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back to article Boffins shine 800Mbps wireless network from flashlight

German researchers have discovered how to fill a room with 800 megabits per second of wireless data using an inexpensive LED setup. "Using red-blue-green-white light LEDs, we were able to transmit 800Mbit/s in the lab," said researcher Klaus-Dieter Langer. "That is a world record for the [visible light communication] method." …

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Joke

That's sorted

OK, so I have the streaming from my server to the TV settled.

Now to enjoy a movie - turn the lights down....

<NO SIGNAL>

Crap.

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redux of the first wireless network

I was at a european business school, and their wireless network was an infrared version of this. And that was 10 years ago. I don't think they got anything close to 800 Mbps though. Maybe closer to 800 kbps. Needed special cards for the clients... and line of sight.

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Meh

Already been a TED talk on this

Not really news? Perhaps the speed?

http://www.ted.com/talks/harald_haas_wireless_data_from_every_light_bulb.html

It does mean you have to keep the lights on...

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Pint

Perfect For A...

...classroom.

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beat me to it

here in NSW with the govt issued laptops it would be one way to stop the darling from accessing the internet when they are not supposed to be

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It'd solve so many issues

An end to people whining about us school network admins cooking their children's brains, being able to have dense wireless users without interference from every nearby house.

The only problem might be the 'slouched over their tablet' way of working with a lot of kids.

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GBE

Unidirectional broadcast-only WLAN.

It's clever, but it I don't see how it can be used for LAN. It's broadcast-only and unidirectional. Sure, they can transfer 4 HD video streams at a time, but I'd like to be able to _choose_ what movie to watch and to be able to pause, skip, etc.

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Anonymous Coward

Of course it's broadcast and unidirectional.

So is every other wireless* technology. If you want two-way communication, you put a transmitter and a receiver at both ends. As for being broadcast only, your computer will just drop the packets it's not interested in. Just like in the current wired or wireless situations.

*Wired technologies work the same, but with a lot more advancements to the point that the underlying mechanisms are not obvious. Thus, they often appear to be bi/multidirectional and uni/multicast. Knowledge of the network topology is required for unicast transmissions and the network card still has to have a device to create the electrical pulses and a seperate device to detect the electrical pulses.

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Bronze badge

Broadcast isn't an issue

But with a bit of decent network design, you could very easily segment your network to limit the broadcasts to those segments - just like with current wireless systems.

Broadcast traffic isn't such a problem in a well designed network.

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Silver badge
Go

A in ADSL

We all use a broadcast-mostly network. the A in ADSL stands for Asymmetric. Downloads are much faster than uploads. Mostly, that's what people want.

And there's no problem having another transmitter-LED on the device receiving the data for the back-channel. Where multiple devices are sharing one access point, you're probably back to the original CSMA-CD Ethernet design. Sense transmit collisions, back off by a random amount, exponentially increase back-off time after exach repeat collision. It's been done with radio (ALOHA and successors), and in a coaxial pipe (original thickwire and thinwire multi-tap Ethernet).

It sounds perfect for aircraft cabins. There's already a spotlight for each passenger ... replace or augment it with a LED and use it for comms as well, to the entertainment display on the seat-back and the passenger's notebook PC (via a USB lightwave-comms adapter). Deploy a long-distance (focussed beam) variant in the airspace at the top of the cabin as the network backbone. Save a small fortune every flight because a considerable weight of copper wire is eliminated. It might even be retro-fittable.

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Boffin

Blocking the beam

Should be possible to get round the problem of beam blocking, in a controlled environment.

For instance, from a central point in the ceiling, fire the beam high up, and have an angled mirror on the wall above and behind the computer. Plus maybe an audible alarm if the beam does still get blocked.

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Joke

Never mind mirrors on monitors to see who's coming up behind you...

Depending on the type of websites you could visit and be interactive with, I'd never been a fan of mirrors placed above and behind the computer,

Oh the images you'd see in the mirror, I'm shuddering already.

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Broadcast only?

@GBE. That problem was solved long ago. Google "1-way satellite".

In this situation, you'd probably use something standard like 802.11x as the back-channel.

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Although imperceptible to the eye

Is it totally transparent to the brain? Is there any risk of triggering epileptic seizures with this..?

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Photosensitive epilepsy

Most people with photosensitive epilepsy are triggered between 16 and 25 Hz. That is well within the range the brain will see as a flicker.

have a look here for more information http://www.epilepsy.org.uk/info/photosensitive-epilepsy

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Silver badge

No risk of triggering an epileptic fit

Flashing at 2-55Hz is naughty. 800Mhz is safe.

http://en.wikipedia.org/wiki/Photosensitive_epilepsy#Web_design

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definitely imperceptible

Modulation in the megahertz range is way above what the eyes can pick up. Waaaaay above. As far as mere biological entities are concerned, it's a fixed light.

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Joke

So..

if epileptic fits are triggered around 20Hz, and this is working at 800MHz, will it trigger 40Mfps (million fits per second)?

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Ru
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Boffin

Ever seen LEDs change brightness?

Like the fancy power lights Apple has made so popular? This is done via PWM, where the power to the LED is pulsed at a high enough frequency that the flicker is imperceptible to the human eye but the total amount of 'on' time in any given time period is reduced to give the illusion of different brightness levels.

Ever seen a nasty old fluorescent light that appears to flicker? Never heard much about those things killing people either.

Whilst I'm at it, boring old AC-driven incandescent lamps flicker too, though not quite to the same degree of course.

