Reply by Necronomicon October 2, 20072007-10-02
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.....
Reply by Necronomicon October 2, 20072007-10-02
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!
Reply by Tim Wescott October 2, 20072007-10-02
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
Reply by Steve Underwood October 2, 20072007-10-02
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
Reply by Eric Jacobsen October 2, 20072007-10-02
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. Eric Jacobsen Minister of Algorithms Abineau Communications http://www.ericjacobsen.org
Reply by Necronomicon October 2, 20072007-10-02
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.
Reply by mnentwig October 2, 20072007-10-02
>> We'll need some serious linearity for that!
Maybe it's only my imagination, but I think I recognize your handwriting. -mn
Reply by Tim Wescott October 2, 20072007-10-02
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 :). At any rate, I would expect that a textbook Eb/No curve doesn't take this into account, at least if it's a basic textbook. You certainly _could_ calculate the effect of the phase shift of the signal due to the PLL, and probably _should_ if you expect the phase noise to be significant. Whether an Eb/No curve that you find in a data book or a paper takes this into account is something that you'd have to verify on a case-by-case basis. -- 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
Reply by Necronomicon October 2, 20072007-10-02
John wrote:
> On Oct 2, 3:38 pm, Tim Wescott <t...@seemywebsite.com> 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. What phase noise > > _does_ do is to raise the noise floor in the presence of nearby carriers > > that wouldn't otherwise cause any problems. > > > > But what constitutes a crappy PLL is not the same for BPSK as 256QAM, > in other words the modulation type matters. >
Correct! Thank you! Last i heard, they still haven't decided on the standard for WiMax, or 802.16, but they were considering 256-QAM. We'll need some serious linearity for that!
Reply by Necronomicon October 2, 20072007-10-02
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.