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May 9, 2007
If you follow SSG, you are likely familiar with Slacker. Slacker is an upstart company that delivers audio content to consumers via the internet at this point, but will be launching a satellite based delivery component this summer.
Slacker will not be launching satellites to get their service running. Instead, they will lease space from existing satellites. Many thought that this seemed to far fetched to be viable. Well, today, and article published by Radio World Newspaper shows that such concepts are indeed viable.
Article Excerpt:Ku-Mobile Could Revive Retired Sats
by Michael Lawton, 5.09.2007
COLOGNE, Germany A German consortium has found a new angle for satellite radio: Using old satellites to deliver file-based programs to listeners in their cars.
Not only does this solution allow for broadcasting to mobile users without the need for terrestrial repeaters, according to proponents; it also allows users to determine their own program preferences.
The European Space Agency, which promoted the project with nine partners, said its team has designed a flat, mobile antenna built into a car roof. The antenna receives Ku frequency band signals from existing satellites, saving ESA from the cost of launching new satellites.
The agency and its partners worked on the system for more than three years. A challenge was that the satellites used by the system were designed to broadcast television signals to large, fixed dish antennas. For use in cars, they needed a new approach to achieve an antenna that they say can be built in easily by car manufacturers.
The prototype system has been tested and found to work, though it will be some time a while before it is commercially available.
“Satellites usually have to be taken out of service, not because they cannot broadcast any more,” said Erich Lutz of the German space agency, which developed the packet-based transmission system and organized the reception tests.
“The problem,” said Lutz, “is that they run out of fuel to power the motors that keep them exactly in [their orbital] position. That is no good for reception by a fixed dish on a house roof, but it is no problem for the dish on a car, because it has to follow the satellite anyway.”
Time on these end-of-life satellites is relatively cheap, consortium members say, and they stay in orbit until the satellite operator is ready to replace them. “There are always several available,” said Lutz, “and when one is ready to be removed, we can send an instruction to the dish to select another.”
But satellite radio signals may be blocked by tall buildings, trees or other obstructions. That’s why Sirius Satellite Radio and XM Satellite Radio back up their transmission system with terrestrial repeaters.
Satellite radio in the United States transmits on S-band. Ku-band transmission may be an issue, detractors say, for two reasons: There is no industry standard and geostationary satellites can have poor coverage in Europe.
This is why instead of transmitting programming streams, the German consortium decided to send packets of data and to reconstruct the packets within the receiver.
Audio is encoded using aacPlus and divided into files that are delivered as separate data packets. After reception by the user, the files are cached, with material lost due to reception problems retrieved from redundant packets sent with a short delay.
As soon as all the packets that make up a complete program arrive, the user can play it, usually just minutes after origination, the proponents say. Received signals can also be stored for later playback.
In addition to the audio files, the satellite also sends separate files with instructions for program reassembly. Several streams can be multiplexed simultaneously, in which case a multiplex configuration file must also be transmitted.......MORE INTERESTING ITEMS FROM THIS ARTICLE HERE.
Clearly the pathway to delivering audio content via satellite is no longer as cumbersome as many people thought.
5/09/2007 09:53:00 PM
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