Re: [Discuss-gnuradio] Calculating additive noise power for known signal

[Marcus Müller]

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, address@hidden
> wrote:
>> Date: Tue, 23 Aug 2016 16:42:33 -0700 (MST)
>> From: Paul Creaser
>> To: address@hidden
>> 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 
>
>
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