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Reflections
RevMike writes "The New York Times (reg required) is reporting that Bell Labs/Lucent has developed a method to multiply the bandwidth of cellular networks by using multipath. Robert Lucky developed the system called Blast. He claims that it should multiply the data rates in existing spectrum 300% to 400%. One prototype took a network from 2.5Mb/s to 19.2 Mb/s. Interestingly, the system works better in cluttered environments." And on a related note, Kimberley Burchett writes "The latest Physics News Update mentions that skyscrapers could actually help wireless communication. 'The more scatterers between the transmitters and receivers, the more channels that are available. For the time being, the communication technique is limited to ultrasonic communication - the electronics necessary for exploiting scatterers with wide-band time-reversal antennas at cell phone frequencies simply don't yet exist.'"
of this article...
Ursula Andress, Catherine Deneuve, and Charo, twice...
If the tech doesnt exist yet, then it's sure to come about soon, if it is required for a new tech. It's the american way-
At least the geek american way...
is it just me or does it seem unlikely that this :]
technology will *ever* exist?
Now all my ladies will get their hourly Mr. Happy visual status updates even quicker. Just one more more reason to go out and get a get picture phone girls!
For the time being, the communication technique is limited to ultrasonic communication - the electronics necessary for exploiting scatterers with wide-band time-reversal antennas at cell phone frequencies simply don't yet exist.'"
What does that mean exactly?....What is it used for, what can it NOT be used for?
wide-band time-reversal antennas ... simply don't exist yet.
And in related news, still no flying cars.
So far, this new millennium sucks.
/syle
"Blast" sounds just like the best technology I want to have smashed up against my head while I'm walking around outside.
Does anyone have any updated statistics on cellular safety? I wonder if this technology will affect that aspect of cellular use?
First, it's people yakking on the cell phone in the movie theater.
Now it going to be people wanking off to their live-feed pr0n delived to their cellular in the movie theater.
Lovely....
I thought that was Robert Blake?
I don't need no instructions to know how to rock!!!!
The latest Physics News Update mentions that skyscrapers could actually help wireless communication.
I never would have imagined that a tall, slender, permanent, cellphone tower-like structure could serve as a cellphone tower.
Reply or e-mail; don't vaguely moderate. Ex-O'Reilly/MIT employee, now a full-time Google employee.
Blocklevel: Practical Information Architecture
With this tech, wi-fi in high-rises can be used by on the ground low-tech mobile users! warchalking to be taken to great new heights !!
PRS.
I can get a whoping 2 k/sec off the wireless network I'm on and that is on a very good day. Usually it's between .5 k/sec and 1 k/sec. All these speed increases in wireless networks but in actual fact the time to market on this product will proably be 20 years. I'm just sick of being teased with the knowledge of all these better networks :)
"I believe in everything in moderation. Including moderation." -Dean DeLeo, Stone Temple Pilots
"...the electronics necessary for exploiting scatterers with wide-band time-reversal antennas at cell phone frequencies simply don't yet exist."
Perhaps if someone would fall and hit their head on the toilet, then they would come up with the means for time-reversal. Tell me future boy, why do we need screen savers on our mobile phone LCD screens?
How are you going to keep them down on the farm once they've seen Karl Hungus?
Bouncing Signals Push the Limits of Bandwidth
By IAN AUSTEN
IT is a phenomenon well known to people who drive through urban high-rise canyons. Just as you stop at a traffic light, the car radio loses its signal. Once the light turns green, the car only has to creep forward a few feet to restore the radio reception.
Those dead spots, which can also cut off cellphone calls and mobile computer communications, are often caused when signals bounce wildly off the surrounding buildings. This scattering creates pockets in which two reflections of the same signal collide and cancel each other out.
Avoiding the undesirable effects of multipath, as this scattering effect is formally known, has long been a preoccupation of people who design wireless communications systems. Now, however, a system developed by Bell Labs actually embraces radio reflections not only to improve reception but also to boost the speed of wireless networks. Prototypes of the system, called Blast, can send data over third-generation, or 3G, cellphone networks at rates about eight times those of 3G.
"Normally multipath is the source of confusion, it's the enemy," said Robert W. Lucky, who recently retired as vice president for applied research at Telcordia Technologies and is familiar with the Bell Labs work. "Here you put the confusion back together Humpty Dumpty style. It's like getting something for nothing."
Gerard J. Foschini, a 40-year veteran of Bell Labs, came up with the theory behind Blast about a decade ago while working on a long-term project to find the limits of a wide variety of technologies. As part of that project, he reviewed the work of Claude Shannon, the Bell Labs mathematician who published a paper in 1948 that established the field of modern information theory. Dr. Shannon's work still provides the basis for much information theory, including the notion of system capacity limits.
