Re: Calculating SNR of an incoming signal

[Alex Batts]

Sorry for the delayed response.

I do have info on the object I am tracking and can calculate the radar
cross section. It is a model rocket that can most likely be estimated as a
cylinder with small error between the two calculations.

The system as a whole will technically be active since we will also be
sending out the sine wave and directing it, but the receiving SDR will not
simultaneously be transmitting. It could technically be considered an
active bistatic system, but since the receiving SDR is the only influence
on range detection we were just going to consider it passive. We will be
using the BladeRF 2.0 Micro xA9.

Yes, EO is electro-optical/a camera system.

Right now I am struggling to set up the equation for the range detection in
gnuradio. There doesn't seem to be any support for inverse log functions or
fractional exponents (or taking the exponent of a non-complex number).
Since I am having to convert to mag^2 to calculate the power, I am working
with floats. Is there a workaround for this that you know of, or is there
an extension/add-on for gnuradio that extends it's mathematics capabilities?

Thank you,

Alex

On Mon, Jun 29, 2020 at 4:43 AM Johannes Demel 
wrote:

> Hi Alex,
>
> please keep this discussion on the mailing list. Thus, I included the
> mailing list in this reply again.
>
> Let's summarize your system
> carrier frequency 5.8GHz
> Radar ranging with reflection loss. Do you have any info on your
> reflecting object? An objects radar cross-section may heavily influence
> your results.
> You stated, you'd work on a passive RF ranging system. The setup you
> describe is active though. I'm curious how you'll convert this to a
> passive system.
>
> What's the signal structure you send? Is it just a sine? Is it random
> QPSK symbols? What's your frontend's carrier frequency? Which SDR
> frontend do you use? A USRP? A HackRF?
>
> As long as your bandwidth definition together with your SNR definition
> is sound, it might work to pre-calibrate your system. You might want to
> do this periodically in case you'll run it for a longer time.
>
> EO (Electro-Optical?)
>
> Cheers
> Johannes
>
> On 26.06.20 18:01, Alex Batts wrote:
> > Hello,
> >
> > Yes, I understand the Nyquist sampling theorem and my hardware
> > limitations. That is why I assumed filtering would not work although I
> > gave it a shot anyways. I am not trying to demodulate any baseband
> > signal, rather I am going to be receiving a reflected signal at around
> > 5.8 GHz and using that signal for range detection. The signal itself
> > will not contain any information, but the strength of the signal is the
> > information I need. However, I need a method for determining, or at
> > least estimating, SNR because that is the key variable that will change
> > throughout my experiment in the radar range equation and will ultimately
> > be the deciding factor to determine how far away the object is. That was
> > why I proposed doing a pre-trial calculation where my source is not
> > transmitting to get the average noise power, and then set that as a
> > constant block and subtract it in real time from my average total power
> > with noise and signal both included. The constant block would then be
> > updated prior to each run.
> >
> > A necessary part of the radar range equation is the transmit power from
> > the source as well as the directivity. The SNR I'll be looking for is at
> > the receiver. So the equation takes care of any signal attenuation.
> >
> > I'm building a passive RF range calculation system in conjunction with
> > an EO object tracking system.
> >
> > Thank you,
> >
> > Alex
> >
> >
> >
> > On Fri, Jun 26, 2020 at 11:14 AM Johannes Demel  > > wrote:
> >
> > Hi Alex,
> >
> > your cut-off frequency needs to be lower than half your sampling
> rate.
> > If your sampling rate is 61.44MHz, your maximum cut-off frequency
> > can be
> > 30.72MHz. And it should probably be a bit lower. You're working in
> > baseband here. It is really important to understand the concepts of
> > digital signal processing. That's also the reason I pointed out
> several
> > resources.
> >
> > SNR calculation itself is not always trivial. You need a way to
> > distinguish samples that should only carry noise energy and those
> that
> > should carry signal energy.
> > Often people distinguish between SNR estimation for AWGN channels and
> > for fading channels. While your estimator will probably not
> distinguish
> > between the two, some estimators just fail for fading channels
> > especially.
> > For OFDM you might want to look into Schmidl preamble based SNR
> > estimation. There might be an M2M4 estimator for symbol based SNR
> > estimation.
> > What kind of system are you using?
> >
> > Cheers
> > Johannes
> >
> >
> > On 26.06.20 15:49, Alex Batts wrote:
> >  > Right, because the filter cutoff frequency needs to be 

Re: Calculating SNR of an incoming signal

[Johannes Demel]

Hi Alex,

please keep this discussion on the mailing list. Thus, I included the 
mailing list in this reply again.


