www.pudn.com > awgn$qpsk.rar > QPSK_RAYLEIGH_draw.m
> QPSK with Rayleigh channel
clear;
> initialization
T=1; > symbol duration
SNR=8; > signal to noise ratio
fc=6/T; > carrier frequence
ml=2; > modulation of level ml£½1 BPSK£¬ml£½2 QPSK
nb=100; > number of transmiting bits
delta_T=T/200; > sampling interval
fs=1/delta_T; > sampling frequency
t=0:delta_T:nb*T-delta_T;
N=length(t); > number of samples
> generate source data
data=randn(1,nb)>0.5;
datanrz=data.*2-1; > translate source data into NRZ code
data1=zeros(1,nb/delta_T);
for q=1:nb
data1((q-1)/delta_T+1:q/delta_T)=datanrz(q);
end > transmiting signal
data2=abs(fft(data1));
> S/P conversion
idata=datanrz(1:ml:(nb-1));
qdata=datanrz(2:ml:nb);
> QPSK modulation
ich=zeros(1,nb/2/delta_T);
for i=1:nb/2
ich((i-1)/delta_T+1:i/delta_T)=idata(i);
end
for ii=1:N/2
a(ii)=sqrt(2/T)*cos(2*pi*fc*t(ii));
end
idata1=ich.*a; > I-channel multiply carrier
qch=zeros(1,nb/2/delta_T);
for j=1:nb/2
qch((j-1)/delta_T+1:j/delta_T)=qdata(j);
end
for jj=1:N/2
b(jj)=sqrt(2/T)*sin(2*pi*fc*t(jj));
end
qdata1=qch.*b; > Q-channel multiply carrier
s=idata1+qdata1; > QPSK modulated signal
> through rayleigh channel
ray_ich=raylrnd(0.8,1,nb/2/delta_T);
ray_qch=raylrnd(0.8,1,nb/2/delta_T);
idata2=idata1.*ray_ich;
qdata2=qdata1.*ray_qch;
s1=idata2+qdata2;
s2=awgn(s1,SNR);
> QPSK demodulation
idata3=s2.*a;
qdata3=s2.*b; > multiply carrier
idata4=zeros(1,nb/2);
qdata4=zeros(1,nb/2);
for n=1:nb/2
ichsum(n)=sum(idata3((n-1)/delta_T+1:n/delta_T))*delta_T;
if ichsum(n)>=0
idata4(n)=1;
else idata4(n)=0;
end
qchsum(n)=sum(qdata3((n-1)/delta_T+1:n/delta_T))*delta_T;
if qchsum(n)>=0
qdata4(n)=1;
else qdata4(n)=0;
end
end > integral and decision
> P/S conversion
demodata=zeros(1,nb);
demodata(1:ml:(nb-1))=idata4;
demodata(2:ml:nb)=qdata4;
> calculate number of error
num_BER=sum(abs(demodata-data))
> plot commends
figure(1)
plot(data1),title('baseband signal');
figure(2)
pwelch(data1,[],[],[],200),title('baseband signal power spectrum');
figure(3)
plot(s),title('modulated signal');
axis([0 500 -3 3]);
figure(4)
pwelch(s,[],[],[],200),title('modulated signal power spectrum');
figure(5)
for i=1:nb/2
plot(idata(i),qdata(i),'ro'),title('constellation');hold on;
axis([-2 2 -2 2]);
plot(ichsum(i),qchsum(i),'*');hold on;
legend('before channel','after channel');
end