226 Satellite Radio

8/7/2019 226 Satellite Radio

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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 or Digital 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, theU.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

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automotive radios would be the largest 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 _n 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

orbit satellites 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.









Fig. 1 The satellite station









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.









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

2.1.1 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 March 18.2001, with "Roll"

following on May 8. XM Radio 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 receiver son the

ground. and the downlink will be in the 2.33-2.34 GHz frequency range. A

spare satellite will be kept 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.









2.1.2 SIRIUS SATELLITE RADIO

Unlike XM, Sirius does not use OED 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 November 30, 2000. A fourth satellite will remain

on the ground, ready to be launched if any of the three active satellitesencounter 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 where the 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 a chipset 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.









2.1.3 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 prime contractor for the satellite is Alcatel Space Industries, and

Matra 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 kbit/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.









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 worlddomination 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.

Fig 2 WoridSpace will be able to broadcast to the majority of the

world's population when its AmeriStar satellite is launched.

WorIdSpace broadcasters 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.

Fig. 3 World space integrated solution

2.2 GROUND REPEATERS

Satellite radio reception, poses threats from weather, 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 from one 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. 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 from the 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 of satellite 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 from one 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.









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 thesatellite 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 analyzed for 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 radio' s 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. Or you 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.

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 selectedchannel 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

Deleo, 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. OM 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









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 are 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 radiosignals "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.









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. Then the 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) isapplied to shape the DAB signal, which consists of a large number of

carriers. The signal is then transposed to the appropriate radio frequency

band, amplified and transmitted.









Fig 4 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.









User Interface

Fig. 5 DAB receiver

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.









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.

The XM satellites have been allocated 12.5 MHz of frequency

spectrum-over sixty times the bandwidth of a single FM radio station. In

contrast, a commercial FM radio station has only 200 kHz of bandwidth.

Also, in FM radio, the modulation signal is limited to frequencies below

15.000 Hz, whereas the satellite radio audio signal is able to extend to

above 20,000 Hz.









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.









6. BIBLIOGRAPHY

1. D. Prabakaran, “WORLD SPACE- Satellite digital audio broadcast

service”. Electronics For You. Nov 2001, Volume 33, No:11.

2. www.xmradio.com

3. www.siriusradio.com

4. www.worldspace.com

5. www.howstuffworks.com









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.









CONTENTS

1 INTRODUCTION 1

2 BASIC COMPONENTS OF SATELLITE RADIO 3

SATELLITES 4

2.11 XM Satellite radio 4

2.12 Sirius Satellite radio 5

2.13 World space Satellite radio 6

GROUND REPEATERS 8

RADIO RECEIVETRS 9

3 TRANSMISSION AND RECEPTION 12

3.1 Generation of DAB signal 13

3.2 Reception of DAB signal 143.3 Frequency of operation 15

3.4 Multipath interference 15

4 ADVANTAGES OVER ANALOG RADIO 16

5 CONCLUSION 17

6 BIBLIOGRAPHY 18






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226 Satellite Radio