OFDM Demodulation problem

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yuvi
yuvi 2011-5-21
hi everybody
i have a matlab code that generates 20 bits and modulate them with OFDM, my problem is that i want to demodulate the signal and receive the same bits
i have tried to demodulate without any success
ANY HELP WILL BE APPRECIATED !
the code :
close all; clear; clc;
N=10;
fs=1e6;
T=1e-3;
% random signal
bit=randint(20,1);
% serial-to-parallel converter
par=reshape(bit,2,10);
% mapper
sym=par'*[2;1];
phase=[-3*pi/4,3*pi/4,-pi/4,pi/4];
phase_sym=phase(sym+1);
% IFFT
for k=0:N-1
i=1;
for t=1/fs:1/fs:T
x(k+1,i)=cos((2*pi*k*t)/T+phase_sym(k+1))+j*sin((2*pi*k*t)/T+phase_sym(k+1));
i=i+1;
end
end
% Base signal
base=sum(x);
subplot(2,2,1), plot(real(base))
% RF signal
f=fs*(-0.5:1/length(base):0.5-1/length(base));
rf=real(base.*exp(j*2*pi*100e3*t));
subplot(2,2,2), plot(f,rf)
% Signal in frequency domain
base_f=abs(fftshift(fft(rf)))/length(base);
subplot(2,2,3), plot(f,base_f)
% First three orthogonal sub-signals
y=[zeros(10,20000),x,zeros(10,20000)];
y2=abs(fftshift(fft(real(y(2,:)))))/length(y);
y3=abs(fftshift(fft(real(y(3,:)))))/length(y);
y4=abs(fftshift(fft(real(y(4,:)))))/length(y);
f=fs*(-0.5:1/length(y):0.5-1/length(y));
subplot(2,2,4), plot(f,y2,'r',f,y3,'b',f,y4,'g')

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回答（1 个）

Yella
Yella 2011-6-14
Am sorry I am not getting ur code... did u do demodulation?....I think u generated to subcarriers of an OFDM system..u didnt convolve the data with channel coefficients before transmitting.. for demodulation u have to convert it back from parallel to serial and do ifft to convert the signal into time domain... thanks

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