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A Wireless Revolution From The Garage
Saige writes "There's an interesting article in this month's Discover magazine about a lone inventor who's managed to develop a new method of wireless transmission that he was told was impossible - using "time-coded ultra-wideband electromagnetic pulses" - something that apparently can offer vast amounts of spectrum, allowing ways around the billion-dollar bidding going on now, with the bonus of better transmission through walls, higher speed/capacity, and higher resolution."
IMAO: In My Assinine Opinion?!?
Dude, don't be so hard on yourself.
> They're trying to get FCC approval since it doesn't cause (enough) harmful interference to take down communications with existing equipment.
This is a wrong assumption. It doesn't matter if you describe/encode information in the time domain, the frequency domain, or any arbitray other domain - the total transmission capacity of your channel is the same. If you add broadband spread-spectrum signals, you do take away capacity, and you _DO_ interfere with the more traditional ways of RF transmission. Spread spectrum signals look like additional noise to narrow-band receivers; the more spread spectrum signals you have, the more noise you get. The more noise you get, the worse the S/N of your narrowband link gets, which degrades the capacity of your narrow band channel.
There's nothing revolutionary or even new about this "ultra wide band" stuff. Wether you describe an RF signal as a superposition of sinusoidals, pulses, wavelets, or any other linearly independent set of base functions simply does not matter.
It isn't VMSK. VMSK was the digital equivilant of that tired old april fool's joke of reducing FM deviation until the signal had essentially no measurable bandwidth. Shannon's Limit shows why it's not workable.
This stuff is real, but the hype and spin is nothing short of amazing. Folks, get an electrical engineering degree and you'll learn that it is hardly revolutionary.
Look up "Costas Loop" on your favorite search engine and you'll see how he stays synchronized. No, you don't need an atomic frequency standard. And by the way, this design as been around since at least the late 1950's.
I first learned about pulse phase modulation from an ARRL publication in 1978 while studying for an Extra Class license. The idea of spreading it further was simply a matter of changing the timing in a pseudo random fashion. BFD.
In any case, UWB is not much of an issue UNLESS you give it to the general public to take everywhere. Before you know it, Radio Astrononomy gets hosed. Next, a few ham radio operators complain. Then a few incidents in airliners regarding Portable Electronic Devices start making GPS go nuts, and before you know it, police radios stop working within a few hundred feet of Starbucks when they start offering wirless internet portals...
That's right, you can be compliant with 47 CFR 15 and still mess with licensed radio services. It's called the near/far problem with spread spectrum. Look it up.
If we could somehow all turn off all of our narrow-band radio gear and magically turn on our computer enhanced digital communicators, we'd all probably love it. But that's not practical. We will have narrowband communications for a very long time to come.
UWB devices will have to avoid trashing GPS frequencies (it's a spread spectrum system too) without introducing filters that introduce excessive group delay distortion. They'll also have to figure out how to get good dynamic range and sensitivity with a very wide band front end that lets in some remarkably powerful signals.
Most computer professionals know so little about the transmission media they use for their LANs and WANs that it's comical. They would love to dispense with FCC licensing but they have no concept of what they're getting in to. Folks, unlicensed operation means you must ceace and desist when a licensed operation asks you to. It also means you must accept any interference you may receive. And people want to build a wireless infrastructure on THAT?
We need the FCC. We need narrowband channels. Just because they're not doing their job poorly doesn't mean it doesn't need doing.
See, for instance, http://www.alpcom.it/hamradio/marconi.html.
erhaps I don't fully understand this invention, but to me it sure looks like snake oil.
You don't understand the technology.
Check out the Ultra WideBand Working Group, time domain (mentioned in the article) and dozens of other sites. The pulses are what makes this thing work and the spectral splattering is exactly intended. They're trying to get FCC approval since it doesn't cause (enough) harmful interference to take down communications with existing equipment.
