Another Eb/No Question

Tim Wescott wrote:
> Ideally your carrier is at exactly one frequency, forever.

So your ideal is for nobody to move? That would certainly help preserve 
oil resources for future generations. :-)

Steve

Necronomicon wrote:
> Tim Wescott wrote:
>> Necronomicon wrote:
>>> Tim Wescott wrote:
>>>> Necronomicon wrote:
>>>>> Does Eb/No, as used in digital communication
>>>>> calculations for signal to noise ratios, take into
>>>>> account the VCO/PLL/Reference phase noise of the carrier(s)?
>>>>>
>>>>> I ask because the phase noise is never really flat, and the Noise
>>>>> Power Spectral Density, or "No", is in Watts/Hz, which is assuming
>>>>> that the noise is flat across all frequencies (white noise).
>>>>>
>>>>> Certainly one could use the integrated phase noise, and just
>>>>> add this to the integrated power of the noise floor, which would
>>>>> be the (Watts/Hz) x (receiver noise band-width).
>>>>>
>>>>> But it seems like Eb/No is only considering an assumed spectrally
>>>>> flat, white-noise, noise floor.
>>>>>
>>>>>
>>>>> Thanks for any clarity on this....
>>>>>
>>>> Unless you have a really crappy PLL the phase noise of your carrier
>>>> won't directly affect the decoding of your signal.
>>>
>>>           This is incorrect.  The PLL phase noise will directly
>>> affect the bit error rate of your demodulation, especially if it's
>>> a 16-QAM or 64-QAM signal.  You'll be able to see the phase
>>> or amplitude shift directly off a displayed constellation.
>>>
>>>          It's less critical if it's a QPSK or BPSK, but the phase
>>> noise
>>> will still affect your BER.
>>>
>>>         And my original question is if the Eb/No takes the
>>> phase noise into account.
>>>
>> I reserve the right to define "crappy PLL" as one that changes the phase
>> enough, within one bit time, to mess up the demodulation.  So, by
>> definition, I'm right :).
>>
> 
>       When you say: "Unless you have a really crappy PLL the phase
> noise of your carrier
> won't directly affect the decoding of your signal"......
> 
>       ......you make it sound like phase noise is not a VCO design
> issue
> when this is clearly not the case, as people are constantly looking
> for ways to increase the Q of their designs, to minimize phase noise,
> especially
> for 802.11a/g, with the higher OFDM data rates.
> 
>        Also, you really meant to say "within one symbol period",
> because you can
> have more than one bit per symbol.
> 
Sorry if it sounded like that.  I'm well aware of the interest and 
difficulty in designing low noise VCOs, and keeping them that way when 
you put them in a PLL.

And yes, I should have said "one symbol period".  Proofreading is good, 
it's too bad it often happens after I post...

-- 

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

Eric Jacobsen wrote:
> On Tue, 02 Oct 2007 11:21:28 -0700, Necronomicon <radio913@aol.com>
> wrote:
>
> >Does Eb/No, as used in digital communication
> >calculations for signal to noise ratios, take into
> >account the VCO/PLL/Reference phase noise of the carrier(s)?
> >
> >I ask because the phase noise is never really flat, and the Noise
> >Power Spectral Density, or "No", is in Watts/Hz, which is assuming
> >that the noise is flat across all frequencies (white noise).
> >
> >Certainly one could use the integrated phase noise, and just
> >add this to the integrated power of the noise floor, which would
> >be the (Watts/Hz) x (receiver noise band-width).
> >
> >But it seems like Eb/No is only considering an assumed spectrally
> >flat, white-noise, noise floor.
> >
> >
> >Thanks for any clarity on this....
>
> The short answer is no.   Eb/No is a power efficiency metric, used
> often to analyze the efficiencies of FEC and modulation in a
> theoretical or simulation sense.   For those cases phase noise is not
> considered since it is implementation specific.   So, in general Eb/No
> does not consider phase noise, nor does it consider imperfections in
> the filters or amplifiers.
>
> That doesn't mean that when you make a lab measurement to calibrate a
> system or measure performance, that phase noise doesn't affect the
> result.   Clearly a measurement made on a practical system will
> include the effects of all impairments, including phase noise. Usually
> this gets lumped into an "implementation loss" term that will include
> phase noise, distortions due to filters and amplifiers, etc., etc.
>

       I would expect this to be the case, as the Eb/No certainly
doesn't consider for example, the IP3s of your amplifier chains,
which would certainly be an impairment if you are in saturation
for a 64-QAM signal.

      The tip-off for me is that the noise power spectral density is
in Watts/Hz, which assumes spectrally flat noise.

       Ok, thanks.

       BTW, your website is wonderfully unprofessional and home-grown!

Tim Wescott wrote:
> Necronomicon wrote:
> > Tim Wescott wrote:
> >> Necronomicon wrote:
> >>> Tim Wescott wrote:
> >>>> Necronomicon wrote:
> >>>>> Does Eb/No, as used in digital communication
> >>>>> calculations for signal to noise ratios, take into
> >>>>> account the VCO/PLL/Reference phase noise of the carrier(s)?
> >>>>>
> >>>>> I ask because the phase noise is never really flat, and the Noise
> >>>>> Power Spectral Density, or "No", is in Watts/Hz, which is assuming
> >>>>> that the noise is flat across all frequencies (white noise).
> >>>>>
> >>>>> Certainly one could use the integrated phase noise, and just
> >>>>> add this to the integrated power of the noise floor, which would
> >>>>> be the (Watts/Hz) x (receiver noise band-width).
> >>>>>
> >>>>> But it seems like Eb/No is only considering an assumed spectrally
> >>>>> flat, white-noise, noise floor.
> >>>>>
> >>>>>
> >>>>> Thanks for any clarity on this....
> >>>>>
> >>>> Unless you have a really crappy PLL the phase noise of your carrier
> >>>> won't directly affect the decoding of your signal.
> >>>
> >>>           This is incorrect.  The PLL phase noise will directly
> >>> affect the bit error rate of your demodulation, especially if it's
> >>> a 16-QAM or 64-QAM signal.  You'll be able to see the phase
> >>> or amplitude shift directly off a displayed constellation.
> >>>
> >>>          It's less critical if it's a QPSK or BPSK, but the phase
> >>> noise
> >>> will still affect your BER.
> >>>
> >>>         And my original question is if the Eb/No takes the
> >>> phase noise into account.
> >>>
> >> I reserve the right to define "crappy PLL" as one that changes the phase
> >> enough, within one bit time, to mess up the demodulation.  So, by
> >> definition, I'm right :).
> >>
> >
> >       When you say: "Unless you have a really crappy PLL the phase
> > noise of your carrier
> > won't directly affect the decoding of your signal"......
> >
> >       ......you make it sound like phase noise is not a VCO design
> > issue
> > when this is clearly not the case, as people are constantly looking
> > for ways to increase the Q of their designs, to minimize phase noise,
> > especially
> > for 802.11a/g, with the higher OFDM data rates.
> >
> >        Also, you really meant to say "within one symbol period",
> > because you can
> > have more than one bit per symbol.
> >
> Sorry if it sounded like that.  I'm well aware of the interest and
> difficulty in designing low noise VCOs, and keeping them that way when
> you put them in a PLL.
>
> And yes, I should have said "one symbol period".  Proofreading is good,
> it's too bad it often happens after I post...
>

     You're clearly a control-systems specialist anyways, so you
have an excuse!

     No worries.....