"He found the ultimate limits," Dr. Foschini said. "But he was basically dealing with one transmitter and one receiver. It was obvious to us that we could deal with many transmitting antennas and many receiving antennas for the same transmission."
So Dr. Foschini began developing mathematical models to see whether sending data through arrays of antennas would expand network capacities.
Antenna arrays have long been used in radar systems. But Dr. Foschini said that radar arrays are used to focus radio beams, whereas he wanted to scatter them. He hoped to discover whether wireless capacity could be boosted by dividing up data in space as well as time. Rather than point-to-point communications, his plan was to create volume-to-volume exchanges.
He had found through mathematical research that the concept would not work if the transmitter had only a single antenna. "If you send the same signal from one antenna many times all radiating in the same band, you come out statistically right where you started," Dr. Foschini said.
Instead, he developed a system that divided data into multiple streams that were then transmitted on the same frequency by several antennas. At the receiving end, the different streams of data were picked up by other antenna arrays.
Normally more than one transmission on a single radio frequency produces nothing but electronic noise. But Blast can make sense out of the noise because of the physical separation of the antennas sending the messages. Processing software reassembles the scattered data streams into their original form.
When Dr. Foschini tested the plan mathematically, the results were surprising. "We found the capacities were enormous - far, far in excess of what people were thinking of,'' he said. "If you put more and more antennas at the transmitting end, the capacity kept increasing. We were coming out with such ridiculously large capacities that at first, we didn't believe it."
Prototype systems proved that the experiments were correct. Each additional antenna added another element of space and because of that, additional capacity.
Just as surprising was the finding that the reflections that plague current wireless systems actually expanded the capacity of Dr. Foshini's system by effectively introducing more points in space. "Heavy scattering, which I always thought was a bad thing, is with this a good thing," he said. In fact, he anticipates that Blast-based wireless systems will work more effectively in Manhattan rather than "somewhere where it's flat as far as the eye can see."
Bell Labs has made prototype chips that would allow Blast to operate at speeds of 19.2 megabits per second over a 3G wireless network. Currently the highest speed those networks can offer is 2.5 megabits per second. Ran Yan, vice president for wireless research at Bell Labs, said that the prototype chips were intended for use in a cellphone or wireless hand-held computer.
Dr. Foschini declined to estimate the ultimate transmission speeds that could be achieved with Blast. One restraint on speed is the intense data processing it requires. With current technology, higher speeds would demand chips that are too large and too power-hungry for hand-held devices.
Dr. Yan said that the first systems offered by Lucent Technologies, the lab's parent company, would probably use just four transmitting antennas. Because wireless data systems operate with high frequencies and the transmitting antennas must be separated by only half a wavelength, he said, it will not be hard to squeeze more antennas into even the most compact mobile phones or palmtop organizers.
Because of economic problems, the wireless industry has been slow to adopt even 3G networks in the United States. So Blast is unlikely to become available soon. But unlike 3G, Blast does not require the construction of new networks. It only needs relatively inexpensive equipment, like new base stations, to be installed on current systems.
"It's a minimal upgrade," Dr. Yan said. "But it will allow service providers to get 300 to 400 percent increases in data rates in first deployments, and much higher quality."
While Lucent is already making network base stations for wireless service providers that can be converted to use Blast, Dr. Lucky anticipates that those companies will wait for the military to pioneer use of the system. He said there were concerns that the complexity of Blast might create unforeseen problems when used by large numbers of people on congested networks.
Assuming that problems do not develop there, however, Dr. Lucky said, the system could completely alter all systems that depend on radio waves. "I had this idea that spectrum was all used up,'' he said. "Now, with new technologies like Blast, maybe spectrum is infinite."
Was the prototype ultrasonic? If so how did they manage 19.2MBPS? 'Cause that would be cool in a known-physics defying way. Maybe when someone reposts the article, I can actually read it and find out...
Roving Web-Teleoperated Robot
Brigham Young University is doing similar work on MIMO (Multiple Input Multiple Output) systems. Here's a link to the lab working on it.
type of multiplexing scheme that they use in new current fiber optic systems to boost performance?
:-P
works with cpus... why not bandwidth ... hehe
or is it some kind of compression scheme where you take the signal transfer and match it to the closest matched wave possible and simply send over an encoding of it instead.
though in other notes.. isn't the best way to boost speed.. just to put more power into it?
