How to add AWGN noise using randn function?

I have a discrete time signal which I generated as follows:

I wish to add AWGN noise using randn() function with mean=0 and variance=0, 0.1, 0.5, 1, 1.5 and 3.

The code i have written is:

How can I modify my function to add the noise and later on, demodulate it back into a matrix (as shown in 'w' array)?