Let's summarize your system
carrier frequency 5.8GHz
Radar ranging with reflection loss. Do you have any info on your 
reflecting object? An objects radar cross-section may heavily influence 
your results.
You stated, you'd work on a passive RF ranging system. The setup you 
describe is active though. I'm curious how you'll convert this to a 
passive system.


What's the signal structure you send? Is it just a sine? Is it random 
QPSK symbols? What's your frontend's carrier frequency? Which SDR 
frontend do you use? A USRP? A HackRF?


As long as your bandwidth definition together with your SNR definition 
is sound, it might work to pre-calibrate your system. You might want to 
do this periodically in case you'll run it for a longer time.


EO (Electro-Optical?)

Cheers
Johannes

On 26.06.20 18:01, Alex Batts wrote:

Hello,

Yes, I understand the Nyquist sampling theorem and my hardware 
limitations. That is why I assumed filtering would not work although I 
gave it a shot anyways. I am not trying to demodulate any baseband 
signal, rather I am going to be receiving a reflected signal at around 
5.8 GHz and using that signal for range detection. The signal itself 
will not contain any information, but the strength of the signal is the 
information I need. However, I need a method for determining, or at 
least estimating, SNR because that is the key variable that will change 
throughout my experiment in the radar range equation and will ultimately 
be the deciding factor to determine how far away the object is. That was 
why I proposed doing a pre-trial calculation where my source is not 
transmitting to get the average noise power, and then set that as a 
constant block and subtract it in real time from my average total power 
with noise and signal both included. The constant block would then be 
updated prior to each run.


A necessary part of the radar range equation is the transmit power from 
the source as well as the directivity. The SNR I'll be looking for is at 
the receiver. So the equation takes care of any signal attenuation.


I'm building a passive RF range calculation system in conjunction with 
an EO object tracking system.


Thank you,

Alex



On Fri, Jun 26, 2020 at 11:14 AM Johannes Demel > wrote:


Hi Alex,

your cut-off frequency needs to be lower than half your sampling rate.
If your sampling rate is 61.44MHz, your maximum cut-off frequency
can be
30.72MHz. And it should probably be a bit lower. You're working in
baseband here. It is really important to understand the concepts of
digital signal processing. That's also the reason I pointed out several
resources.

SNR calculation itself is not always trivial. You need a way to
distinguish samples that should only carry noise energy and those that
should carry signal energy.
Often people distinguish between SNR estimation for AWGN channels and
for fading channels. While your estimator will probably not distinguish
between the two, some estimators just fail for fading channels
especially.
For OFDM you might want to look into Schmidl preamble based SNR
estimation. There might be an M2M4 estimator for symbol based SNR
estimation.
What kind of system are you using?

Cheers
Johannes


On 26.06.20 15:49, Alex Batts wrote:
 > Right, because the filter cutoff frequency needs to be at least
half the
 > sampling rate, I figured I would not be able to use a filter
since the
 > bladeRF I will be using has a 61.44 MHz sampling rate and I will be
 > operating in the GHz range.
 >
 > What I will probably end up having to do is do a pre-run calibration
 > where the tone is not playing, use a complex to mag^2 and average
power
 > combination, set that as a constant block, and then subtract the
 > calibrated constant from the total power when the tone is on to
get the
 > most accurate possible signal power. While not ideal because it
is not a
 > truly live SNR calculation, it is the best workaround that avoids
the
 > filter I can think of.
 >
 > If there are any other suggestions to get a more live/real time SNR
 > calculation I am open to that as well.
 >
 > Thank you for the help,
 >
 > Alex
 >
 >
 >
 > On Fri, Jun 26, 2020 at 4:17 AM Johannes Demel
mailto:de...@ant.uni-bremen.de>
 > >> wrote:
 >
 >     Hi Alex,
 >
 >     "0 < fa <= sampling_rate/2" is correct and should always be
 >     enforced. If
 >     you try to set your filter cut-off frequency at >=
samp_rate/2, you'll
 >     experience aliasing.
 >
 >     After reading your mails, I get the impression you try to set
your
 >   

Re: Calculating SNR of an incoming signal

[Johannes Demel]

Hi Alex,

your cut-off frequency needs to be lower than half your sampling rate.
If your sampling rate is 61.44MHz, your maximum cut-off frequency can be 
30.72MHz. And it should probably be a bit lower. You're working in 
baseband here. It is really important to understand the concepts of 
digital signal processing. That's also the reason I pointed out several 
resources.


