clear all;
% To specify the power of X to be 0 dBW and add noise to produce
% an SNR of 10dB, use:
X = sqrt(2)*sin(0:pi/8:6*pi);
Y = awgn(X,10,0);
% To specify the power of X to be 3 Watts and add noise to
% produce a linear SNR of 4, use:
Y1 = awgn(X,4,3,'linear');
% To cause awgn to measure the power of X and add noise to
% produce a linear SNR of 4, use:
Y2 = awgn(X,4,'measured','linear'); % 
subplot(411);
plot(X);
subplot(412);
plot(Y);
subplot(413);
plot(Y1);
subplot(414);
plot(Y2);