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.

Re:This never stopped FM

[owlmeat]

It's a different problem when you have the data trasmitter right next to the sat receiver. When the transmitter is on, the front end of the receiver will be overloaded even though the signal is from a different band. Look up "desense" with google for a better explaination.

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". ;-)

Re:Sirius are a bunch of whiners

[Anonymous Coward]

The only reliable sat-based communications I know of use directional dish antenna's.

Actually, it's doable with and omni antenna. I did it in the Army all the time. We had a planar array high gain we used when stopped and the omni when moving.

Harmonics

[jessohyes]

I used to work on Transmitters and Receivers and I can say that 55MHZ is a lot of seperation. The one thing that we were concerned about was something called Harmonics and Intermodulation Distortion. IE: a frequency of lets say 225 MHZ might also have a Harmonic at 450 MHZ etc... They were normally multiples of the original frequency. But the transmitters that we worked on also had power levels of approx 10,000 watts per transmitter (HF) and very large directional antennas. I'm thinking that these wifi cards are putting out signals in the order of milliwatts so interference should be very localized if any at all. I doubt that Intermodulation Distortion could cause such a wide shift in frequency as well.

sort of

[Skuld-Chan]

do you know how spread spectrum technology works? If set up properly only recievers with a certian psuedo random sequence would recieve their transmitters that frequency hop with the exact same sequence - which is probably why the usaf claims their awacs network is un-jammable. No the protocols won't save it - but spread spectrum will.

The beauty of spread spectrum is on narrow band recievers the only interference you hear is low background noise. I have no idea if 802.11 is spread spectrum or narrow band - but either way there's room for more devices on there.

Re:Three Questions

[Anonymous Coward]

Nice thinking, but it will not work in this case. While each of these have products in 2.4 spectrum, these do not need the high powered antennas. The only ones who will use these will be the fixed wireless internet access provider. Obviously siruss will be using part of the bandwidth for 2 way and want to make sure of none interference/competition.
Smart. With Bush in office, it is almost certain that they will be able to get it passed.
A little bit of money in bush/ashcroft goes a long way.

Re:Three Questions

[satanami69]

3) Which side has more money?

One of the largest partners with Sirius radio is Ford. I looked into Sirius back when they called themselves cdradio. Basically, Ford, Chrysler, BMW, Mercedes-Benz, Jaguar, Volvo, Mazda, Dodge and Jeep® will all be installing AM/FM/SAT radios using Kenwood, Panasonic, Clarion and Jensen satellite receivers. Ford will be the first company to include the satellite recievers as the stock recievers in newer model cars. So, it's pretty easy to see who has the most money behind it, but moreso who has the most politics to shuffle.

I hope that the satellite pay-per-month with no ads model fails, or at least is not popular enough to not have a free version. I'd much rather recieve free radio at the higher quality signal and deal with some adverts.

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.

The Facts

[6L6GT]

Here are some things that should be known:
802.11b devices come under FCC regulation part 15. That means they must NOT interfere with licenced operation, and they must ACCEPT interference from licenced operators. Keeping that in mind. As a person licenced to use the 2.4Gc band (among others) I can put up 1500 Watt FM TV repeater on that band and there is nothing that the wireless internet folks can do about it. Part 15 devices are the lowest of the low (even lower than CB) when it comes to radio spectrum use. With being said, the FCC is likeley to grant Sirius's request.

BTW Sirius cannot keep crap out of their receivers that is 55Mc away? I've done better than that on the 2.4Gc band, building my own stuff.

Filters, RF lighting, and UWB

[MediaBoy77]

IANAE - I am not an engineer... But that's never stopped the non-lawyers from expounding on legal matters around here.

There are several issues that haven't been addressed in this thread. If you haven't read the actual petition (http://us.share.geocities.com/nospamcarl/sirius_f cc.pdf), you should. (Per the earlier poster, you probably need to copy and paste that URL into your browser for geocities to work.

First, much of the petition deals with RF lighting and UWB. I'm new to RF lighting, but I remember the last UWB thread on /., and plenty of folks were claiming it was the end of the world for all tranmissions that weren't UWB. Sirius seems to be making the same claim here.

Has anyone done interference testing with 2.4GHz devices and RF lighting? Would RF streetlamps disable Bluetooth and 802.11b freenets?

Secondly, Sirius isn't asking the FCC to ban 802.11b. They're asking the FCC to make WiFi manufacturers put stronger filters on their transmitters. Quoting from the petition:

Because the lower edge of the 2.4GHz band is only 55 MHz from the top edge of the SDARS's spectrum, the filter mechanism that Part 15 and Part 18 devices currently use to limit their out-of-band emissions may be insufficient to satisfy the proposed aggregate field strength limit within the SDARS band (clip).... Petitioner does not anticipate that designing filtering mechanisms to comply with the proposed field strength limitations will be technically difficult for manufacturers of future Part 15 and Part 18 devices to accomodate.

Obviously, the wireless industry disagrees. But they also claim this would force them to retrofit existing devices, which simply isn't in Sirius' petition at all. The actual proposed rule change is on pg. 26:

...Petitioner requests that the Commission establish a rule to limit their [Part 15 and Part 18 devices] aggregate field strength for out-of-band radiated emissions between 2320 and 2345 MHz to 8.6 (micro)V/m at 3m (18.7 dB(micro)V/m) on a free space, co-polarized basis measured in a 1MHz bandwidth. The above limit would go into effect 18 months after the date of final adoption of the rule and apply to all devices manufactured thereafter. (emphasis mine)

So the real questions seem to be: 1) how hard would it be for 802.11b makers to follow that proposed rule change, and 2) Would this mean the end of RF lighting and UWB?