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How to add to a signal white gaussian noise of exact SNR?

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lincolndsp

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matlab question

How can I accurately add to my signal white
gaussian noise of exact SNR in dB (in POWER not
voltage terms)?
when I use awgn(...) function it seems
to me the noise has more power than I
set in its SNR parameter.
 

matlab question

Added after 24 seconds:

Hi

That is not really true, after adding the awgn to your signal by the awgn() function, you can substract your original signal and then calculate the energy of both signals, this will clear your doubts. Mind the dB conversion.

Sal
 

matlab question

Y = AWGN(X,SNR) adds white Gaussian noise to X. The SNR is in dB.
The power of X is assumed to be 0 dBW. If X is complex, then
AWGN adds complex noise.

Y = AWGN(X,SNR,SIGPOWER) when SIGPOWER is numeric, it represents
the signal power in dBW. When SIGPOWER is 'measured', AWGN measures
the signal power before adding noise.
 

Re: matlab question

hi...
i m giving u somepart of Eric Cosby's program, u can use it to calculate it...

%suppose u have Tx_data, and now u want add awgn noise
SNR=13; % in dB
Tx_signal_power = var(Tx_data);
%
linear_SNR = 10^(SNR/10);
noise_sigma = Tx_signal_power/linear_SNR;
noise_scale_factor = sqrt(noise_sigma);
%
noise = randn(1, length(Tx_data))*noise_scale_factor;



REGARDS
 

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    lincolndsp

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