Published on Apr 02, 2024
Satellite systems are ideally suited for television and radio distribution, providing high-quality, high-reliability, low-maintenance, flexible alternatives to terrestrial systems. Unlike terrestrial microwave systems, there are no towers or repeaters to maintain, no radio fades to degrade performance, no extensive troubleshooting to diagnose problems and far less land to lease.
Your capital investment for a satellite network is also much lower, especially in areas with difficult terrain. Receive stations can be deployed in a fraction of the time it would take to install a terrestrial system
With the advent of digital modulation and compression techniques, crystal clarity can be achieved with both video and audio, while at the same time minimizing transmission costs and ensuring the privacy of your network.
The signals you receive are virtually identical to those generated at the studio. With newer-generation satellites, occupied satellite bandwidths can be as little as 9 MHz for a TV signal and its associated (stereo) audio channels. Stereo radio signals can be multiplexed with the TV signal or transmitted on separate narrowband digital carriers. Only stations designated by your control center will be able to decode your transmissions, thus ensuring privacy.
Solid-state transmitter equipment is rapidly becoming the standard for new installations. Although initially more expensive, solid-state equipment enjoys the advantage of reduced maintenance costs for the life of the equipment.
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.
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.
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.
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.
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.
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