Bollocks. I'd bet money Buck Rodgers has one.
And Shatner.
Bob Lucky, who doesn't even work at Bell Labs any more (he bounced over to Telcordia), didn't do this work, Gerard Foschini did, as you could tell by reading the article.
-Tom Duff
in Welsh
How droll.
But the electronics don't exist and it might be years away and it does not work yet with celluar frequencies and it might just be easier cheaper and all around make more sense to just use existing technology but pump up the number/amount of frequencies.
Now that is news and it matters!
It took the physics guys this long to figure out that a beowulf cluster of skyscrappers works better ?
Ducks...;)
I dont quite follow... is this saying its now possible to travel back in time using a cell phone?
Morphing Software
Didn't Sega Genesis have blast processing back in 1990??
Yet Another Variant of the old "Get DSL/Cable performance out of your old 14.4k modem" story? Sorry, but "plus 400% data rate" stinks. Show it in the field with a few thousand parallel users and I'll believe it.
Denken hilft.
It's great to hear that technology is improving. I almost dread getting calls from my friends with cellular phones, because the sound quality is so bad and they frequently get disconnected.
But I'm a little skittish about jumping into this hole, hog. We still haven't seen any unbiased studies on the effects of cellular phones on the brain (where people hold their phones while talking) and the reproductive organs (where they keep them when they're not).
I don't know if we want to double, treble, or quadruple their radiation emissions before we know what the effects on living tissue will be. What government department does this sort of thing fall under? The FCC? If there isn't one, then one should be created. Just my two cents.
Karma: Good (despite my invention of the Karma: sig)
FOR RELEASE WEDNESDAY OCTOBER 16, 2002
Chips developed by Bell Labs will enable mobile devices to receive more than 19 megabits of data per second on 3G networks
Bell Labs demoes 19.2Mbps 3G chips
By John Leyden
Posted: 18/10/2002 at 13:28 GMT
There are places where the networks are not touching,and there are places where they are-Boeing's Lori Gunter
There's the bullet: "...Simply don't yet exist"
At least as it is, the plan doesn't call for more clutter. Most cities are ugly enough as they are.
Official North Korea Website Site Still Sucks, and Uses Macromedia Fireworks 3.0
Robert Lucky had nothing to do with BLAST development. He was a VP of research and worked for Telchordia, not Bell Labs.
Didn't we see this a couple months ago?
Another case of modding based on the parent's author, it appears. Another case of mod abuse, thanks to the anonymous modification system.
Please, mods, try to take grudges out of the process, okay?
So the Guy that developed this, do they call him "Mr. Lucky" ?
There are some people that if they don't know, you can't tell 'em.
From what I gather, the technology improves bandwidth for transmissions on one frequency. CDMA uses multiple frequencies and has already twice the bandwidth capacity. Any ideas if CDMA can have an improvement? Since what we are getting to is the information theory maximum, CDMA should get there too., but the article is silent on that. :-( ?
Does this also mean I'll never get broadband on cellphones unless we use a different frequency
.ACMD setaloiv siht gnidaeR
What they're proposing is a method of using channels from adjoining (or not so adjoining) cells to improve bandwidth, making the assumption that the adjoining cells has bandwidth to spare. Now, if you're having trouble getting a call through on your EXISTING cell (or data connection, or whatever), what makes you think that stealing bandwidth from adjoining, likely equally-congested, cells is going to help?
C'mon, moderators, get your noses out of Slashdot's collective ass and mod quality posts up. The parent post, while it may not be amazing, is not offtopic! He's absolutely right, and it should be modded Insightful.
See the Press Release
OK, I'm a physical chemist, and this junk drives me up the wall.
All these journalists assume that the wattage is what matters, and that being 1 cm from a 4 watt transmitter could be unhealthy. However, the wattage is irrelevant - Einstein showed this with the photoelectric effect. Basically, it is the frequency of the radiation that is dangerous, not the wattage, because one photon interacts with one electron - so the number of photons is irrelevant. For example, which would you rather be near - a 100W light bulb, or a 1W gamma ray emitter? Thought so...;)
To give you a baseline, cancer due to radiation occurs because photons of succicient energy actually break chemical bonds in your DNA. This requires low-UV or better to accomplish. That's why sunburn gives you cancer. Now, compare this to radio waves, which are far, FAR to low in energy to accomplish anything of the sort. In fact, radio waves are even to low to excite the vibrational or rotational states of a molecule (which is how a microwave oven works), so there is no risk of "cooking" your brain, either.
