%?MATLAB?script?for?System?Simulation?Homework?#2

clear;
clc;

%?Carrier?frequency?for?modulation?and
%?demodulation
Fc?=5e6;
%??
%?QPSK?transmitter?
%?
data_len=5000;%??Input?binary?data?of?5MHz
input=randint（1data_len）;

%Series?to?Parallel
for?i=1:data_len
????if?rem（i2）==1???????%the?remainder?of?i/2
???????if?input（i）==1
??????????I（i）=1;
??????????I（i+1）=1;
???????else
??????????I（i）=-1;
??????????I（i+1）=-1;
???????end
????else
???????if?input（i）==1
??????????Q（i-1）=1;
??????????Q（i）=1;
???????else
??????????Q（i-1）=-1;
??????????Q（i）=-1;
???????end
????end
end
%?Zero?insertion
zero=5;????%?Sampling?rate?is?25MHz
for?i=1:zero*data_len
????if?rem（izero）==1
???????Izero（i）=I（fix（（i-1）/zero）+1）;
???????Qzero（i）=Q（fix（（i-1）/zero）+1）;
????else
???????Izero（i）=0;
???????Qzero（i）=0;
????end
end

%Pulse?shaping?filter
NT?=50;
N=2*zero*NT;
Fs=25e6;
rf=0.1;
psf=rcosfir（rfNTzeroFs‘sqrt‘）;

Ipulse=?conv（Izeropsf）;
Qpulse=?conv（Qzeropsf）;

%Modulation
for?i=1:zero*data_len+N
????t（i）=（i-1）/（Fc*zero）;
????Imod（i）=Ipulse（i）.*sqrt（2）*cos（2*pi*Fc*t（i））;
????Qmod（i）=Qpulse（i）.*（-sqrt（2）*sin（2*pi*Fc*t（i）））;
end
sum=Imod+Qmod;
%
%?QPSK?Receiver
%
%?Demodulation
for?i=1:zero*data_len+N
????Idem（i）=sum（i）.*sqrt（2）*cos（2*pi*Fc*t（i））;
????Qdem（i）=sum（i）.*（-sqrt（2）*sin（2*pi*Fc*t（i）））;
end

%?Matched?filter
mtf=?rcosfir（rfNT?zeroFs‘sqrt‘）;
Imat?=?conv（Idemmtf）;
Qmat?=?conv（Qdemmtf）;

%?Data?selection
for?i=1:zero*data_len
????Isel（i）=Imat（i+N）;
????Qsel（i）=Qmat（i+N）;
end
%?Sampler
for?i?=?1:data_len
????Isam（i）=?Isel（（i-1）*zero+1）;
????Qsam（i）=?Qsel（（i-1）*zero+1）;
end

%??Decision?threshold
threshold?=?0.5;?????????%how?to?determine
for?i?=?1:data_len
????if?Isam（i）>=?threshold
???????Ifinal（i）=?1;
????else
???????Ifinal（i）=?-1;
????end
????if?Qsam（i）?>=?threshold
???????Qfinal（i）?=?1;
????else
???????Qfinal（i）=?-1;
????end
end

%??Parallel?to?Series
for?i?=?1:data_len
????if?rem（i?2）==?1
???????if?Ifinal（i）==?1
??????????final（i）=1;
???????else
??????????final（i）=?0;
???????end
????else
???????if?Qfinal（i）?==?1
??????????final（i）=?1;
???????else
??????????final（i）=?0;
???????end
????end
end

figure（1）
plot（20*log（abs（fft（input））））
axis（[0?data_len?-40?100]）
grid
title（‘Spectrum?of?Input?binary?data‘）

figure（2）
subplot（221）
plot（20*log（abs（fft（I））））
axis（[0?data_len?-40?140]）
grid
title（‘Spectrum?of?I-channel?data‘）

subplot（222）
plot（20*log（abs（fft（Q））））
axis（[0?data_len?-40?140]）
grid
title（‘Spectrum?of?Q-channel?da