SNR calculation itself is not always trivial. You need a way to 
distinguish samples that should only carry noise energy and those that 
should carry signal energy.
Often people distinguish between SNR estimation for AWGN channels and 
for fading channels. While your estimator will probably not distinguish 
between the two, some estimators just fail for fading channels especially.
For OFDM you might want to look into Schmidl preamble based SNR 
estimation. There might be an M2M4 estimator for symbol based SNR 
estimation.

What kind of system are you using?

Cheers
Johannes


On 26.06.20 15:49, Alex Batts wrote:
Right, because the filter cutoff frequency needs to be at least half the 
sampling rate, I figured I would not be able to use a filter since the 
bladeRF I will be using has a 61.44 MHz sampling rate and I will be 
operating in the GHz range.


What I will probably end up having to do is do a pre-run calibration 
where the tone is not playing, use a complex to mag^2 and average power 
combination, set that as a constant block, and then subtract the 
calibrated constant from the total power when the tone is on to get the 
most accurate possible signal power. While not ideal because it is not a 
truly live SNR calculation, it is the best workaround that avoids the 
filter I can think of.


If there are any other suggestions to get a more live/real time SNR 
calculation I am open to that as well.


Thank you for the help,

Alex



On Fri, Jun 26, 2020 at 4:17 AM Johannes Demel > wrote:


Hi Alex,

"0 < fa <= sampling_rate/2" is correct and should always be
enforced. If
you try to set your filter cut-off frequency at >= samp_rate/2, you'll
experience aliasing.

After reading your mails, I get the impression you try to set your
filter cut-off frequency at your carrier frequency $f_c$ + bandwidth/2
$B/2$. Or something in that range. That won't work in baseband.
Effectively, your signal at $f_c$ goes through a mixer and is shifted
such that it would appear at $0$ in your baseband signal.

There's a lot of digital signal processing fundamentals involved. I
like
the explanations given in [0]. Though, of course there are well known
books such as the ones by Proakis or Sklar on the topic.

Cheers
Johannes

[0] https://dspillustrations.com/pages/index.html

On 25.06.20 22:22, Alex Batts wrote:
 > The effective noise bandwidth is part of the calculation. I'm
using the
 > radar range equation.
 >
 > My purpose for including the bandwidth in my response was that
any time
 > I try to use a filter with a frequency greater than my sampling
rate/2 I
 > get an error returned. I agree that ideally I would use a band-pass
 > filter with very narrow cutoffs to best capture the signal in its
 > entirety, however, I can't because the frequency I'm trying to
set my
 > filter at is more than half my sampling rate, giving me an error.
Maybe
 > there is something askew with that error and it's something else,
but it
 > returns saying 0 < fa <= sampling_rate/2
 >
 > On Thu, Jun 25, 2020 at 3:27 PM Marcus Müller mailto:muel...@kit.edu>
 > >> wrote:
 >
 >     Hi Alex,
 >
 >     On 25/06/2020 21.00, Alex Batts wrote:
 >      > I'm sampling an incoming signal, but only around 2 MSps.
 >      >
 >
 >     and that's fine! that's the *equivalent* baseband, it has all
the same
 >     information as the RF signal.
 >
 >      > I need the signal power to noise power ratio at the
receiver as
 >     part of
 >      > my range calculation.
 >
 >     Yes, but you'd always want to do that "signal to noise" only
in the
 >     bandwidth that actually contains your tone; the rest will
just contain
 >     more noise, interferers... to make your measurement worse.
 >
 >      > So I would need to be able to distinguish between
 >      > the power of the tone vs the power of the surrounding
noise and use
 >      > those two numerical values in an equation to calculate the
range.
 >
 >     You need to define "surrounding"! Your signal doesn't get
worse by
 >     applying a filter that only selects your tone and as little
else as
 >     possible. So you should do that – it makes your SNR better.
Hence, your
 >     Signal power estimate gets more reliable (which you
definitely want).
 >
 >     (that 

Re: Calculating SNR of an incoming signal

[Alex Batts]

Right, because the filter cutoff frequency needs to be at least half the
sampling rate, I figured I would not be able to use a filter since the
bladeRF I will be using has a 61.44 MHz sampling rate and I will be
operating in the GHz range.

What I will probably end up having to do is do a pre-run calibration where
the tone is not playing, use a complex to mag^2 and average power
combination, set that as a constant block, and then subtract the calibrated
constant from the total power when the tone is on to get the most accurate
possible signal power. While not ideal because it is not a truly live SNR
calculation, it is the best workaround that avoids the filter I can think
of.

If there are any other suggestions to get a more live/real time SNR
calculation I am open to that as well.