Ultimately, when pressed, these cell-phone-cancer freaks point at two cases where some habitual cell-phone user got cancer on the right side of his brain. Ergo, it was the cell phone. These "doctors" (and I use the term loosely) have never proposed any sort of mechanism or ANYTHING to explain how it could occur. Because it can't.
Bottom line, you have a better chance of getting cancer from your own body heat (you emit infrared radiation) than you do from a cell phone.
-Looking for a job as a materials chemist or multivariat
Okay, okay. I didn't read the article properly first time through. This is multipath from antennae at the same location, not from antennae at different locations. Mod -1, Dumbass :)
Reflections!!! more like celda
It took the physics guys this long to figure out that a beowulf cluster of skyscrappers works better ?
What's cool is that taking a signal of a given bandwidth, splitting it, bouncing it, and recombining it is actually better. It's a bit like saying that a Beowulf cluster made of 3 1GHz PIV's would beat the crap out of a single 3GHz PIV system - which should not happen. Crazy!
-Looking for a job as a materials chemist or multivariat
MIT's Technology Review covered this in May 2002 in its "Five Patents to Watch"
"One restraint on speed is the intense data processing it requires. With current technology, higher speeds would demand chips that are too large and too power-hungry for hand-held devices."
So is this the next killer app to fund chip research?
"I'm about to drop the hammer and dispense some indiscriminate justice!"
Then, maybe I'll be able to receive more than one HDTV channel.
This is new? Blast was described YEARS AGO! ...requires quite a lot of processing power at the mobile phone to pull it off. Maybe the reannouncement means Blast is getting a second chance- the first time around, it obviously was not ready for prime-time.
Can you imagine a Beowulf cluster of these? Oh... CLUTTER. Forget it.
First how is it possible to gain bandwith using 'clutter' ? here is how. imagine that you and I are both in our cars at a stop light and listening to the same rasio station. Only my radio can barely get the staion and yours does fine. If I pull my car forward a few feet, suddenly my reception improves. What happened is that the multi-path interference made my car sit in a node and your sit at a maximum.
Now if there had been more than one radio transmitter and some dude back at the station had changed the relative phase of the antennas he could have put your car in a node and my car in maximum. Thus by changing the relative phases of antenna one can direct the signal to whichever car you want. If we now differenlty modulate the signals on the antenna's we could send one signal to one car and the other signal to another car. Thus by recycling the same broadcast channel we have doubled our bandwidth.
But there is a problem here. How does the guy at the station know how to adjust the phases of the transmitters to get this spatial separation? the answer is he cant know unless he knows where both of us are and where all of the building are, and the moving cars,etc... basically impossible to compute beforehand.
So instead what you do is have the car transmit a signal on the same frequency that is coded to say 'hi i'm car #1'. The guy at the station receives this signal on his antennas and notes the relative phase of the singals on each. Now by time reversal symmetry, if he broadcast at those phases all of the multi-path signals would converge in phase on my car's antenna. Likewise he can pick out car number 2 and so on.
Furthermore i'f the clutter is changing or almost equivalently if I am driving my car, he can just keep updating the relative phases and track my car's antenna.
So the missing ingredient here is some way to detect phases and re-transmit phases in real time. One approach is to have a reference signal all of the transmitters are locked to that from which they could compute the phases they need to re-transmit. This is potentially compuationally expensive since we also have to demodulate and detect all the signals as well.
another approach is to simply phase conjugate the incoming signal, amplify it, remodulate it witht he signal, and rebroadcast it. Thus the outgoing signal is the time reversed image of the incoming signal. We never need to actually measue the phase.
there are lots of ways of 'phase conjugating' as signal but I'm not enough of a microwave jock to say how you do it in that region of the spectrum. In the optical band region there are lots of ways using non-linear optics. However none of these are wide band. They only work at specific (laser) wavelengths that can be created coherently. From the comments in the article I am assuming this is true in the microwave regime as well. When you get down to the ultra-sonic regime you get to frequencies (mega hertz) where you can do this electronically directly. So that is proably why its accoustic.
interestingly there are a number of approaches to making passive approximate phase conjugate mirrors using engineered materials (bulk element transmission lines) that do operate in the microwave regime. these however are not advanced enough for practical use yet. currenly they are finding use as light weight stealth materials aimed at radar invisibility. But probably within 5 to ten years these will be practical enough for the applications envisioned here.
I might specualte that just as the development of electronics was first spurred by military use and then by consumer use. This might happen here too.
and if some bozo complains about my typing skills I will adjust the phases of my heat ray to melt their brain.
Some drink at the fountain of knowledge. Others just gargle.
