satellite radio full report
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Satellite radio full report.DOC (Size: 557 KB / Downloads: 546)
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.
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, 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 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.
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:
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.
2.1.1 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 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 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.
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 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 project and implimentationed listening area who cannot conventional radio station. WorldSpace says it has a potential audience of about 4.6 billion listeners spanning five continents.
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.
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 reÃ‚Â¬transmit 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 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 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 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 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 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.
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 Ã‚Â¬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) is applied 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.
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.
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.
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.
1. D. Prabakaran, WORLD SPACE- Satellite digital audio broadcast service. Electronics For You. Nov 2001, Volume 33, No:11.
1 INTRODUCTION 1
2 BASIC COMPONENTS OF SATELLITE RADIO 3
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 14
3.3 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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How the Study Was Conducted
1,505 telephone interviews were conducted in July 2003
• National U.S. random sample
• Spring 2003 Arbitron diarykeepers age 12+
• 98.4% of the sample had driven or ridden as a passenger in non-public transportation vehicles (car/truck/van, etc.) in the last month
•Roughly 40% of those who are interested in the concept of satellite radio have never heard of XM or Sirius.
•Those who plan to get satellite radio in the next year or are very interested in the concept tend to be consumers who are spending the most time in their cars. They have the longest commute times and also spend time in their cars for work purposes.
Consumers interested in satellite are some of radio’s biggest listeners.
•Satellite radio has tapped into a need of prospective customers by offering local traffic reports.
•No surprise that those interested in satellite radio tend to be early adaptors of new technology and likely to visit new stores.
• Those interested in satellite radio might be getting the service with their new vehicle. Roughly a third of those interested are planning a new vehicle purchase in the next twelve months.
•The southern U.S. seems to have more than its share of those interested in satellite radio.
Satellite candidates are road warriors.
“How many miles combined have you traveled in a car either
as a driver or passenger in the last seven days?”
Satellite candidates are big commuters.
“How much time do you usually spend commuting to work one way?”
In addition to long commutes,
satellite candidates also spend time
in their cars for work.
“How much time do you usually spend driving your
car for your job during a typical day?”
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