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

310 SAMPLING AND ANALOG-TO-DIGITAL CONVERSION
A/53 for broadcast transmission, proposed by the Advanced Television Systems Committee
(ATSC), was finalized by the FCC in the United States.
The GA HDTV standard is based on a 16:9 aspect ratio (motion picture aspect ratio)
rather than the 4:3 aspect ratio of NTSC television. HDTV uses MPEG-2 compression at
1 9.39 MbiUs and a digital modulation format called 8-VSB (vestigial sideband), which uses
an eight-amplitude-level symbol to represent 3 bits of information. Transmission is in 207-
byte blocks, which include 20 parity bytes for Reed-Solomon forward error correction. The
remaining 187-byte packet format is a subset of the MPEG-2 protocol and includes headers
for timing, switching, and other transmission control.
The Advanced Television Systems Group, the successor to the Grand Alliance, has been
developing standards and recommended practices for HDTV. These are found, along with a
great deal of other information, on their website: http://www.atsc.org/.
6. 9 MATLAB EXERCISES
In the MATLAB exercises of this section, we provide examples of signal sampling, signal
reconstruction from samples, uniform quantization, pulse-coded modulation (PCM), and delta
modulation (DM).
Sampling and Reconstruction of Lowpass Signals
In the sampling example, we first construct a signal g(t) with two sinusoidal components of
I -second duration; their frequencies are 1 and 3 Hz. Note, however, that when the signal
duration is infinite, the bandwidth of g (t) would be 3 Hz. However, the finite duration of the
signal implies that the actual signal is not band-limited, although most of the signal content
stays within a bandwidth of 5 Hz. For this reason, we select a sampling frequency of 50
Hz, much higher than the minimum Nyquist frequency of 6 Hz. The MATLAB program,
Exsampl e. m, implements sampling and signal reconstruction. Figure 6.39 illustrates the
original signal, its uniform samples at the 50 Hz sampling rate, and the frequency response of
the sampled signal. In accordance with our analysis of Section 6.1, the spectrum of the sampled
signal gr (t) consists of the original signal spectrum periodically repeated every 50 Hz.
% (Exsampl e.m)
% Example of sampling , quantization , and zero-order hold
clear;clf;
td=0 .002 ; %original sampling rate 500 Hz
t= [O:td:1.J; %time interval of 1 second
xsig=sin (2*pi*t) -sin(6*pi*t); % 1Hz+3Hz sinusoids
Lsig=length (xsig) ;
ts=0 .02;
%new sampling rate = 50Hz .
Nfactor=ts/td;
% send the signal through a 16-level uni form quantizer
[s_out, sq_out , sqh_out ,Delta, SQNR] =sampandquant (xsig, 16, td, ts) ;
% receive 3 signals:
% 1. sampled signal s_out
% 2. sampled and quantized signal sq_out
% 3. sampled , quantized, and zero-order hold signal sqh_out
%