[Success Story]
Satellite Radio Gets Serious
Sirius Satellite Radio delivers 100 channels of CD-quality music, sports, and news to auto and home receivers.
All electronic design engineers face design challenges, but few have to face the enormous undertaking that confronted the engineers who decided to build a next-generation satellite system to deliver high-quality digital audio to U.S. vehicles and homes.
It's not easy or inexpensive. But if you haven't already experienced it, the outcome is more than spectacular, far better than you would expect from radio (see "Test Report," p. 44). This is the story about how Sirius Satellite Radio (www.sirius.com) developed and launched its system.
WHAT IS IT? Sirius Radio is one of two satellite radio companies licensed by the FCC to deliver digital audio by satellite. This service, more formally known as Digital Audio Radio Service (DARS), was established in 1992. After many applications and reviews, the FCC whittled the number of applicants down and granted broadcast rights to Sirius and its competitor XM Satellite Radio (www.xmradio.com). These companies paid for this spectrum—Sirius $89 million and XM $92 million. The license authorizes broadcast rights in the microwave S-band at 2.3 GHz. After many years of system development, satellite launches, and receiver design, both companies launched their services in 2002.
The primary application for this service is constant coast-to-coast coverage of radio for cars. We have all experienced the problem of trying to listen to radio on a long trip. Both AM and FM stations fade in and out as we drive into and out of their coverage area. And signal reception is generally poor as well as variable. With the DARS systems, radio coverage throughout the 48 continental states is solid and continuous.
Sirius and XM each offer 100 channels of digital radio, mostly music channels but also news, sports, and other entertainment formats. Special car radios have been designed, and as of last year, were offered as an option by most major vehicle manufacturers. Sirius receivers are available as an option in Ford/Lincoln/Mercury vehicles as well as those of DaimlerChrysler, BMW, Jaguar, Porsche, Mercedes-Benz, Volvo, Mazda, and several others. XM radios are available primarily in GM vehicles. At $12.95 per month, the Sirius service offers the benefit of commercial-free music 24/7. After-market auto receivers and home receivers are also available at most popular consumer electronic stores, such as Best Buy, Circuit City, Good Guys, Sound Advice, Tweeters, and Crutchfield by mail order.
THE SPACE SEGMENT There are two basic ways to cover a given area with satellites. The traditional approach and the one used by most space communications systems is to put up a geostationary satellite over the desired area. Geostationary satellites are put into a circular orbit around the equator about 22,300 miles (yes, miles) from earth. In such an orbit, the satellite speed matches the rotation of the earth, so the satellite is always overhead to any observer or station on earth. Sirius' competitor XM Radio uses this system with two satellites providing full U.S. coverage. The equatorial geostationary orbit is unique and currently jammed with satellites side by side only a few degrees apart. As with the frequency spectrum, we're simply running out of space.
Sirius takes the other approach of using elliptical orbits. The company has three elliptical orbits over the U.S. They are geosynchronous, meaning that their rotational period is 24 hours just like a geostationary satellite. The satellite apogee (high point) is 29,200 miles over Canada and the perigee (low point) is 14,900 miles. The orbits function in a way where two satellites are over the U.S. at all times. The satellites are spaced eight hours from one another, and each satellite is over the U.S. for about 16 hours. All three transmit the same data.
The elliptical orbits offer the advantage of a very high angle of coverage. With a conventional geostationary satellite, the line-of-sight path runs at a very low angle of elevation above the equator (about 30°) to the south from the U.S. Because microwave transmissions are direct-line-of-sight, signals from geostationary satellites encounter many more obstacles like trees and buildings. With elliptical orbits, the satellites are more directly overhead (always above 60°) and thereby avoid most earth obstacles. Yet at such distances, the attenuation from satellite to earth is enormous. Typical signal strength in the U.S. is −102 dBi, meaning that a hot receiver is needed.
All communications satellites are space-based repeaters that receive an uplinked signal, which is translated to another frequency and retransmitted back to earth. In the Sirius system, the digitized music and talk is uplinked from studios in New York City and retransmitted back to earth.
Mike Ledford, VP of engineering for Sirius, explains the system. Sirius is assigned 12.5 MHz of spectrum from 2320 to 2332.5 MHz centered on 2.32625 GHz (2326.25 MHz). This spectrum is roughly divided into thirds. One third is assigned to transmitting satellite #1 (TDM1) centered at 2322.3 MHz, one third to the terrestrial repeater network (more on that later) centered on 2326.25 MHz, and one third to transmitting satellite #2 (TDM2) centered on 2330.2 MHz. This gives each satellite roughly 4-MHz bandwidth.
"Does this mean that I can pick up radio stations from York, Pa. in Pittsburgh or Butler, Pa.?"
Yes, and maybe even as far as Clarion or Erie, Pa. Hope this helps!
Anonymous -December 17, 2005 (Article Rating: )
I find this article informative but slanted in the fact that it talks about the technical marvel that is Sirius but yet when you look at the receivers they are clearly behind XM. Sirius has nothing close the the XM2Go models and only recenly released a receiver that will compete with the SkyFi2. The SkyFi 2 has been out for over a year and will be seeing an upgrade soon so Sirius will still be playing catchup. another thing I noticed about the difference in receivers is heat. The Sirius units give off a lot of heat and some even have fans to keep them cool. XMs units on the other hand appears to be smaller and give off a lot less heat (with the exceptionl of the Sony XM01-C).
