FCC Petitioned to Restrict 2.4GHz Band

Mean_Nishka writes: "Internet News is reporting that satellite radio provider Sirius is petitioning the FCC to regulate and hinder providers of 802.11b based networks. Sirius claims their radios operate at frequencies only 55mhz lower than wifi's range, and fear that Wifi users could interfere (especially mobile and internet service providers). This could effectively kill free networks nationwide..."

Comments

802.11 Interference

[SkewlD00d]

802.11 interferes w/ the head-tracker we use at our school for 3D stuff. We basically need a TEMPEST-protected room so we can play w/ our 3d toys.

Maybe sirius should use 3D differential phase decoding to "listen" to a frequency at a location. Basically, two or more antennas allow you to discriminate among different sources, just like how your ears and brain work; as a practical example, using three antennas prevent jamming of GPS by enemy noise sources. The GPS antijam method uses constellation position prediction and real-time kinematic (motion) compensation (doppler shift, etc.) upon the sender's signal and receiver's motion, note this is wholy listener-side compensation, no mods to GPS constellation are needed for antijam technology. If sirius is broadcast-only, then they need to mod their receivers to use this type of technology. Why force restrictions on existing equipment for people trying to be fancy w/ their new toys? Screw em if they can't play w/ others already out on the field.

We can get alot more bandwidth if we use this type of technology along with CDMA-type encoding. It might be slightly more expensive and logistically prohibitive, but economical use of bandwidth demands it.

Sirius are a bunch of whiners

[BeBoxer]

The fact is that 802.11b channels are only 25MHz wide. And 802.11b equipment is quite capable of working with adjoining 'cells' butted right up against each other. Check out this table. The non-overlappig channels are 1,6 and 11. Total center-to-center separation? 50Mhz between channels 1 and 11 with room for a channel in between. If Sirius has a problem with 802.11b I'm going to hazard a guess it's because their receivers are crap. I'll bet that they are receiving part of the legitimate 802.11b signal.

I've actually run tests to see how well two access points work if you locate them close together (about 4 feet). You can see a writeup of all the tests I did here: Interference Tests. When I tried to run two laptops connected to two access points on channels 1 and 6, I found a little interference. Not much. Maybe a 20% drop in total thruput. Once I went to channels 1 and 7 (30MHz separation) the two access points operated with no detectable interference at all. The aggregate thruput was basically 2x the thruput of a single access point. (Note that the 209% and 212% results are because I was using laptop to ap traffic as the baseline, but the equipment I was using produced higher thruput in the ap to laptop direction)

While the interference at channels 1 and 6 technically shouldn't happen, no body in their right mind puts two access points four feet apart and tries to run them both at full bore. So the radios could be a little better. But even in this worst-case scenario, all interference disappeared at 30MHz separation. And Sirius is complaining about 55MHz separation? Almost twice the distance?

What Sirius is finding out is that the idea of transmitting from a satallite to a non-directional antenna is extremely hard. That's probably why the other sat radio company XM plans to spend ~$250,000,000 dollars building a system of terrestrial repeaters! It's hard to link to, but check out the 10-Q SEC filing on their web site if you don't belive me. I can't find it now, but another SEC filing in there goes into detail about the need for repeaters because they know their signal can't be reliably received inside a major metropolitan area.

If Sirius has burned thru $3 billion and still doesn't have a reliable system, well boo hoo. The only reliable sat-based communications I know of use directional dish antenna's. (Please don't use GPS as a comeback because it doesn't have to work in a lot of places that a car radio has to, and it carries almost no information in the signal.) Irridium tried it and failed. Sirius apparently can't get it to work, and I'm going to guess that they will soon be history. As for XM, well, I think they got it to work, but only by spending a fortune on repeaters so most of their customers probably aren't even using the satellites! I think XM is going to go down the tubes anyway since they probably need to get at least 1,000,000 paying customers this year to keep going.

So I think Sirius and XM are going to follow Irridium down the tubes. And life will go on. As every good capitalist knows, massive failures prove the resiliancy of our system. That's what's know as "The Enron Axiom". ;-)

Read the petition here!

[cmoney]

One of my projects at work was to build a database and web interface capable of distributing across the country every single document filed with the FCC every single day. Well it's finally found a purpose! Enough patting myself on the back...read the original Sirius petition here: http://www.geocities.com/nospamcarl/sirius_fcc.pdf . (38 pages all scanned and not OCRd so it's 1.6MB) (If this doesn't work, try copy and pasting the URL directly. For some reason, it didn't work for me clicking directly from Slash.)

It's got some good info in it. At the very least, you'll find out that it's part of a bigger request for comments by the FCC on "whether it [the FCC] should change its emissions limits for the restricted bands above 38.6 GHz, and whether the Commision should apply its emissions limits to receivers that tune above 960 MHz." It's also got some of Sirius' technical evidence in support of their claims.

And here's a choice quote:

Impact on Deployment and Service to Underserved Communities
If the Commission fails in its duty to ensure SDARS [Satellite Digital Audio Radio Service] interference protection from Part 15 and Part 18 devices, the rapid deployment of digital audio radio services will be significantly threatened. As the Commission has noted in past orders, SDARS holds the promise of providing continuous service of digital radio in the form of 200 audio channels that will offer consumers a tremendous increase in choices of audio programming. If protected from harmful interference, SDARS will dramatically reduce the disparity in access to radio by making enormous programming choices available to 45 million underserved consumers in the US, particularly those in rural areas, who currently have access to only a small number of radio stations.

BTW, this is a public document. I'm not sure if it's on fcc.gov yet but it should be someday...if you can wade through their multiple search engines and multiple data formats. You'll be able to track any replies.