add white gaussian noise

I tried to add noise to a signal. The signal noise ratio must be 0 dB. I tried with

   signal_noise=awgn(signal,0,'measured')

Is there any method?

Answer 1

[OCDER]

signal_noise=awgn(signal,1,'measured')

SNR = 1 means 0 dB.

[Jessie Bessel]

Ok.Any method, without awgn?

[OCDER]

noise = sig * randn(size(signal)); %sig is your standard dev.
signa_noise = signal + noise       %you have to determine value of "sig". 
                                   %sig = std(signal)  ?

Answer 2

[Meg Noah]

@Jessie Bessel

% signal is a sine wave of 2 Hz
nSamples = 1000;
f = 2; % [Hz]
time        = linspace(0, 2, nSamples+1);
signal   = sin(2*pi*f*time);

signal_noise=awgn(signal,0,'measured');

% calculate the signal power
signalPower = sum((signal).^2)./nSamples;

% the gaussian white noise
noiseValues = signal_noise - signal;

% verify the Signal-to-Noise value
noisePower = sum(noiseValues.^2)/numel(noiseValues);
SNR = 10*log10(signalPower/noisePower);
fprintf(1,"standard deviation of noise = %f\n", std(noiseValues));

standard deviation of noise = 0.720478

fprintf(1,"SNR: %f\n", SNR);

SNR: -0.158400

% Method WITHOUT the awgn
% SNR in db is 10log(Psignal/Pnoise)
snrDb = 0; % [dB]
 
% noise power such that signal power is 10 dB more 
% 10 = 10 log (Ps / Pn)
% Pn is variance which for zero mean gaussian noise 
% is essentially - square sum of all samples -> divided by numSamples
noiseStd = sqrt(signalPower / 10^(snrDb/10));
noiseMean = 0;

% generate the gaussian white noise
noiseValues = noiseStd*randn(nSamples,1) + noiseMean;

% verify the Signal-to-Noise value
noisePower = sum(noiseValues.^2)/numel(noiseValues);
SNR = 10*log10(signalPower/noisePower);
fprintf(1,"noiseStd: model input: %f simulation output: %f\n", noiseStd, std(noiseValues));

noiseStd: model input: 0.707107 simulation output: 0.699265

fprintf(1,"SNR: %f\n", SNR);

SNR: 0.094870