Thank you for the help,

Alex



On Fri, Jun 26, 2020 at 4:17 AM Johannes Demel 
wrote:

> Hi Alex,
>
> "0 < fa <= sampling_rate/2" is correct and should always be enforced. If
> you try to set your filter cut-off frequency at >= samp_rate/2, you'll
> experience aliasing.
>
> After reading your mails, I get the impression you try to set your
> filter cut-off frequency at your carrier frequency $f_c$ + bandwidth/2
> $B/2$. Or something in that range. That won't work in baseband.
> Effectively, your signal at $f_c$ goes through a mixer and is shifted
> such that it would appear at $0$ in your baseband signal.
>
> There's a lot of digital signal processing fundamentals involved. I like
> the explanations given in [0]. Though, of course there are well known
> books such as the ones by Proakis or Sklar on the topic.
>
> Cheers
> Johannes
>
> [0] https://dspillustrations.com/pages/index.html
>
> On 25.06.20 22:22, Alex Batts wrote:
> > The effective noise bandwidth is part of the calculation. I'm using the
> > radar range equation.
> >
> > My purpose for including the bandwidth in my response was that any time
> > I try to use a filter with a frequency greater than my sampling rate/2 I
> > get an error returned. I agree that ideally I would use a band-pass
> > filter with very narrow cutoffs to best capture the signal in its
> > entirety, however, I can't because the frequency I'm trying to set my
> > filter at is more than half my sampling rate, giving me an error. Maybe
> > there is something askew with that error and it's something else, but it
> > returns saying 0 < fa <= sampling_rate/2
> >
> > On Thu, Jun 25, 2020 at 3:27 PM Marcus Müller  > > wrote:
> >
> > Hi Alex,
> >
> > On 25/06/2020 21.00, Alex Batts wrote:
> >  > I'm sampling an incoming signal, but only around 2 MSps.
> >  >
> >
> > and that's fine! that's the *equivalent* baseband, it has all the
> same
> > information as the RF signal.
> >
> >  > I need the signal power to noise power ratio at the receiver as
> > part of
> >  > my range calculation.
> >
> > Yes, but you'd always want to do that "signal to noise" only in the
> > bandwidth that actually contains your tone; the rest will just
> contain
> > more noise, interferers... to make your measurement worse.
> >
> >  > So I would need to be able to distinguish between
> >  > the power of the tone vs the power of the surrounding noise and
> use
> >  > those two numerical values in an equation to calculate the range.
> >
> > You need to define "surrounding"! Your signal doesn't get worse by
> > applying a filter that only selects your tone and as little else as
> > possible. So you should do that – it makes your SNR better. Hence,
> your
> > Signal power estimate gets more reliable (which you definitely want).
> >
> > (that also highlights why I have a bit of doubt on your measurement
> > methodology – if your SNR depends on receiver bandwidth, then how
> much
> > does it actually tell you about the range, unless you specify the
> > bandwidth alongside with it?)
> >
> > Think about it: we typically assume noise to be white, i.e. to have
> > identical power spectral density all over the spectrum, e.g. -170
> > dBm/Hz.
> >
> > Now, if your receiver bandwidth is set to 2 MHz (because that's what
> > your SDR is probably configured to filter out if you ask for 2 MS/s),
> > then you get twice as much noise power than if you set the sampling
> > rate
> > to 1 MS/s.
> >
> > It's the same thing that I always let students figure out by
> themselves
> > the first time they use the lab spectrum analyzer:
> > Feed a 2 GHz -60 dBm tone into the spectrum analyzer.
> > Set the resolution bandwidth of the spectrum analyzer to 1 MHz, and
> > tell
> > me what the SNR is. Now set the resolution bandwidth to 300 kHz and
> > tell
> > me again.
> > You get as much "N" in your SNR as you let through your system. In
> the
> > case of the spectrum analyzer, every point on the display is the
> power
> > in 1 MHz (or 300 kHz) of filter. In the case of 

Re: Calculating SNR of an incoming signal

[Johannes Demel]

Hi Alex,

"0 < fa <= sampling_rate/2" is correct and should always be enforced. If 
you try to set your filter cut-off frequency at >= samp_rate/2, you'll 
experience aliasing.


After reading your mails, I get the impression you try to set your 
filter cut-off frequency at your carrier frequency $f_c$ + bandwidth/2 
$B/2$. Or something in that range. That won't work in baseband.
Effectively, your signal at $f_c$ goes through a mixer and is shifted 
such that it would appear at $0$ in your baseband signal.


There's a lot of digital signal processing fundamentals involved. I like 
the explanations given in [0]. Though, of course there are well known 
books such as the ones by Proakis or Sklar on the topic.


