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Radio broadcasts are immensely popular in the developing countries,
and would be even more so if sound quality was enhanced and if
programmes could reach the whole of the population. In fact,
radio might even become a remarkable development tool. What is
the key to development? An alternative to terrestrial short wave
or frequency modulation broadcasting systems. What is the solution?
Satellites and digital transmission. Combining the two will provide
Espace of France to deliver the Satellite System under a turnkey
contract due for completion for the first region (Africa, Middle
East) by the end of 1998, for Asia by the beginning of 1999,
and for Latin America by mid-1999. WorldSpace or the Revolution
in the Air Waves a quick way to deliver high quality sound, a
wide choice of programmes, easy reception, and even multimedia
services to over four billion listeners who are currently underserved.
WorldSpace will be the first worldwide digital radio broadcasting
System to use direct satellite transmission. On the eve of the
21st century, it will be nothing less than a revolution for people
in Africa, the Middle East, Asia, and Latin America... a revolution
in the air waves.
In 1995, the U.S. company WorldSpace selected Alcatel.
WorldSpace
... Three geostationary satellites
... An exceptional choice of radio programmes
... Unrivalled sound quality
RADIO BROADCASTING FOR 4.5 BILLION LISTENERS
Listeners, broadcasters and advertisers will enjoy numerous advantages.
Numerous programmes with excellent sound quality
- Programmes with rich content: music, local information, world-wide
news, discussion, live sport... but also educational and public
service programmes and multimedia content services (radiomessaging,
low bit-rate video, etc.).
- Radio stations transmitting in multiple languages.
- Near-CD sound quality.
- Low-cost receivers specially designed for digital satellite
broadcasting, as portable as traditional radio sets.
A new market for broadcasters
- Geographical coverage of 14 million km (5,400,000 square
miles).
- Digitally enabled image and text enhancement of programmes.
- Homogeneous, stable sound quality for easy listening.
- Lower broadcasting cost than for terrestrial networks.
New targets for advertisers
- An immense audience with a keen appetite for original, high
quality programmes that can be financed by advertising.
- The economical advantage of a broadcasting system that can
simultaneously reach vast territories and an enormous population.
Three very powerful geostationary satellites (AfriStar, AsiaStar,
AmeriStar) and their earth infrastructure will enable up to 4.5
billion potential listeners to directly receive dozens of programmes
with remarkably easy listening on new-generation, low-cost receivers.
The range and wealth of programming will be accompanied by near
CD quality sound and multimedia services such as e-mail, text
reception, and the ability to download software and other low
bit-rate applications. WorldSpace's customers will include: international
private radio broadcasters; public service short wave broadcasters
who will use the System to provide a new, enhanced reception
quality; private local and national radios that could extend
their audience overnight; international bodies such as the United
Nations, the World Health Organisation (W.H.O.) or UNESCO that
will be offering general interest programmes in the areas of
health, education and development.
Alcatel Espace, Prime Contractor for the WorldSpace System
Initially an equipment supplier, then European leader in payloads,
Alcatel Espace is now the prime contractor for the WorldSpace
System. At the head of an industrial consortium, Alcatel Espace
is responsible for overall System engineering and validation,
including construction and launch of the satellites designed
for the mission.
Alcatel Espace is involved in three contracts:
- Overall System Supply
This contract concerns all activities related to the WorldSpace
mission. Alcatel Espace is responsible for System engineering
right through to the validation of the global architecture in
operation, and for providing the uplink station and receiver
prototypes.
- In-Orbit Delivery of the hree Satellites
Alcatel Espace coordinates the industrial process linked to the
Space egment: design, manufacture and esting of payloads, satellite
ntegration, production of the ssociated Ground Control Segment,
aunch of the satellites and early rbit operations. This contract
also ncludes the supply of the Mission, business and Infrastructure
Segments. hese Segments, as well as he Ground Control Segment,
will e installed on five continents.
- Operations Support his contract includes writing he
operation and certification rocedures for the System control
ersonnel. This mission will be onducted from a technical centre
located at Alcatel Espace premises in Toulouse, France.
Technical characteristics of each satellite
Three-axis-stabilised EUROSTAR platform design.
- Launch mass: 2 750 kg
- Span (solar panels deployed): 28 m
- Max. E.I.R.P.(Equivalent Isotropic Radiated Power):
- 53 dBW at centre of coverage
- Power Consumption: 6 kW
- In-orbit lifetime: 15 years
- Launcher: Ariane IV/V
The WorldSpace system overview
The WorldSpace System comprises three geostationary satellites
at the following orbital locations:
- AfriStar, at 21° East, for Africa and the Middle East,
- AsiaStar, at 105° East, for Asia,
- AmeriStar, at 95° West, for Central and South America,
Each satellite covers a zone defined by three spot beams.
The System configuration is identical for each region:
- The Space Segment
Includes the satellite and associated ground control segment
which provides continuous control of satellite operation. The
ground control segment is composed of two TCR (Telemetry, Command
and Ranging) stations, and a Satellite Control Centre.
