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- %------------------------------------------
- % EE359 final project, Fall 2002
- % Channel estimation for a MIMO-OFDM system
- % By Shahriyar Matloub
- %------------------------------------------
- clear all;
- %close all;
- i=sqrt(-1);
- Rayleigh=1;
- AWGN=0; % for AWGN channel
- MMSE=0; % estimation technique
- Nsc=64; % Number of subcarriers
- Ng=16; % Cyclic prefix length
- SNR_dB=[0 5 10 15 20 25 30 35 40]; % Signal to noise ratio
- Mt=2; % Number of Tx antennas
- Mr=2; % Number of Rx antennas
- pilots=[1:Nsc/Ng:Nsc]; % pilot subcarriers
- DS=5; % Delay spread of channel
- iteration_max=200;
- %%%%%%%%%%%%%%%%%%%%%%%%%%%%
- % Channel impulse response %
- %%%%%%%%%%%%%%%%%%%%%%%%%%%%
- if (Rayleigh)
- N=50;
- fm=100;
- B=20e3;
- fd=(rand(1,N)-0.5)*2*fm;
- theta=randn(1,N)*2*pi;
- c=randn(1,N);
- c=c/sum(c.^2);
- t=0:fm/B:10000*fm/B;
- Tc=zeros(size(t));
-
- Ts=zeros(size(t));
- for k=1:N
- Tc=c(k)*cos(2*pi*fd(k)*t+theta(k))+Tc;
- Ts=c(k)*sin(2*pi*fd(k)*t+theta(k))+Ts;
- end
- r=ones(Mt*Mr,1)*(Tc.^2+Ts.^2).^0.5;
- index=floor(rand(Mt*Mr,DS)*5000+1);
- end
- MEE1=zeros(1,length(SNR_dB));
- MEE2=zeros(1,length(SNR_dB));
- for snrl=1:length(SNR_dB)
- snrl
- estimation_error1=zeros(Mt*Mr,Nsc);
- estimation_error2=zeros(Mt*Mr,Nsc);
- R1=besselj(0,2*pi*fm*(Nsc+Ng)/B);
- sigma2=10^(-SNR_dB(snrl)/10);
- aa=(1-R1^2)/(1-R1^2+sigma2);
- bb=sigma2*R1/(1-R1^2+sigma2);
- for iteration=1:iteration_max
- %iteration
- if AWGN==1
- h=ones(Mt*Mr,1);
- else
- phi=rand*2*pi;
- h=r(index+iteration)*exp(j*phi);
- %h=rand(Mt*Mr,DS);
- h=h.*(ones(Mt*Mr,1)*(exp(-0.5).^[1:DS]));
- h=h./(sqrt(sum(abs(h).^2,2))*ones(1,DS));
- end
- CL=size(h,2); % channel length
- data_time=zeros(Mt,Nsc+Ng);
- data_qam=zeros(Mt,Nsc);
- data_out=zeros(Mr,Nsc);
- output=zeros(Mr,Nsc);
- for tx=1:Mt
- data_b=0*round(rand(4,Nsc)); % data
- data_qam(tx,:)=j*(2*(mod(data_b(1,:)+data_b(2,:),2)+2*data_b(1,:))-3)+...
- 2*(mod(data_b(3,:)+data_b(4,:),2)+2*data_b(3,:))-3;
- for loop=1:Mt
- data_qam(tx,pilots+loop-1)=(1+j)*(loop==tx); % pilots
- end
- data_time_temp=ifft(data_qam(tx,:));
- data_time(tx,:)=[data_time_temp(end-Ng+1:end) data_time_temp];
- end
-
- for rx=1:Mr
- for tx=1:Mt
- output_temp=conv(data_time(tx,:),h((rx-1)*Mt+tx,:));
- output(rx,:)=output_temp(Ng+1:Ng+Nsc)+output(rx,:);
- end
- np=(sum(abs(output(rx,:)).^2)/length(output(rx,:)))*sigma2;
- noise=(randn(size(output(rx,:)))+i*randn(size(output(rx,:))))*sqrt(np);
- output(rx,:)=output(rx,:)+noise;
- data_out(rx,:)=fft(output(rx,:));
- end
- %%%%%%%%%%%%%%%%%%%%%%
- % Channel estimation %
- %%%%%%%%%%%%%%%%%%%%%%
-
- H_act=zeros(Mt*Mr,Nsc);
- H_est1=zeros(Mt*Mr,Nsc);
- H_est2=zeros(Mt*Mr,Nsc);
- i=1;
- for tx=1:Mt
- for rx=1:Mr
- H_est_temp=data_out(rx,pilots+tx-1)./data_qam(tx,pilots+tx-1);
- %H_est_temp2=aa*abs(H_est_temp1)+bb*abs(H_est2((rx-1)*Mt+tx,:));
- h_time=ifft(H_est_temp);
- h_time=[h_time zeros(1,Nsc-length(h_time))];
- H_est1((rx-1)*Mt+tx,:)=fft(h_time);
- H_est2((rx-1)*Mt+tx,:)=((aa*abs(H_est1((rx-1)*Mt+tx,:))+bb*abs(H_est2((rx-1)*Mt+tx,:)))...