Overall I believe XM to be ahead in technology while Sirius definitely has a lock on the live sports events although if you prefer sports talk then XM is better. The question one needs to ask themselves is do you like to listen to the game or listen to the shows that talk about the games...I personally prefer the Fox Sports and Sporting News Radio method of covering the NFL with guys at all the locations giving updates but that is a personal choice.
Kurto2021 -July 03, 2005
since the satellite receiver on my white car is quite large and black, I wonder if it can be painted with automotive paint?
Anonymous -April 16, 2005 (Article Rating: )
Very interesting and informative. Only one more question about Sirius--If I'm traveling to South America, will I still be able to listen to it? Thanks.
Erich -January 22, 2005 (Article Rating: )
Send me a schematic and workup for the receiver. As hastily compiled, each error is compounded to the point of "just optimum," and with 40% to 50% of terrestrial radio hanging in the balance, perhaps you will ally toward intelligence.
Paul T. Knisely -October 25, 2004
Does this mean that I can pick up radio stations from York, Pa. in Pittsburgh or Butler, Pa.?
Rhonda Marie Rose -October 24, 2004
What are the manufacturers of the satellite radios?
Izzy -October 07, 2004
If Bill or anyone else would like to receive digital broadcasts in remoter areas, such as much of Africa, they should check out 'worldspace' satellite radio, which requires a subscription, or 'DRM', (www.drm.org) which is due in around 2005, and will be free.
Robert -January 16, 2004
I spend a lot of my life in desolate parts of the earth....from this article is it safe to assume that Sirius sats are broadcasting, say, over Africa?
Bill -January 04, 2004
intersting information but the received rf level is rather dBm not dBi?
Alex Pummer -October 08, 2003
What is the forcast for the subscription costs for next 3 years? Currently, it seems quite pricey since most people who would would get this service are probably already paying for cable TV, which also provides music stations. I can't see spending $12.95 a month for my car when I am already paying for cable TV at Home. I hope the price goes down soon to maybe $6.00, then maybe I'll get a subscription. Maybe you can get me a deal?
Thanks, Derek
Derek Balavac -September 09, 2003
Great. My friend sent me a Friends & Family promotion for Sirius to get a free reciever if I sign up for the service. I wanted to know if XM or Sirius had the better technological advantage. Thank you giving me a very technical understanding of the system. You lost me on the chip design part, but I figured there are guys that specialize in that stuff so I don't need to worry about that part. I was more curious about signal aspects.
P.S. I found this article by searching Google.
Thanks, Peter Pflanz
Peter Pflanz -September 02, 2003
I did not see any mention of the actual codec(s) used, only the bandwidth differences between music and talk streams. I've listened to both XM and Sirius and even though music stations sound pretty much identical, there is a tremendous difference in talk station quality. Sirius talk stations have a very discernable warbling, whereas this is not heard on XM. I attribute this to different codecs used by Sirius and XM. I would be interested to learn about the differences. The warbling is so bad that if I can get the same station on FM (NPR, for example), I will turn off Sirius and switch on FM. Talk stations are literally unlistenable on Sirius vs. XM.
Richard Steele -August 28, 2003
Excellent in-depth explaination of SIRIUS technology.
W Reed -August 20, 2003
I have heard these 2 companies use different types of satellite hardware. Is that true? If so, what are the pros and cons?
Very good arcticle.
Darrell -August 20, 2003
Great Article! You guys sure did your homework on this one.
Daniel Goddard -August 20, 2003
I discovered this article via a message on the Raging Bull Sirius investor chat board.
Extremely well written. Best layman-understandable explanation of the various facets of this complex technology I have seen. As an active shareholder, I am grateful for all "fair and balanced" reporting. Thank you.
William Peavey -August 19, 2003
These radio chips don't sound too different from the GSM stuff in mass production, except for the higher bandwidth, which isn't really a RF problem. GSM chips also have to have very agile synthesisers, particularly for GPRS operation. They're also mostly direct conversion, which saves money on all those expensive IF filters. And have a severe power budget -- not applicable in a vehicle.
Nevertheless, must have been an interesting design job.
allan hurst -August 19, 2003
After reading this article, I am in awe of the tremendous efforts made by the people of SIRIUS. I believe this to be one of the greater engineering marvels of our time. Clearly, this is the work of great minds. Thank You for sharing this with us. Encore!
John Shiels -August 19, 2003
Gentlemen:
Excellent article full of useful and interesting information. I found it extremely useful. Keep up the good work!
Townsend Pinnix
Townsend Pinnix -August 19, 2003
Your Comments:
Enter the text from the image below
Please refresh the page if you have trouble reading this text.
Search Electronic Design
Web Seminar
Sponsored By:
Title: Read Pacing: A Performance Enhancing Feature of PCI Express Gen 2 Switch Devices
Reprints
)
)