Bouncing Signals Push the Limits of Bandwidth
By IAN AUSTEN
T is a phenomenon well known to people who drive through urban high-rise canyons. Just as you stop at a traffic light, the car radio loses its signal. Once the light turns green, the car only has to creep forward a few feet to restore the radio reception.
Those dead spots, which can also cut off cellphone calls and mobile computer communications, are often caused when signals bounce wildly off the surrounding buildings. This scattering creates pockets in which two reflections of the same signal collide and cancel each other out.
Avoiding the undesirable effects of multipath, as this scattering effect is formally known, has long been a preoccupation of people who design wireless communications systems. Now, however, a system developed by Bell Labs actually embraces radio reflections not only to improve reception but also to boost the speed of wireless networks. Prototypes of the system, called Blast, can send data over third-generation, or 3G, cellphone networks at rates about eight times those of 3G.
"Normally multipath is the source of confusion, it's the enemy," said Robert W. Lucky, who recently retired as vice president for applied research at Telcordia Technologies and is familiar with the Bell Labs work. "Here you put the confusion back together Humpty Dumpty style. It's like getting something for nothing."
Gerard J. Foschini, a 40-year veteran of Bell Labs, came up with the theory behind Blast about a decade ago while working on a long-term project to find the limits of a wide variety of technologies. As part of that project, he reviewed the work of Claude Shannon, the Bell Labs mathematician who published a paper in 1948 that established the field of modern information theory. Dr. Shannon's work still provides the basis for much information theory, including the notion of system capacity limits.
"He found the ultimate limits," Dr. Foschini said. "But he was basically dealing with one transmitter and one receiver. It was obvious to us that we could deal with many transmitting antennas and many receiving antennas for the same transmission."
So Dr. Foschini began developing mathematical models to see whether sending data through arrays of antennas would expand network capacities.
Antenna arrays have long been used in radar systems. But Dr. Foschini said that radar arrays are used to focus radio beams, whereas he wanted to scatter them. He hoped to discover whether wireless capacity could be boosted by dividing up data in space as well as time. Rather than point-to-point communications, his plan was to create volume-to-volume exchanges.
He had found through mathematical research that the concept would not work if the transmitter had only a single antenna. "If you send the same signal from one antenna many times all radiating in the same band, you come out statistically right where you started," Dr. Foschini said.
Instead, he developed a system that divided data into multiple streams that were then transmitted on the same frequency by several antennas. At the receiving end, the different streams of data were picked up by other antenna arrays.
Normally more than one transmission on a single radio frequency produces nothing but electronic noise. But Blast can make sense out of the noise because of the physical separation of the antennas sending the messages. Processing software reassembles the scattered data streams into their original form.
When Dr. Foschini tested the plan mathematically, the results were surprising. "We found the capacities were enormous - far, far in excess of what people were thinking of,'' he said. "If you put more and more antennas at the transmitting end, the capacity kept increasing. We were coming out with such ridiculously large capacities that at first, we didn't believe it."
Prototype systems proved that the experiments were correct. Each additional antenna added another element of space and because of that, additional capacity.
Just as surprising was the finding that the reflections that plague current wireless systems actually expanded the capacity of Dr. Foshini's system by effectively introducing more points in space. "Heavy scattering, which I always thought was a bad thing, is with this a good thing," he said. In fact, he anticipates that Blast-based wireless systems will work more effectively in Manhattan rather than "somewhere where it's flat as far as the eye can see."
Bell Labs has made prototype chips that would allow Blast to operate at speeds of 19.2 megabits per second over a 3G wireless network. Currently the highest speed those networks can offer is 2.5 megabits per second. Ran Yan, vice president for wireless research at Bell Labs, said that the prototype chips were intended for use in a cellphone or wireless hand-held computer.
Dr. Foschini declined to estimate the ultimate transmission speeds that could be achieved with Blast. One restraint on speed is the intense data processing it requires. With current technology, higher speeds would demand chips that are too large and too power-hungry for hand-held devices.
Dr. Yan said that the first systems offered by Lucent Technologies, the lab's parent company, would probably use just four transmitting antennas. Because wireless data systems operate with high frequencies and the transmitting antennas must be separated by only half a wavelength, he said, it will not be hard to squeeze more antennas into even the most compact mobile phones or palmtop organizers.
Because of economic problems, the wireless industry has been slow to adopt even 3G networks in the United States. So Blast is unlikely to become available soon. But unlike 3G, Blast does not require the construction of new networks. It only needs relatively inexpensive equipment, like new base stations, to be installed on current systems.
