function ifreq_N = demod_ifreq (iphase)
%function [ifreq_N, mean_ifreq] = demod_ifreq (iphase)

%Gererate the Instantaneous Phase
%
global k Fc Fd Fs n;

N = length(iphase);
ifreq(2:N) = iphase(2:N) - iphase(1:N-1);
ifreq(1) = ifreq(2);   

% reduce the non-expected Pulse.
for i = N-1:-1:2;
    if abs( ifreq(i) )  > 1 ; 
        ifreq(i) = ifreq(i+1);
    end
end

%ifreq = ifreq*Fs +Fc;
%mean_ifreq = sum( ifreq )/N;
%ifreq_c = ifreq - mean_ifreq;  %% Non-linear Instaneous Phase (NL_iphase)
ifreq_c = ifreq;

ifreq_N = ifreq_c *Fs/2/Fd; % change to Inst. Freq.


%%%%%%%%%%%%%%%%%%%%%%%%%%
%% Plot the Instantaneous Phase & Frequency

%下面是屏蔽原來的畫圖程序
%%for i = 1:1     % Set 1:0 to cancel the plot function.
    
%%figure (931);
%%subplot (2,1,1);
%%stairs ((1:N), iphase);
%%title ('Demodulated Instantaneous Phase');

%%subplot (2,1,2);
%%stairs ((1:N), ifreq);
%%title ('Demodulated Instantaneous Frequence');

%%end