It's way cool stuff. Check the UWB link provided; they want to use this for positioning, through-wall "radar" and communications. It has very serious potential. If I can find the EDN issue which gave an in-depth study of this I'll post back.
The square arial works on the idea of having two dipoles that are linked via the two cross-pieces. Since you design antennas, you can probably go into more detail on this concept, but as I understand it, it's essentially a self-amplifying arial.
It's a small world and it smells funny; I'd buy another if it wasn't for the money; Take back what I paid (SoM)
This scheme sounds strangely too familiar to
. html
VMSK. (a fraud perpetrated by Hal Walker).
There's an excellent treatment of it by Phil Karn (of KA9Q fame) at http://people.qualcomm.com/karn/papers/vmsk/index
If you want to resolve picosecond pulses, you need electronics that can pass frequencies up to 1 THz.
Not really. In fact, there is probably no frequency higher than 200MHz on the chip, but it can control the phase of the signal with very fine resolution.
Here is how this might work:
Start with a ring oscillator (basically an odd number of NOT gates in a ring) and lock it onto a reference frequency with a phase-locked-loop. Use a multiplexer to tap the signal at different locations along the loop. This gives you the same signal at different phases, but the resolution isn't quite down to tens of picoseconds yet. The next step is to use another multiplexer and a series of carefully tuned delay elements to further improve the resolution. You now have a pulse generator that can modulate the position of individual pulses with a resolution of tens of picoseconds by a digital control word.
This can all be manufactured with standard CMOS processes on a chip.
It may take millions of dollars to develop this technology and make the process repeatable enough, but once you have it, making many copies of the circuit is cheap.
The low power usage results from the fact that an ultrawideband signal does not suffer from fading - if there are no sines then different reflections of the same signal can't arrive out of phase and cancel out each other. Most wireless systems take a very wide margin to accomodate for this type of fading.
-
Stop worrying about the risks of nuclear power and start worrying about the risks of not using nuclear power.
Not only that, it was posted to /. on april 10th 1999. See http://slashdot.org/articles/99/04/10/1920203.shtm l
This is just like television, only you can see much further.
As a firm believer in TANSTAAFL, I wonder what kind of interference this system will generate. The EM spectrum already suffers from severe noise pollution in many areas. Think about that when you run your computer with the case off.
Mea navis aericumbens anguillis abundat
So it's like digital CW.
I'm a loner Dottie, a Rebel.
Very well said HuskyDog.
Just for people with a more CS oriented background: Consider Shannon's information theorem, given particular signal and noise levels and bandwidth, there is a fixed amount of entropy (=bits of information) that you can put through it.
Mr Larry Fullerton simply spreads out hist signal across a very wide bandwidth, stealing a little bit of entropy from each frequency. But since the spread is so wide it is only a very very little bit of entropy, such that current frequency-domain transmission systems will not notice a degradation. And since large parts of the spectrum that Larry's signals cover are still unused, he is 'stealing' entropy from a lot of frequencies where nobody is even using it, let alone be affected by the raised noise floor. Hence, he will be able to broadcast a lot of entropy (bits per second) without hampering any of the existing broadcast systems.
The bandwidth of Larry's system is still limited by the pulse slope of his chips and by signal distortion by his antenna's, hence the bandwidth his system covers is not infinite, hence at any bit rate, he will always raise the noise floor all over the spectrum when he transmits. And I'm sure that when he increases the bitrate of his transmitter enough, he is also increasing the amount of transmitted power without increasing the bandwidth of the tranmission, hence he is increasing the noise floor that the other communication systems will experience.
So, concluding: there will be a practical limit on how many bits you can transmit with that system, but I'm sure it can make the effectiveness of how we use our available air bandwidth a lot better.
I agree with HuskyDog's next to last statement though: A spread-spectrum technique with a sufficiently wide spreading achieves the same effect and should be capable of achieving the same level of efficiency. It could be though that Larry's chips will be smaller (read:cheaper) than a spread-spectrum chip trying to get the same bandwidth.
