SATELLITE RADIO by Franklin Umoh

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SATELLITE RADIO by Umoh .A. Franklin Page 1

TABLE OF CONTENTS

ABSTRACT 2

CHAPTER 1

INTRODUCTION 3

CHAPTER 2

BASIC COMPONENTS OF SATELLITE RADIO .. 3

2.1 SATELLITES . 5

XM Satellite radio ... 6 Sirius Satellite radio . 7 World space Satellite radio .. 8

2.2 GROUND REPEATERS 10

2.3 RADIO RECEIVETRS .. 11

CHAPTER 3

TRANSMISSION AND RECEPTION .. 14

3.1 Generation of DAB signal 153.2 Reception of DAB signal .. 163.3 Frequency of operation . 173.4 Multipath interference .. 17

CHAPTER 4

ADVANTAGES OVER ANALOG RADIO. 18

CONCLUSION. 19

REFERENCES

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ABSTRACT

Satellites are one of the greatest achievements of mankind.

They have been used for various applications like communication,

military application, weather forecasting and so on. They play a big

role in the case of television channels and other entertainment

networks. One of the latest applications of satellites is the satellite

radio.

Satellite radio is a subscriber based radio service that broadcast

directly from satellites. It is an advanced form of mobile radio service

where one can receive compact disc quality music and other entertainment

channels. Even if the person is miles away from the radio station, the

quality of the program is not affected. The paper deals with the basic

structure of the satellite radio and its transmission and reception

procedures.


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CHAPTER 1

INTRODUCTION

We all have our favorite radio stations that we preset into our car radios,

flipping between them as we drive to and from work, on errands and around

town. But when travel too far away from the source station, the signal breaks up

and fades into static. Most radio signals can only travel about 30 or 40 miles from

their source. On long trips that find you passing through different cities, you

might have to change radio stations every hour or so as the signals fade in and

out.

Now, imagine a radio station that can broadcast its signal from more than

22,000 miles (35,000 kill) away and then come through on your car radio with

complete clarity without ever having to change the radio station.

Satellite Radio orDigital Audio Radio Service (DARS) is a subscriber

based radio service that is broadcast directly from satellites. Subscribers will be

able to receive up to100 radio channels featuring Compact Disk digital quality

music, news, weather, sports talk radio and other entertainment channels.

Satellite radio is an idea nearly 10 years in the making. In 1992, the U.S.

Federal Communications Commission (FCC) allocated a spectrum in the "S"

band (2.3 GHz) for nationwide broadcasting of satellite-based Digital Audio

Radio Service (DARS). In 1997, the FCC awarded 8-year radio broadcast

licenses to two companies, Sirius Satellite Radio former (CD Radio) and XM

Satellite Radio (former American Mobile Radio). Both companies have been

working aggressively to be prepared to offer their radio services to the public by

the end of 2000. It is expected that automotive radios would be the largest


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application of Satellite Radio.

The satellite era began in September 2001 when XM launched in selected

markets followed by full nationwide service in November. Sirius lagged slightly,

with a gradual rollout beginning in February, including a quiet launch in the Bay

Area on June 15. The nationwide launch comes July 1.

To the average user, these systems will look very similar to conventional

AM/FM radio systems, whether they are used in the home, office, or on the road.

However, the real difference is in what the listener won't see. Rather than

receiving a signal from a tower antenna of a local radio station, these new radios

will receive signals from a set of satellites in geosynchronous orbit. Programming

will be up linked from ground stations to the satellites and then broadcast back to

large geographic areas.

The programming will be up linked to the three geostationary orbitsatellites and then rebroadcast directly to radios in the vehicles of CD Radio

subscribers. Ground based repeaters will be used in urban areas to provide a clear

and uninterrupted radio signal.

* Pictures showing the satellite station


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CHAPTER 2

BASIC COMPONENTS OF SATELLITE RADIO

Each company has a different plan for its broadcasting system, but the

systems do share similarities. Here are the key components of the three satellite

radio systems:

SATELLITES GROUND REPEATERS RADIO RECEIVERS

At this time, there are three space-based radio broadcasters in various stages of

development:

XM Satellite Radio launched commercial service in limited areas of the United

States on September 25, 2001. (They were originally going to launch service

September 12. but postponed the event because of the terrorist attacks on the

United States.)

