Hi Andy, > 3. HF systems are the only other systems I'm familiar with that deal > with impulsive noise. HF communications systems often employ FEC and > interleavers to combat impulsive noise. Powerline comms typically suffer from that kind of noise. Think of someone switching on lights. Or a commutator in the motor of the washing mashine that someone carelessly attached to your communication channel!
Best regards, Marcus On 24.08.2016 19:55, Andy Walls wrote: > On Wed, 2016-08-24 at 12:00 -0400, discuss-gnuradio-requ...@gnu.org > wrote: >> Date: Tue, 23 Aug 2016 16:42:33 -0700 (MST) >> From: Paul Creaser >> To: Discuss-gnuradio@gnu.org >> In a real system the signal would be a preamble, which would normally be used >> for synchronization purposes at the receiver end (For example PLC system). >> >> "I'm not quite sure what you mean by "cyclic noise", but the example you >> give is 50 Hz (or 60 Hz) hum, so a narrowband interference." >> >> Cyclic noise, perhaps my understanding is incorrect. In a PLC system, the >> noise rejection system uses a Zero Cross detection to detect the beginning >> of a power cycle (50Hz/60Hz). During the cycle at the same phase point, >> noise repeatedly occurs. So on a scope you would see a nice sine wave for >> the power and noise which repeats at the same phase point in the power >> cycle. > Ah, now I understand: a periodic noise impulse. So definitely not an > AWGN. > > >> This is different from the 50 Hz noise I suggested previously. However the >> idea/hope is that this noise is narrow band noise and because of its >> repetitive behaviour, > Impulsive noise is usually broadband. Signals that are concentrated in > the time domain are spread out in the frequency domain, and vice versa > (this falls out from the Fourier transform). > > A periodic, broadband noise impulse is essentially going bump up the > noise floor for a short time every 50th (or 60th) of a second. > > > >> .i.e. occurring in the same point in the cycle, and >> relatively stable amplitude, it should be possible to remove it from a known >> signal. >> >> I will take on board all the useful advice and continue my studies. >> > So I have a couple of thoughts: > > 1. The LMS adaptive filter I suggested earlier won't do much good in the > face of broadband periodic noise impulses. It still may help with > equalizing a poor channel, since PLC transmission lines are usually of > uncontrolled and unknown quality. > > 2. Your communication system should still use appropriate channel > filters and pulse matched filters, to mitigate the effects of broadband > noise that shows up outside your channel of interest. > > 3. HF systems are the only other systems I'm familiar with that deal > with impulsive noise. HF communications systems often employ FEC and > interleavers to combat impulsive noise. > > 4. Adaptive noise cancellation techniques may help here, but I'm no > expert on them. A quick Google turns up some decent material. > > 5. If you track the timing of the impulsive noise bursts, is it feasible > to have your system schedule its communications between the bursts? (I > don't know your topology.) Think of it as a TDMA timeslot clock. :) > 1/60th of a second at 9600 symbols/second is 160 symbols. > > -Andy > > > _______________________________________________ > 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