gusucode.com > 基于梳状导频的OFDM信道估计 > ofdm2.m
%基于梳妆导频的OFDM信道估计
clear all;
close all
clc;
IFFT_bin_length=128;%ifft长度
carrier_count=100;%子载波数
bits_per_symbol=2;%每符号比特数
symbols_per_carrier=12;%一桢符号数，一桢包括很多的符号。
LI=7 ; %导频之间的间隔
Np=ceil(carrier_count/LI)+1;%16 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;%2400一祯比特数
carriers=1:carrier_count+Np;%116 子载波加导频
GI=8; % guard interval length
N_snr=20; % 每比特信噪比
snr=5; %信噪比间隔k
%------------------------------------------------------------
% 初始化
X=zeros(1,N_number);%2400个bit
X1=[];X2=[];X3=[];X4=[];X5=[];X6=[];X7=[];
Y1=[];Y2=[];Y3=[];Y4=[];Y5=[];Y6=[];Y7=[];
XX=zeros(1,N_number);%2400
dif_bit=zeros(1,N_number);%2400
dif_bit1=zeros(1,N_number);%2400
dif_bit2=zeros(1,N_number);%2400
dif_bit3=zeros(1,N_number);%2400
X=randint(1,N_number);%产生二进制随即序列（非0即1）2400
%--------------------------------------------------------
%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;%已调信号bit流0.7071 - 0.7071i 0.7071 - 0.7071i 0.7071 + 0.7071i。。。。。（1*1200）
%---------------------------------------------------------
%产生随机导频信号
%--------------------------------------------------------
train_sym=randint(1,2*symbols_per_carrier);%1*24
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;% 0.7071 - 0.7071i -0.7071 - 0.7071i -0.7071 - 0.7071i 1*12
training_symbols2=training_symbols1.';%12*1
training_symbols=repmat(training_symbols2,1,Np);%12*16 复制第一列变成16列
%disp(training_symbols)
pilot=1:LI+1:carrier_count+Np;%导频插入位置序号1 9 17 25 33 41 49 57 65 73 81 89 97 105 113
if length(pilot)~=Np
pilot=[pilot,carrier_count+Np];%最后一列变成导频1 9 17 25 33 41 49 57 65 73 81 89 97 105 113 116
end
%--------------------------------------------------------
%串并转换
X2=reshape(X1,carrier_count,symbols_per_carrier).';%12*100，12个复信号符号，100列载波
%---------------------------------------------------------
%插入导频
signal=1:carrier_count+Np;%1*116
signal(pilot)=[];%1*100 有效数据的位置。
X3(:,pilot)=training_symbols;%先放入16列导频
X3(:,signal)=X2;%再放入12*100，100列子载波，共12*116
%X3=cat(1,training_symbols,X2);
IFFT_modulation=zeros(symbols_per_carrier,IFFT_bin_length);%12*128
IFFT_modulation(:,carriers)=X3;%116列后补12列全0子载波，12*128 子载波数+导频数+补零=傅里叶变换的数据。
%IFFT_modulation(:,conjugate_carriers)=conj(X3);
X4=ifft(IFFT_modulation,IFFT_bin_length,2);%每个符号128点ifft 获取发送信号的时域数据。
%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));%12*136先转置，再变成1*1632复信号流
%---------------------------------------------------------
%信道模型:带多普勒频移的瑞利衰落信道
fd=50; %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=[3 4 5 6 10 14]; %各径的延迟
fs=9600;
T=1/fs; %系统采样周期
th=[90 0 72 144 216 288]*pi./180;%相移
h=zeros(1,carrier_count);%1*100
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+th(k))));
%h1=a(k)*exp(j*((2*pi*T*fd*d(k)/carrier_count)));
hh=[hh,h1];
end
h(d+1)=hh;%3 4 5 6 10 14处有多径效应
%noise=randn(1,length(X7))+j.*randn(1,length(X7));
%===================================================
% Fs=9600; %采样频率
% Ts=1/Fs; %采样间隔
% Fd=100; %Doppler频偏，以Hz为单位
% tau=[0,0.001,0.0018,0.002,0.005,0.01]; %多径延时，以s为单位
% pdf=[0,0,0, 0, 0,0]; %各径功率，以dB位单位
% chan=rayleighchan(Ts,Fd,tau,pdf);
% data=[1,zeros(1,carrier_count-1)];%脉冲信号数据，该矩阵长度要适中，冲激序列
% % data=ones(1,4);
% h=filter(chan,data); %脉冲响应，与chan进行卷积，相当于采样，得到信道h（t）
% temp=conv(X7,h);
% Tx_data_temp=ifft(temp);
% Tx_data=Tx_data_temp(1:12*136);
%===================================================
channel1=zeros(size(X7));%1*1632
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+channel5+channel6;%6径干扰后的数据流1*1632
%----------------------------------------------------------------
%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=-20:snr:N_snr %0:8:40
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).';%先变成136*12，再转置成12*136，恢复成行为符号，列为载波
%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);%每行的符号进行128点fft 12*128
Y3=Y4(:,carriers);%去掉尾部12列原补零点， 12*116，得到有效的接收数据矩阵。
%-------------------------------------------------------------
%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);%用LS估计得到的导频部分的信道信息。
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
%%把第k+1与k个信道数据均匀分开，然后在第k的基础上相加，得到内插指
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
for j=1:12
Hls_time(j,:)=ifft(HLs(j,:),128);
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;
%-------------------------------------------------------------
% figure
% for j=1:size(Hls1,1)
% HLs_time(j,:)=ifft(Hls1(j,:),16);
% end
% HLs_time=HLs_time(:,1:100);
% stem(abs(HLs_time(2,:)))
%-------------------------------------------------------------
i=-20:snr:N_snr;
figure
semilogy(i,BER,'-*r');
hold on;
semilogy(i,BER1,'-og');
hold on;
grid on;
legend('No Channel Estimation','LS Channel Estimation');
hold off