Cheers
Johannes

[0] https://dspillustrations.com/pages/index.html

On 25.06.20 22:22, Alex Batts wrote:
The effective noise bandwidth is part of the calculation. I'm using the 
radar range equation.


My purpose for including the bandwidth in my response was that any time 
I try to use a filter with a frequency greater than my sampling rate/2 I 
get an error returned. I agree that ideally I would use a band-pass 
filter with very narrow cutoffs to best capture the signal in its 
entirety, however, I can't because the frequency I'm trying to set my 
filter at is more than half my sampling rate, giving me an error. Maybe 
there is something askew with that error and it's something else, but it 
returns saying 0 < fa <= sampling_rate/2


On Thu, Jun 25, 2020 at 3:27 PM Marcus Müller > wrote:


Hi Alex,

On 25/06/2020 21.00, Alex Batts wrote:
 > I'm sampling an incoming signal, but only around 2 MSps.
 >

and that's fine! that's the *equivalent* baseband, it has all the same
information as the RF signal.

 > I need the signal power to noise power ratio at the receiver as
part of
 > my range calculation.

Yes, but you'd always want to do that "signal to noise" only in the
bandwidth that actually contains your tone; the rest will just contain
more noise, interferers... to make your measurement worse.

 > So I would need to be able to distinguish between
 > the power of the tone vs the power of the surrounding noise and use
 > those two numerical values in an equation to calculate the range.

You need to define "surrounding"! Your signal doesn't get worse by
applying a filter that only selects your tone and as little else as
possible. So you should do that – it makes your SNR better. Hence, your
Signal power estimate gets more reliable (which you definitely want).

(that also highlights why I have a bit of doubt on your measurement
methodology – if your SNR depends on receiver bandwidth, then how much
does it actually tell you about the range, unless you specify the
bandwidth alongside with it?)

Think about it: we typically assume noise to be white, i.e. to have
identical power spectral density all over the spectrum, e.g. -170
dBm/Hz.

Now, if your receiver bandwidth is set to 2 MHz (because that's what
your SDR is probably configured to filter out if you ask for 2 MS/s),
then you get twice as much noise power than if you set the sampling
rate
to 1 MS/s.

It's the same thing that I always let students figure out by themselves
the first time they use the lab spectrum analyzer:
Feed a 2 GHz -60 dBm tone into the spectrum analyzer.
Set the resolution bandwidth of the spectrum analyzer to 1 MHz, and
tell
me what the SNR is. Now set the resolution bandwidth to 300 kHz and
tell
me again.
You get as much "N" in your SNR as you let through your system. In the
case of the spectrum analyzer, every point on the display is the power
in 1 MHz (or 300 kHz) of filter. In the case of your Qt plot, it's the
power in a FFT bin. There's (f_sample)/(FFT length) bandwidth to each
bin; so your graphical analysis hinges on the setting of sample rate
and
FFT length (also, on window choice and labeling, and software
convention). Proportionally!

It's really hard to define "SNR" for 0-bandwidth, i.e. a single tone
(having a single tone, actually, gets tricky physically, but there's a
lot of people who could tell you more about oscillators than I could).

If you'd be fair, the only choice for the noise filter bandwidth would
be 0 Hz, because if you chose any wider, you always get more noise. But
in 0 Hz, there's actually 0 noise power! So, that doesn't work.

Instead, you need to define SNR exactly on the bandwidth your detection
system will have to use. That's a design parameter you haven't
mentioned
so far!

 > This
 > is why I referenced the green and red lines on the qt gui freq.
display,
 > this would seem to give me signal strength in dB.

Hopefully, above explained how much these lines depend on your
configuration and aren't "SNR".

Cheers,

Re: Calculating SNR of an incoming signal

[Alex Batts]

The effective noise bandwidth is part of the calculation. I'm using the
radar range equation.

My purpose for including the bandwidth in my response was that any time I
try to use a filter with a frequency greater than my sampling rate/2 I get
an error returned. I agree that ideally I would use a band-pass filter with
very narrow cutoffs to best capture the signal in its entirety, however, I
can't because the frequency I'm trying to set my filter at is more than
half my sampling rate, giving me an error. Maybe there is something askew
with that error and it's something else, but it returns saying 0 < fa <=
sampling_rate/2

On Thu, Jun 25, 2020 at 3:27 PM Marcus Müller  wrote:

