function[x] = add_noise(waveform, EbN0db, rate, a) % waveform is input data, EbNOdb is set by user, rate is the data rate, a is fam.
   en = 10^(EbN0db/10);      % convert Eb/N0 from unit db to normal numbers
   L_c = 4*a*en*rate; 	% reliability value of the channel
   sigma = 1/sqrt(2*rate*en); 	% standard deviation of AWGN noise
   x = waveform + sigma * rand