XM radio rides the fast lane

If you buy a GM car next year, you'll probably have a direct connection to the satellites.

GM will offer XM radio as a feature in twenty-five 2003-year car models, next to AM and FM on the radio dial. For a monthly subscription of $9.99, users can hear 100 channels of digital-quality sound with an uninterrupted signal from coast to coast. Seventy-one channels are music, and 29 are sports, talk, entertainment, and children's subjects. It's available today in electronics retail stores, in long-haul trucks, and, since November, in Cadillac's 2002 DeVille and Seville.

What's the difference between earth-bound and outer space radio? A huge array of listening choices and an enormous engineering challenge.

Still in its infancy, XM radio technology has 76,000 users so far, all in the U.S., including 2,000 installed in Cadillacs this year (XM's investors include GM, as well Honda, Clear Channel, and DirecTV).

It's a tricky thing for a moving car to track and play satellite transmissions. From XM's broadcast center in Washington, D.C., the original radio signal is changed from audio to digital, compressed and encoded, then beamed to the company's two geostationary satellites, nicknamed "Rock" and "Roll."

Those satellite receivers then do error correction (if needed), and download the signal to an XM receiver in your car, which must unscramble and decompress the signal before down-converting it to an audible frequency that it changes from digital to audio, and transmits over your car speakers. Sounds impossible, but a lot of it is commonly done in devices like cell phones and DVD players.

Yet the end-to-end challenge was still daunting-to move a signal from broadcast booth to satellite to repeater to automobile, XM needs four million bits/sec of bandwidth to carry all 100 channels. During development, if the system was off by a single bit (a frame of 432 millisec), the radio would produce total silence. But once they finally perfected the timing, it was hardwired into the chips.

To achieve such accuracy, XM chose to use relatively simple parts from many suppliers, instead of betting everything on a single solution. The resulting design process was a lesson in collaboration.

"At the time we started, we had to push existing silicon technology to its limits," says Stell Patsiokas, the company's executive vice president of technology and engineering. "It was the first time anyone created a commercial integration between terrestrial and space technologies, and it was the first time a chip set was available before the infrastructure" (broadcast booth, radio sets, and satellites).

XM used four ingredients to make it work, he says: engineering talent, technology partners, a unique development process, and "the power of The Force-there is no way we're going to fail; we cannot fail."

The technology partners all began their work in the fall of 1999, but from his XM headquarters in Boca Raton, FL, Patsiokas had trouble putting all the pieces together. The combination of different cultures, languages, time zones, and companies made it impossible to integrate the various pieces of software from around the world.

So in late July, 2000, he resorted to extraordinary measures: "I invited them all here to Florida and I took their passports, and didn't let them go home until we were done," he says. "It was 40 days of hell."

At the beginning, they all suffered from stress when the system wouldn't work. "Then you'd get two minutes of music, and something would crash," Patsiokas says. "Then five minutes before a crash. And then when it finally worked, we played it for weeks on end. We played "Money for Nothing" by Dire Straits-I got really sick of that song."

Their challenge was to develop custom chips before they'd created the physical infrastructure. So the team worked with Fraunhofer, a German developer of compression algorithms, to create a simulated signal generator for the six carriers: two satellites and four terrestrial repeaters. Next, they had to replicate the receiver-they used Aptics' System Explorer MC3 to emulate a physical chip with software code. Instead of waiting 10 weeks for a chip fabricating plant to create each experimental design, they could make a working model overnight.

In creating the finished chips, ST Microelectronics first had to decide which technology to use. It could have gone with aggressive, 0.18mu technology, but it opted for greater reliability and chose the mature, 0.25mu level, ST's Mike Kasparian says. Then it chose to use two chips in the system-STA400 and STA450, a channel decoder and a source decoder-and to let XM purchase the SDRAM and main micro system controller from independent suppliers. ST also faced design challenges such as limited dashboard space and RFI/EMI from the high-speed chips interfering with AM and FM signals.

Meanwhile, the clock was ticking. Competitor Sirius (New York City) was building a similar system of commercial-free, digital radio. In contrast to XM, Sirius uses three satellites to broadcast its 60 channels of music and 40 of sports. Its monthly subscription fee is marginally higher ($12.95) and its partners are slightly different, including stereo makers Kenwood, Jensen, Panasonic, and Clarion, and automotive investors DaimlerChrysler and Ford. So far, it seems there's room in the market for both companies, but they're still racing to win the first customers.

So XM set a frantic pace to build a network of terrestrial repeaters to capture and amplify the satellites' broadcast signals. That required 814 refrigerator-sized repeaters, scattered around the continental U.S. "It's like building 800 houses at the same time, and coordinating all the plumbers and carpenters and painters," Patsiokas says.

ST completed the chipset development in late 2000, and had shipped 335,000 XM chipsets to radio manufacturers through the end of the first quarter of 2002, Kasparian says. In May and June of 2001, the two satellites were launched into geostationary orbit. And in early September, XM prepared to launch the radios...but the Sept. 11 disaster delayed that event until Sept. 26, with full rollout by Nov. 12.

What's next? ST says it plans to shrink its hardware onto the smaller chip format, and then to combine the system onto a single chip. The next step after that may be to spread satellite radio beyond cars, although they won't reveal when either step may happen.

Patsiokas also hints at new applications, since the hard work of developing the original infrastructure is now behind him: "The integration and coordination between all those groups is what XM is all about," he says.

For more information about chips from STMicroelectronics: Enter 533