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

12.12 MATLAB Exercises 723
% It shows how little lowpass Tx filter may have distorted the signal
plotPSD_comparison
% Apply a 2-ray multipath channel
mpath= [l O O -0.83) ; % multipath delta(t)-0 .83 delta(t-3T/ 8)
%
or use mpath= [l O O .45) ;
% time-domain mu ltipath channel
h=conv (conv (prcos, pcmatch) ,mpath ) ;
hscale=norm (h) ;
xchout=conv (mpath, xchout ); % apply 2-ray mu ltipath
xrxout=conv ( xchout ,pcmatch) ; % send the signal through matched filter
% separately from the noise
delaychb=delayrc+3 ;
out_mf=xrxout (delaychb+l :f_ovsamp :delaychb+L*f_ovsamp) ;
clear xrxout ;
% Generate complex random noise for channel output
noiseq=randn (L* f_ovsamp ,l)+j*randn (L* f_ovsamp, 1) ;
% send AWGN noise into matched filter first
noiseflt=filter (pcmatch, [1] ,noiseq) ; clear noiseq;
% Generate sampled noise after matched filter before scaling it
% and adding to the QAM signal
noisesamp=noiseflt (l:f_ovsamp :L* f_ovsamp, 1) ;
clear noiseq noiseflt;
Es=lO*hscale;
% symbol energy
% Call decision feedback equalizer receiver to work
dfe
SERdfe=SEReq;
for ii=l:9;
Eb2Naz (ii)=2*ii;
Q(ii)=3*0. S*erfc ( sqrt ((2*10 (Eb2Naz (ii) *0.1)/5) / 2));
%Compute the Analytical BER
end
% use the program plotQAM_results to show results
plotQAM_results
linear_eq
At the receiver, once the signal has passed through the root-raised-cosine matched filter, the T­
spaced samples will be sent into the DFE. The subroutine program df e . m implements the DFE design
and the actual equalization. The DFE design requires the receiver to first estimate the discrete channel
response. We use the first 200 QAM symbols as training data for channel estimation. We then compute
the SER of the DFE output in dfe . m. The necessary program dfe . mis given here
% MATLAB PROGRAM <dfe .m>
% This is the receiver part of the QAM equalization
% that uses Decision feedback equalizer (DFE)
%
Ntrain=200;
Nch=3;
SEReq= [J; SERneq= (];
% Number of training symbols for Equalization
% Order of FIR channel (=length-1)