DIGITAL RADIO -- The
Eureka 147 DAB System
THE THIRD AGE OF BROADCASTING
The First Age of Radio Broadcasting - the era of AM-1910.
The Second age - FM services -1950.
The 'Third Age of broadcasting – DAB (Digital Audio
Broadcasting)-1995
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An outline of the Eureka 143 system
Hi-fi and more services are always the targets of radio
broadcast.
The solution to increasing the capacity and versatility of
sound broadcast is digital.
THE UNIQUE BENEFITS OF DAB
•High-quality digital audio.
•Rugged, reliable delivery
•Efficient use of the limited radio frequency spectrum available
•Flexibility and choice
•System features
•Added-value system features
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TECHNICAL OVERVIEW OF THE
EUREKA 147 SYSTEM
Eureka 147 DAB is a reliable, multi-service, digital radio
broadcasting system, designed specifically for robust reception by
mobile, portable, and fixed receivers, using simple non-directional
antennas.
The Eureka 147 System comprises three main elements. These are:
•MUSICAM Audio Coding
•Transmission Coding & Multiplexing
•COFDM Modulation
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DAB signal generation
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DAB reception
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MUSICAM Audio Coding
Masking Pattern Universal Sub-band Integrated Coding And
Multiplexing.
the system codes only audio signal components that the ear will hear, and
discards any audio information that, according to the psychoacoustical
model, the ear will not perceive
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TRANSMISSION CODING & MULTIPLEXING
The frame-based DAB multiplex comprises three distinct elements:
•The Synchronisation Channel
•The Fast Information Channel (FIC)
•The Main Service Channel (MSC)
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COFDM MODULATION
Coded Orthogonal Frequency Division Multiplexing
(COFDM).
COFDM uses many carriers -- up to 1536, spaced at
1 kHz separation for DAB -- with each carrier
independently modulated using differential
QPSK(quadrature phase shift keying).
Affords some protection against multipath echoes
Ref:Alard M. and Lassalle R., 1987, "Principles
of modulation and channel coding for digital
broadcasting for mobile receivers.".EBU Technical
Review No. 224 pp. 168-190.
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ROLL OUT OF DAB IN THE UNITED KINGDOM
In the United Kingdom, 12.5 MHz of Band III spectrum
from 217.5 - 230 MHz has been allocated to DAB
This will accommodate seven multiplexes each of which
can
carry six high-quality stereo services or a greater
number of mono ones, plus data.
The guard interval provides the DAB system with
immunity to long delay echoes. There is little
difference between another transmitter transmitting
exactly the same signal and an echo. It is possible to
provide a wide area broadcast using a number of
transmitters, all broadcasting the same signal.--single
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frequency network.