> Hi Alex,
>
> On 25/06/2020 21.00, Alex Batts wrote:
> > I'm sampling an incoming signal, but only around 2 MSps.
> >
>
> and that's fine! that's the *equivalent* baseband, it has all the same
> information as the RF signal.
>
> > I need the signal power to noise power ratio at the receiver as part of
> > my range calculation.
>
> Yes, but you'd always want to do that "signal to noise" only in the
> bandwidth that actually contains your tone; the rest will just contain
> more noise, interferers... to make your measurement worse.
>
> > So I would need to be able to distinguish between
> > the power of the tone vs the power of the surrounding noise and use
> > those two numerical values in an equation to calculate the range.
>
> You need to define "surrounding"! Your signal doesn't get worse by
> applying a filter that only selects your tone and as little else as
> possible. So you should do that – it makes your SNR better. Hence, your
> Signal power estimate gets more reliable (which you definitely want).
>
> (that also highlights why I have a bit of doubt on your measurement
> methodology – if your SNR depends on receiver bandwidth, then how much
> does it actually tell you about the range, unless you specify the
> bandwidth alongside with it?)
>
> Think about it: we typically assume noise to be white, i.e. to have
> identical power spectral density all over the spectrum, e.g. -170 dBm/Hz.
>
> Now, if your receiver bandwidth is set to 2 MHz (because that's what
> your SDR is probably configured to filter out if you ask for 2 MS/s),
> then you get twice as much noise power than if you set the sampling rate
> to 1 MS/s.
>
> It's the same thing that I always let students figure out by themselves
> the first time they use the lab spectrum analyzer:
> Feed a 2 GHz -60 dBm tone into the spectrum analyzer.
> Set the resolution bandwidth of the spectrum analyzer to 1 MHz, and tell
> me what the SNR is. Now set the resolution bandwidth to 300 kHz and tell
> me again.
> You get as much "N" in your SNR as you let through your system. In the
> case of the spectrum analyzer, every point on the display is the power
> in 1 MHz (or 300 kHz) of filter. In the case of your Qt plot, it's the
> power in a FFT bin. There's (f_sample)/(FFT length) bandwidth to each
> bin; so your graphical analysis hinges on the setting of sample rate and
> FFT length (also, on window choice and labeling, and software
> convention). Proportionally!
>
> It's really hard to define "SNR" for 0-bandwidth, i.e. a single tone
> (having a single tone, actually, gets tricky physically, but there's a
> lot of people who could tell you more about oscillators than I could).
>
> If you'd be fair, the only choice for the noise filter bandwidth would
> be 0 Hz, because if you chose any wider, you always get more noise. But
> in 0 Hz, there's actually 0 noise power! So, that doesn't work.
>
> Instead, you need to define SNR exactly on the bandwidth your detection
> system will have to use. That's a design parameter you haven't mentioned
> so far!
>
> > This
> > is why I referenced the green and red lines on the qt gui freq. display,
> > this would seem to give me signal strength in dB.
>
> Hopefully, above explained how much these lines depend on your
> configuration and aren't "SNR".
>
> Cheers,
> Marcus
>
>

Re: Calculating SNR of an incoming signal

[Marcus Müller]

Hi Alex,

On 25/06/2020 21.00, Alex Batts wrote:

I'm sampling an incoming signal, but only around 2 MSps.



and that's fine! that's the *equivalent* baseband, it has all the same 
information as the RF signal.


I need the signal power to noise power ratio at the receiver as part of 
my range calculation. 


Yes, but you'd always want to do that "signal to noise" only in the 
bandwidth that actually contains your tone; the rest will just contain 
more noise, interferers... to make your measurement worse.


So I would need to be able to distinguish between 
the power of the tone vs the power of the surrounding noise and use 
those two numerical values in an equation to calculate the range. 


You need to define "surrounding"! Your signal doesn't get worse by 
applying a filter that only selects your tone and as little else as 
possible. So you should do that – it makes your SNR better. Hence, your 
Signal power estimate gets more reliable (which you definitely want).


(that also highlights why I have a bit of doubt on your measurement 
methodology – if your SNR depends on receiver bandwidth, then how much 
does it actually tell you about the range, unless you specify the 
bandwidth alongside with it?)


Think about it: we typically assume noise to be white, i.e. to have 
identical power spectral density all over the spectrum, e.g. -170 dBm/Hz.


Now, if your receiver bandwidth is set to 2 MHz (because that's what 
your SDR is probably configured to filter out if you ask for 2 MS/s), 
then you get twice as much noise power than if you set the sampling rate 
to 1 MS/s.


