[Success Story]
Satellite Radio Gets Serious
Sirius Satellite Radio delivers 100 channels of CD-quality music, sports, and news to auto and home receivers.
THE RECEIVERS While the space segment of the Sirius system is by far the most expensive and complex, the receivers also presented a major challenge, along with substantial cost. Sirius hired Lucent to design the chip set that would form the basis for all auto and home radios. At one time, Lucent, now Agere Systems (www.agere.com), had as many as 100 designers working on the horrifically complex radio chip set.
Although the design is a superheterodyne, it's nothing like those we're most familiar with because of the diversity functions and other features. The chip set, originally packaged in seven chips, now uses four chips in its latest incarnation. Most of it is made with 0.14-µm biCMOS. An even newer version will use fewer chips that take advantage of the continuing smaller feature size and newer chip processing technologies.
Figure 2 shows a simplified block diagram of the Agere chip set. Note that there are two antenna inputs. Of course, the satellite antenna is the main one. But if you live in an area where the signal only comes through via the terrestrial repeaters, a different antenna is needed. The input chip houses the gallium-arsenide (GaAs) low-noise amplifier (LNA) and the down-conversion mixers. After the usual IF filtering and amplification in the second chip, the signal is digitized in the third chip. Resulting data is then sent to the baseband chip for all processing. The baseband chip includes an ARM core plus Agere's DSP16000 core. A 4-Mbyte by 16 SDRAM and a 256k by 16 flash memory handle all storage chores.
The receivers themselves are made by a variety of manufacturers, including Alpine, Clarion, Delphi Delco, Jensen, Kenwood, Panasonic, Pioneer, Sony, and Visteon. Your first Sirius receiver will probably come with a new vehicle purchase. But after-market auto and home receivers are now available, too (Fig. 3).
A critical part of the satellite receiver is its antenna. It's built into the vehicle when you purchase a factory-installed model. After-market models, including home receivers, require that you add an antenna. Vehicle antennas, which use left-hand circular polarization (LHCP), have a gain in the 2-dBic range. Terrestrial repeater antennas, on the other hand, utilize linear vertical polarization and have a typical gain of 3 dBic. The antennas normally come with a built-in GaAs LNA.
SIRIUS SUCCESS Is Sirius a success? Technically, for sure. It's a real triumph of electronic design and implementation. Give Agere a hand as well for a brutally difficult but successful chip design. As a business enterprise, the final word is still out. As Sirius' founder Rob Briskman told me, the total up-front investment so far is about $2 billion, not your usual venture-capital funded deal.
Nevertheless, subscriptions are increasing daily. Once most vehicles get their Sirius radio options, the service will grow significantly. Auto manufacturers are rolling out more models with satellite radio options each year, and, as more consumers become familiar with their options, you'll begin to see more after-market auto and home satellite radios. XM even has a portable satellite radio boom box that's sure to be popular. The system sells itself if you can get a chance to test it.
So while the main objective of Sirius and XM right now is to become profitable from their existing systems, the future holds some interesting possibilities for the technology. With a satellite system that can downlink digital data streams reliably anywhere in the U.S., it seems likely that we will also see other digital services develop. As Sirius' Mike Ledford says, "think video to the back seat."
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