Sirius Satellite Radio is now operational in the United States, with its official

launch on July I, 2002.

WorldSpace is already broadcasting in Africa and Asia, and will begin

broadcasting in South America sometime soon.

XM Satellite radio and Sirius Satellite Radio have both launched such a service.

Satellite radio, also called digital radio, offers' uninterrupted, near CD-quality

music beamed to the radio from space.


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Taking a closer look, you will see slight variances in the three satellite radio

companies' systems. In the next three sections, we will profile each of the

companies offering satellite radio services.

2.1 SATELLITES

XM SATELLITE RADIO

XM Radio uses two Boeing HS 702 satellites, appropriately dubbed

"Rock" and "Roll," placed in parallel geostationary orbit, one at 85 degrees west

longitude and the other at 115 degrees west longitude. Geostationary Earth orbit

(GED) is about 22.223 miles (35,764 km) above Earth, and is the type of orbit

most commonly used for communications satellites. The first XM satellite,

"Rock," was launched on 18th

March 2001, with "Roll" following on 8th

May XMRadio has a third HS-702 satellite on the ground ready to be launched in case one

of the two orbiting satellites fails.

XM Radio's ground station transmits a signal to its two GED satellites.

Which bounce the signals back down to radio receivers on the ground and the

downlink will be in the 2.33-2.34 GHz frequency range. A spare satellite will bekept on the ground for emergencies. The radio receivers are programmed to

receive and unscramble the digital data signal, which contains up to 100 channels

of digital audio. In addition to the encoded sound, the signal contains additional

information about the broadcast. The song title, artist and genre of music are all

displayed on the radio. In urban areas, where buildings can block out the satellite

signal, ground transmitters supplement XM's broadcasting system.


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SIRIUS SATELLITE RADIO

Unlike XM, Sirius does not use GED satellites. Instead, its three SS/L-1300

satellites form an inclined elliptical satellite constellation. Sirius says the elliptical

path of its satellite constellation ensures that each satellite spends about 16 hours

a day over the continental United States, with at least one satellite over the

country at all times. Sirius completed its three-satellite constellation on 30th

November, 2000. A fourth satellite will remain on the ground, ready to be

launched if any of the three active satellites encounter transmission problems.

The Sirius system is similar to that of XM. Programs are beamed to one of the

three Sirius satellites, which then transmit the signal to the ground where the

radio receiver picks up one of the channels within the signal. Signals are also be

beamed to ground repeaters for listeners in urban areas wherethe satellite signal

can be interrupted.

While XM offers both car and portable radios, Sirius is concentrating on the car

radio market. The Sirius receiver includes two parts -- the antenna module and

the receiver module. The antenna module picks up signals from the ground

repeaters or the satellite. Amplifies the signal and filters out any interference. The

signal is then passed on to the receiver module. Inside the receiver module is achipset consisting of eight chips. The chip set converts the signals from 2.3

gigahertz (GHz) to a lower intermediate frequency. Sirius also offers an adapter

that allows conventional car radios to receive satellite signals.


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WORLDSPACE

So far, WorldSpace has been the leader in the satellite radio industry. It put two

or its three satellites, AfriStar and AsiaStar, in geostationary orbit before either of

the other two companies launched one. AfriStar and AsiaStar were launched in

October 1998 and March 2000, respectively. AmeriStar, which will offer service

to South America and parts of Mexico, is not yet scheduled for launch. Each

satellite transmits three signal beams carrying more than 40 channels of

programming, to three overlapping coverage areas or about 5.4 million square

miles (14 million square km) each. Each of WorldSpace satellites' three beams

can deliver over 50 channels of crystal clear audio and multimedia programming

via the 1,467- to 1,492- megahertz (MHz) segment of the L-band spectrum,

which is allocated for digital audio broadcasting.

