31-01-2013, 10:45 AM
SATELLITE RADIO
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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.
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.
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 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.
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 threesatellite
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.
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.
[attachment=49012]
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.
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.
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 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.
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 threesatellite
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.
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.