It's the same thing that I always let students figure out by themselves 
the first time they use the lab spectrum analyzer:

Feed a 2 GHz -60 dBm tone into the spectrum analyzer.
Set the resolution bandwidth of the spectrum analyzer to 1 MHz, and tell 
me what the SNR is. Now set the resolution bandwidth to 300 kHz and tell 
me again.
You get as much "N" in your SNR as you let through your system. In the 
case of the spectrum analyzer, every point on the display is the power 
in 1 MHz (or 300 kHz) of filter. In the case of your Qt plot, it's the 
power in a FFT bin. There's (f_sample)/(FFT length) bandwidth to each 
bin; so your graphical analysis hinges on the setting of sample rate and 
FFT length (also, on window choice and labeling, and software 
convention). Proportionally!


It's really hard to define "SNR" for 0-bandwidth, i.e. a single tone 
(having a single tone, actually, gets tricky physically, but there's a 
lot of people who could tell you more about oscillators than I could).


If you'd be fair, the only choice for the noise filter bandwidth would 
be 0 Hz, because if you chose any wider, you always get more noise. But 
in 0 Hz, there's actually 0 noise power! So, that doesn't work.


Instead, you need to define SNR exactly on the bandwidth your detection 
system will have to use. That's a design parameter you haven't mentioned 
so far!


This 
is why I referenced the green and red lines on the qt gui freq. display, 
this would seem to give me signal strength in dB.


Hopefully, above explained how much these lines depend on your 
configuration and aren't "SNR".


Cheers,
Marcus



smime.p7s
Description: S/MIME Cryptographic Signature

Re: Calculating SNR of an incoming signal

[Alex Batts]

I'm sampling an incoming signal, but only around 2 MSps.

I need the signal power to noise power ratio at the receiver as part of my
range calculation. So I would need to be able to distinguish between the
power of the tone vs the power of the surrounding noise and use those two
numerical values in an equation to calculate the range. This is why I
referenced the green and red lines on the qt gui freq. display, this would
seem to give me signal strength in dB.

On Thu, Jun 25, 2020 at 2:51 PM Marcus Müller  wrote:

> But you're sampling something, or else you couldn't process this in GNU
> Radio. So, I'm a bit confused about what you're actually doing.
>
>
> On 25/06/2020 20.48, Alex Batts wrote:
> > Sorry, I'm new to the mailing list as well.
> >
> > How would you recommend isolating the tone power? A band pass filter
> > wouldn't work at that frequency since there isn't an SDR that can sample
> > that high. Would that be where the Phase Locked Loop comes into play?
> >
> > Thank you for your help to this point,
> >
> > Alex
> >
> > On Thu, Jun 25, 2020 at 1:41 PM Marcus Müller  > > wrote:
> >
> > Hi Alex,
> >
> > can you make sure to reply to the mailing list, not just me alone?
> > Others usually take interest in discussion, too :)
> >
> > Well, then it's easy.
> >
> > Total signal power is simply the average magnitude square of your
> > received signal
> > You just need to subtract the power of the tone (that's its squared
> > amplitude) and get the noise power.
> >
> > Divide these two, and you get SNR.
> >
> > However, since this is the description of a Radar that assumes its
> > targets are stationary, you'd probably use a PLL to remove the noise
> > bandwidth drastically, so not quite sure that kind of SNR
> > measurement is
> > extremely useful for realistic system comparison!
> >
> > Best regards,
> > Marcus
> > On 24/06/2020 16.58, Alex Batts wrote:
> >  > Hello,
> >  >
> >  > __ __
> >  >
> >  > The incoming signal is going to be a specific tone, probably
> > around 5.8
> >  > GHz. I am going to be using it for radar range detection. My SDR
> > will
> >  > just passively receive the reflected signal off of the object and
> > use
> >  > the SNR in the range calculation.
> >  >
> >  > __ __
> >  >
> >  > Thank you,
> >  >
> >  > __ __
> >  >
> >  > Alex
> >  >
> >  > __ __
> >  >
> >
>
>

Re: Calculating SNR of an incoming signal

[Marcus Müller]

But you're sampling something, or else you couldn't process this in GNU 
Radio. So, I'm a bit confused about what you're actually doing.



On 25/06/2020 20.48, Alex Batts wrote:

Sorry, I'm new to the mailing list as well.

How would you recommend isolating the tone power? A band pass filter 
wouldn't work at that frequency since there isn't an SDR that can sample 
that high. Would that be where the Phase Locked Loop comes into play?


Thank you for your help to this point,

Alex

On Thu, Jun 25, 2020 at 1:41 PM Marcus Müller > wrote:


Hi Alex,

can you make sure to reply to the mailing list, not just me alone?
Others usually take interest in discussion, too :)

Well, then it's easy.

Total signal power is simply the average magnitude square of your
received signal
You just need to subtract the power of the tone (that's its squared
amplitude) and get the noise power.

Divide these two, and you get SNR.