- The Mission Segment
The Mission Centre, in constant contact with the ground control
segment and the business segment, manages broadcaster access
to the satellite and frequency band allocation. The Communication
System Monitoring centre controls the quality of downlink signals.
- The Broadcast Segment
This includes studio and uplink station equipment via which broadcasters
access the satellites: individual VSAT-type terminals and hub
stations shared by several broadcasters.
- The Radio Segment
Comprises millions of receivers that will enable listeners to
pick up the programmes of their choice. These receivers are equipped
with electronic chip sets capable of decoding digital radio signals
(they will also be able to receive conventional radio broadcasts).
- The Business Segment
Enables the management of channel reservations and billing.
- The Infrastructure Segment
Communication networks link the sites that make up these different
segments and are spread over five continents.
The WorldSpace system Operating Principle
A simple concept and a flexible System: broadcasters will have
access to the satellite, via either a small individual station,
or a central hub station. Leading edge techniques will be used
to transmit the digital programmes to the satellite. The satellite
will then send the signal down to listeners.
Two access modes, two payloads: each satellite will carry
an innovative payload that will implement baseband processing
- appearing for the first time in a commercial programme - and
a more conventional "bent-pipe" (or "transparent")
payload.
- Innovative methods: on-board signal processing
All broadcasters using the WorldSpace System will access the
satellite directly in FDMA (Frequency Division Multiple Access)
mode in the X band (7,025 to 7,075 MHz) from their own individual
uplink stations. This mode has been selected because of the flexibility
that it delivers when multiple, independent uplink stations are
being used. In the studio, the broadcaster multiplexes the audio
programmes and/or multimedia services, on a Broadcast Channel.
The uplink station splits the Broadcast Channel into Prime Rate
Channels, each with a capacity of 16 kbps, for transmission to
the satellite. The uplink can handle up to 288 Prime Rate Channels.
The digital processor on board the satellite demultiplexes and
demodulates the Prime Rate Channels at baseband level, and converts
them to TDM (Time Division Multiplexing) for L band transmission
of the signal to listeners.
- Conventional method: "transparent" communication
This method enables several broadcasters to access a hub station,
capable of broadcasting bundles of programmes. This station receives
multiplexed broadcasting channels, splits them into Prime Rate
Channels, then performs the same processing as the digital processor.
The TDM signals (a maximum of three) are transmitted in the X
band to the satellite which converts the frequency and sends
the L band signals to the radio receivers.
- Transmission capacity and sound quality
Each of the three beams transmits two TDM signals (1 TDM signal
= 96 Prime Rate Channels of 16 kbps each): one by the on-board
processing payload, the other by the "transparent"
payload. Each satellite broadcasts 192 x 16 kbps channels per
beam or coverage zone. The multiplexing technique adopted by
WorldSpace will support combinations of radio programmes. In
this way each user in a coverage zone will be able to receive:
- 96 "mono" radio stations
- or 48 "stereo FM" stations
- or 24 CD quality programmes
- or a combination of the above.
For downlinks, the WorldSpace System uses the L frequency
band (1,467 to 1,492 MHz) allocated by the International Telecommunications
Union (ITU) for digital satellite broadcasting services. Once
the listener has selected a frequency, the receiver's integrated
circuits will extract the required TDM signal (identical in all
access modes) and decode it to restore the original sound. The
programmes are digitally coded using the MPEG* 1/2 layer III
compression standard. The resulting sound quality for listeners
and the number of programmes received will depend on the digital
bit-rate chosen by the broadcaster: from 16 kbps for monophonic
sound to 128 kbps for CD-comparable sound quality. In the future,
the System may support digital bit-rates of up to 1.5 Mbps for
data distribution.
An innovative payload design baseband digital processor
The dual payload carried by WorldSpace satellites has been designed
by Alcatel Espace at its Toulouse premises to supply the highest
possible digital broadcasting performance and the highest level
of reliability throughout the satellites lifetime:
The baseband digital processor : the core of the on-board processing
payload:
- simultaneously demodulates the Prime Rate Channels
from the uplink
- uses a matrix to route each of the Prime Rate Channels
- formats the time division multiplexing.
- On-board baseband processing enhances performance
in three areas: uplink and downlink control, uplink station management
and downlink control signal.
The broadcasting channel management is very flexible:
- any uplink channel can be broadcast in L band simultaneously
on one, two or three beams;
- each uplink channel is monitored;
- the choice of uplink channels composing each TDM downlink
signal is constantly controlled.
- The high L band power is achieved by a pair of 150
watt traveling wave tube amplifiers (TWTA) operating in parallel.
- The ability to set frequencies, in both reception
and transmission, makes the System very flexible.
- In orbit antenna reconfiguration allows antenna coverage
optimization and enables one satellite to replace another whenever
necessary.
With the WorldSpace System, radio takes a decisive step forward.
The use of digitalization and audio data compression technologies,
combined with satellite transmission, is the biggest single breakthrough
since the advent of short wave radio in 1920. Alcatel Espace
is proud of its industrial partnership with WorldSpace and of
its technical contribution to the System development. |