XM Satellite Radio

XM Satellite Radio {{nasdaq|XMSR}} is a satellite radio (DARS) service in the United States based in Washington, DC and controlled by News Corporation's DirecTV, General Motors, American Honda, Hughes Electronics, and several private investment groups.

Technology

XM provides digital programming directly from three satellites in geostationary orbit above the equator. XM-1 ("Rock") and XM-2 ("Roll") are co-located at 85 degrees west longitude and XM-3 ("Rhythm") is located 115 degrees west longitude in addition to a network of ground-based repeaters. The combination of three satellites and a ground-based repeater network is designed to provide gap-free coverage anywhere within the continental U.S. Unfortunately, XM-1 and XM-2 are suffering from a generic design fault on the Boeing 702 series of satellites, which means that their lifetimes will be shortened to approximately six years (instead of the design goal of 15 years). To compensate for this flaw, XM-3 was launched earlier than anticipated and moved into XM-2's previous location. XM-2 was then moved over next to XM-1, where each satellite operates only one transponder to conserve energy.

Related Topics:
Geostationary orbit - Longitude - Boeing - 702

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

The XM signal uses 12.5 MHz of the S band: 2332.5 to 2345.0 MHz. XM has agreed to provide 128 kilobits per second of its bandwidth to OnStar Corporation for use with XM-enabled GM vehicles, regardless of whether their owners are XM subscribers. American Honda also retains the right to some of the company's bandwidth to transmit coded traffic information directly to navigation systems using TMC technology.

Related Topics:
S band - OnStar - GM - TMC

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Audio channels on XM are digitally compressed using the aacPlus codec from Coding Technologies for most channels, and the AMBE codec from Digital Voice Systems for some voice channels.

Related Topics:
AacPlus - AMBE

~ ~ ~ ~ ~ ~ ~ ~ ~ ~