Sirius and XM, which are now one company, use this band to transmit digital radio from their satellites and also from ground-based transmitters (terrstrial repeaters) that fill in coverage gaps due to building and terrain blockage of the satellite signals.
According to the FCC (FCC 10-82), "The Commission's rules define SDARS - commonly known as "satellite radio" – as "[a] radiocommunication service in which audio programming is digitally transmitted by one or more space stations directly to fixed, mobile, and/or portable stations, and which may involve complementary repeating terrestrial transmitters, telemetry, tracking and control facilities." Thus, SDARS is primarily a satellite-delivered service in which programming is sent directly from satellites to subscriber receivers either at a fixed location or in motion. Because a direct line of sight is generally required in order to receive an acceptable satellite signal, ground-based terrestrial repeaters are used in many areas to re-transmit the same signals provided by satellites directly to subscribers in order to maintain adequate signal power. These areas include "urban canyons" between tall buildings, heavily foliaged areas, tunnels, and other places where obstructions could limit satellite visibility or cause multipath interference from reflected signals.
"Licenses to provide SDARS within the United States were awarded by auction in early April, 1997. The two winners of the auction – XM and Sirius – were each assigned 12.5 megahertz of spectrum for their exclusive use on a primary basis. XM and Sirius launched their satellites and began commercial operations in 2001 and 2002, respectively. As of March 31, 2010, Sirius XM reported it had 18,944,199 subscribers in the conterminous United States.
"On August 5, 2008, the Commission approved the merger of XM and Sirius, which have subsequently combined to form a merged entity called "Sirius XM." In the merger proceeding, the Commission found that significant engineering differences in the XM and Sirius infrastructures make integration of the two systems difficult in the short term. In addition, the Commission noted that XM and Sirius had each invested significantly in their existing infrastructure, with the expectation of operating this infrastructure for years to come. Thus, despite the merger of the two companies, the XM and Sirius satellite and repeater infrastructures will operate as separate, legacy systems, at least in the near term.
"Sirius XM offers hundreds of channels of music, entertainment, news, and sports programming on the Sirius and XM satellite radio networks, as well as weather and data information services for maritime, aeronautical, and other purposes. SDARS radio receivers are used in cars, trucks, boats, aircraft, and homes – and are available for portable use..."
Acccording to SiriusXM, their satellite signals cover the 48 contiguous states, and 200 miles "off shore."
Historical Information on SDARS
The following is historical information on SDARS from Benn Kobb's 2001 book Wireless Spectrum Finder. That book is now (c) SpectrumWiki.com:
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The principal worldwide band for audio broadcasting direct to the public from satellites (Broadcasting-Satellite Service (Sound) or BSS) is the so-called L-band, 1452—1492 MHz.
That band falls within aeronautical test telemetry spectrum in the U.S. (see 1435—1525 MHz).
As an alternative, the International Telecommunication Union (ITU) allocated the S-band, 2310—2360 MHz, for domestic satellite audio broadcasting in the U.S. Other nations, especially Canada, criticized this action as detrimental to the realization of a uniform worldwide service in the L-band.
The ITU also allocated 2520—2670 MHz for BSS national and regional systems for community reception. (India and Mexico also are authorized to use the S-band for BSS.)
Against ferocious opposition from conventional broadcasters, the FCC eventually allocated 2320—2345 MHz to satellite Digital Audio Radio Services (SDARS or DARS). “Satellite DARS will provide continuous radio service of compact disc quality for all listeners and will offer an increased choice of over-the-air audio programming,” the FCC said.
No other significant terrestrial U.S. users are in the S-band, but adjacent countries operate terrestrial fixed point-to-point, fixed point-to-multipoint, and aeronautical mobile telemetry systems in the band. Satellite DARS operators must take precautions to avoid interference with the systems of other nations.
Sirius and XM
There are two SDARS licensees : Sirius Satellite Radio (2320—2332.5 MHz), formerly Satellite CD Radio and XM Satellite Radio (2332.5—2345 MHz), formerly American Mobile Radio.
These companies won their licenses by bidding $83 million and $89 million, respectively, at an April 1997 auction. The FCC concluded that only enough spectrum existed in the S-band for two SDARS licensees of 12.5 MHz each. The FCC requires that SDARS receivers be capable of picking up broadcasts from both of the licensees.
The licensees must deploy hundreds of terrestrial repeaters, ground transmitters that relay broadcasts from satellites. Most of the gap-fillers will be in urban areas where obstructions inhibit satellite reception.
Sirius will use three satellites in inclined elliptical orbits will offer a service directed mainly to vehicle radios. Sirius-1 and Sirius-2 had been launched at this writing. The major investors in Sirius include Ford and Loral.
XM will use two geostationary satellites (officially designated “Rock” and “Roll”) that are directed both to vehicle and portable radios. XM’s major investors include GM and its DirecTV business; Clear Channel Communications; and Liberty Media, in addition to its founder, Motient Corp., formerly American Mobile Satellite Corp.
Uplink stations in 7.025—7.075 GHz feed these satellites. They use frequencies in the S-band in 3.7—4.2 GHz, and 5.925—6.425 GHz for telemetry and control, operation during transfer to final orbit, and for contingency purposes.
Other SDARS-Related Issues
Sirius and XM might have faced competition from SDARS service in the Wireless Communications Service (WCS) band. A group of WCS licensees applied for permission to use their licenses to provide SDARS (see 2305—2310 MHz). They later abandoned the idea.
The FCC licensed, originally on an experimental basis only, the WorldSpace SDARS system to broadcast in the L-band (see 1435—1525 MHz). It later granted full authorization to the Washington, D.C.-based WorldSpace, but does not permit the company to serve U.S. audiences.
NASA’s Goldstone Solar System Radar operates at 2320 MHz and 8.56 GHz in the Mojave Desert northeast of Los Angeles. Scientists used it to observe Comet Hyakutake when it passed within 9.3 million miles of Earth in 1996.
SDARS interference is expected to make radar astronomy operations at 2320 MHz “nearly impossible,” according to NASA’s Jet Propulsion Laboratory.
The 2310—2390 MHz spectrum is one of many restricted bands in which the FCC Part 15 rules permit unlicensed devices to emit only very low level emissions.
***** (End of historical information from Wireless Spectrum Finder)
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