function [Acn, N_nw] = demod_Acn (yi, yq)

%%%%%%%%%%%%%%%%%%%%%%%
% Gererate the Normalized-Centred Instantaneous Amplitude of Intercepted Segments.
%
global k Fc Fd Fs n;

N = length(yi);
%An = sqrt( yi(1:N)^2 + yq(1:N)^2 );
Ai = sqrt( yi.*yi + yq.*yq );

%%%%%%%%%%%%%%%%%%%%%
% Nomalize and centralize the Ai.
mean_Ai = ( sum(Ai) ) / N;
%mean_Ai = 0.6;     for 2ASK Signals. 
An =  Ai / mean_Ai;
Acn = An -1;

for i = 1:N-1
    if abs(Acn(i)) < 0.1  %%  !!!
        Acn(i) = Acn(i+1);
    end
end


N_nw = 0;   % Number of Non-Weak samples.
%%%%%%%%%%%%%%%
%the Non-weak segment extraction function is impletmented in demod_nonweak.m
%for i = 1: N
%    if (An(i) >= 1 )  %%%% Non-weak segment Threshold.
%        N_nw = N_nw +1;
%    end
%end


%%%%%%%%%%%%%%%%%%%%%
%% Plot the Acn

%下面是屏蔽原來的畫圖程序
%%for i=1:1       % set to 1:0 to cancel the plot function.
    
%%figure (211);

%%subplot (3,1,1);
%%plot ( (1:N) , Ai );
%%hold on;
%%plot ( (1:N) , ones(1,N)*mean_Ai);
%%plot ( (1:N) , ones(1,N)*0.6, ':r');
%%hold off;

%%subplot (3,1,2);
%%plot ( (1:N) , An );

%%subplot (3,1,3);
%%plot ( (1:N) , abs(Acn) );

%%end