OFDM中LS和DFT信道估计算法matlab程序实现及比较

附 录
程序：
clear all;
close all;
fprintf('OFDM信道估计仿真\n\n');
carrier_count=64;%-----------载波数目
num_symbol=50;%--------------OFDM符号个数
Guard=8;%--------------------循环前缀
pilot_Inter=8;%--------------导频间隔
modulation_mode=16;%---------调制方式
SNR=[0:2:20];%-------------信噪比取值
NumLoop=15;%-----------------循环次数
num_bit_err=zeros(length(SNR),NumLoop);
num_bit_err_dft=zeros(length(SNR),NumLoop);
num_bit_err_ls=zeros(length(SNR),NumLoop);
MSE=zeros(length(SNR),NumLoop);
MSE1=zeros(length(SNR),NumLoop);
MSE2=zeros(length(SNR),NumLoop);
%%%%%%%%%%%%%%%%%%%%%%%主程序循环%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
for c1=1:length(SNR)
fprintf('\n\n\n仿真信噪比为%f\n\n',SNR(c1));
for num1=1:NumLoop
%---------------产生发送的随机序列——————————————-
BitsLen=carrier_count*num_symbol;
BitsTx=randint(1,BitsLen);
%---------------符号调制---------------------------------------
Modulated_Sequence=qammod(BitsTx,modulation_mode);
%---------------导频格式---------------------------------------
pilot_len=carrier_count;
pilot_symbols=round(rand(1,pilot_len));
for i=1:pilot_len
if pilot_symbols(1,i)==0
pilot_symbols(1,i)=pilot_symbols(1,i)-1;
else
pilot_symbols(1,i)=pilot_symbols(1,i);
end
end
pilot_symbols=pilot_symbols';
%----------------计算导频和数据数目----------------------------
num_pilot=ceil(num_symbol/pilot_Inter);
if rem(num_symbol,pilot_Inter)==0
num_pilot=num_pilot+1;
end
num_data=num_symbol+num_pilot;
%----------------导频位置计算----------------------------------
pilot_Indx=zeros(1,num_pilot);
Data_Indx=zeros(1,num_pilot*(pilot_Inter+1));
for i=1:num_pilot-1
pilot_Indx(1,i)=(i-1)*(pilot_Inter+1)+1;
end
pilot_Indx(1,num_pilot)=num_data;
for j=0:num_pilot
Data_Indx(1,(1+j*pilot_Inter):(j+1)*pilot_Inter)=(2+j*(pilot_Inter+1)):((j+1)*(pilot_Inter+1));
end
Data_Indx=Data_Indx(1,1:num_symbol);
%----------------导频插入-------------------------------------
piloted_ofdm_syms=zeros(carrier_count,num_data);
piloted_ofdm_syms(:,Data_Indx)=reshape(Modulated_Sequence,carrier_count,num_symbol);
piloted_ofdm_syms(:,pilot_Indx)=repmat(pilot_symbols,1,num_pilot);
%----------------IFFT变换———————————————————
time_signal=sqrt(carrier_count)*ifft(piloted_ofdm_syms);
%----------------加循环前缀------------------------------------
add_cyclic_signal=[time_signal((carrier_count-Guard+1:carrier_count),:);time_signal];
Tx_data_trans=reshape(add_cyclic_signal,1,(ca

rrier_count+Guard)*num_data);
%----------------信道处理--------------------------------------
Tx_signal_power=sum(abs(Tx_data_trans(:)).^2)/length(Tx_data_trans(:));
noise_var=Tx_signal_power/(10^(SNR(c1)/10));
Rx_data=awgn(Tx_data_trans,SNR(c1),'measured');
%----------------信号接收、去循环前缀、FFT变换-----------------
Rx_signal=reshape(Rx_data,(carrier_count+Guard),num_data);
Rx_signal_matrix=zeros(carrier_count,num_data);
Rx_signal_matrix=Rx_signal(Guard+1:end,:);
Rx_carriers=fft(Rx_signal_matrix)/sqrt(carrier_count);
%----------------导频和数据提取--------------------------------
Rx_pilot=Rx_carriers(:,pilot_Indx);
Rx_fre_data=Rx_carriers(:,Data_Indx);
%----------------导频位置信道响应LS估计------------------------

pilot_patt=repmat(pilot_symbols,1,num_pilot);
pilot_esti=Rx_pilot./pilot_patt;
%----------------LS估计的线性插值———————————————
int_len=pilot_Indx;
len=1:num_data;
for ii=1:carrier_count
channel_H_ls(ii,:)=interp1(int_len,pilot_esti(ii,1:(num_pilot)),len,'linear');
end
channel_H_data_ls=channel_H_ls(:,Data_Indx);
%----------------LS估计中发送数据的估计值----------------------
Tx_data_estimate_ls=Rx_fre_data.*conj(channel_H_data_ls)./(abs(channel_H_data_ls).^2);
%----------------DFT估计--------------------------------------
Tx_pilot_estimate_ifft=ifft(pilot_esti);
padding_zero=zeros(1024,7);
Tx_pilot_estimate_ifft_padding_zero=[Tx_pilot_estimate_ifft;padding_zero];
Tx_pilot_estimate_dft=fft(Tx_pilot_estimate_ifft_padding_zero);
%----------------DFT估计的线性插值———————————————
int_len=pilot_Indx;
len=1:num_data;
for ii=1:carrier_count
channel_H_dft(ii,:)=interp1(int_len,Tx_pilot_estimate_dft(ii,1:(num_pilot)),len,'linear');
end
channel_H_data_dft=channel_H_dft(:,Data_Indx);
%----------------DFT估计中发送数据的估计值----------------------
Tx_data_estimate_dft=Rx_fre_data.*conj(channel_H_data_dft)./(abs(channel_H_data_dft).^2);
%----------------DFT符号解调------------------------------------
demod_in_dft=Tx_data_estimate_dft(:).';
demod_out_dft=qamdemod(demod_in_dft,modulation_mode);
%----------------LS符号解调------------------------------------
demod_in_ls=Tx_data_estimate_ls(:).';
demod_out_ls=qamdemod(demod_in_ls,modulation_mode);
%----------------误码率的计算----------------------------------
for i=1:length(BitsTx)
if demod_out_dft(i)~=BitsTx(i)
num_bit_err_dft(c1,num1)=num_bit_err_dft(c1,num1)+1;
end
if dem

od_out_ls(i)~=BitsTx(i)
num_bit_err_ls(c1,num1)=num_bit_err_ls(c1,num1)+1;
end
end
end
end
BER_dft=mean(num_bit_err_dft.')/length(BitsTx);
BER_ls=mean(num_bit_err_ls.')/length(BitsTx);
%%%%%%%%%%%%%%%%%%%a%%%%%%%%主程序循环换结束%%%%%%%%%%%%%%%%%%%%%%%%%%%%
figure
semilogy(SNR,BER_dft,'-mp',SNR,BER_ls,'-k+');
title('OFDM系统的LS和DFT信道估计');
xlabel('SNR'),ylabel('BER')
legend('LS信道估计','DFT信道估计');