And then there is HuskyDog's point about the wide bandwidth antenna's... One of the reasons why occupied bandwidth per channel is limited is the fact that antenna's inherently have a maximum gain dependent on the structure of the antenna (segment sizes etc) and that the more wideband an antenna should be, the larger it gets and/or the lower the signal strength you get from it.
--- Hindsight is 20/20, but walking backwards is not the answer.
Well, maybe it is a form of spread spectrum. Each "trillionth" of a second, the transmitter sends a "pulse". It is either slightly ahead of, or slightly trailing, the timer signal. As it's a "pulse", it *is* a sinusoidal wavefront, comprised of the fundamental, and the third, fifth, seventh (and so on) harmonic.
It looks doable, with a phase-locked loop to tell you whether your signal was leading the timebase (a digital "1") or trailing it (a digital "0"). What I don't understand is why he has to use a "pulse" at all? Why not just phase-0shift modulate a carrier signal?
All the pulses do is splatter harmonics every which way, providing no real benefit. It's not like you receive a "pulse", per se, what you receive is a whole huge pile of very brief signals on a gazillion different frequencies.
Perhaps I don't fully understand this invention, but to me it sure looks like snake oil. Has he ever looked at an FFT of his signal? I think not. I also suspect that, while he may be bright, the inventor hasn't actually studied rf theory.
It's not a hard mistake to make. I did the same myself, years ago, before learning more about fourrier transforms and what they tell us.
Lemon curry?
A guy I know named Cooper Lee used to run a company where this little fact was the sole reason for their profit margin.
The company that he and his grandfather put together, called Tmex, run telecommunications services between the US and Mexico over ATM using Astroterra's (now known as OpticalAccess) LOS products. The beauty of their solution is that by doing this they can hop the border between the US and Mexico without having to pay costly interconnect charges to Telmex (the Mexican telephone monopoly) and whatever US carrier their client is using.
Rather, they just tie in to the local lines in the US and Mexico. They also skirt all the pesky regulations of having to obtain the same frequency spectrum in two countries at one (as would be the case with microwave and other RF technologies).
All this with just a box on top of a Howard Johnson's hotel in the US, and a tower in Mexico 5 miles apart.
-- "I am disrespectful to dirt. Can you not see that I am serious!"
Conspicuously absent in the article is mention of the inherent security of this communications scheme. The low power of the signal combined with a pseudo random sequencer makes this signal virtually indestiguishable from noise. One needs to be within a couple of *feet* to detect a transmitter.
I know the Pentagon/Nat'l security apparatus aren't especially keen to have devices based on this enter the civilian domain very soon. The FCC will surely play a part in regulating the timetable.
As a curious aside, if alien civilizations are using this type of communication or any other which strives to make its signal indistinguishable from noise to anyone but the intended receiver, SETI will never pick them up.
Well, it does say he's been working on it for decades, so some of us have heard of it. Assorted info in the field can be found in aGoogle search "wideband+pulses".
Now we're all gonna have to dip into our pockets so that SETI can add search capabilities for *this*. Man, I wish the aliens would just go rap on G. Dubya's noggin and say "Howdy" instead making us waste all this energy on screensavers that probably are gonna result in jack squat.
Aliens on the brain... And my ass hurts. Hmm.
- Rev.
Note the company's website promotes the idea of police using this stuff for through-wall radar. Remember that thermal imagers have led to people getting arrested because their garage gave off more heat than the cops liked when they drove down the street...
Next people will be getting arrested because the cops saw them leaning over their coffee table too frequently... or maybe in Georgia the cops will use the radar to see some oral-to-body-part contact that happens to be illegal down in the South.
This is a bad thing.
--Rob
Isn't part of the point of this approach that frequency allocation would be unnecessary if everyone used this type of signal? And that the "dirtying" of "other people's" spectrum is not noticable? IOW, the only people who should give a shit are those whose "property" will be devalued by abundance? I'll shed a tear for Time Warner, honest.
