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DOD vs. 802.11b
goombah99 writes "The NY times (reg required) reports that "The Defense Department, arguing that an increasingly popular form of wireless Internet access could interfere with military radar, is seeking new limits on the technology". It would seem they have a good point; radar is an essential for both defense and civilian aviation as well as ship navigation in tight quarters. Critics of the restrictions contend technology can limit the interference, but what proof is there to these assertions? Sure we all want wireless internet but maybe there should be more careful review of its consequences."
-dB
"It if was easy to do, we'd find someone cheaper than you to do it."
Most modern radars have attenuation and can handle a wide range of RF frequencies. This can be from 0.5 GHz to 40 GHz. Mobile phones and current WIFI inhabit the 2.5 GHz range (commonly refered to as CD band) and is dealt with seperately to the rest of the microwave bands (E-J and K). A WIFI adapter will NOT jam a military radar but rather show up as an unknown emitter which in a time of war will generally cause the ship/plane/helicopter to go "defensive" and defend against the potential threat!
---- "I would be careful in separating your weirdness, a good quirky quantum weirdness, from the disturbed weirdnes
WiFi operates as a Part 15 device. Part 15 users must except any interference and not cause any. That's the price of not having to have a license.
A radar may have a very high ERP (effective radiated power), but the signal returned from an illuminated target is small. You have the path loss to and from the target. That is what makes it possible to jam a radar with a modest transmitter.
Mea navis aericumbens anguillis abundat
According to this article it was a modification of existing radar.
Some aviation experts suspect the Serbs used a crude version of passive radar -- plugging computers into their existing air defense system -- to locate an F-117A Nighthawk stealth bomber, shot down in 1999.
Also from the article:
John Hansman, professor of aeronautics and astronautics at the Massachusetts Institute of Technology, said passive radar is still in its "infancy, but is something that will lead to new stealth research."
"This is another trick that will force stealth researchers to push forward," Hansman said.
All in all just another iteration in spy v spy.
Good to know our up and coming naval officers have a good grasp on the concepts of contemporary technology.
I've,
Done a lot of civilian radar track data analysis and I can tell you that radar data is already littered with LOTS (and I mean LOTS) of inaccuracy.
I've seen cases where the data loss was so bad that I can hardly imagine the situation where joe-schmoe-bin-ladin with his laptop and homemade radar jamming equipment could make it any worse.
It's one of those situations where if you knew what the ingrediants were you might not want to eat it.
I certainly don't have a problem with the DOD wanting to limit radio encroachments into vital wavelengths.
But, sometimes I get the feeling that the military is crying wolf when the wolf has been there the entire time and nobody in the know is brave enough to admit it.
Caution: Contents under pressure
More likely than ignorance, they (DOD scientists and engineers) are probably concerned that this new use of spectrum previously allocated for air traffic control, weather data collection, and defense purposes will cause problems for OLD radar equipment that IS NOT capable of changing frequencies. You know, the backwards compatibility problem. There are billions and billions of dollars worth of government (military and civilian) radar systems that could be affected, and no one is talking about paying to replace or upgrade those systems to eliminate the potential for interference.
Reading (somewhat between the lines of) the article, I find explicitly or implicitly the following points:
I don't see a big conspiracy here ... just two groups of people that don't quite agree with the technical points raised by the other side, and a number of issues that need more study before everyone will be happy.
While I wouldn't mind faster and more capable WiFi, I'd much rather that the tech industry be forced to make changes to ensure that interference won't be a problem NOW than having to do so AFTER someone's web surfing causes a plane to disappear from air traffic control screens ....
The problem isn't "high-speed tower-hopping."
The problem is that the signal from one cell phone at altitude hits many cell towers at once, interfering with other callers.
The word "cellular" means that the system uses small areas called cells. The primary reason for for this article is to allow the same frequencies to be used in multiple separate cells at the same time, by different users. From an airplane, all of those cells are hit at once.
Cellular architecture is one method of improving spectrum efficiency, and was mandated by the FCC for that reason.
The only good weather is bad weather.
There is so much misinformation in both the NY Times article and the discussion here on /., I just have to set the record straight:
:)
1) The DoD is concerned about the 5 GHz U-NII (Unlicensed National Information Infrastructure) band -- which is where 802.11a (not 802.11b) operates. This is a recently opened band.
2) There is no way the DoD can mount a plausible objection to 802.11b, as it operates in the 2.4 GHz ISM (Industrial, Scientific, and Medical) band. The ISM band is the home to microwave ovens, which frequently "leak" 30 times more RF than an 802.11b "intentionally" transmits. There are industrial applications of the 2.4 GHz ISM band that emit KILOWATTS of RF. The 2.4 GHz band is, in essence, the junkyard of the microwave spectrum.
3) The IEEE 802.11 committee is already working on interference mitigation techniques to make 802.11 radios more "friendly" to radar in the 5 GHz band. This is the work of Task Group H. The two major innovations being hammered out in that task group are DFS and TPC (dynamic frequency selection and transmit power control). Both of these are mandated by the European Union's regulatory bodies, in order to open up 5 GHz for 802.11 radios. When ratified, this will lead to an 802.11h radio, which is functionally analogous to 802.11a, but with DFS and TPC. At that time it is likely that 802.11a will wither on the vine, being replaced with 802.11h in the U.S. also. (Note: 802.11a is legal only in the U.S. today. And DoD is basically following the EU's lead in expressing concern about interference to radar. That's what the NYT article meant about Europe being "ahead" in this matter.)
4) While the FCC is in charge of CIVILIAN use of the RF spectrum, they are not the sole arbiter of RF in the United States. The rest of the job is done by the NTIA (National Telecommunications and Information Administration), which is the caretaker for government use of spectrum. For the FCC to open up the 5 GHz spectrum, they needed approval from the NTIA first (which they got).
Summary: "But the times they are a' changin."
Basically the DoD is trying to head off proliferation of 802.11a before it's too late. Of course, the market leading vendors (e.g. Atheros) are none too happy about this, and I don't blame them. Changing the rules after they invest many millions in development of a product on the basis of an expectation of marketability would make even the most accommodating entrepreneur cranky
Actually it's even worse than this. Resolving 100m at 5GHz requires an antenna more than 175m in diameter (significantly larger than a football field!). So with a reasonably-sized antenna, there is an increased chance of finding one (or more than one) Wi-fi station in that pixel.
more likely he would have acted on his plan to attack Al Qaeda:
The Bush administration sat on a Clinton-era plan to attack al-Qaida in Afghanistan for eight months because of political hostility to the outgoing president and competing priorities, it was reported yesterday.
Rather than sit on it.
Meanwhile, Clinton, with the Legislature spending most of their time sniffing blue dresses for presidental spunk, lacked the support necessary to invade Afghanistan and take out Bin Laden.
Bush's team thus has two major mistakes to answer for: not listening when Berger and Mr Clarke outlined the threat in briefings they provided for Condoleezza Rice and, when they did get around to taking action, letting Bin Laden escape.
However, I agree that one can't really fault Bush for not giving the order to blow civilian airliners out of the sky on 9/11, I don't think even Jack Ryan would have been that on the ball.