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 …
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.
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.
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.
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.
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.
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.
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.
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....
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.
>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).
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 ?
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......
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.
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.
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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