"It's a minimal upgrade," Dr. Yan said. "But it will allow service providers to get 300 to 400 percent increases in data rates in first deployments, and much higher quality."
While Lucent is already making network base stations for wireless service providers that can be converted to use Blast, Dr. Lucky anticipates that those companies will wait for the military to pioneer use of the system. He said there were concerns that the complexity of Blast might create unforeseen problems when used by large numbers of people on congested networks.
Assuming that problems do not develop there, however, Dr. Lucky said, the system could completely alter all systems that depend on radio waves. "I had this idea that spectrum was all used up,'' he said. "Now, with new technologies like Blast, maybe spectrum is infinite."
... a couple of years ago. Here is our story from then.
Eric Smalley
"I'm just here to regulate funkiness."
Does anyone have a good understanding of the underlying physics? I'm a little tired of wading throught the troll-bait of the postings here which just decreases the signal to noise ratio.
... I'm a software geek and I wouldn't know the typical cell phone frequency.)
One point that came out in the article was that the signal was being transmitted from an array of antenas and received by an array of antennas. This says to me, that they're using the phase shift of the signal somehow to increase the bandwidth, but if the transmitter array is only a half-wavelength in extent then the phase shift in time is only on an order of 1ns. (I'm assuming the wavelength is comparable to the size of a cell phone
--
I hate sigs.
I hate sigs (especially yours which is a waste of my bandwidth)
That wouldn't be J. Robert Lucky of "Kill Dr. Lucky" fame now, would it?
Intelligent Antennas and BLAST for 3G - CDMA
BLAST Technical Background
Lucent has a 'BLAST'
ISART-98 V-BLAST Presentation
BLAST High-Level Overview
BLAST Technical Background
I get a headache after talking on my cell phone with your mom.
The guy didn't want to say what the upper limit on BLAST would be - that implies that it might be substantially higher than 19.2MB/s, a lot higher.
The current BLAST implementation is designed to recycle existing equipment. If you designed your stuff from the ground up with BLAST in mind, would that imply a much higher throughput?
I wonder how the receiver puts the signals back together...
Power level isn't irrelevant. Radio waves CAN cause damage.
The way in which the damage is done is dependent on frequency. UV and gamma/X-ray radiation is high enough in energy that it can directly cause severe damage to molecules (such as our DNA) - This is why it causes cancer, even if relatively little of it is absorbed by the body.
Visible light doesn't do much damage because very little gets absorbed by the body - Most gets reflected.
RF can be VERY dangerous because unlike visible light, it can penetrate the body. In some cases (HF most likely up to VHF) it goes right through without interacting. At the UHF/microwave regions, this changes - Significant percentages start getting absorbed by the body. 2.4 GHz is particularly nasty because of a molecular resonance with H20 - Water absorbs around here readily, which is why it's not primarily a communications band and why microwave ovens operate at 2.4 GHz.
That said - Cell phones aren't dangerous, because they only emit 200 milliwatts (digital) and 600 milliwatts (analog) - That's not enough to cause significant heating. You won't feel it, you won't notice it, your body generates and dissipates far more heat on its own. Furthermore, the high-power analog mode only occurs in the 900 MHz band, never in the PCS band where absorption is higher.
Also, if someone were to be injured by excess RF, it wouldn't be cancer. Cancer modifies DNA, RF merely heats up cells to the point where they die.
retrorocket.o not found, launch anyway?
Microwave Phase Conjugation using Discrete Superconducting Elements for Retrodirective Antenna Applications
IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 46, NO. 11, NOVEMBER 1998 Microwave Phase Conjugation Using Antenna Arrays
Microwave Phase Conjugation Using Artificial Nonlinear Microwave Surfaces
A Retrodirective Array Using Balanced Quasi-optical FET Mixers with Conversion Gain
Bzzzt. Cellphones typically operate in one of several bands, including 0.8 GHz, 0.9 GHz, 1.8 GHz and 1.9 GHz. The latter two are not "far, far to low" -- microwave ovens operate at 2.45 GHz. They are well within the same octave (10x or 2x, take your pick :)
Sure, FM radio and TV are well below the microwave range, but we're not all holding VHF transmitters to our heads.
I'm not saying that ionizing radiation or heating radiation is what causes the complaints we've all heard of (headaches, loss of focus, etc.). But the frequencies ARE approaching the range of microwae ovens, and I think we WILL eventually find a provable scientific evidence of harm via cellphone radiation.
One simple rule for its versus it's
The article is called "Reflections". The subject of the research was the increase of bandiwidth by taken advantage of multipath, yet the person who submitted this seems to find interesting that bandwidth efficiency increases in a cluttered environment.
