UWB Wireless Access Could Be Here Soon 82
fluppy88 writes: "802.11b doesn't have anything on UWB. With a potential of 1000M bits/sec it blows the pants out of 802.11b and doesn't eat up the tightly controlled spectrum. This article on CNN gives an interesting introduction to UWB, another candidate in the future of wireless." It was mentioned here a while ago, but much more mired in controversy about whose idea it was. Now there are several companies which seem anxious to get products based on UWB to market -- if it's approved.
And now what... (Score:1)
<a href = "http://www.80211-planet.com/news/article/0,4000,
802.11a 54-100Mb/sec</a>
(the hell with the alphabet's order i guess?
Now my question is, are these "standards" going to be backward compatible like ethernet on a switch or are we going to see technologie switch every 3 months?
Re:oops, correct link. (Score:1)
(damnit, i have to type more text than HTML tag to get past the lameness filter Argh!!)
802.11a 54-100Mb/sec [80211-planet.com]
As Long as... (Score:1)
Hooking up some 70 dollar wireless ethernet cards makes 802 pretty damn cool, even if it is only an 11mbit (compared to 1000) connection.
Re:As Long as... (Score:2, Insightful)
Affects GPS (Score:3, Informative)
I wonder what that means? The FCC is going to kill this quick if it messes with GPS, which is IMO, more important.
All of the subjectivity in (how one defines unacceptable) will probably cause everyone to take a few more years before they start doing anything with this.
Gotta pick one or the other... (Score:4, Interesting)
But there is concern that UWB transmissions, especially for UWB devices that will operate below about 2 GHz, will interfere with other broadcasts. These include the Global Positioning System (GPS), public safety nets, air traffic, marine navigation and communications, AM and FM radio, and television broadcasts, to name just a few.
Where do they get these guys? First he says that it doesn't use any spectrum...then he says that anything below 2 GHz will interfere with existing Nav and Comm systems. Gotta be one or the other. Can't be both.
(BTW pulse transmissions do take up spectrum, even if they don't have a carrier...)
Re:Gotta pick one or the other... (Score:5, Informative)
Where do they get these guys? First he says that it doesn't use any spectrum...then he says that anything below 2 GHz will interfere with existing Nav and Comm systems. Gotta be one or the other. Can't be both.
Yes, it can be both
UWB works by sending single-cycle pulses. The information is carried by when the pulse is transmitted with respect to a reference.
Since there is no carrier, it doesn't affect a specific part of the spectrum. However, since there is no carrier, it affects all parts of the spectrum by adding to the noise floor. That is what the big problem with this technology is and why the FCC is looking so closely at it. The UWB Consortium [uwb.org] has more information.
Personally I don't see a problem with raising the noise floor for this technology because, as I understand it, it raises the floor uniformly and, if I understand this correctly, the actual number of devices transmitting doesn't play into this.
I've been interested in this for a while. Time Domain [time-domain.com] (warning, flash-heavy site) is a company which has been playing with this for a long long time. I was rather skeptical of this when I first heard of it but my opinions on it are changing. Hell even EDN [ednmag.com] had an article on it.
The only thing I don't quite grok is how they can get two devices to have such rock-solid stable time references (we're talking sub-picosecond jitter) without secondary clock transmitters and keep them that way. If anyone out there can help shed some light on it I'd love to hear from you.
Re:Gotta pick one or the other... (Score:2)
Let me get this straight. You "don't mind raising the noise floor for something like this," when it would be affecting GPS, public safety nets, air traffic, marine navigation and communications?
Sure, gotta surf your porn from the bathroom, but if some Cessna commits CFIG (controlled flight into ground) because its pilot thought it was somewhere else, eh, so what.
This is exactly why there is an FCC.
Re:Gotta pick one or the other... (Score:3, Insightful)
Let me get this straight. You "don't mind raising the noise floor for something like this," when it would be affecting GPS, public safety nets, air traffic, marine navigation and communications?
Don't jump to conclusions, you may hurt yourself.
What I was wanting to say (and I am thankful for the number of technical responses) was that I am in favour of UWB for short-range communications. I do not like the idea of spewing out tens of watts (or even watts) of noise. I was thinking more along the lines of replacing the sub-watt communications systems used today for things like cordless phones, wireless mics, R/C cars, wireless keyboards/mice, 802.11[ab] and Bluetooth. I'm very much in favour of freeing up chunks of the spectrum and instead allocating them to better causes or for rather to communications links which can better exist in that spectrum. Yes UWB will raise the noise floor but again, in the miliwatt range and below I think this would be acceptable, but I have not done the studies to verify it.
As far as UWB being used for high speed long range links, I would imagine that the pilot of the Cessna would not be flying across the well-documented and regulated link, and that such a link would use super-directional antennas to avoid the amount of splatter.
Not just the noise floor... (Score:5, Informative)
Yes, it can be both
No it can't.
There is only so much spectrum. The faster you change the signal, the broader the chunk of spectrum you use.
You can use it for a shorter time, and end up with the same time-bandwidth product.
You can control signal intensity more finely to encode more bits, until the ambient noise (or weaker interfering signals) would confuse the decoder.