Of course, if I read the article correctly, the transmitter and receiver have to be coded to the same random "seed" - the same one that keeps the signal from producing harmful interference - which means that this technology is immediately useful for things like local wireless nets, walkie-talkies, etc. That's a long way from the Ultimate Wireless Solution.
Boss of nothin. Big deal.
Son, go get daddy's hard plastic eyes.
Expanding a vast wasteland since 1996.
What about fractal antennas? I thought those fixed a lot of the problems associated with transmitting/recieving wideband. I haven't heard anything about them recently, but I'm curious what you might have to say about them.
They told me it was impossible to write a virus for win95. We did it before the first beta was released. Impossible is highly overrated.
How we know is more important than what we know.
If that really is Larry, he's lost some hair since the last I saw him. And grown a beard.
---
satire, n: 1) witty language used to convey insults or scorn; 2) a form of humor lost on most slashdot moderators.
Must be different. I'm talking about Andre
I meant that if that really is Larry Fullerton's photo with the article, he's changed a lot since I've seen him last. But then, I've lost a bit off the top myself since he's seen me.
---
satire, n: 1) witty language used to convey insults or scorn; 2) a form of humor lost on most slashdot moderators.
Well, it is possible what he is doing is equivelant to a single-sideband radio, using the phase locked oscillators to reconstruct the signal. This mights justify their low power claims. Doesn't really sound like it to me, though. I should read the whitepaper on their website.
:)
But the fact remains--to resolve 1ps pulses, you need electronics that can handle 1THz. That doesn't seem so likely to me
Not to mention that keeping two physically seperated clocks in lock-step with sub-picosecond accuracy is not exactly easy.
Well, the reason we are running out of spectrum is because high-bandwidth applications take a lot of spectrum.
Now part of the problem is that you always lose some of the spectrum when you divide it into channels finely. Upon further reading on their website, it looks to me like they aren't really going for particularly high bandwidth, but just being able to have many, many channels. After reading a large chunk of their whitepaper, I am skeptical that it is as scalable as they say, but it comes off as a lot more plausable than the articles linked to.
As a bit of historical context, every few years someone comes up with a brand new revolutionary way of dividing up the spectrum into channels that is incredibly efficient. Two that come to mind are CDMA and FHSS (used by cell phones and some wireless lans, respectively). In each case, once they make it to actual production and deployment it turns out they vastly overestimated the number of channels that can work simultaneously without causing severe degredation. I doubt this will be any different.
My best guess for the deadly factor is multi-pathing. While the pulsed nature of the radio should prevent destructive interference that causes cell phone fadeout in doors, it will probably substantially reduce the number of channels they can use before they start causing problems.
- A full duplex 1.3 GHz system with an average output power of 250 microWatts, and a variable data rate of either 39 kbps or 156 kbps. The radio has been tested to beyond 16 kilometers (10 miles).
- A full duplex 1.7 GHz walkie-talkie with an average output power of 2 milliWatts, a data rate of 32 kbps and a range of 900 meters. The unit was also capable of measuring the distance between radios with an accuracy of 3 cm (0.1 ft).
- A simplex 2.0 GHz data link with an effective average output power of 50 microWatts, a data rate of 5 Mbps at bit error rate (BER) of 0 with no forward error correction (FEC) and a range of 10 meters (32 ft) through two walls inside an office building.
Also, their pulses are not remotely square, but gausian monocycles of the form: V=t*e^(-t^2). In addition to low power, they claim that they can do really dense channelization by using different clock sequences -- very similar to the way FHSS works, only by varying the time base, rather than frequency hopping.Another plausable advantage is that since they don't use continious waves, multi-pathing isn't a big problem. The wave packets from the two paths are completely distinguishable, and therefore do not interfere. However, this makes each path look like a seperate transmitter on a different channel. So you sacrifice total bandwidth (by reducing the number of channels availbable) in exchange for reducing fade-out from point of destructive interference.
