communication - Matlab Code for BER Calculation in a Optical Wireless System -


i simulated visible light communication (vlc) system awgn (additive white gaussian noise) channel , plotted ber (bit error rate) against ebno. used led (light emitting diode) impulse response , convolved signal produced transmitting. results not ok. means ber fixed or 0.5. pam-dmt (pulse amplitude modulation-discrete multi-tone) system transmitter 50*50 array of leds. input binary sequence modulated pam modulator. used make ofdm symbols pam-dmt algorithm. ofdm symbols modulated led intensity , transmitted channel. @ receiver side, after demodulating received symbols, received binary sequence compared input binary sequence calculate ber. in each ofdm symbol, there data carriers, pilot symbol carriers , null carriers. think problem scheme use cut extended length (made convolving led input led impulse response) of transmitted signal @ receiver side. me if wrong? in advance.

here matlab code:

clear,clc;  close all;  %%  k=4;m=2^k; %4 bits per pam symbol%  c=3*1e8;  %m/ns  f_3db=15e6;%1/ns  n=32;  r=0.54;%responsivity @ a/w%  ro=0.8;% reflection coefficient  ar=1e-4;  index=1.5;  carier_freqspac=f_3db/n;  t_sym=1/f_3db;%the time of pam symbol 0.5us or 500ns.  tb=t_sym/k;  rb=1/tb;  t_ifft=1/carier_freqspac;  l_cp=n/4;  t_cp=t_sym*l_cp;  t_ofdmsym=t_ifft+t_cp; %ofdm symbol duration 4us%  l_ofdm_sym=n+l_cp;  n_pilot_carrier=n/16;  n_null=n/16;  n_data_carrier=n-n_null-n_pilot_carrier;  nofdm=2e4;  ttran_ofdm_sym=((n_data_carrier+n_pilot_carrier)*t_sym)+t_cp;  rb_ofdm=((n_data_carrier+n_pilot_carrier)*k)/ttran_ofdm_sym;% @ b/s  hpammod=comm.pammodulator(m,'bitinput',true);  hpam_demod=comm.pamdemodulator(m,'bitoutput',true);    %pilots in 1st half  if n==32;  ps=[1];  elseif n==64;  ps=[-1 1];  elseif n==128;  ps=[-1 -1 1 1];  end;  input_b=randi([0,1],nofdm*(n_data_carrier/2)*k,1);  n_bit=length(input_b);  pam_sym=step(hpammod,input_b);  n_pamsym=n_bit/k;  pam_sym=reshape(pam_sym,n_data_carrier/2,nofdm);  pam_sym_ps_1st=[];  if n==32;  i=1:nofdm;  pam_sym_ps_1st=1j.*[0;pam_sym(1:14,i);ps(1)];  pam_sym_ps_1st=[pam_sym_ps_1st pam_sym_ps_1st];  pam_sym_ps_2nd=circshift(conj(flipud(pam_sym_ps_1st)),1);   pam_sym_ps_2nd=[pam_sym_ps_2nd pam_sym_ps_2nd];  end;  elseif n==64;  i=1:nofdm;  pam_sym_ps_1st=1j.*[0;pam_sym(1:14,i);ps(1);0;pam_sym(15:28,i);ps(2)];  pam_sym_ps_1st=[pam_sym_ps_1st pam_sym_ps_1st];  pam_sym_ps_2nd=circshift(conj(flipud(pam_sym_ps_1st)),1);   pam_sym_ps_2nd=[pam_sym_ps_2nd pam_sym_ps_2nd];  end;    elseif n==128;  i=1:nofdm;  pam_sym_ps_1st=1j.*   [0;pam_sym(1:14,i);ps(1);0;pam_sym(15:28,i);ps(2);0;pam_sym(29:42,i);ps(3);0;pam_sym(43:56,i);ps(4)];  pam_sym_ps_1st=[pam_sym_ps_1st pam_sym_ps_1st];  pam_sym_ps_2nd=circshift(conj(flipud(pam_sym_ps_1st)),1);   pam_sym_ps_2nd=[pam_sym_ps_2nd pam_sym_ps_2nd];  end;  end;  ifft_in=[pam_sym_ps_1st;pam_sym_ps_2nd];  ifft_out=ifft(ifft_in,n);  cp=ifft_out(n-l_cp+1:n,:);  ofdm_sym=[cp;ifft_out];  ofdm_sym1=reshape(ofdm_sym,l_ofdm_sym*nofdm,1);% p/s%  uni_ofdm_sym=(ofdm_sym1+abs(ofdm_sym1))./2;  % t=0:t_sym:100e-9;%ns  t=0:t_sym:100e-9;%ns  n_led=2500;  hled=(n_led).*exp((-2*pi*f_3db).*t);  hled=hled./sum(hled);  ledin=48e-6*n_led+uni_ofdm_sym;  optsig=r.*conv(ledin,hled);  l=length(optsig)-length(ofdm_sym1);  ebno_db=0:20; snr_db=ebno_db+10*log10((n/n+l_cp))...  +10*log10(((n_data_carrier+n_pilot_carrier)/n))+10*log10(k);  ber=zeros(1,length(snr_db));  rr=1:length(snr_db);  inoisy=awgn(optsig,snr_db(rr),'measured');  inoisy1=inoisy((1+floor(l/2)):(floor(l/2)+length(ofdm_sym1)));  inoisy22=reshape(inoisy1,l_ofdm_sym,nofdm);  fft_in=inoisy22(l_cp+1:n+l_cp,:);  fft_out=fft(fft_in,n);  if n==32; fft_out2=fft_out(2:15,:); ps=fft_out(16,:); hprim=ps/ps;  elseif n==64; f1=fft_out(2:15,:); f2=fft_out(18:31,:); fft_out2=[f1;f2]; ps1=fft_out(16,:)/ps(1);ps2=fft_out(32,:)/ps(2); hprim=[ps1;ps2];  elseif n==128; f1=fft_out(2:15,:); f2=fft_out(18:31,:); f3=fft_out(34:47,:); f4=fft_out(50:63,:); fft_out2=[f1;f2;f3;f4];  ps1=fft_out(16,:)/ps(1);ps2=fft_out(32,:)/ps(2);ps3=fft_out(48,:)/ps(3);ps4=fft_out(64,:)/ps(4); hprim=[ps1;ps2;ps3;ps4]; end;  fft_out3=2.*imag(fft_out2);  fft_out4=reshape(fft_out3,n_data_carrier*0.5*nofdm,1);  demoded_sig=step(hpam_demod,fft_out4);  ber1=xor(input_b,demoded_sig);  ber(1,rr)=sum(ber1)/length(ber1) end;  semilogy(ebno_db,ber,'g-s','linewidth',2.5,'markersize',8);grid on;


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