y = awgn(x,snr) adds white Gaussian noise to the vector signal x. The scalar snr specifies the signal-to-noise ratio per sample, in dB.
This syntax assumes that the power of x is 0 dBW.
其中，0dBW的意思就是輸入信號的能量要歸一化為1，在bpsk調制下，X歸一化為+1和-1
Gaussian noise is defined as the noise with a Gaussian amplitude distribution.
This says nothing of the correlation of the noise in time or of the spectral density of the noise.
Labeling Gaussian noise as 'white' describes the correlation of the noise.