www.pudn.com > OFDMReception.rar > OFDMReception.m

%DVB-T 2K Reception 
clear all; 
close all; 
Tu=224e-6; %useful OFDM symbol period 
T=Tu/2048; %baseband elementary period 
G=0; %choice of 1/4, 1/8, 1/16, and 1/32 
delta=G*Tu; %guard band duration 
Ts=delta+Tu; %total OFDM symbol period 
Kmax=1705; %number of subcarriers 
Kmin=0; 
FS=4096; %IFFT/FFT length 
q=10; %carrier period to elementary period ratio 
fc=q*1/T; %carrier frequency 
Rs=4*fc; %simulation period 
t=0:1/Rs:Tu; 
tt=0:T/2:Tu; 
%Data generator 
sM = 2; 
[x,y] = meshgrid((-sM+1):2:(sM-1),(-sM+1):2:(sM-1)); 
alphabet = x(:) + 1i*y(:); 
N=Kmax+1; 
rand('state',0); 
a=-1+2*round(rand(N,1)).'+i*(-1+2*round(rand(N,1))).'; 
A=length(a); 
info=zeros(FS,1); 
info(1:(A/2)) = [ a(1:(A/2)).']; 
info((FS-((A/2)-1)):FS) = [ a(((A/2)+1):A).']; 
carriers=FS.*ifft(info,FS); 
%Upconverter 
L = length(carriers); 
chips = [ carriers.';zeros((2*q)-1,L)]; 
p=1/Rs:1/Rs:T/2; 
g=ones(length(p),1); 
dummy=conv(g,chips(:)); 
u=[dummy; zeros(46,1)]; 
[b,aa] = butter(13,1/20); 
uoft = filter(b,aa,u); 
delay=64; %Reconstruction filter delay 
s_tilde=(uoft(delay+(1:length(t))).').*exp(1i*2*pi*fc*t); 
14 
s=real(s_tilde); 
%OFDM RECEPTION 
%Downconversion 
r_tilde=exp(-1i*2*pi*fc*t).*s; %(F) 
figure(1); 
subplot(211); 
plot(t,real(r_tilde)); 
axis([0e-7 12e-7 -60 60]); 
grid on; 
figure(1); 
subplot(212); 
plot(t,imag(r_tilde)); 
axis([0e-7 12e-7 -100 150]); 
grid on; 
figure(2); 
ff=(Rs)*(1:(q*FS))/(q*FS); 
subplot(211); 
plot(ff,abs(fft(r_tilde,q*FS))/FS); 
grid on; 
figure(2); 
subplot(212); 
pwelch(r_tilde,[],[],[],Rs); 
%Carrier suppression 
[B,AA] = butter(3,1/2); 
r_info=2*filter(B,AA,r_tilde); %Baseband signal continuous-time (G) 
figure(3); 
subplot(211); 
plot(t,real(r_info)); 
axis([0 12e-7 -60 60]); 
grid on; 
figure(3); 
subplot(212); 
plot(t,imag(r_info)); 
axis([0 12e-7 -100 150]); 
grid on; 
figure(4); 
f=(2/T)*(1:(FS))/(FS); 
subplot(211); 
plot(ff,abs(fft(r_info,q*FS))/FS); 
grid on; 
subplot(212); 
pwelch(r_info,[],[],[],Rs); 
%Sampling 
r_data=real(r_info(1:(2*q):length(t)))... %Baseband signal, discretetime 
+1i*imag(r_info(1:(2*q):length(t))); % (H) 
figure(5); 
subplot(211); 
stem(tt(1:20),(real(r_data(1:20)))); 
axis([0 12e-7 -60 60]); 
grid on; 
15 
figure(5); 
subplot(212); 
stem(tt(1:20),(imag(r_data(1:20)))); 
axis([0 12e-7 -100 150]); 
grid on; 
figure(6); 
f=(2/T)*(1:(FS))/(FS); 
subplot(211); 
plot(f,abs(fft(r_data,FS))/FS); 
grid on; 
subplot(212); 
pwelch(r_data,[],[],[],2/T); 
%FFT 
info_2N=(1/FS).*fft(r_data,FS); % (I) 
info_h=[info_2N(1:A/2) info_2N((FS-((A/2)-1)):FS)]; 
%Slicing 
for k=1:N, 
a_hat(k)=alphabet((info_h(k)-alphabet)==min(info_h(k)-alphabet)); % 
(J) 
end; 
figure(7) 
plot(info_h((1:A)),'.k'); 
title('info-h Received Constellation') 
axis square; 
axis equal; 
figure(8) 
plot(a_hat((1:A)),'or'); 
title('a_hat 4-QAM') 
axis square; 
axis equal; 
grid on; 
axis([-1.5 1.5 -1.5 1.5]);