%
% FUNCTION 8.3 : "cp0801_Gnoise2"
%
% Introduces additive white Gaussian noise over signal
% 'input'.
% Vector 'exno' contains the target values of Ex/No (in dB)
% 'numpulses' is the number of pulses composing the input
% signal
% 
% Multiple output signals are generated, one signal for
% each target value of Ex/No. The array 'output' contains
% all the signals (input+AWGN), one signal per row.
% The array 'noise' contains the different realization of 
% the Gaussian noise, one realization per each row.
%
% Programmed by Guerino Giancola
%

function [output,noise] = ...
   cp0801_Gnoise2(input,exno,numpulses)

% -------------------------------
% Step One - Introduction of AWGN
% -------------------------------

Ex = (1/numpulses)*sum(input.^2);  % measured energy per
                                   %  pulse
ExNo = 10.^(exno./10);             % Ex/No in linear units     
No = Ex ./ ExNo;                   % Unilateral spectral
                                   %  density
nstdv = sqrt(No./2);               % Standard deviation for
                                   %  the noise

for j = 1 : length(ExNo)
        
    noise(j,:) = nstdv(j) .* randn(1,length(input));
    output(j,:) = noise(j,:) + input;
    
end