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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."
Well, they'd better tighten up the radars to deal with it else they've just given an off the shelf solution to interfering with these radars, and told interested parties about it.
Consider the impact of a Beowulf cluster of these!
Last I checked it was the FCC that was responsible for the allocation of spectrum in the United States and territories. They are the arbitrator of interference issues. In short: I use WiFi, if there is a problem then the FCC, not me, is to blame.
Remember, Amateurs built the ark. Professionals built the Titanic
Choice quotes: "might cause interence", "not right now, but maybe in the future"... This is the Pentagon spreading FUD, and knowing the predilictions of the current administration, it all bodes very ill for wireless in general and WiFi in particular. In my quick scan of the article I didn't see any mention of 5Ghz or 802.11a, so it rationalizations that the Pentagon is looking at the UII band are misplaced.
Consider yourselves warned.
A well-crafted lie appears unquestionable - Dama Mahaleo
Baloney yourself!
Neither software defined radio nor the Open Spectrum initiative renders interference problems obsolete. Saying otherwise is about as meaningful as saying that modern computing repeals the 2nd Law of Thermodynamics!
Radios of any sort increase the energy in the bandwidth that they use. This is true whether they are narrowband traditional radios or ultramodern, cellularized, spread spectrum or ultra-wideband radios of the future.
Any radio receiver has to pull its desired signal out of the ambient noise. That noise consists of natural noise (thermal noise, spherics, astronomical sources, etc) and man-made noise (either noise-like signals or coherent signals). Many radio systems must operate close to the theoretical edge of practicality. The military and reconnaisance organizations especially need to operate with very small noise margins - their ability to do so is one of their advantages.
Increasing the ambient signal levels do degrate the capabilities of these systems. That is trivially proven.
Open Spectrum is an approach to improve bandwidth sharing. That is all it is - it is not a magic panacea that somehow makes interference vanish. Software Defined Radio is simply processing radio signals in software. It also doesn't change the underlying physics.
Consider the issue of radar... radar operates with an inverse-fourth law (the radar equation). The return signal is inversely proportional to the fourth power of the range. Normal radio operates by an inverse square law. Thus radar is especially vulnerable to interference.
To put a little numeracy in here... let's look at a 5GHz space based radar. Assume it outputs 1000 watts peak power (power is very expensive in orbit, you know) from an altitude of 150 miles. Assume the antenna shapes this to 100,000 watts effective radiated power (ERP).
By the time this reaches the earth, it is about 1E-7 watts per square meter. Assume the radar wants to image an area of 100 meters. This is 1E-3 watts or 1 milliwatt. A *single* WiFi stations puts out 10s of milliwatts. Thus if you have one WiFi per 100 square meters, you will have ambient "noise" of 20-30 decibells above the radar signal.
So, this is not a trivial issue. Of course, coherent integration can overcome much higher SNR's, but only at a cost (it requires much more time per resolution area, reducing the overall capability of the system).
In other words, there ain't no free lunch.
The Pentagon has the services of the best experts around to advise it on issues like this. Discounting their objections out of hand is arguing from either ignorance or opinion, not science or engineering. Determining whether their objections are appropriate in this case is a matter for analyses far more complex than will appear on slashdot, and in some cases, probably will require access to very sensitive classified information.
The only good weather is bad weather.
If he had gotten up and actually acted, the planes would have been followed by fighter planes, and given authorization, shot down before they got close enough to take out the towers.
I notice your conspicuous use of the plural term "towers" above. Do you honestly mean to suggest that on the morning of 9/11, before the first tower was struck, it was appropriate and justifiable behavior to shoot down airliners that were flying off-course?
Let's take the discussion further. Let's move to just after the first plane crash. Do you expect the president of the United States to authorize the destruction of every airliner in U.S. airspace which is off-course because one happened to run into a building?
I don't know what a careful decision on the part of the Commander in Chief to use deadly force against innocent civilians looks like in your political universe, but I sleep better at night knowing that my president is reluctant to take such action.