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

6. 9 MATLAB Exercises 315
% ts new sampling period
% NOTE : td*fs must be a positive integer;
% Function outputs :
%
s out - sampled output
%
sq_out - sample-and-quantized output
%
sqh_out- sample, quantize, and hold output
%
Delta - quantization interval
%
SQNR - actual signal to quantization noise ratio
if (rem(ts/td, 1)==0)
nfac=round (ts/td) ;
p_zoh=ones (l,nfac) ;
s_out=downsampl e(sig_in,nfac) ;
[sq_out ,Delta, SQNR] =uniquan (s_out ,L) ;
s_out=upsampl e(s_out ,nfac) ;
sqh_out=kron (sq_out ,p_zoh) ;
sq_out=upsample (sq_out ,nfac );
else
warning ('Error ! ts/td is not an integer! ');
s_out= [] ;sq_out= [l ;sqh_out= [l ;Delta= [] ;SQNR= [l ;
end
end
The MATLAB program ExPCM . m provides a numerical example that uses these two
MATLAB functions to generate PCM signals.
% (ExPCM .m)
% Example of sampling, quantization , and zero-order hold
clear;clf;
td=0 .002 ;
t= [ O : td : 1 . l ;
%original sampling rate 500 Hz
%time interval of 1 second
xsig=sin (2*pi*t) -sin (6*pi*t) ; % 1Hz+3Hz sinusoids
Lsig=length (xsig) ;
Lfft=2-ceil ( log2 (Lsig) +l) ;
Xsig=fftshift (fft (xsig,Lfft) );
Fmax=l/(2*td) ;
Faxis=linspace (-Fmax , Fmax,Lfft) ;
ts=0 .02;
%new sampling rate 50Hz .
Nfact=ts/td;
% send the signal through a 16-level uniform quantizer
[s_out, sq_out,sqh_outl, Delta, SQNR] =sampandquant (xsig , 16,td, ts) ;
% obtained the PCM signal which is
% - sampled , quantized, and zero-order hold signal sqh_out
% plot the original signal and the PCM signal in time domain
figure (l) ;
subplot (211) ;sfigl=plot (t,xsig, 'k' ,t, sqh_outl (l:Lsig) , 'b');
set (sfigl , 'Linewidth ' ,2) ;
title ('Signal {\it g} ({\it t} ) and its 16 level PCM signal ')