In any case, anyone interested should check out this whitepaper more info. I doubt this is a scalable as they claim, but they do have some interesting ideas, and the single-chip positioning and radar sounds cool, too.
Not to be a naysayer, but this really isn't that remarkable. In particular, it basically has exactly the same constraints as "normal" frequency domain signals. In particular, it has to take up the same sized region of the spectrum as conventional broadcasting, and all of your electronic components have to work at the same high frequency to resolve data.
If you want to resolve picosecond pulses, you need electronics that can pass frequencies up to 1 THz.
That isn't to say there aren't applications, and I am going to read their whitepapers to see how they get such phenomenally low power usage, even when constrained by the inverse square law, but it isn't a revolutionary technology that is going to eliminate the bandwidth problem.
Short-range transmitters with closely spaced receivers connected by fibers could solve the bandwidth problem, but A) would require massive investment in infrastructure and B) be no better or worse than Bluetooth type proposals using more conventional radio technology.
Check out the ARRL's response to the FCC (including references to the Qualcomm report). A primary concern is:
the broad nature of the interfering signal . . . indicates that any interference would extend to all VHF and UHF amateur bands." That particular report dealt with lab tests to assess the impact of UWB emissions on PCS phones using code division multiple access (CDMA).
Sure UWB gives you more bandwidth... by using other user's licensed frequencies. It's like bragging about how much faster your PC goes when you stealthly sneak distributive processing apps into other PCs without their authorization.
*scoove*
how about s/less weakly/weaker/
-- free as in swatantryam - not soujanyam.
its pronounced doo-mass
-- free as in swatantryam - not soujanyam.
Ultrawideband is not exactly new, I worked on a UWB radar almost 10 years ago. It has promise, but it also has problems that you don't see with traditional carrier based methods- since you are talking about picosecond resolution, communication with a reciever that is moving with respect to your transmitter is hard- in a picosecond, light travels about .3 mm. Virtually any motion can cause your reciever to start looking at the wrong part of the data- since the data is all time-coded.
Many have said that you can't detect UWB, but usually, they are looking at it with a traditional carrier based spectrum analyzer- you can't see it, but it is there. It just looks like additional noise. which looks very similar to spread spectum- which is exactly what UWB is, but you're spreading the spectrum very, very wide- an impulse in the time domain is uniform (all frequencies, equal amplitude) in the frequency domain.
Time domain has been around, and pretty big in the UWB arena for a long time, but most of what they have is vapor- big promises, but they fail to deliver. There are other players in the field, Aetherwire is one of the other biggies of UWB. There has been a huge amount of money poured into UWB, but dreadfully little usable technology.
Why is the above post marked as troll? The poster is right - it's spread spectrum technology. What's new here?
Not quite. The use of an autocorrelated pulse receiver brings many interesting possibilities to the table beyond what DSSS or FHSS can do. You end up with a hell of a lot more process gain, for one thing.
I wish I understood how the correlator synchronizes itself to the desired time sequence... that's the part I've been unable to grok in the last two or three articles that have been published on TD technology.
Dahlmann tightly grips the knife, which he may have no idea how to use, and steps out into the plain.
The LLNL micropower impulse radar site is mostly hype. There's been a lot of loose talk out of LLNL about how this is a great, cheap technology. Actually, it doesn't work very well. The wideband receiver is sensitive to narrowband noise. Despite years of hype, the one application that's actually shipping is from Bindicator, an company which builds the boring, but essential, devices that measure how full a bin, silo, or tank is. The micropower impulse radar thing is great for measuring piles of solids, where you can't use a float. Typically units like this go inside a metal tank or silo, so they're shielded. (Previous technology for doing that job involved units like the Bindicator Mark III Yo-Yo, which lowers a weight until the cable goes slack, then winds it up again. Noncontact methods are a big win.)
