bit per noise energy density, bit error probability, bandwidth and some more parameters. Regards Patrick -- Engineers motto: cheap, good, fast: choose any two Patrick Strasser <patrick dot strasser at tugraz dot at> Student of Telematics, Graz Univ. of Technology, Austria ------------------------------------------------------------------------------ Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ _______________________________________________ Freetel-codec2 mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/freetel-codec2
