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Using Visible Light for Data Transfer
James Evans writes "Wired has an article about a New Zealand company which has developed a technology to transmit data at speeds up to 400Mbps up to 4km. They are working to have it more resistant to changes in weather, as well as increasing the distance. It has a number of advantages, including lack of federal regulation of the spectrum, as it is of course, visible light."
In related terrestrial networking news, waytoomuchcoffee writes "Science Blog reports that the backbone for the World's Fastest Network is up and running. It's a fiber optic 40 gigabit per second connection between Chicago and LA. Teragrid is a project by the National Science Foundation designed to link up supercomputer centers."
How long do you suppose the lack of federal regulation will last?
Some places do have ordinances against light pollution. I wonder how this would fit in. Also, will it come with a warning, such as "Do not look at transmitter with remaining good eye"?
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LAck of regulation is nice, but is there really a lot of regulation for InfraRed and UltraViolet?
It sounds like a VERY nice system for short-range, non-critical communictaions, but personally, I can't think of any points I would want to communicate to where I have line-of-sight... If I could get an inexpensive device that could communicate for about 10 miles, I would certainly get several.
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Doesn't this just sound like fiber optics without the fiber?
I seem to remember this being done a long time ago. I've got an electronics book with a schematic for a serial 28k transmitter using visible light.
--Quentin
This company has a history of off beat and - doubtful "inventions". Then agin maybe they have learn't a lesson or two about "science"...
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You see? You see? Your stupid minds! Stupid! Stupid!
Doing Free Space Optics isn't new. It's been done for many years now, although primarily with laser-based systems.
I work for a company that is currently developing a LED-based FSO system -- Omnilux.
The big push now in the FSO market is to find the right balance between performance and cost. Too many companies were trying too hard to push data longer distance, then faster, costs be damned.
Consider this, most cellphones around the world operate at 1500MHZ and so have a seemingly impressive maximum THEORECTICAL data transfer rate of 750Mbits/sec. Unfortunately due to physical contraints on modulation systems a good rule of thumb is that the actual data rate provided is about 1/2000 of this and so we end up with around 375 Kbits/sec that is just coming out with 3G systems.
You should really read up on communications theory, especially the basic stuff done by Shannon, Nyqvist and all the others.
The theoretical limit for a digital signal modulated in a perfect noiseless analog channel is infinity for any frequency! Where you get your numbers from I have no idea but they are totally incorrect!
And if you hava a noisy channel the theoretical maximum is dependent on the bandwidth and the noise, nothing else. And just because a signal hase a basefrequency of 1.5 GHz doesn't mean that it has a bandwidth of 1.5 GHz. Go check, all mobile phones have a much, much smaller bandwidth. We are talking orders of magnitude here.
reminds me of a slashdot story a while back about a group of people that was able to get your data transfer by looking at your (external) modem's LED.
I mean, same thing except, well, faster...
The cool part, though, is that now the router's status LEDs are actually good for something. You can theoretically face two routers toward eachother and that's IT! done! until some idiot walks between them. ha!
but really though, The thing with radio we seem to not be able to do with light yet is frequency modulation. If we can do that, I think we can push some very serious bandwidth through this spectrum.
The data-hiding possibilities are immense. you can technically send humongous amouts of data through a TV set, even, if it was made of as many LEDs as there are pixels, and by varying the each LED just ever-so-slighly. You can be watching the TV for pictures, and your Aibo would be sitting beside you, downloading zillions of bytes of data, and gaining consciousness (sorry just watched the animatrix, heh).
My life in the land of the rising sun.
But after reading the article, and seeing how they'd use LEDs (they don't say how big though), and the bandwidths involved, the lights would seem to be constanly on, do you think?
That'd mean no real lightwave pollution (it's all line-of-sight) and little visual pollution or distractions due to thousands of flashing lights?
Of course, I still have to wonder about the effects of different weather. I see it'll still work with a hand moving in front of it, but what about heavy smog days, or blizzards? Would torrential rain make problems with light refraction??
I guess it beats training swallows to carry coconuts engraved with data packets from rooftop to rooftop (they could grip 'em by the 'usks)
Hats off to the Kiwis for this one though, it sounds pretty exciting :)
Woohoo! I can't wait to see my IT Manager scaling our office building to deal with pigeons nesting on the transmitter!
"Nature will find a way..."
A very important point is that Infra Red light is absorbed by the cornia (outside) of the eye and dosnt penatrate to the retina where it can cause real damage. Visable light does penetrate (obviously) to the retina and WILL fuck your eyes up. I've worked with IR lasers for a few years, they are much safer than visable light devices.
Also saying use of visable light avoids licencing isues is a bit misleading.