AfriStar is positioned in a 210 East geosynchronous orbit and is controlled

by the WorldSpace Operations Center located in Washington, DC. The primecontractor for the satellite is Alcatel Space Industries, andMatra Marconi Space

built the EuroStar 2000+ satellite bus. The uplink frequencies are 7.025-7.075

GHz, and the downlink frequencies are 1.452-1.492 GHz. Each AfriStar

downlink spot beam has capacity for ninety-six 16 kb/s mono-AM-quality signals

that can be combined for fewer channels of higher audio quality. The downlink

signals in each spot beam are combined into two Time Division Multiple Access(TDMA) carriers. Uplink signals can be accepted as TDMA signals from control

stations or individually as Frequency Division Multiple Access (FDMA) signals

from originating program locations.


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WorldSpace also launched AsiaStar in March 2000, a DBS radio satellite

that currently covers Asia (1050 East orbit). In late 2000, WorldSpace plans to

launch AmeriStar (950 West orbit) to cover Latin America.

The United States is not currently part of WorldSpace's coverage area. The

company has invested in XM Radio and has an agreement with XM to share any

technological developments. WorldSpace is going beyond one nation and eyeing

world domination of the radio market. That might be overstating the company's

intent a bit. But WorldSpace does plan to reach the corners of our world that most

radio stations cannot. There are millions of people living in WorldSpace's

projected listening area who cannot conventional radio station. WorldSpace says

it has a potential audience of about 4.6 billion listeners spanning five continents.

* WorldSpace will be able to broadcast to the majority of the world's population

when its AmeriStar satellite is launched.

WorldSpacebroadcasters uplink their signal to one of the three satellites through

a centralized hub site or an individual feeder link station located within the global

uplink beam. The satellite then transmits the signal in one, two or all three beams

on each satellite. Receivers on the ground then pick up the signal and provide

CD-quality sound through a detachable antenna.


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* World space integrated solutiond

2.2 GROUND REPEATERS

Satellite radio reception, poses threats fromweather, tall building and mountains

that can potentially interfere with broadcasts.

To avoid the interference caused by tall structures, both Sirius and XM Radio are

supplementing their satellite coverage with terrestrial transmitters, called ground

repeaters. If the satellite radio antenna is blocked by a skyscraper, it should pick

up signals fromone of the ground repeaters.

Getting signals from a satellite to receivers in cars or in the home is a tall order.

Although the microwaves the satellites rely on are able to penetrate the

atmosphere from space, they need a "direct line of sight" and can only reach their

target if unimpeded by obstacles such as trees, houses, or thunderstorms.


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Therefore, ground-based repeaters are needed to prevent service interruption in

cities where tall buildings otherwise would block the line of sight between radio

receivers and the satellites. XM has employed more than 1,000 of these terrestrial

repeaters, which have been strategically placed throughout the continental United

States to receive the XM signal directly fromthe satellites, and then retransmit it

to XM radios in cars and homes. These repeaters have been installed in densely

populated cities, on the roofs of buildings, and in mountainous areas where line of

sight can be difficult to maintain.

2.3 THE SATELLITE RADIO RECEIVER

Existing AM/FM car radio will not be able to receive satellite radio broadcasts.

Two options are available. Replacement of the radio with a 3-band capable

receiver (AM, FM, Sirius or XM Satellite). Radios can be purchased as a dealer

option or can be directly purchased at consumer retail stores, mail order and

Internet stores. All major manufactures are prepared to provide radios capable ofsatellite radio reception.

A second option is the purchase an adaptor for existing AM/FM radios. The

adaptor will contain the satellite receiver, along with display and control

functions. Sirius and XM have developed slightly different technologies which

mean that you can purchase a radio capable of receiving satellite broadcasts fromone company or the other but not both. You need a receiver, about the size of

squashed shoe box, which goes under a car in the trunk, along with a fist-sized

antenna that sits on the roof or trunk lid.