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@Haff thanks

Cheers - wasn't aware what the relevant ranges were, now I am :)

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FAIL

@Ru

As someone who has photo-induced seizures, yes, I HAVE heard of fluorescent tubes hurting people. The last seizure I had required two pins and a screw to fix a broken and dislocated shoulder. Followed by half a year of rehabilitation to restore full movement to my arm.

"The flicker of a faulty fluorescent strip light, however, could trigger a seizure in people with photosensitive epilepsy." --http://www.epilepsy.org.uk/info/photosensitive-epilepsy/triggers#lights

But I'm sure your ignorance is FAR better proof then the millions who have epilepsy and seizure disorders.

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Silver badge

I give it two days

before sales bods make flash presentations that need 1Gb.

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Anonymous Coward

Already been invented...

... the issue of light blocking can be solved by transmitting the light down some form of hollow glass light fiber. Quick, patent it!

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JB
Happy

Practical Wireless

Reminds me very much of a 'light beam telephone' project I saw in a 1970 edition of Practical Wireless. I wonder how that would have coped with 800Mbps?

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Silver badge

Memory 'flash'!

I think I've still got that copy somewhere. On the cover, it has something that looked like car headlights to give focussed transmission and reception. Strange I should have kept it, because I did not buy PW regularly.

Boy, does my memory work in weird ways!

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Ru
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Boffin

Go search for RONJA

10 megabit LED-based point-to-point networking device. Probably the spiritual descendant of the device you're talking about.

Point to point optics can be way faster, certainly; the wikipedia page has what it allegedly a gigabit-speed device. The interesting thing about this new invention is that it is fast and broadcastable, not merely point to point.

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Mushroom

MITM

Brings a whole new meaning to the 'Man In the Middle' attack... haha

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FAIL

removal of wires

How exactly? You still need the wired back haul to the room. Personally I'd rather the hospital paid for a nice reliable cable if they need network access so that the receiver/transmitter doesn't get block for any reason.

Or you know, use maybe a tube to focus the light beams to a specific point in the room....

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Bronze badge

Yes, can you imagine...

Every time a doctor gets to a bed with their tablet computer, they reach over and plug in a network cable... That'd be hygienic and an efficient way of doing things. Wireless is efficient and convenient.

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Happy

Wireless back haul

Why do you need a wired back haul?

Given the propensity for most office buildings to have an artificial ceiling, you could quite happily have a network in the roof operating over light links

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Anonymous Coward

How does it cope with

reflections off walls, etc?

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Ru
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Meh

Hospitals and planes, blah blah blah

Rather more careful development and testing of the hardware used in these environments would mean you could use perfectly sensible radio networking instead. People can, and do, use conventional mobile phones, sattelite phones and WLAN devices in planes. Emergency service radios are often used in and around hospitals, and then there are pagers and so on and so forth.

In the most sensitive locations, such as intensive care or an operating theatre, fixed line devices are perfectly justifiable.

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Boffin

Amazing ...

Why do people think that hospitals are a no-go region for wireless or radio networks?

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GBE

Wifi is widely used in hospitals

>Why do people think that hospitals are a no-go region for wireless or radio networks?

Good question. All the hospitals I've been to in the past 5 years or so have had WAPs hanging from the hallway ceilings every 20 yards or so. The residents push around official hospital laptops on wheeled pedestals that use wifi to access the Hospital records system, half the patients and guests have laptops or smartphones using the guest wifi network, and much of the staff have some other small wifi enabled gadget (used to be palm-pilots or pocket-sized windows PDAs, now it's ipods and smartphones).

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And for those interested ...

RadCom (the journal of the Radio Society of GB) has been running a series of articles about a number of different amateurs who've been experimenting with long range transmission by light. By carefully focussing both transmitter and receiver with lenses they've got up to some quite impressive distances - which is actually not easy in this country as it needs very careful choice of locations to get a long line of sight.

But as said, it's not new. Didn't heliographs go back to ancient greek times ?

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Joke

"The inability for light to penetrate walls..."

There's a known solution for that. It's all done with pixies and dinner plates in "Legend".

I must admit to being rather taken with the idea of a network that *really does* need all the little pixies doing their stuff together in order to work properly......

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I did it in the 60s

A school friend and I had some fun doing this in the 1960s, using a torch bulb as the source and a photo transistor as the detector - an OCP71 IIRC.

Not quite so fast but we got speech transmission.

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Me too, in the 60s

I wired a torch bulb across a radio's speaker terminals and used a CDS sensor and amp. A bit muffled. The Mk II version placed the bulb in its original reflector - was able to transmit accross the street (at night). We didn't have LEDs then, or much in the way of silicon devices.

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What's wrong with IR?

So, why do we have to use visible light and disturb people with the light. What is wrong with IR at various frequencies, in the same way as they are using visible at various frequencies?

I know my TV has a much lower bandwidth but it seems to work reasonably well at receiving signal from the remote even when there is stuff in the way. OK, if you block the tx/rx close to the device then it does fail, but "shadows" from objects in mid distance aren't a problem. A couple of tx/rx pairs per room, well spaced should be able to cover most of the room.

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Boffin

TEMPEST

This reminds me of a security threat identified at least 15 years ago. In those days, everyone was using cathode-ray-tube electron botherers as computer display devices. Although they looked to the human eye like arrays of pixelated informative goodness they were in fact (of course) just one pulsing dot racing repeatedly along the scan lines.

With a suitable photodiode, one could detect the pulsations of light from the screen reflected from the walls, and reconstruct the display from the time domain variations in brightness. Thus, for sufficiently secret systems, it wasn't enough to angle the screen away from the windows, one had to draw the blinds. Or have no windows at all. That one worked, too.

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