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%author：liuqingwei May 12th 2006 9:40 PM. %OFDM Channel Estimation Based on Comb Pilot %IFFT_bin_length: IFFT和FFT的点数 %carrier_count: 子载波个数 %bits_per_symbol: 每符号上的比特数 %symbols_per_carrier: 每桢的OFDM符号数 %Ｘ：欲发送的二进制比特流 clear all; clc; IFFT_bin_length=128; carrier_count=100; bits_per_symbol=2; symbols_per_carrier=12; LI=7 ; %导频之间的间隔 Np=ceil(carrier_count/LI)+1;%导频数 %加1的原因：使最后一列也是导频 N_number=carrier_count*symbols_per_carrier*bits_per_symbol; carriers=1:carrier_count+Np; GI=20; % guard interval length N_snr=40; % 每比特信噪比 snr=8; %信噪比间隔 %------------------------------------------------------------ % vector initialization X=zeros(1,N_number); X1=[]; X2=[]; X3=[]; X4=[]; X5=[]; X6=[]; X7=[]; Y1=[]; Y2=[]; Y3=[]; Y4=[]; Y5=[]; Y6=[]; Y7=[]; XX=zeros(1,N_number); dif_bit=zeros(1,N_number); dif_bit1=zeros(1,N_number); dif_bit2=zeros(1,N_number); dif_bit3=zeros(1,N_number); X=randint(1,N_number);%产生二进制随即序列（非0即1） %-------------------------------------------------------- %QPSK调制：(1 1)->pi/4;(0 1)->3*pi/4;(0 0)->-3*pi/4;(1,0)->-pi/4; s=(X.*2-1)/sqrt(2); sreal=s(1:2:N_number); simage=s(2:2:N_number); X1=sreal+j.*simage; %--------------------------------------------------------- %产生随机导频信号 %-------------------------------------------------------- train_sym=randint(1,2*symbols_per_carrier); t=(train_sym.*2-1)/sqrt(2); treal=t(1:2:2*symbols_per_carrier); timage=t(2:2:2*symbols_per_carrier); training_symbols1=treal+j.*timage; training_symbols2=training_symbols1.'; training_symbols=repmat(training_symbols2,1,Np); %disp(training_symbols) pilot=1:LI+1:carrier_count+Np; if length(pilot)~=Np pilot=[pilot,carrier_count+Np]; end %-------------------------------------------------------- %串并转换 X2=reshape(X1,carrier_count,symbols_per_carrier).'; %--------------------------------------------------------- %插入导频 signal=1:carrier_count+Np; signal(pilot)=[]; X3(:,pilot)=training_symbols; X3(:,signal)=X2; %X3=cat(1,training_symbols,X2); IFFT_modulation=zeros(symbols_per_carrier,IFFT_bin_length); IFFT_modulation(:,carriers)=X3; %IFFT_modulation(:,conjugate_carriers)=conj(X3); X4=ifft(IFFT_modulation,IFFT_bin_length,2); %X5=X4.'; %加保护间隔（循环前缀） for k=1:symbols_per_carrier; for i=1:IFFT_bin_length; X6(k,i+GI)=X4(k,i); end for i=1:GI; X6(k,i)=X4(k,i+IFFT_bin_length-GI); end end %--------------------------------------------------------- %并串转换 X7=reshape(X6.',1,symbols_per_carrier*(IFFT_bin_length+GI)); %--------------------------------------------------------- %信道模型:带多普勒频移的瑞利衰落信道 fd=100; %多普勒频移 r=6; %多径数 a=[0.123 0.3 0.4 0.5 0.7 0.8]; %多径的幅度 d=[2 3 4 5 9 13]; %各径的延迟 T=1; %系统采样周期 th=[90 0 72 144 216 288]*pi./180;%相移 h=zeros(1,carrier_count); hh=[]; for k=1:r %deta=[zeros(1,d(k)-1),1,zeros(1,carrier_count-d(k))]; h1=a(k)*exp(j*((2*pi*T*fd*d(k)/carrier_count))); %h1=a(k)*exp(j*((2*pi*T*fd*d(k)/carrier_count))); hh=[hh,h1]; end h(d+1)=hh; %noise=randn(1,length(X7))+j.*randn(1,length(X7)); %-------------------------------------------------------- channel1=zeros(size(X7)); channel1(1+d(1):length(X7))=hh(1)*X7(1:length(X7)-d(1)); channel2=zeros(size(X7)); channel2(1+d(2):length(X7))=hh(2)*X7(1:length(X7)-d(2)); channel3=zeros(size(X7)); channel3(1+d(3):length(X7))=hh(3)*X7(1:length(X7)-d(3)); channel4=zeros(size(X7)); channel4(1+d(4):length(X7))=hh(4)*X7(1:length(X7)-d(4)); channel5=zeros(size(X7)); channel5(1+d(5):length(X7))=hh(5)*X7(1:length(X7)-d(5)); channel6=zeros(size(X7)); channel6(1+d(6):length(X7))=hh(6)*X7(1:length(X7)-d(6)); %--------------------------------------------------------------- Tx_data=X7+channel1+channel2+channel3+channel4; %--------------------------------------------------------------- %--------------------------------------------------------------- %---------------------------------------------------------------- %加高斯白噪声 