%Program 1
%qpsk_fading.m
%******************************* Preparation part ************************  
sr=1000; %設碼元速率為1000
ml=2;
fc=10;    %fc是載波頻率
nd=1000;  %設置傳輸碼元個數，
br=sr*ml;  %bit率
ebn0=5;   %EB/N0=5
%****************************** data generation **************************
data1=rand(1,1000*ml)>0.5;  %產生服從0—1分布隨機數
%***************************** qpsk modulation ***************************
t=-500*1/sr+1/sr:1/sr:500*1/sr;
n=length(t);
data2=data1*2-1;        %轉化成－1，1的序列
[ich,qch]=qpskmod(data2,1,nd,ml);
tich=ich.*cos(2*pi*fc*t); %Qpsk調制，I signal碼元乘載波
tqch=qch.*sin(2*pi*fc*t); %Q signal碼元乘載波
ampitude_modulated=tich+tqch;
                               %%%提取星座圖1
%**************************** Rayleigh fading *************************
[tich2,tqch2]=ray(tich,tqch); %調用Rayleigh fading的產生
n1=sqrt(tich2.*tich2+tqch2.*tqch2);  %Rayleigh fading I和Q信號的幅度均方值
tich2=tich.*n1;
tqch2=tqch.*n1;
%***************************** Attenuation Calculation******************
spow=sum(tich.*tich+tqch.*tqch)/nd;
attn=0.5*spow*sr/br*10.^(-ebn0/10);
attn=sqrt(attn);
%***************************** AGWN ************************************
[ich2,qch2]=comb(tich2,tqch2,attn); %加性高斯白噪聲   
recieved_amplitude=ich2+qch2;
                             %%%提取星座圖2
%**************************** qpsk demodulation ************************
rich=ich2.*cos(2*pi*fc*t);       %對I信號分量解調
rqch=qch2.*sin(2*pi*fc*t);       
ampitude_demodulated=rich+rqch;
%[demodata]=qpskdemod(ich2,qch2,1,nd,ml);
%*************************** BER ********************************
%demodata=zeros(1,ml*nd);      
demodata((1:1),(1:ml:ml*nd-1))=rich((1:1),(1:nd))>=0;  %對I分量判決
demodata((1:1),(2:ml:ml*nd))=rqch((1:1),(1:nd))>=0;    %對Q分量判決
%noe=sum(abs(data1-demodata));  %計算誤碼率
%*************************** draw the figure **********************
figure(2); %%%%%source圖形
plot(data2);
title('Source figure');

figure(3);
plot(t,ampitude_modulated);%%%qpsk調制后的圖形
title('figure after modulation');
figure(100);   %%%%星座圖1
plot(tich,tqch,'.');
title('constellation before channel');

figure(4);%%%%%%%%%%% qpsk+raylaigh_fading圖形
plot(t,recieved_amplitude);
title('figuer qpsk+Raylaigh _ fading');
figure(101);   %%%%星座圖2
plot(ich2,qch2,'.');
title('constellation after channel');

figure(5);%%%%%%%%%%%%%% 解調信號圖形
plot(t,ampitude_demodulated);
title('figure after demodulation');

figure(6);
plot(demodata);
title('figure after demodulation11');