基于matlab实现的OFDM具有很强的抗多径和抗频率选择性衰落的能力

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)); % 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]);