Optical Cellphones

foondog writes "Here is a story over at News.com about optical cellphones. It seems that the Department of Defense has given a grant to the University of California to develop optical cellphones that are faster and more secure. This sounds a little strange to me since you would need a line of site with no obstacles in the way to use this. The article doesn't explain how this might work."

Comments

Is this UWB? Are they confusing light with all EM?

[Erpo]

A different technology in widespread use employs a method called wavelength division multiplexing, in which each cell phone uses a different wavelength of light, according to the researchers. In contrast, optical CDMA would encode each pulse, or bit of information, across a segment of wavelengths. The receiver uses a key to decode the signal and re-create the original pulse.

This sounds a lot like Ultra Wideband to me. Also, I'm guessing from reading the article that the author is confusing visible light with radio EMR.

Re:LOS

[FatHogByTheAss]

You're kidding, right? You can't possibly be this uninformed.

Do you have any idea how much laser power is needed to nail a geosynch sattelite?

Very little. 1500 mJ, specificaly. It's done every day.

let alone burn through the atmosphere and any possible cloud cover.

Uhhh... only if you're in the visible light spectrum. Some wavelengths will pass right through clouds (and other objects, like the earth) completely unphased.

Or how about the laser platform aiming and stability? a shake of less than 0.01mm in the sattelite will make the beam dance around on the planet over a 1 square mile area.

How about it? Do you know we bounce lazers off mirrors on the moon that are about a meter wide, and we bounce the same lazer off satelites all the time.

Not.. no way, no how... not sattelite.

Better call University of Texas and tell them to knock it off, because apparently, what they are doing can't be done.

Here's a quarter, kid. Go buy a clue.

Optical Communications to Keep Bombs Away

[Crispin Cowan]

This kind of technology is particularly important to the Army for men in the field. The reason is that in the near future, any kind of broadcast RF will result in a bomb down your shorts in a big hurry: smart weapons will home in on any radio frequency they can find, and destroy it. Thus talking on the cell phone, walkie-talkie, whatever, will mean instant death to a soldier.

Thus the Army must have some kind of non-broadcast communications system. I have no direct knowledge of how they would do it, but it isn't hard to imagine. For example, suppose low-flying satelites broadcast a signal. Handsets on the ground listen for that signal, and then point a highly directional antenna (LASER, focussed RF or microwave, whatever) at the satelite, and then starts transmitting a narrow beam.

There is not enough economic motive to develop this for purely commercial purposes. But once it is developed for the military, the commercial benefits are there to deploy it. Directional signalling means much less interference, and therefore much less consumption of precious spectrum, and less need for those pesky and expensive cell towers.

Crispin
----
Crispin Cowan, Ph.D.
Chief Scientist, WireX Communications, Inc.
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