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freqdomain_simu.m
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%载波间隔13kHz,1024路，共13.31M左右带宽，Ng=Nfft/4,用QPSK为26.6Mbps
%7.69*10^-5s=76.9us/OFDM符号 13k个OFDM符号/s
%76.9/1027=0.075us每采样点即Ts=0.07512us
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%555%%%%%%%%%%%%%
clear all
close all
clc
NgType=1; % NgType=1/2 for cyclic prefix/zero padding|对于CP或ZP，NgType=1或2
nt='CP';
Ch=1; % Ch=0/1 for AWGN/multipath channel|对于AWGN/多径瑞利信道，channelCh=0/1
chType='CH'; Target_neb=500;
%%
Ntap=8;
PowerdB=[-4 -7.5 -9.5 -11 -15 -26 -30 -30 ]; % Channel tap power profile 'dB'|信道抽头功率特性 'dB'
Delay=[0 1 3 8 15 28 55 108]; % Channel delay 'sample'|信道时延（采样点）
PowerdB=PowerdB(1:Ntap);
Delay=Delay(1:Ntap);
Power=10.^(PowerdB/10); % Channel tap power profile 'linear scale'|信道抽头功率特性（线性尺度）
Ntap=length(PowerdB); % Chanel tap number|信道抽头数
Lch=Delay(end)+1; % Channel length|信道长度
%Lch=150;
%%
Nbps=2; M=2^Nbps; % Modulation order=2/4/6 for QPSK/16QAM/64QAM|调制阶数=2/4/6：QPSK/16QAM/64QAM
Nfft=1024; % FFT size|FFT大小
Ng=Nfft/8; % Ng=0: Guard interval length|GI的长度，没有保护间隔时，Ng=0
%Ng=3;
Nsym=Nfft+Ng; % Symbol duration|符号周期
norms=[1 sqrt(2) 0 sqrt(10) 0 sqrt(42)];
%%
%%%%%%%导频设计
Nps=4;%导频间隔为4
Np=Nfft/Nps;%导频数目
Nd=Nfft-Np;%数据子信道数
nSTO=0;%NSTO为负数数时估计提前，正数时估计之后；
%%
SNR=[0:5:40]; % EbN0 % Number of iterations for each EbN0|对于每一个EbN0的迭代次数
Nframe=200; % Number of symbols per frame|每一帧的符号数
file_name=['OFDM_BER_' chType '_' nt '_' 'GL' num2str(Ng) '.dat'];
fid=fopen(file_name, 'w+');
%%
for i=1:length(SNR)
randn('seed',1); rand('seed',1);
Ber=0;%误码率
Neb=0; Ntb=0; % Initialize the number of error/total bits|初始化错误比特数/总比特数
sigPow=0; % Signal power initialization|初始信号功率
MSE=zeros(1,9);
for nsym=1:Nframe %一帧有Nframe个符号
X= randi([0,M-1],1,Nd); % bit: integer vector
Xp = 2*(randn(1,Np)>0)-1; %产生导频
X_mod= qammod(X,M)/norms(Nbps);
x_GI=zeros(1,Nsym); %欲留带导频的发送序列
%% 形成一个OFDM符号
ip=0; pilot_loc=[];
X_symbol=zeros(1,Nfft);%X_symbol为一个OFDM符号
for n=1:Nfft %在特定位置插入导频
if mod(n,Nps)==1
X_symbol(n)=Xp(floor(n/Nps)+1) ;pilot_loc=[pilot_loc,n];ip=ip+1;
else X_symbol(n)=X_mod(n-ip);
end
end
x= ifft(X_symbol,Nfft); %点数为Nfft
x_GI = [x(Nfft-Ng+1:Nfft) x]; % Add CP|加循环前缀
%% 信道仿真
channel=(randn(1,Ntap)+j*randn(1,Ntap)).*sqrt(Power/2); %8个抽头复信道
h=zeros(1,Lch); h(Delay+1)=channel; % cir: channel impulse response|信道脉冲响应
% h=h(1:Lch);%取前7径
H_orignal= fft(h,Nfft); channel_length = length(h); % True channel and its time-domain length|实际信道和它的长度
H_orignal=H_orignal/norm(H_orignal,'fro');
h_temp=ifft(H_orignal,Nfft);
h=h_temp(1:Lch);
rolloff = 0.25;
span = 6;
sps =4;
b=rcosdesign(rolloff,span,sps);
x_GI=upfirdn(x_GI,b,sps);
H_power_dB = 10*log10(abs(H_orignal.*conj(H_orignal))); % True channel
