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 1

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

2

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 3

DAB signal generation

4

DAB reception

5

MUSICAM Audio Coding

M

asking Pattern

U

niversal

S

ub-band

I

ntegrated

C

oding

A

nd

M

ultiplexing.

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 6

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) 7

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.

8

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

9

frequency network.