B. P. Lathi, Zhi Ding - Modern Digital and Analog Communication Systems-Oxford University Press (2009)

726 DIGITAL COMMUNICATIONS UNDER LINEARLY DISTORTIVE CHANNELS
s_cyc=reshape ( p_cyc ,37*Lfr, 1) ;
% P/S conversion
Psig=l0/32;
% average channel input power
chsout=filter ( channel ,1,s_cyc) ; % generate channel output signal
clear p_td p_cyc s_data s_cyc ; % release some memory
noiseq= ( randn (37*Lfr,l)+j *randn (37*Lfr, l) );
SEReq= [];
for ii=l :31,
SNR(ii)=ii-1;
% SNR in dB
Asig=sqrt (Psig*lO A (-SNR(ii) /10) )*norm ( channel) ;
x_out=chsout+Asig*noiseq;
% Add noise
x_para=reshape (x_out ,37,Lfr) ;
% S/P conversion
x_disc=x_para (6:37, :);
% discard tails
xhat_para=fft (x_disc);
% FFT back to f-domain
z_data=inv (diag (hf) ) *xhat_para ; % f-domain equalizing
% compute the QAM decision after equalization
deq=sign (real ( z_data) ) +sign (real ( z_data) -2) +sign (real (z_data) +2 )+...
j*{ s ign(imag ( z_data) )+sign ( imag ( z_data) -2) +sign(imag ( z_data) +2 ) );
% Now compare against the original data to compute SER
SEReq= [SEReq sum (p_data~=deq,2)/Lfr];
end
for ii=l :9,
SNRa (ii)=2*ii-2 ;
Q(ii)= 3*0. 5*erfc ( sqrt ((2*10 A (SNRa (ii)*0.1)/5) /2) );
%Compute the Analytical BER
end
% call another program to display OFDM Analysis
ofdmAz
The main MATLAB program Ex12_3 .m completes OFDM modulation, equalization, and detection.
Because the subcarriers (subchannels) have different gain and, consequently, different SNR, each
of the 32 subcarriers may have a different SER. Thus, simply comparing the overall SER does not tell the
full story. For this reason, we can call another program ofdmAz . m to analyze the results of this OFDM
system.
% MATLAB PROGRAM <ofdmAz .m>
% This program is used to analyze the OFDM subcarriers and their
% receiver outputs.
% Plot the subcarrier gains
figure (2) ;
stem(abs (hf) ) ;
xlabel ('Subcarrier label ');
title ('Subchannel gain' );
% Plot the subchannel constellation scattering after OFDM
figure (3) ;
subplot (221) ;plot ( z_data (l,1:800) , '.')
% subchannel 1 output
ylabel ('Imaginary' );
title (' (a) Subchannel 1 output ') ;axis ('square' );
subplot (222);plot (z_data (10,l:800) ,'.');
% subchannel 10 output