Error_ber=[];%误比特率 Error_ber1=[]; Error_ber2=[];%误比特率 Error_ber3=[]; %Error_ser=[];%误符号率 for snr_db=0:snr:N_snr code_power=0; code_power=[norm(Tx_data)]^2/(length(Tx_data));%信号的符号功率 %bit_power=var(Tx_data); bit_power=code_power/bits_per_symbol;%比特功率 noise_power=10*log10((bit_power/(10^(snr_db/10))));%噪声功率 noise=wgn(1,length(Tx_data),noise_power,'complex');%产生GAUSS白噪声信号 Y7=Tx_data+noise; %------------------------------------------------------- %串并变换 Y6=reshape(Y7,IFFT_bin_length+GI,symbols_per_carrier).'; %去保护间隔 for k=1:symbols_per_carrier; for i=1:IFFT_bin_length; Y5(k,i)=Y6(k,i+GI); end end Y4=fft(Y5,IFFT_bin_length,2); Y3=Y4(:,carriers); %------------------------------------------------------------- %LS信道估计 H=[]; Y2=Y3(:,signal); Rx_training_symbols=Y3(:,pilot); Rx_training_symbols0=reshape(Rx_training_symbols,symbols_per_carrier*Np,1); training_symbol0=reshape(training_symbols,1,symbols_per_carrier*Np); training_symbol1=diag(training_symbol0); %disp(training_symbols) training_symbol2=inv(training_symbol1); Hls=training_symbol2*Rx_training_symbols0; Hls1=reshape(Hls,symbols_per_carrier,Np); HLs=[]; HLs1=[]; if ceil(carrier_count/LI)==carrier_count/LI for k=1:Np-1 HLs2=[]; for t=1:LI HLs1(:,1)=(Hls1(:,k+1)-Hls1(:,k))*(t-1)./LI+Hls1(:,k); HLs2=[HLs2,HLs1]; end HLs=[HLs,HLs2]; end else for k=1:Np-2 HLs2=[]; for t=1:LI HLs1(:,1)=(Hls1(:,k+1)-Hls1(:,k))*(t-1)./LI+Hls1(:,k); HLs2=[HLs2,HLs1]; end HLs=[HLs,HLs2]; end HLs3=[]; for t=1:mod(carrier_count,LI) HLs1(:,1)=(Hls1(:,Np)-Hls1(:,Np-1))*(t-1)./LI+Hls1(:,Np-1); HLs3=[HLs3,HLs1]; end; HLs=[HLs,HLs3]; end %Hls1=Hls.'; %H=repmat(Hls1,symbols_per_carrier,1);%将导频扩展成symbols_per_carrier*carrier_count矩阵 Y1=Y2./HLs; %------------------------------------------------------------------- %------------------------------------------------------------- %并串变换 YY=reshape(Y2.',1,N_number/bits_per_symbol); YY1=reshape(Y1.',1,N_number/bits_per_symbol); %------------------------------------------------------------ %QPSK解调 y_real=sign(real(YY)); y_image=sign(imag(YY)); y_re=y_real./sqrt(2); y_im=y_image./sqrt(2); y_real1=sign(real(YY1)); y_image1=sign(imag(YY1)); y_re1=y_real1./sqrt(2); y_im1=y_image1./sqrt(2); r00=[]; r01=[]; r10=[]; r11=[]; for k=1:length(y_real); r00=[r00,[y_real(k),y_image(k)]]; end; for k=1:length(y_real1); r10=[r10,[y_real1(k),y_image1(k)]]; end; for k=1:length(y_re); r01=[r01,[y_re(k),y_im(k)]]; end; for k=1:length(y_re1); r11=[r11,[y_re1(k),y_im1(k)]]; end; XX(find(r01>0))=1; %------------------------------------------------------------- %计算在不同信噪比下的误比特率并作图 dif_bit=s-r01; dif_bit1=s-r11; ber_snr=0; %纪录误比特数 for k=1:N_number; if dif_bit(k)~=0; ber_snr=ber_snr+1; end end; ber_snr1=0; %纪录误比特数 for k=1:N_number; if dif_bit1(k)~=0; ber_snr1=ber_snr1+1; end end Error_ber=[Error_ber,ber_snr]; Error_ber1=[Error_ber1,ber_snr1]; end BER=zeros(1,length(0:snr:N_snr)); BER1=zeros(1,length(0:snr:N_snr)); BER=Error_ber./N_number; BER1=Error_ber1./N_number; %------------------------------------------------------------- %---------------------------------------------------------