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The receiving end is virtually the same for both companies, but the satellite

configurations are different: XM Radio will use two satellites, and Sirius will use

a combination three. These receivers, somewhat akin to AM/FM tuners, are made

up of two parts: an "active" antenna and a receiving module.

XM and Sirius Radio will work similarly. Each will beam a combination

of original and syndicated programming to orbiting communications and

terrestrial satellites which will send out signals to the satellite radio receivers.

These receivers, somewhat akin to AM/FM tuners, are made up of two parts: an

"active" antenna and a receiving module.

The antenna is active because it basically looks for available signals to

pick up from. Satellites it recognizes. When it finds them, it amplifies them,

filters out any accompanying noise and interference, and then sends them to the

receiver, where most of the real work is done. En route to the receiver, the signals

are converted from analog to digital. Once in the digital realm, they are analyzedfor quality, and then processed and combined to produce the best digital "image"

of the sound. The receiver also decrypts the signals and finally converts them

back to analog audio, which can be sent to the radios speakers so one can hear it.

The receiver connects to your existing car radio through a device called

an FM modulator that puts the signal on an unused portion of the FM band. Oryou can buy a car radio called a "head unit" by industry insiders that's "satellite

ready" to make a direct wired connection for maximum audio quality.

On the open road, the receivers pick up a signal from orbiting satellites.

Sirius and XM have also built repeater stations on the ground in major

metropolitan areas to maintain reception when the satellites are blocked by

buildings or other large structures.


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One receiver utilizes a vehicles existing FM radio. A small flat 2" disk

antenna is attached to the outside of the vehicle, a processing unit is placed in the

trunk or dashboard and a display and control screen mounted next to the vehicle's

FM radio. The display screen indicates the selected channel number, channel

name, song title and artist.

Each receiver contains a proprietary chipset. XM began delivering

chipsets to its XM radio-manufacturing partners in October 2000. The chipset

consists of two custom integrated circuits designed by ST Microelectronics. XM

has partnered with Pioneer, Alpine, Clarion, Delphi Deleon, Sony and Motorola

to manufacture XM car radios. Each satellite radio receiver uses a small, car-

phone-sized antenna to receive the XM signal. General Motors has invested about

$100 million in XM, and Honda has also signed an agreement to use XM radios

in its cars. GM began installing XM satellite radio receivers in selected models in

early 2001.

WorldSpace satellite receivers are capable of receiving data at a rate of

128 kilobits per second (Kbps). The receivers use the proprietary StarMan chip

set, manufactured by STMicroelectronics, to receive digital signals from the

satellites


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CHAPTER 3

TRANSMISSION AND RECEPTION

Digital radio works by combining two digital technologies to produce an

efficient and reliable radio broadcast system.

Firstly, an audio compression system, called MPEG, reduces the vast amount of

digital information required to be broadcast. It does this by discarding sounds that

will not be perceived by the listener. For example, very quiet sounds that is

masked by other louder sounds and hence not required to be broadcast, and

efficiently packages together the remaining information.

The second technology, COFDM (Coded Orthogonal Frequency Division

Multiplex) ensures that signals are received reliably and robustly, even in

environments normally prone to interference. Using a precise mathematical

relationship, the digital data signal is split across 1,536 different carrier

frequencies, and also across time. This process ensures that even if some of the

carrier frequencies are affected by interference or the signal disturbed for a short

period of time, the receiver is still able to recover the original sound.

The interference which disturbs FM reception, caused by radio signals

"bouncing" off buildings and hills (multipath) is eliminated by COFDM

technology. It also means that the same frequency can be used across the entire

country, so no re-tuning of sets is necessary when traveling, or taking a portable

receiver to a different area.

Instead of having a different frequency for each radio station, digital radio

combines several services together in what is called a multiplex.


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The multiplex has a gross capacity of 2,300,000 bits which are used for

carrying audio, data and an in-built protection system against transmission errors.

Of these about half the bits are used for the audio and data services. Throughout

the day, the data capacity allocated to each service can be varied by the

broadcaster.