Duh! The more cluttered the environment, the more reflections occur, the stronger the multipath phenomenon.
I would have thought this would have been an obvious line of thought. Apparently not.
On to more technical stuff now:
I assume that the modelling these folks have made either uses a Ricean distribution or an m-Nakagami one. If it's Ricean (or Nakagami for large m), it means they have a strong LOS (line-of-sight) component and a multitude of nLOS components, which will be Rayleigh distributed. By having lots of reflections, their LOS components weakens, but their Rayleigh components (effects of multipath, already weak) become even more weakened. Thus they have a clearer signal; one which the equalizer at the Rx end can more easily discriminate.
Therein lies the problem though. Do you remember that until a few months ago, no 3G phones existed, solely because the equilizer couldn't handle the load? Well, this is bound to happen now! Sure, the LOS components are easier to be discriminated against the nLOS ones, but due to the nature of the environment (high clutter) the number of components rises (exponentially, if i am not mistaken).
This whole thing is being and has been researched, as the evolution of 3G. This is where the 3G people want the scheme to go, but frankly having seen what it can do, this sort of thing will only appear at the end of 3G's life and will be the big argument for migrating to 4G.
That is of couse, unless 3G's span is pushed back by 3-4 years until 2008-2012... In short, don't hold your breath.
/. Where the truth
This is old news. Check out the technical background article from September 1998. Essentially they are creating a set of parallel paths, using multiple transmit and receive antennas, by using signal processing at the receivers to separate out the individual signals (which are, of course, affected by multipath).
"What's cool is that taking a signal of a given bandwidth, splitting it, bouncing it, and recombining it is actually better. It's a bit like saying that a Beowulf cluster made of 3 1GHz PIV's would beat the crap out of a single 3GHz PIV system - which should not happen. Crazy!"
What's even cooler is that this technique will work with other open-air radio transmissions. Maybe not as effective, but with some minor chamges...
Obviously they hired that kid who programmed his own browser.
I wonder how many lines of code and how much time this job took?
First and foremost, this was developed at Bell Labs. (People I knew when I was a Bell Labs were doing on the research.)
Robert Lucky was at Telcordia, not Bell Labs. The New Yorks Times articles notes this. So, editors, please do a vague glance in the general direction of the article and the article summary before posting..
Second, this is old news. Here is a general scientific article on the underlying basis for the technology from September 2001:
http://www.aip.org/pt/vol-54/iss-9/p38.html
Kevin
" Just register once and *shock, horror!* remember the freaking login/password!
I really don't blame you for AC'ing that comment."
Ummm...***shock***horror*** The freakin login/password expires. And yea I've registered in the past. Got anything else smart to say?
It seems to me, that if you need to place the antennas at least a halfwave away, this is going to definitely limit the number of antennas on portable devices.
At 1800mhz the halfwave is 3.12" so you are talking about maybe two antennas in a small cell phone. At 3000mhz were still talking 1.87".
So unless we are talking really high frequencies, I'm not sure how practical this is for really small devices.
Personally, I would be happy to get a full half wave antenna on my current cell phone, rather than the internal crap they've been doing recently.
Sorry. There are two possible phenomena at work here. First is the possible damage to DNA from radiation. This is impossible, as mentioned. Second is possible heating by absorption of microwave radiation (I assume you mean water). These frequencies at which water does so are actually quite narrow, and a 1.9 GHz cell phone will not be absorbed much at all by water. Otherwise, your cell phone reception would go to shit on a humid day. I could send you a microwave absorption spectrum of water, and show you that it doesn't happen at 1.9.
-Looking for a job as a materials chemist or multivariat
Back around 1980, when I had occasion to consult the Bell System Technical Journal, his name turned up on significant research papers which were 10-20 years old even then. Not surprising he became VP of research.
In fact, by reversing the experiment and sending signals from each of the receivers back to the transmitter (an arrangement known as a time-reversal antenna, Update 190) it is possible to ensure that with the scatterers, a transmitter array can send multiple unique signals that are only detectable by the intended receivers.
what you descibed is how to rephase several spatially diverse receivers. but this is not what the article was about. in the article the 5 receviers are independent receivers, (e,g. separate cell phones).
if you want to know how it works read the article or the poster you replied to.
The wireless field has had multiuser detection hyped for ages and ages. The gains are real, and eventually we're going to have the signal processing capability to do it; however, power control will be a major problem. CDMA systems can use power control because only one receiver is important (that would be the base station); how would you get power control for MUD?