However, since this is the description of a Radar that assumes its
targets are stationary, you'd probably use a PLL to remove the noise
bandwidth drastically, so not quite sure that kind of SNR
measurement is
extremely useful for realistic system comparison!

Best regards,
Marcus
On 24/06/2020 16.58, Alex Batts wrote:
 > Hello,
 >
 > __ __
 >
 > The incoming signal is going to be a specific tone, probably
around 5.8
 > GHz. I am going to be using it for radar range detection. My SDR
will
 > just passively receive the reflected signal off of the object and
use
 > the SNR in the range calculation.
 >
 > __ __
 >
 > Thank you,
 >
 > __ __
 >
 > Alex
 >
 > __ __
 >





smime.p7s
Description: S/MIME Cryptographic Signature

Re: Calculating SNR of an incoming signal

[Alex Batts]

Sorry, I'm new to the mailing list as well.

How would you recommend isolating the tone power? A band pass filter
wouldn't work at that frequency since there isn't an SDR that can sample
that high. Would that be where the Phase Locked Loop comes into play?

Thank you for your help to this point,

Alex

On Thu, Jun 25, 2020 at 1:41 PM Marcus Müller  wrote:

> Hi Alex,
>
> can you make sure to reply to the mailing list, not just me alone?
> Others usually take interest in discussion, too :)
>
> Well, then it's easy.
>
> Total signal power is simply the average magnitude square of your
> received signal
> You just need to subtract the power of the tone (that's its squared
> amplitude) and get the noise power.
>
> Divide these two, and you get SNR.
>
> However, since this is the description of a Radar that assumes its
> targets are stationary, you'd probably use a PLL to remove the noise
> bandwidth drastically, so not quite sure that kind of SNR measurement is
> extremely useful for realistic system comparison!
>
> Best regards,
> Marcus
> On 24/06/2020 16.58, Alex Batts wrote:
> > Hello,
> >
> > __ __
> >
> > The incoming signal is going to be a specific tone, probably around 5.8
> > GHz. I am going to be using it for radar range detection. My SDR will
> > just passively receive the reflected signal off of the object and use
> > the SNR in the range calculation.
> >
> > __ __
> >
> > Thank you,
> >
> > __ __
> >
> > Alex
> >
> > __ __
> >
>
>

Re: Calculating SNR of an incoming signal

[Marcus Müller]

Hi Alex,

can you make sure to reply to the mailing list, not just me alone? 
Others usually take interest in discussion, too :)


Well, then it's easy.

Total signal power is simply the average magnitude square of your 
received signal
You just need to subtract the power of the tone (that's its squared 
amplitude) and get the noise power.


Divide these two, and you get SNR.

However, since this is the description of a Radar that assumes its 
targets are stationary, you'd probably use a PLL to remove the noise 
bandwidth drastically, so not quite sure that kind of SNR measurement is 
extremely useful for realistic system comparison!


Best regards,
Marcus
On 24/06/2020 16.58, Alex Batts wrote:

Hello,

__ __

The incoming signal is going to be a specific tone, probably around 5.8 
GHz. I am going to be using it for radar range detection. My SDR will 
just passively receive the reflected signal off of the object and use 
the SNR in the range calculation.


__ __

Thank you,

__ __

Alex

__ __





smime.p7s
Description: S/MIME Cryptographic Signature

Re: Calculating SNR of an incoming signal

[Marcus Müller]

Hi Alex,

one's signal is another person's noise... You need to define of what 
nature your signal is, and then you can (often) quite easily build an 
SNR estimator for that specific signal :)


Best regards,
Marcus

On 24/06/2020 14.58, Alex Batts wrote:

Hello,

I am relatively new to GNU Radio and I am trying to calculate the SNR of 
an incoming signal. On the QT Gui frequency display it shows a red line 
and a green line which I take to be the average noise power and average 
signal power of the incoming signal (from my RTL SDR) respectively. Is 
there any way I can utilize in real time the values of these two lines 
to calculate an SNR? If not, is there a way to determine a value at a 
specific frequency/average value over a range of frequencies for this 
calculation?


Thank you in advance,

Alex




smime.p7s
Description: S/MIME Cryptographic Signature

Calculating SNR of an incoming signal

[Alex Batts]

Hello,

I am relatively new to GNU Radio and I am trying to calculate the SNR of an
incoming signal. On the QT Gui frequency display it shows a red line and a
green line which I take to be the average noise power and average signal
power of the incoming signal (from my RTL SDR) respectively. Is there any
way I can utilize in real time the values of these two lines to calculate
an SNR? If not, is there a way to determine a value at a specific
frequency/average value over a range of frequencies for this calculation?

Thank you in advance,

Alex