The UK Government has allocated seven multiplexes on the radio spectrum 217.5

230.0 MHz, which will be used for BBC and Commercial Radio for national

regional and local services. Each multiplex can carry a mixture of stereo and

mono audio Services and data services too; the number of each dependent on the

quality required.

3.1 GENERATION OF THE DAB SIGNAL

How each service signal is coded individually at source level, error

protected and time interleaved in the channel coder is shown in Figure 3.1. Thenthe services are multiplexed in the Main Service Channel (MSC), according to a

pre-determined, but adjustable, multiplex configuration. The multiplexer output is

combined with Multiplex Control and Service information, which travel in the

fast Information Channel (FIC), to form the transmission frames in the

Transmission Multiplexer. Fig 3.1 Finally, Orthogonal Frequency Division

Multiplexing (OFDM) is applied to shape the DAB signal, which consists of alarge number of carriers. The signal is then transposed to the appropriate radio

frequency band, amplified and transmitted.


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Fig 3.1 Generation of DAB signal

3.2 RECEPTION OF A DAB SIGNAL

Figure 3.2 demonstrates a DAB receiver. The DAB ensemble is selected

in the analogue tuner, the digitized output of which is fed to the OFDM

demodulator and channel decoder to eliminate transmission errors. The

information contained in the FIC is passed to the user interface for service

selection and is used to setup the receiver appropriately. The MSC data is further

processed in an audio decoder to produce the left and right audio signals or in a

data decoder (packet Demux) as appropriate.


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Fig. 3.2 DAB receiver (User Interface)

3.3 FREQUENCY OF OPERATION

Digital radio is operated in a frequency range of between 215 - 230 MHz

(Mega Hertz). This part of the radio spectrum is sometimes called Band III, or

VHF, and was previously used for some television transmissions and by the

military. The central frequency for the BBC National Multiplex is 225.648MHz.

3.4 MULTI PATH INTERFERENCE

Multipath interference occurs when radio waves bounce off buildings,

hills, or other obstacles. This means the waves reach the set at different times,

causing interference. This is a particular problem in the car. Digital radio sets

have processors which filter out interference and correct errors, such as those

caused by multipath, so no interference. In fact, digital radio is designed to use

multipath to its advantage.


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CHAPTER 4

ADVANTAGES OVER ANALOG RADIO

Conventional analog radio cannot meet this standard, simply because of

the technology used and the transmission environment in which it is broadcast.

As well unlike AM and FM - digital radio reception is virtually immune

to interference, which means there are no static growls or 'multi path' echoes

(caused by signal reflections off buildings or topographical features) to make

listening unpleasant at home, or in the car. In short, digital radio eliminates the

noise that creeps into analog radio transmission and reception

The reason digital radio is so reliable is because it employs a 'smart' receiver.

Inside each digital radio receiver there is a tiny computer: a computer capable of

sorting through the myriad of reflected and atmospherically distorted

transmissions and reconstructing a solid, usable signal for the set to process.

In contrast, an un-intelligent analog receiver cannot differentiate the useful

information from the useless noise. It reproduces the entirety of whatever signal it

is tuned to: static, 'multipath' echoes, and all.


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CHAPTER 5

CONCLUSION

For the listener, digital radio will be more than just 'the best sound on the

airwaves', it will be an intelligent communications device that will offer more

services and conveniences than can be provided by conventional analog

technology.

For the broadcaster, digital radio is not just a way to stay competitive with

other forms of digital sound, but one that offers numerous new business

opportunities as well.

It is a bright future for listeners and broadcasters alike: a future that truly

promises to provide 'the best sound on the airwaves' for the world.


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REFERENCES

http://www.seminar.com/article/sdr_1.html, http://www.spinnakerlabs.com/Satellite digital radio.pdf http://www.worldspace.com http://xmradio.com/whatisxm/index.xmc http://www.seminarsonly.com http://www.siriusradio.com http://www.nigcomsat.net D. Prabakaran, WORLD SPACE- Satellite digital audio broadcast service.

Electronics for You. Nov 2001, Volume 33, No:11.

www.howstuffworks.com

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SATELLITE RADIO by Franklin Umoh