An Introduction to
Digital Terrestrial Television
(DTT) Broadcasting
September 2004
What is DTT ?
Analogue Terrestrial Television (Existing)
Analogue TV signals received
via aerial or communal aerial
broadcast distribution (CABD)
system for viewing on TV set
Currently four free-to-air TV
programme channels in HK
Use analogue transmission
Digital Terrestrial Television (Coming)
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Use digital transmission
Decoder
Digital TV signal received
via aerial or CABD system and
decoded for viewing on TV set
Supports more free-to-air
TV programme channels plus
high definition TV
How to receive Digital Terrestrial Television ?
How to Receive DTT ?
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Decoder
External decoder added
between TV socket and
conventional TV set
OR
Integrated digital TV set
with decoder built in
Benefits of DTT
Improved reception and picture quality
Support new services like high definition
television (HDTV) and multimedia /
interactive services
Carry more contents in one channel
Support mobile / portable reception
Better use of frequency spectrum
Release valuable frequency spectrum for
other uses after full migration from
analogue to digital broadcasting
DTT Improves Reception of Television Signals
Analogue weak signal
causes snowy pictures
Radio signals weaken over distance and due to blockings
Digital clear picture
can be received at a
lower signal level
DTT Improves Television Picture Quality
Analogue multi-path reflections
from tall buildings cause ghosting
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Digital clear picture and no
ghosting
Decoder
DTT Supports High Definition Television
Analogue TV (Standard Definition)
Digital TV (High Definition)
Resolution up to 575 lines
(vertical) x 720 pixels
(horizontal)
Resolution up to 1080 lines
(vertical) x 1920 pixels
(horizontal)
Aspect ratio 4:3
Aspect ratio 16:9 (Widescreen)
Stereo sound
Multi sound channels (e.g.
Dolby 5.1 multi-channel sound)
DTT Supports Multi-Channel Programmes and
Multimedia Contents
Digital
broadcasting
Digital
frequency
Channel
A frequency channel with
digital transmission can
carry one high definition TV
programme channel plus
multi-sound channels and
data services
OR
Digital
frequency
Channel
Analogue
broadcasting
Analogue
frequency
Channel
four standard definition TV
programme channels plus
multi-sound channels and
data services
A frequency channel with
analogue transmission can
carry one standard definition
equivalent TV programme
channel only
DTT Supports Reception by Mobile /
Portable Devices
Analogue fixed
reception only
Analogue
broadcasting
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Digital
broadcasting
Decoder
Digital fixed and
mobile reception
DTT Makes More Efficient Use of Radio Spectrum
Multi-Frequency Network
Single-Frequency Network
(Used by Existing Analogue TV)
(Used by DTT only)
Channel 21, 23, 25, 27
Channel 34, 38, 42, 44
Temple Hill
Castle Peak
Cloudy Hill
Channel 30
Temple Hill
Castle Peak
Cloudy Hill
Channel 49, 51, 53, 55
Different transmitters use different
frequency channels to carry the same
TV programme channels
Different transmitters use the same
frequency channel to transmit the
same TV programme channels
Many frequency channels are
required to cover the service area
Only one frequency channel is
required to cover the service area
Release of Valuable Frequency Spectrum after
Analogue Switch-off and Full Migration to Digital
Existing Status
The existing
spectrum can be
used for
transmitting only 4
analogue channels
and some digital
channels
After Analogue
Switch-off
The whole
spectrum can be
used for digital
broadcasts and
other
applications
digital
Some spectrum can only be
used for digital broadcast
(maximum 5 multiplexes)
analogue
ATV Home
ATV World
TVB Jade
TVB Pearl
digital
digital broadcasting services
spectrum released
for digital broadcasts and
other applications
Timetable for Implementation of DTT
Analogue
Broadcasts
Only
Analogue
Existing four
free TV
programmes
Now
Simulcast starts (By 2007)
Simultaneous
Analogue and
Digital Broadcasts
(Simulcast)
Analogue
Digital
Digital
Digital
New HDTV
and/or multichannel
programmes
Simulcast
Period
Analogue broadcasts
to be switched off
Digital
Broadcasts
Only
Digital
Digital
Digital
Digital
Digital
Analogue
Switchoff
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More about DTT in Hong Kong
Please visit the following websites for more information about DTT
in Hong Kong:
1. Communications and Technology Branch, Commerce, Industry and
Technology Bureau (http://www.citb.gov.hk/ctb)
2. Office of the Telecommunications Authority (http://www.ofta.gov.hk)
