% FSK-FM方案的可解調問題。
% 高斯噪聲 SNR = 2OdB;并假設鏡像信號非常小。仿真設置5％。
clear all;
clc ;
% ******************
% 定義兩個基帶信號的相關參量
L = 5;
w1 = 2*pi*5;
w2 = 2*pi*1;

t = 0:8/2599:8;
R1C = 0.03;
snr = 20;
Ref = 4;

k =2*pi*4;
x = 0:10/29:10;
y = 0:10/29:10;
% 隨機信號
rd =  randint(1,10);

for i = 1:length(x)
 
    theta1 = sqrt(x(i)^2+(y(i)-L/2)^2);
    theta2 = sqrt(x(i)^2+(y(i)+L/2)^2);
   
    s_a1 = cos(w1*t-k*theta1);
    s_a2 = cos(w2*t-k*theta1);
    s_b1 = cos(w1*t-k*theta2);
    s_b2 = cos(w2*t-k*theta2);
    
%  FSK 調制
        for m = 1:10
            M=(m-1)*260+1:(m*260); 
              srand(M) = (rd(m)*4+Ref)*ones(1,260);
                if srand(:,M) ~= Ref
                    s1(M) = s_a1(M)*4;
                else 
                    s1(M) = s_a2(M)*4;
                end
        end
        
        for m = 1:10
            M=(m-1)*260+1:(m*260); 
              srand(M) = (rd(m)*4+Ref)*ones(1,260);
                if srand(:,M) ~= Ref
                    s1_image(M) = s_b1(M)*4;
                else 
                    s1_image(M) = s_b2(M)*4;
                end
        end    
% FM 調制
Fs = 120;
Fc = 20;
dev = 1;
s1_fmmod = fmmod(s1,Fc,Fs,dev); 
s1_image_fmmod = fmmod(s1_image,Fc,Fs,dev);
s1_fmmod_awgn = awgn(s1_fmmod,snr);
s1_image_fmmod_awgn = awgn(s1_image_fmmod,snr);
% 疊加
% s_fmmod =  s1_fmmod+s1_image_fmmod;
s_fmmod = s1_fmmod_awgn+0.05*s1_image_fmmod_awgn;
t_diff = t(2:end);
% 微分
s_diff = abs(diff(s_fmmod)./diff(t))/100;
% 包絡處理
sfilter = 1/R1C*exp(-t_diff/R1C)/3;
sfft = fft(s_diff).*fft(sfilter)/100;
sifft = ifft(sfft);
% 作圖
figure(2)
subplot(411),plot(t,s1_image);
xlabel('(a)')
subplot(412),plot(t,s_fmmod);
xlabel('(b)')
axis([0 8 -3 3])
subplot(413),plot(t_diff,s_diff);
xlabel('(c)')
subplot(414),plot(t_diff,sifft);  
xlabel('(d)')
end