- .*H_est1((rx-1)*Mt+tx,:))./abs(H_est1((rx-1)*Mt+tx,:));
- if (tx>1)
- H_est1((rx-1)*Mt+tx,:)=[H_est1((rx-1)*Mt+tx,Nsc-tx+2:Nsc) H_est1((rx-1)*Mt+tx,1:Nsc-tx+1)];
- H_est2((rx-1)*Mt+tx,:)=[H_est2((rx-1)*Mt+tx,Nsc-tx+2:Nsc) H_est2((rx-1)*Mt+tx,1:Nsc-tx+1)];
- end
- H_act((rx-1)*Mt+tx,:)=fft([h((rx-1)*Mt+tx,:) zeros(1,Nsc-CL)]);
- error1=(abs(H_act((rx-1)*Mt+tx,:)-H_est1((rx-1)*Mt+tx,:)).^2);
- error2=(abs(H_act((rx-1)*Mt+tx,:)-H_est2((rx-1)*Mt+tx,:)).^2);
- %error=(abs(H_act((rx-1)*Mt+tx,:)-H_est((rx-1)*Mt+tx,:)).^2)./(abs(H_act((rx-1)*Mt+tx,:)).^2);
- estimation_error1((rx-1)*Mt+tx,:)=estimation_error1((rx-1)*Mt+tx,:)+error1;
- estimation_error2((rx-1)*Mt+tx,:)=estimation_error2((rx-1)*Mt+tx,:)+error2;
- %subplot(Mt*Mr,3,i),plot([0:Nsc-1],abs(H_act((rx-1)*Mt+tx,:))); i=i+1;
- %subplot(Mt*Mr,3,i),plot([0:Nsc-1],abs(H_est((rx-1)*Mt+tx,:))); i=i+1;
- %subplot(Mt*Mr,3,i),plot([0:Nsc-1],abs(error)); i=i+1;
- end
- end
- end
- estimation_error1=estimation_error1/iteration_max;
- estimation_error2=estimation_error2/iteration_max;
- %estimation_error=min(estimation_error,10*iteration_max*ones(size(estimation_error)));
- %for i=1:Mt*Mr
- % subplot(Mt*Mr,2,2*i-1),plot([0:Nsc-1],estimation_error1(i,:));
- % subplot(Mt*Mr,2,2*i),plot([0:Nsc-1],estimation_error2(i,:));
- %end
- MEE1(snrl)=sum(sum(estimation_error1))/(Mt*Mr*Nsc);
- MEE2(snrl)=sum(sum(estimation_error2))/(Mt*Mr*Nsc);
- end
- plot(SNR_dB,10*log10(MEE1));
- hold on;
- plot(SNR_dB,10*log10(MEE2),'r');
- %H_act=fft([h_zeros(1,Nsc-CL)]).';
- error1=(abs(H_act-H_est1).^2)./(abs(H_act).^2);
- error2=(abs(H_act-H_est2).^2)./(abs(H_act).^2);
- %%%%%%%%%
- % Plots %
- %%%%%%%%%
- fig=4;
- i=1;
- subplot(fig,1,i),plot([0:length(H_act)-1],abs(H_act)); i=i+1;
- subplot(fig,1,i),plot([0:length(H_est1)-1],abs(H_est1)); i=i+1;
- subplot(fig,1,i),plot([0:length(H_est2)-1],abs(H_est2)); i=i+1;
- subplot(fig,1,i),plot([0:length(error1)-1],error1); i=i+1;
- subplot(fig,1,i),plot([0:length(error2)-1],error2);
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