As to my knowlage, no country regulates visable, IR or even UV unless in lasers (or other sources) where they may get to the powers likey to cause physical danger (not very relavent here, less so with IR rather than visable light).
Put your hand up if you need a licence for your IR TV remote controal!
Anyway, a practical solution would be to use lasers of differnet wavelengths and swich to the correct one depending on weatehr conditions. EG fog attenuates some wavlengths strongly, rain scatters a differnt set of wavelengths more readily, etc (As a crude example, consider the different wavelenghs reaching your eyes from the sun in these different weather conditions)
This technique of swithing to the most aproprate wavelength for the conditions is used in army laser range finders.
Anyone quoted by a reporter knows how little they understand
Don't believe what you read is the truth.
So what if they operate at 1500MHz? It is the bandwidth that is important. Example: Radio stations operate at 90-110MHz range. But each one has a bandwidth of around 30Khz.
So, first of all, the cellphones have a bandwidth allocated within a frequency range around 1.5Ghz. Let's take GSM, which is the most widely used standard:
In case you don't understand, it is simple. If you have a single signal at 1.5Ghz frequency, you could get a data rate equalling half the frequency. However when you transmit data you basically cause side-frequencies to appear in your spectrum. Do not assume that just because the system transmits at the base frequency of 1.5Ghz that the signal spectrum will be just a point at 1.5Ghz and 0 everywhere else. The spectrum will spread. If you use up all your possible bandwidth the spectrum will take up all the frequencies from 0 to 1.5Ghz.
Furthermore, consider the fact that there are many cellphones, sharing infrastructure. The protocol does both time-division and frequency-division multiplexing. While a *single* cellphone could perhaps work with a station at .75Gbit, this ceases to be the case when you add a few thousand cellphones. The band is subdivided to a pre-specified number of sub-bands - not only that, but there is also some time-division multiplexing going on, with each cellphone only doing rx/tx at a fraction of the total time.
Of course, the same is true for all electromagnetic wave devices.
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Why is everyone acting like this is a new thing? Hams have been doing the same thing for years. There have been construction articles in popular electronics mags for years about going digital with a pair of LEDs.
-- Ed Carp, N7EKG erc@pobox.com PGP KeyID: 0x0BD32C9B What I'm up to: http://intuitives.mine.nu
I'm not too clear on how this works. Wouldn't it be quite easy to disrupt a beam of light, through physical or other means? Seems you could put a piece of aluminum foil in it's path or disrupt the beam with other beams quite easily. And what about safety issues? Is it visible to drivers? I remember reading that when PARC first had a line of sight laser to connect two buildings across a highway, during inclement weather drivers would crash while distracted. If it's too high, would have to worry about aircraft. And since a laser can damage your eyes, wonder if this type of light can as well.
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I've followed the FSO development for some years now and I wonder if this is finally the commercially breakthrough.. shtml ?tid=172 ... where some came up with the idea of an
BUT... I'm really afraid of all these big telco spiders, lobbying for total regulation of this kind of technology. There was a post on eventual WiFi regulation in the US:
http://yro.slashdot.org/yro/02/12/08/0156246
telecom company conspiracy... and for FSO, it's basically the same, the same "terrorists-use-it"-arguments apply.
Look at all the nice pictures of house to house
meshes at www.omnilux.net, the ISP people is suggested that they control the last mile, i.e. the inter-house connections. Ahh, labels that say: "The equipment on top of your roof is the isp's property. Any modification and/or circumvention strongly prohibited". A real nightmare. And this would prevent real changes in network topology, from the hierarchical-telephone-network type to the flat networks current protocols and computers
should be able to handle.
Not that I want to rant too much, but I'm very afraid looking at the development in other areas...
How long do you suppose the lack of federal regulation will last?
I don't know about the US. (The FCC has been moving to open, rather than close, bands for some time now.) But it's already banned in Britain.
You probably already know that radio broadcasting in Britain is (or was a few years back - just in case they've changed their mind) a government monopoly. People tried to work around that in various ways.
One of them was a company that did a cute hack: They shined an infrared laser straight up, and modulated it with an entire FM band full of radio stations (similar to the way you can put a private FM band on a cable TV wire). Anybody who wanted to could mount a photocell or infrared-sensing diode (in a little telescope) on their window sill, point it at the invisible pillar of light, and couple it to a radio to receive the new band. Business model was to rent the stations out as commercial broadcast stations with all of London as target market.
The agency in charge of the British radio monopoly (British Post Office?) complained. And parlement extended the top end of their jurisdiction from whatever the previous legal end of the microwave spectrum was to infinity.
So in Britain, if it's electromagnetic energy (even gamma rays) and you can use it to beamcast or broadcast information, you need a license.
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