snr = SNR(i)+10*log10(Nbps);%时域信噪比
y = conv(x_GI,h);
%end
sigPow = mean(y.*conj(y));
y_GI=awgn(y,SNR(i),'measured');
y_GI=upfirdn(y_GI,b,1,sps);
y_GI=y_GI(span+1:length(y_GI)-6);
noisePow=sigPow*10^(-SNR(i)/10);
y_data_pilot=y_GI(Ng+1:Nsym);%去除保护间隔
Y_data_pilot=fft(y_data_pilot); %先fft,再频域均衡
%% 不同估计方法比较
for q=1:3
if q==1
[H_est,H_est2] = LS_CE( Y_data_pilot,Xp,pilot_loc,Nfft,Nps,'linear'); method='LS-linear'; % LS estimation with linear interpolation
elseif q==2
[H_est,H_est2] = LS_CE( Y_data_pilot,Xp,pilot_loc,Nfft,Nps,'spline'); method='LS-spline'; % LS estimation with spline interpolation
else
H_est3 = MMSE_CE( Y_data_pilot,Xp,pilot_loc,Nfft,Nps,h,10*log10(1/noisePow)); method='MMSE'; % MMSE estimation
end
%对LS进行DFT内插，MSE(456)相同，
htt=ifft(H_est2,Np);
hh=[htt zeros(1,Nfft-Np)];
H_LSdft=fft(hh,Nfft);
H_est_power_dB = 10*log10(abs(H_est.*conj(H_est)));
h_est = ifft(H_LSdft);
if(q==3)
h_est3=ifft(H_est3);
h_DFT = h_est3(1:Lch);
else
h_DFT=h_est(1:Lch);
end
H_DFT = fft(h_DFT,Nfft); % DFT-based channel estimation
H_DFT_power_dB = 10*log10(abs(H_DFT.*conj(H_DFT)));
MSE(q) = MSE(q) + norm(H_orignal-H_est,'fro');
MSE(q+3) = MSE(q+3) + norm(H_orignal-H_LSdft,'fro');
MSE(q+6) = MSE(q+6) + norm(H_orignal-H_DFT,'fro');
end
H_shift=H_DFT; % Channel frequency response|信道频率响应
Y_shift=Y_data_pilot;
Xmod_r= Y_shift./H_shift; % Equalizer - channel compensation|均衡器
data=zeros(1,Nd);%存解调数据
ip = 0;
for k=1:Nfft
if mod(k,Nps)==1, ip=ip+1; else data(k-ip)=Xmod_r(k); end
end
X_r=qamdemod(data*norms(Nbps),M);
Neb=Neb+sum(sum(de2bi(X_r,Nbps)~=de2bi(X,Nbps)));
Ntb=Ntb+Nfft*Nbps; %[Ber,Neb,Ntb]=ber(bit_Rx,bit,Nbps);
end %对应Nframe次个符号一帧
MSEs(i,:) = MSE/(Nframe);
if i==0
sigPow= sigPow/Nsym/Nframe/N_iter;
fprintf('Signal power= %11.3e\n', sigPow);
fprintf(fid,'%%Signal power= %11.3e\n%%EbN0[dB] BER\n', sigPow);
else
Ber = Neb/Ntb;
fprintf('SNR=%3d[dB], BER=%4d/%8d =%11.3e\n',SNR(i), Neb,Ntb,Ber)
fprintf(fid, '%d\t%11.3e\n', SNR(i), Ber);
if Ber<1e-6, break; end
end
end
%%%%%信道估计归一化均方误差
for count=1:length(SNR)
NMSE(count,:)=20*log10( MSEs(count,:)./( norm(H_orignal,'fro') ) );
end %计算归一化均方误差
figure(3)
plot(SNR,NMSE(:,1),'r--d');hold on
plot(SNR,NMSE(:,2),'b--s');hold on
plot(SNR,NMSE(:,9),'k--h');hold on
plot(SNR,NMSE(:,3),'k--h');hold on
plot(SNR,NMSE(:,4), 'g--d');hold on
plot(SNR,NMSE(:,7),'r--d');hold on
plot(SNR,NMSE(:,8),'b--s');hold on
legend('LS linear interpolate','LS spline interpolate ','MMSE with dft ','only MMSE','LS DFT interpolate','linear with DFT denoise','spline with DFT denoise');
xlabel('SNR');ylabel('NMSE(dB)');title('LS linear interpolate for channel estimation');
if (fid~=0), fclose(fid); end
disp('Simulation is finished');
figure
plot_ber(file_name,Nbps,SNR);