求助matlab的QPSK解调代码 有调制的代码
这个程序写得很好的，可是解调怎么写？%file name: qpsk.m
%Written by Dr. James S. Kang, Cal Poly Pomona.
%Plot of QPSK waveform and spectrum.
%d = input data such as .
%fb = data rate in bps.
%fc = carrier frequency.
%Ac = Amplitude of the carrier.
%fstart = start frequency for spectrum plot.
%fend = end frequency for spectrum plot.
%To run the program, try
% >>qpsk(,500,1000,1,0,4000)<Enter>
function = qpsk(d,fb,fc,Ac,fstart,fend);
N=size(d,2); %N = number of data bits.
if rem(N,2) == 1
N=N+1
d(N)=0
end
N2=N/2;
M=32; %M = number of samples per bit duration.
tb=1/fb;tc=1/fc;
Nc=floor(M*tc/tb); %Nc = number of samples per period of carrier.
step=tb/M; %step = sampling interval.
for j = 1:N
if d(j) == 1
for i = 1:M
m((j-1)*M+i)=1;
end
else
for i = 1:M
m((j-1)*M+i)=-1;
end
end
end
for j = 1:N2
if d(j*2-1) == 1
for i = 1:2*M
mi((j-1)*2*M+i)=1;
si((j-1)*2*M+i)=Ac*cos(2*pi*(i-1)/Nc);
end
else
for i = 1:2*M
mi((j-1)*2*M+i)=-1;
si((j-1)*2*M+i)=Ac*cos(2*pi*(i-1)/Nc+pi);
end
end
if d(j*2) == 1
for i = 1:2*M
mq((j-1)*2*M+i)=1;
sq((j-1)*2*M+i)=Ac*sin(2*pi*(i-1)/Nc);
end
else
for i = 1:2*M
mq((j-1)*2*M+i)=-1;
sq((j-1)*2*M+i)=Ac*sin(2*pi*(i-1)/Nc+pi);
end
end
end
for k=1:M*N
t(k)=(k-1)*step;
s(k)=si(k)+sq(k);
end
figure
subplot(3,1,1)
plot(t,m)
grid
%xlabel('Time')
ylabel('Amplitude')
title('Input Waveform')
subplot(3,1,2)
plot(t,mi)
grid
%xlabel('Time')
ylabel('Amplitude')
title('I Channel Waveform')
subplot(3,1,3)
plot(t,mq)
grid
xlabel('Time')
ylabel('Amplitude')
title('Q Channel Waveform')
figure
subplot(3,1,1)
plot(t,si)
grid
%xlabel('Time')
ylabel('Amplitude')
title('I Channel Modulated Waveform')
subplot(3,1,2)
plot(t,sq)
grid
%xlabel('Time')
ylabel('Amplitude')
title('Q Channel Modulated Waveform')
subplot(3,1,3)
plot(t,s)
grid
xlabel('Time')
ylabel('Amplitude')
title('QPSK Waveform')
%
%Spectrum of QPSK
%
M1=64; %M1 = number of points per lobe.
fstep=fb/M1; %fstep = freq. step.
Nf=floor((fend-fstart)/fstep); %Nf = total number of freq. points computed.
for i = 1:Nf
f(i)=(i-1)*fstep+fstart;
if f(i) == fc S(i)=Ac^2*tb;
else
S(i)=(Ac^2*tb)*(sin(pi*(f(i)-fc)*2*tb)/(pi*(f(i)-fc)*2*tb))^2;
end
end
for i = 1:Nf
dBS(i) = 10*log(S(i));
if dBS(i) < -200 dBS(i)=-200; end
end
figure
subplot(2,1,1)
plot(f,S)
grid
%xlabel('Frequency')
ylabel('Magnitude')
title('QPSK Spectrum (Linear)')
subplot(2,1,2)
plot(f,dBS)
grid
xlabel('Frequency')
ylabel('Magnitude')
title('QPSK Spectrum (dB)')
end
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