>...assume the symbol T=1 
clear all 
close all 
bit_in = randint(1e3, 1, [0 1]); 
bit_I = bit_in(1:2:1e3); 
bit_Q = bit_in(2:2:1e3); 

data_I = -2*bit_I+1; 
data_Q = -2*bit_Q+1; 

data_I1=repmat(data_I',20,1); 
data_Q1=repmat(data_Q',20,1); 

for i=1:1e4 
data_I2(i)=data_I1(i); 
data_Q2(i)=data_Q1(i); 
end; 

t=0:0.1:1e3-0.1; 

f=0:0.1:1; 
xrc=0.5+0.5*cos(pi*f); 

data_I2_rc=conv(data_I2,xrc)/5.5; 
data_Q2_rc=conv(data_Q2,xrc)/5.5; 

f1=1; 
t1=0:0.1:1e3+0.9; 

I_rc=data_I2_rc.*cos(2*pi*f1*t1); 
Q_rc=data_Q2_rc.*sin(2*pi*f1*t1); 
QPSK_rc=(sqrt(1/2).*I_rc+sqrt(1/2).*Q_rc); 

>>..demodulation 
I_demo=QPSK_rc.*cos(2*pi*f1*t1); 
Q_demo=QPSK_rc.*sin(2*pi*f1*t1); 

I_recover=conv(I_demo,xrc); 
Q_recover=conv(Q_demo,xrc); 
I=I_recover(11:10010); 
Q=Q_recover(11:10010); 
t2=0:0.05:1e3-0.05; 
t3=0:0.1:1e3-0.1; 


data_recover=[]; 
for i=1:20:10000 
data_recover=[data_recover I(i:1:i+19) Q(i:1:i+19)]; 
end; 


ddd = -2*bit_in+1; 
ddd1=repmat(ddd',10,1); 
for i=1:1e4 
ddd2(i)=ddd1(i); 
end 


figure(1) 
subplot(4,1,1);plot(t3,I);axis([0 20 -6 6]); 
subplot(4,1,2);plot(t3,Q);axis([0 20 -6 6]); 
subplot(4,1,3);plot(t2,data_recover);axis([0 20 -6 6]); 
subplot(4,1,4);plot(t,ddd2);axis([0 20 -6 6]); 

> figure(2) 
> subplot(2,1,1);plot(t1,I_rc);axis([0 1e3+0.9 -3 3]); 
> subplot(2,1,2);plot(t1,Q_rc);axis([0 1e3+0.9 -3 3]); 
> 
> figure(3) 
> subplot(2,1,1);plot(t1,data_I2_rc);axis([0 1e3+0.9 -3 3]); 
> subplot(2,1,2);plot(t1,data_Q2_rc);axis([0 1e3+0.9 -3 3]); 
> 
figure(4) 
subplot(2,1,1);plot(data_I2);axis([0 10000 -3 3]); 
subplot(2,1,2);plot(data_Q2);axis([0 10000 -3 3]);