The Basics of Satellite Radio Systems

Satellite radio systems are the consumer's access to space-based audio technology, offering uncensored, commercial-free programming that comes in crystal clear no matter where you are. But how do they actually work?

The most basic explanation is as follows: programming is transmitted to a communications space satellite, which beams a digital signal back to earth. The signal is encrypted, so it can only be picked up by special proprietary equipment. The signal can be broadcast across more than 22,000 miles and received by the end user with absolutely no deterioration in clarity or sound quality.

But the basics are only a small part of what makes satellite radio systems work. Many innovations and the use of cutting-edge communications technology have bought digital radio a long way from where it begins just over a decade ago.

Digital radio was actually operating in the early 1990s, with Washington-based Worldspace Corp. providing fixed-location satellite radio to Europe, Asia, and parts of Africa. However the technology did not take off in the US until 1992, when the Federal Communications Commission established the Digital Audio Radio Service (DARS) which contained certain segments of radio frequency for satellite broadcast.

Two companies bid for and won licenses to broadcast in the allotted frequencies: American Mobile Radio, which later became XM Radio, paid $ 93 million for licensing, and Sirius Satellite Radio forerunner CD Radio paid $ 89 million. XM made its nationwide debut in 2001, and Sirius followed in 2002.

Although both companies offer more than 100 channels of commercial-free programming that's available anywhere in the US, they took different technological routes to achieve universal coverage.

XM's system relations on two powerful geostationary satellites positioned directly above the equator, which are programmed to move in synchronization with the movement of the earth. To overcome interference from physical obstacles such buildings and mountains, the XM service service relies on a network of repeaters, which are antennas that receive the radio signal from the satellites and retransmit it to the subscriber's receiver.

The Sirius system is based on a trio of satellites that travel in figure-8 shaped orbits. Because these orbiting satellites can rise much higher than geostationary satellites, interference from physical objects is minimized and a large network of repeaters is unnecessary. To keep the signal steady during the eight hours daily that the Sirius satellites' orbit takes them to the other side of the earth, the company leases capacity on a geostationary satellite which feeds the signal to subscribers.

Satellite radio service also depends on digital compression technology, a technique that uses sophisticated algorithms to compress as much material as possible on the available bandwidth.