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Re: [Discuss-gnuradio] BER over air

From: Mostafa Alizadeh
Subject: Re: [Discuss-gnuradio] BER over air
Date: Mon, 29 Dec 2014 16:28:08 +0330

Hi Marcus, 

I completely agree to the statement. But take a look at this simple model: 

y(t) = h(t) * x(t) + n(t).

'y' is the received signal, 'h' is the channel response (here I assumed that the channel is linear as a filter), 'x' is the desired signal and 'n' is noise and the sign '*' is the convolution. Hence, if we try to find signal (x) power to noise (n), it implies that the 'h' is somehow estimated. Again, consider that noise and channel are different both statistically and in nature.

take look at the  "Tom Rondeau"s website: 


He said: 

" In the case of an SNR estimator, though, I thought about this and had to come to the conclusion that the only way to handle this is to have an estimator that you can plug in variables for your channel model, which of course assumes that you have or can estimate these parameters."

So we need acquire 'h'. 


On Mon, Dec 29, 2014 at 3:42 PM, Marcus Müller <address@hidden> wrote:
Hello Mostafa,
On 12/29/2014 12:55 PM, Mostafa Alizadeh wrote:
I finally got to this point that if one need to measure SNR, it means that he/she has to eliminate all the other channel effects as well as receiver uncertainties, (like fading, shadowing, Doppler shift, carrier frequency and phase offsets etc.) to have a correct estimate of SNR.
SNR is relative to signal. Signal is what you define it to be. You can say "I measure my SNR after equalizing and perfect synchronization", you could also say "the power of the signal coming out of the receiver amplifier relative to the noise generated in that amplifier, before any filtering". It's all up to your definition. I will never cease to repeat that.

There is no physical entity SNR to measure. When you say "SNR is XY dB", it is utterly meaningless unless you define what your signal is and where in your signal processing chain you determine the SNR.
Otherwise, he/she coudln't obtain signal-to-noise power ratio. 

Remember the received signal formulation I mentioned before: 
y(t) = h(t) * x(t) + n(t).

Thank you all. Any interesting ideas would be appreciated.
... you're still asking for easy ideas how to solve your problem which is complicated. You will have to accept the fact that SNR is not a universal measure with a "right" way to measure for any kind of signal, any kind of channel, any kind of system.


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