qpsk_ber.m

这是有关matlab结课作业

%...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;
% plot(t,data_I2);axis([0 1e3 -2 2]);

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;
n0=randn(size(t1));
I_rc=data_I2_rc.*cos(2*pi*f1*t1);
Q_rc=data_Q2_rc.*sin(2*pi*f1*t1);
QPSK_rc_n0=(sqrt(1/2).*I_rc+sqrt(1/2).*Q_rc)+n0;

%%..demodulation
I_demo=QPSK_rc_n0.*cos(2*pi*f1*t1);
Q_demo=QPSK_rc_n0.*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;




% figure(1)
% subplot(3,1,1);plot(t3,I);axis([0 10 -6 6]);
% subplot(3,1,2);plot(t3,Q);axis([0 10 -6 6]);
% subplot(3,1,3);plot(t2,data_recover);axis([0 10 -6 6]);
% 
% figure(2)
% subplot(2,1,1);plot(I_rc);axis([0 10000 -3 3]);
% subplot(2,1,2);plot(Q_rc);axis([0 10000 -3 3]);
% 
% figure(3)
% subplot(2,1,1);plot(data_I2_rc);axis([0 10000 -3 3]);
% subplot(2,1,2);plot(data_Q2_rc);axis([0 10000 -3 3]);

bit_recover=[];
for i=1:20:20000
    if sum(data_recover(i:i+19))>0
        data_recover_a(i:i+19)=1;
        bit_recover=[bit_recover 1];
    else
        data_recover_a(i:i+19)=-1;
        bit_recover=[bit_recover -1];
    end
end

error=0;

dd = -2*bit_in+1;
ddd=[dd'];
ddd1=repmat(ddd,20,1);
for i=1:2e4
    ddd2(i)=ddd1(i);
end
for i=1:1e3
    if bit_recover(i)~=ddd(i)
        error=error+1
    end
end

p=error/1000



subplot(2,1,1);plot(t2,ddd2);axis([0 100 -2 2]);
subplot(2,1,2);plot(t2,data_recover_a);axis([0 100 -2 2]);