The Time Domain's website is timedomain.com (flash plugin required, tho).
If you open yourself to the foo, You and foo become one.
The FCC and other government institutions are always going to have a hand in anything that scatters signal at RF.
My bet is on optical line-of-sight being developed by companies like Terabeam. OK, right now it's expensive technology only practical for corporate customers. So were computers 30 years ago.
The advantage of LOS technology is that there is no shared spectrum, and therefore no legitimate need to regulate. The only people who might want to regulate it are neighborhood associations, for aesthetic reasons. However, most of them have accepted satellite dishes so a well designed optical LOS transceiver should pass also.
Regardless of who or how, the problem will be solved. One day, people will pay only the cost of the transceiver, and they will get free internet, phone, you name it. I told this to my Dad, who owns stock in the phone company and it made him a bit nervous. I told him not to sell yet, but in 20 to 30 years you might not want to be holding stock in any of the companies that sell bandwidth.
For all intensive purposes, "whom" is no longer a word. That begs the question, "who cares"?
The bottom line is that there is a fundamental limit to how much data can pass through a given amount of radio spectrum in a given period of time. Let's say you have 100 MHz of bandwidth available and 100 signal sources each generating enough data to fill 1 MHz of bandwidth. Now, we can divy up the spectrum in several different ways.
The obvious one is to place each source on a different frequency and since each one is 1 MHz wide we can just fit them all in. This is called frequency division multiplexing and its how FM radio works.
Next, we could get each signal to buffer 1 second of data and then transmit it at 100 times normal speed for 1/100th of a second. Increasing the data rate increases the bandwidth so each signal is now 100 MHz wide and uses the entire available spectrum, but if we get them to transmit one after the other we get 100 bursts each 1/100th second long and once again the channel is full. This is called time division multi access (TDMA) and it is how your GSM cellphone works.
Lastly, we can take each signal and mix it with a very high speed pseudo random data stream. The signal gets much wider, but the energy per unit bandwidth goes down. At the other end the received signal is mixed with the same random stream and the original signal re-appears. The maths is complex, but it turns out that if I spread each signal out to fill the 100 MHz then I can just about get them all in without them interfering with each other too much. This is called code division multiple access (CDMA) and is how GPS and 3rd generation cellphones work.
Now for the important bit. As you can see, we have 3 different ways to get 100 signals into out 100 MHz of bandwidth. We can choose any one of them, but we can't choose all three. If our 100MHz is already full of TDMA signals and we put 100 CDMA signals in the same spectrum then they will interfere.
Now, if I have a bandwidth which isn't being fully utilised (suppose for example I have only 10 frequency multilexed signals in my 100 MHz) then I can slip in a few CDMA signals and all will be well, but only a few. If I bung 50 in then the FM signals will start to suffer interference.
What Mr Fullerton has done is basically produced a modified version of CDMA which is spread over a very wide band. The radio spectrum is still not used very efficiently, so there is enough room over that huge bandwidth for quite a few of his transmitters to be fitted in. Provided that their average power is low and there not too close to your receiver. But you don't get something for nothing. He's not using new spectrum, just old spectrum in a different way. We could achieve exactly the same effect by taking conventional CDMA and just making the random bit stream much faster.
Finally, there are costs to his approach which is related to the huge bandwidth and that is making an effecient wideband antenna. As someone who designs antennas for a living I can tell you that making a wideband antenna which is efficient means sacrificing gain or size or both.
Basically you have to hunt around for it a bit.
Its a bit like tuning a radio except you are adjusting the phase not the frequency.
Typically, you have the receiver have an oscillator that is running just a bit slower or faster (just a bit).
That will mean that the phase of the receiver will gradually slide relative to the transmitter. When they finally line up, the filter will light up, then you can adjust the oscillator to match the transmitter speed.
