AirFiber Laser Networks: 622mbps

shinar writes: "In the LA Times, AirFiber announced the July/August avaliability of a new last-mile replacement for fiber: a wireless laser system delivering up to 622 mbps. It's a short-range system, mainly viewed as a delivery system within cities. It's being tested in Dallas, Tokyo, and Madrid, and projected for first commercial release in July or August. Not huge or revolutionary-a few other companies are working on the same sort of thing-but it might be a blessing for people in high-population density areas. "

Comments

interference

[blackdefiance]

would snow, hail, or a hard rain disrupt this?

Network interference

[Kaa]

I see major problems with carrier-pigeon network interfering with the laser one.

Initially, as the flights of pigeons would be blocking the laser's line-of-sight, the laser network will suffer: "I am sorry, sir, the packets can't get through -- there are pigeons in the way!".

Eventually I would expect the laser network to deal with this problem technologically, that is, upgrade their lasers to military power. At this point, the carrier-pigeon network will begin to suffer casualties, and notices like "Caution! Dead pigeons falling out of the sky!" will have to be posted around the laser network sites.

Later we may expect carrier pigeons to be fitted with mirror-shielded armor and the network lasers to be outfitted with tracking devices, but that's going to take some time...

"Packets? What packets? There is a pigeon shoot going on!"

Kaa

Bingo! That's exactly the problem...

[ATKeiper]

You nailed it right on the head. The article mentions that this technology will be weather dependent and need to be adjusted not only for a hard rain, but even for fog. And what if a bird flies in the way of your transmitting laser? Ooops, there goes my download.

It's an interesting idea for people who can't use other technologies because of their location, but I doubt it'll have any wide consumer market, when there are so many other established (and more reliable) technologies.

See this related article: Science-fiction staple new entry in high-speed Net (C|Net News.com, 22 Mar 00)

A. Keiper
The Center for the Study of Technology and Society
Washington, D.C.

Not an insoluble problem

[Tau Zero]

As you go into the infrared, the influence of fog drops; once the wavelength of the light gets to be much larger than the droplet size, they stop scattering very effectively. If you use a larger lens (say, a fresnel lens instead of a small glass lens) the effect of blocking a small area diminishes. Besides, I'm sure your router is capable of handling the effects of a brief dropout in the signal, and that's all a bird is going to give you.

Free-space optical transmission has distinct advantages over radio and microwave, notably a lack of licensing restrictions and extremely high transmission rates. Would you put up with 2 Mbps when you could have 100 Mbps or more? Neither would I. If I ran an ISP in an area where fog was infrequent (say, from Los Angeles down to San Diego and east to Austin TX or so) this would be a great way to roll out digital services at speeds DSL cannot even dream of, while still being able to make money off a sparsely distributed subscriber population. This will drive the demand curve which will then make it possible to get fiber all the way to the service entrance. It's not the end-all, but it's a great foot in the door.
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Re:further concerns

[Tau Zero]

can't even slight amounts of scattering seriously distort the data being transmitted?

They'll attenuate it, but distortion isn't much of a factor. Visualize it this way: the transmitter emits a train of pulses, which travel at the speed of light. For the pulses to be distorted, something has to either block stronger or weaker parts preferentially (a non-linearity), or delay part of the pulse so that it starts interfering with the next pulse. For this to happen with light going through fog, a substantial part of the pulse would have to follow a longer path. This requires at least two (and possibly three) scattering events: one off the line of sight and one back toward the receiver (assuming the receiver is not highly directional and only taking signal directly from the transmitter, in which case you need a bounce back onto the line of sight and then a third bounce to send it to the receiver). As you can see just from hand-waving, the probability of a photon coming in with a delay is vastly smaller than it being lost. Thus, distortion isn't a big worry.

I'm rather curious about upload vs. download speeds.

That's going to depend on the exact technology used, and the tradeoffs chosen by the designers.

But mightn't minor tremors (in an area which, like much of California, is prone to seismic activity) inspire a need to perpetually realign the trasmitting and receiving gear?

Sure. If you need accurate pointing to an arc-minute, anything that jiggles the optics by that much or more is going to screw up your system. (This includes birds landing on it, squirrels climbing on it, the wind blowing it around...) On the other hand, the same technology which we use to make CD players which focus themselves and follow tracks wherever they waver ought to be able to make a self-aligning laser transceiver. If CD drive prices are any guide, they'll be cheap in quantity.
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