OFDM 系统仿真，分析了 AWGN 信道和瑞利衰落信道下的 ber 曲线

% OFDM_basic.m %MIMO-OFDM Wireless Communications with MATLAB�� Yong Soo Cho, Jaekwon Kim, Won Young Yang and Chung G. Kang %?2010 John Wiley & Sons (Asia) Pte Ltd clear all NgType=1; % NgType=1/2 for cyclic prefix/zero padding if NgType==1, nt='CP'; elseif NgType==2, nt='ZP'; end Ch=0; % Ch=0/1 for AWGN/multipath channel if Ch==0, chType='AWGN'; Target_neb=100; else chType='CH'; Target_neb=500; end figure(Ch+1), clf PowerdB=[0 -8 -17 -21 -25]; % Channel tap power profile 'dB' Delay=[0 3 5 6 8]; % Channel delay 'sample' Power=10.^(PowerdB/10); % Channel tap power profile 'linear scale' Ntap=length(PowerdB); % Chanel tap number Lch=Delay(end)+1; %Channel length Nbps=4; M=2^Nbps; % Modulation order=2/4/6 for QPSK/16QAM/64QAM Nfft=128; % FFT size Ng=3; %Nfft/4; % Ng=0: Guard interval length %Ng=Nfft/4; Nsym=Nfft+Ng; % Symbol duration Nvc=128-84; % Nvc=0: no virtual carrier Nused=Nfft-Nvc; EbN0=[0:1:20]; % EbN0 N_iter=1e3; % Number of iterations for each EbN0 Nframe=3; % Number of symbols per frame sigPow=0; % Signal power initialization file_name=['OFDM_BER_' chType '_' nt '_' 'GL' num2str(Ng) '.dat']; fid=fopen(file_name, 'w+'); norms=[1 sqrt(2) 0 sqrt(10) 0 sqrt(42)]; % BPSK 4-QAM 16-QAM for i=0:length(EbN0) randn('state',0); rand('state',0); Ber2=ber(); % BER initialization Neb=0; Ntb=0; % Initialize the number of error/total bits for m=1:N_iter % Tx______________________________________________________________ X= randi([0,M-1],1,Nused*Nframe); % bit: integer vector Xmod= qammod(X,M,0,'gray')/norms(Nbps); if NgType~=2, x_GI=zeros(1,Nframe*Nsym); elseif NgType==2, x_GI= zeros(1,Nframe*Nsym+Ng); % Extend an OFDM symbol by Ng zeros end kk1=[1:Nused/2]; kk2=[Nused/2+1:Nused]; kk3=1:Nfft; kk4=1:Nsym; for k=1:Nframe if Nvc~=0, X_shift= [0 Xmod(kk2) zeros(1,Nvc-1) Xmod(kk1)]; else X_shift= [Xmod(kk2) Xmod(kk1)]; end x= ifft(X_shift); x_GI(kk4)= guard_interval(Ng,Nfft,NgType,x); kk1=kk1+Nused; kk2= kk2+Nused; kk3=kk3+Nfft; kk4=kk4+Nsym; end if Ch==0, y= x_GI; % No channel else % Multipath fading channel channel=(randn(1,Ntap)+j*randn(1,Ntap)).*sqrt(Power/2); h=zeros(1,Lch); h(Delay+1)=channel; % cir: channel impulse response y = conv(x_GI,h); end if i==0 % Only to measure the signal power for adding AWGN noise y1=y(1:Nframe*Nsym); sigPow = sigPow + y1*y1'; continue; end % Add AWGN noise________________________________________________ snr = EbN0(i)+10*log10(Nbps*(Nused/Nfft)); % SNR vs. Eb/N0 noise_mag = sqrt((10.^(-snr/10))*sigPow/2); y_GI = y + noise_mag*(randn(size(y))+j*randn(size(y))); % Rx_____________________________________________________________ kk1=(NgType==2)*Ng+[1:Nsym]; kk2=1:Nfft; kk3=1:Nused; kk4=Nused/2+Nvc+1:Nfft; kk5=(Nvc~=0)+[1:Nused/2]; if Ch==1 H= fft([h zeros(1,Nfft-Lch)]); % Channel frequency response H_shift(kk3)= [H(kk4) H(kk5)]; end for k=1:Nframe Y(kk2)= fft(remove_GI(Ng,Nsym,NgType,y_GI(kk1))); Y_shift=[Y(kk4) Y(kk5)]; if Ch==0, Xmod_r(kk3) = Y_shift; else Xmod_r(kk3)= Y_shift./H_shift; % Equalizer - channel compensation end kk1=kk1+Nsym; kk2=kk2+Nfft; kk3=kk3+Nused; kk4=kk4+Nfft; kk5=kk5+Nfft; end X_r=qamdemod(Xmod_r*norms(Nbps),M,0,'gray'); Neb=Neb+sum(sum(de2bi(X_r,Nbps)~=de2bi(X,Nbps))); Ntb=Ntb+Nused*Nframe*Nbps; %[Ber,Neb,Ntb]=ber(bit_Rx,bit,Nbps); if Neb>Target_neb, break; end end 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('EbN0=%3d[dB], BER=%4d/%8d =%11.3e\n', EbN0(i), Neb,Ntb,Ber) fprintf(fid, '%d\t%11.3e\n', EbN0(i), Ber); if Ber<1e-6, break; end end end if (fid~=0), fclose(fid); end disp('Simulation is finished'); plot_ber(file_name,Nbps);