You know, I just wrote up something like 4 long paragraphs explaining this, but I figured that the following link to a PDF at Lucent's website would do just nicely...It's kind of basic, but I think it's sufficient for an overview.
_ Pr esentation.pdf
http://www.lucent.com/livelink/090094038000e509
Summary: Phased-array beam steering at receiver picks out one of four (in this particular Lucent Chip's case)transmitting antennas, and the system does this for all for transmitting antennas in parallel, then combines the received data.
No this has nothing to do this spatial diversity. Read the article. this is a single antenna per vehicle (or cell phone). its new stuff,not mubmo jumbo.
All these 25-year-old dot-com kids who are worried that they're too old to be CEOs should know the world was different once.... the article described Forschini as a 40-year veteran of the Labs, and it's unlikely to have been a typo for "40-year-old".
Bill Stewart
New Fast-Compression-only CPR http://preview.tinyurl.com/dy575ks
It's possible that the "hand-held devices" that this technology is too large for are the laptops, not the phones, in which case, yes, we'd like some new chips please :-) Maybe the old MicroUnity project could be finished... By the way, if you're going to do phased-array things with antennas, might as well have fun doing them with microphones and speakers and skip the headset entirely. One of the Microunity folks was playing with this a few years ago; you could do really impressive things if you had the signal-processing horsepower available, which their chip, had it ever become what they wanted, would have done; maybe current DSPs can provide enough horsepower today.
Bill Stewart
New Fast-Compression-only CPR http://preview.tinyurl.com/dy575ks
Microwaves ARE radio waves.
Most people define the beginning of the "microwave" region as somewhere between 1 GHz and 2 GHz. This doesn't mean that they are no longer radio waves.
Microwave ovens operate at 2.4 GHz. (Note: This is the main reason that 2.4 GHz is an unlicensed band, which is where 802.11b/g hardware operates, as do 2.4 GHz cordless phones.)
The band allocation for UMTS (3G GSM cellular) is approximately 2110-2170 MHz. (2.11-2.17 GHz). This is only 10% lower in frequency than microwave ovens. The PCS band, which is where MANY cell phones operate, is 1.9 GHz. And even 900 MHz is absorbed by the body reasonably well. Not quite as well as at 2.4 GHz, but still enough that I would not want to be closer than a foot to any transmitter over 20 watts.
The reason cell phones aren't dangerous has nothing to do with frequency - And has everything to do with their power. Analog phones (except for portable/car units) are 600 mW, digital CDMA is 200 mW.
Note: 200 mW of UV/gamma/X-ray CAN be dangerous, since instead of general heating, it essentially causes "bit flipping" in your DNA. 99.999999% of the time, that flipped "bit" does nothing or kills the cell, but every once in a while the right part of the DNA is corrupted and the cell becomes cancerous.
Also, the field strengh is more critical than the total power. Being in front of a directional antenna is far worse than being near an omni, and the inverse square law is your friend. But even 5 watts at 144 MHz can give you an RF burn if you get too close to the antenna. (At that power level, it's basically physical contact, but even a thin insulator won't help you, unlike with DC or low-frequency AC.)
retrorocket.o not found, launch anyway?
Btw, where does "non-ionizing" radiation officially start? Because even near-uv can cause damage to DNA...just wondering.
Now, if what you meant was to limit that to cell-phone levels, fine. But that's not what you said. Claiming ex post facto that it should be obvious is weak.
Since this was a post *about* cell phones, I think that's a reasonable assumption. I mean, any statement can be proven false if extended to ridiculous or out-of-context conclusions. I mean, did you call your classical physics teacher an idiot because Newton's laws were proven "wrong" by Einstein? Similarly, I would maintain that extending discussions of megawatt (or even kilowatt) transmitters to a discussion of cell phones certainly meets that standard.
And, by the way, if you're not able to hear objective criticism of your statements without taking it personally, maybe you would be better served not to make them.
I can take criticism, and I can return it. And if you criticize, you should expect your rebuttals held to a higher standard than that which you're criticizing. What I find annoying is nitpicking at posts where someone failed to state the obvious, when all parties realize what was implied. Or did you honestly think I was speaking of universal truths regarding the deletrious effects of radiative power?
-Looking for a job as a materials chemist or multivariat
I cannot overemphasize the importance of good grammar.
What a crock. I could easily overemphasize the importance of good
grammar. For example, I could say: "Bad grammar is the leading cause
of slow, painful death in North America," or "Without good grammar, the
United States would have lost World War II."
-- Dave Barry, "An Utterly Absurd Look at Grammar"
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