-WolfWithoutAClause
"Gravity is only a theory, not a fact!"IBM is one of Time Domain's chip suppliers. Here's the news release from IBM.
...here's the google cache'd link.
Instead, you enter the "key" which represents the pattern of the time coded signal and your receiver will then be able to decode the transmission being sent. That, or I don't know what I'm talking about. ;)
I'm honestly wondering what applications this might have if, instead of transmitting over the "air" it were to be used as a communications protocol over fiber, coax, etc.
Could this be a means to come up with a super high capacity firewire, usb, SCSI, etc.? Multiple "devices" could listen on the same "cable" for the data intended for it.
(Of course, with its intended application for ultra-high resolution of objects through walls (even better than radar), its most likely first profitable application will be for pr0n.)
...this has a huge potential for wireless communications. Because a chip is needed on both ends of the signal, it's possible with this to send and receive digital data securely between two devices (laptop computers, mobile phones, etc). Since up to 40 million digital pulses can be transmitted per second, this sort of secure communication would be essentially uncrackable.
You see, it's this type of exploration of the strange that results in something quite useful...
What I am curious about is the size of the chips and board and case required for the transmitter and receiver. The article mentions using this to find lost keys (by attaching a transmitter I assume) so I take it that it would be quite small.
Either way, it's hats off to the dude - I always hated it when my teachers told me something was impossible - time to dust off that old time machine in the basement...
I donate all spillover Karma to the charity of my choice... Ada was still a babe despite what people may say...
A lot of production hassles will have to be worked out before these kind of devices become easily mass produced. EEs go through great pains to avoid building anything that will require setting exact frequencies or tuning servo or PLL-style feedback loops. Doing such things in quantity with current mass-produced component tolerances will be difficult. Not that it cannot be worked out, but it adds to the cost.
Second, this sort of tech works really good when you are the only one on the block. Get everybody and all their electronic fodlops to have one of these, and the noise floor goes up. Which means the reliability goes down dramatically.
*whup* "Get along, little electrons. Heeyah!"
Meant to post this to the discussion on genetics... came back and clicked on the wrong thread grrr!
Forgive me, and mod the above down.
(sob!) My precious Karma... =P
-Kasreyn
Kasreyn: Cheerfully playing the part of Devil's Advocate to hairtrigger
It doesn't matter how you share the spectrum - using narrow frequency bands or using uniquely shaped pulses. Amount of information that can be transferred over the same part of the spectrum will be the same. You can try to transfer more, but all you will see is more interference and higher Bit Error Rate.
Code division/ time division (the invention is an extreme case of time division) actually has some advantages over frequency division, but only under moderate to above moderate saturation of the spectrum. Under high saturation, the data rate and error rate degrade even faster than with frequency division.
Sorry, no miracles here. This area is studied very well.
Also worth mentioning, that pulse transmitters will cause a lot of interference with existing systems. They will only live well with each other, but not with narrowband systems. They will give a lot of annoying clicks in your FM radio.
http://www.aetherwire.com/
I've been watching this subject for a couple of years now... The first link I found was at Lawrence Livermore National Laboratory's MIR site, where they have a very similar setup.
Here are a couple of applications:
Cheap radar. These things, since they are spread spectrum, don't interfere with each other and are ideal for watching reflected signals (since you are the sender and know the chirping pattern you used to transmit with)
Complicated imaging. They had some pictures of a larynx -- instead of doing speech recogintion on sound waves, they were doing it by watching the actual parts of the body that move to form the sounds!
Even more complicated imaging. They had a 3-d radar system to detect reinforcement rods in concrete. Pretty neat
The above site also has the FCC rules regulating the transmission (since these are single pulses, not repetitive waves, the FCC isn't sure what to do with them) and LLNL's response. One curious thing about ultra-wide radar is that the frequency response of the antennas themselves are the limiting factor on what frequencies actually get transmitted -- so aftermarket antennas might not be so easy to use since they are a vital part of the circuit.
