AWGN - Add White Gausian Noise.
to generate white gaussian noise u need function that generates random numbers with gaussian distribution (example randn in matlab)
If your enviroment doesnt have gaussian distributed random generator you have to make one using standard random generator ( ex. rand function). So u have to:
1. u = rand; generate uniform random variable (0,1) (rand function)
2. convert it to Reyleigh distributed random variable r = sqrt(2*log(1/(1-u)));
3. wgn = r*cos(2*pi*u) |your gaussian distributed random variable|
as for concept: generally noise encountered in physical systems got Gaussian probability distribution rather then uniform distibution. (u can read more in wiki on that topic)