HIV Crosses Species Barrier... into Muppets
This is pretty old news. Posted April 27, 2000:
y /pulse_technology_000427.html
http://www.space.com/businesstechnology/technolog
The early adopter in me thinks this is wonderful, and can't wait to buy it. Where's the global-access web-surfing PDAs?
The pragmatist in me realizes we won't see this for many years. How long have we waited for Bluetooth?
The Democrat in me thinks this could bring widespread, afordable telecommunications to the masses, and should be encouraged. What's the problem, FCC, why won't you approve this?
The free-market capitalist in me says this could disrupt the established players in the business and should be watched closely. Who should I buy? Who should I short?
The Republican in me says this would disrupt the established players in many businesses and must be stopped. Why isn't the FCC working to ban this subversive activity?
The cynic in me notes who's in charge now. Guess who will win?
If all this should have a reason, we would be the last to know.
The real value of this technology is military use. These signals have an EXTREMELY low probablility of detection/intercept. I don't know that I see any great commercial advantages here (maybe wireless LANs in urban areas where "ghosting" is a problem), but this stuff will probably be appearing in military gear in the near future.
There's no free lunch with spread spectrum signals. They do not magically provide more information carrying capacity, lower probability of intercept or defense against intentional jamming.
All modulation techniques use a set of basis vectors to transmit information. The traditional non-spread sprectrum methods use the frequency, amplitude or phase of a sinusoid as a basis. Spread spectrum methods use "weirder" bases, such as pseudo-random codes. The only real differences between the SS methods and the traditional ones are that the SS bases are highly unlikely to look like "common" interfering signals (carriers, impulse noise, etc.) and that they tend to have a wider bandwidth as well.
"Ultra wideband" is just another spread spectrum technique that uses the time position of pulses as its basis set.
There is only so much bandwidth out there and the amount of data you can send through it is bounded by the Shannon limit which is a function of bandwidth and noise floor. Any signal you transmit, no matter what modulation technique it uses, will interfere with other signals, at the very least by raising the noise floor, and thus lowering the Shannon limit for that section of the spectrum. It may be possible to demonstrate that a few ultra-wideband signals don't interfere with exisitng transmissions, but that certainly won't be the case for a large number of ultra-wideband signals.
The one advantage of ultra-widband is that it has very good time resolution because of the short pulses, and since the speed of light is constant, this equates to very good spatial resolution. Lawrence Livermore Labs was demonstrating something called "micropower impulse radar" (MIR) based on these techniques a number of years ago. This was the gadget that lets you "see" through walls. The range was very short, but it did work. This looks like the best application of ultra-wideband.
I hope the FCC isn't fooled by snake-oil claims of non-interference and unlimited bandwidth. They should not approve ultra-wideband for normal communications use.
God I love people like this. They're told it can't be done, and they obsess until they develop a solution. These are usually the greatest inventions, IMAO, because they shake up the world, and hopefully make people think a bit farther outside of the box.
If god had intended you to be naked, you would have been born that way.
If time domain methods caught on widely, we'd have to partition the space of sequences into different "bands" so that particular users are guaranteed a certain amount of bandwidth. In the end, we'd have replaced our frequency based system with a time domain based system and we'd greatly increase the cost and complexity of even the simplest transmitters. That's a nice deal for shareholders of companies pushing that technology, but it isn't for everybody else.
Maybe eventually, it does make sense to move to time domain systems. But let's make that step deliberately and without believing in the existence of some magical, hitherto undiscovered bandwidth.
...and 25 or 6 to 4?
"Picosecond timing is the key to Larry Fullerton's radio pulse technology..."
Ok, now we need atomic clocks in our cell phones, no danger there.. hehe.
Yeah, The FCC will snatch this up as soon as anyone perfects it ! Isnt it lame, but oh so true ? -- Dan DanCclark.com
Why is this website so kickass ?? Find out for yourself --> Danny D