You can direct your signal so that most of the energy goes toward the receiver rather than spreading out uniformly (though this gets harder as the bandwidth gets wider).
You can restrict its polarization to one of a complimentary pair, leaving the complimentary polarization's half of the spectrum free (or using it for a second or a return signal).
... A radar (with its very directional antenna) will show only a wedge of light in the direction of your transmitter. (Which is how the authorities will find you to shut you down - if they get there before the neighbors with the torches and pitchforks.)
But that's IT.
If two transmitters are hitting a receiver with energy in the same chunk of spectrum they interfere. Spread the actual bits around so they're transmitted redundantly in different parts of the spectrum (not just hop the carrier to put a burst of bits in one chunk and move on) and you might be able to pull them out of some interference. But then you've used up several times as much spectrum in the first place - as have the interfering signals from other users of the same scheme.
UWB works by sending single-cycle pulses. The information is carried by when the pulse is transmitted with respect to a reference.
Since there is no carrier, it doesn't affect a specific part of the spectrum. However, since there is no carrier, it affects all parts of the spectrum by adding to the noise floor. That is what the big problem with this technology is and why the FCC is looking so closely at it. The UWB Consortium [uwb.org] has more information.
This scheme doesn't "not use spectrum". It uses the ENTIRE spectrum - up to the limit of the transmitting equipment. The shorter the pulse (so you can space them more closely and send more bits) the higher the limit. When it talks it steps on EVERYTHING - one pulse, one "POP" in a radio, one fleck of snow on a TV screen, one bright spot on a radar. The has to be above the noise floor itself to be heard - and the "noise floor" includes all those other signals it's interfering with.
If your data rate is low you can keep the signal weak - at the receiver. The pulses spread out their energy over an enromous chunk of bandwidth, so your reciever can measure the energy over the whole specrtum and recover the desired data from the other signals-assuming there is only ONE transmitter using this scheme, of course.
But electromagnetic signals fall off with inverse-square. Near the transmitter you're not just "raising the noise floor". You're generating a continuous lightning bolt.
Want to send data a hundred miles? Imagine you were doing this with VISIBLE light. You're modulating an arc light at your transmitter, bright enough that the output of a solar cell a hundred miles away has more signal from your arc light than from all the other light sources (including any other arc lights) combined. Now imagine somebody on your block trying to read morse-code flashes from a distant colored lightbulb, using his own solar cell and a color filter.
Run a protocol so the radio versions of your "arc lights" take turns and you can run a network. (Think of running "Ethernet" in the real aether.) But that's ALL you'll be able to run. Goodbye TV, goodbye AM and FM radio, goodbye aircraft band, police band, CB,
Meanwhile, just as the time-limited signal of time-domain modulation schemes selectively "punch a hole" in the time distribution of the signals of the frequency-domain modulation services, the frequency-domain modulation signals selectively punch holes in time-domain modulation signals. The "hole" is in the form of pattern sensitivity - selective interference with those bit patterns that correspond to the energy distribution of the frequency-domain signal. Your pulse strength has to be great enough to "shout down" this interfering signal, or those bit patterns just don't go through uncorrupted.
Time-domain and frequency-domain signals don't play well together. And the time-domain kids got to the playground first. Do you want ANOTHER war with broadcast media? Remember, if they lose it's their death, so they'll fight REAL HARD.
You can avoid the war by shaping your pulses so the energy stays in a limited band (at the cost of limiting your data rate correspondingly). But within that band you can only use time-domain schemes. You've "divided the playground". And the smaller the hunk of playground you got, the lower your data rate. Shaping your pulses stretched them out - and you have to move them farther apart to tell them apart at the receiver. How much playground do you think you can get for your gang's exclusive use?
Personally I don't see a problem with raising the noise floor for this technology because, as I understand it, it raises the floor uniformly and, if I understand this correctly, the actual number of devices transmitting doesn't play into this.
Each one of those "arc lights" raises the noise floor - by a bunch. More noise means you can't measure the signal from the desired "arc light" as accurately - which means you get less bits-per-second from it.
The total number of bits-per-second available to ALL transmitters at any given receiving antenna is a constant described by Nyquist: 2 * bandwidth in cycles-per-second * base-2 log of the signal-to-noise ratio.
But the distribution in space of the "raised noise floor" is a face-down morning-glory flower. Like those surfaces where they roll a ball bearing to demonstrate orbits, but upside-down.
Imagine a rubber sheet: You grabbed it at your transmitter and stretched it WAY up - until the sheet at the distant receiver was raised enough that the receiver could detect you yanking. And your neighbor's TV antennas are up on the peak with you. (And so is your network antenna...)
The only thing I don't quite grok is how they can get two devices to have such rock-solid stable time references (we're talking sub-picosecond jitter) without secondary clock transmitters and keep them that way. If anyone out there can help shed some light on it I'd love to hear from you.
You sacrifice a part of your bandwidth to send a pre-defined, typically repetitive, synchronization signal, to keep the receiver synchronized with the transmitter. Think of the start/stop bits on a serial line, the framing bits in T1, T3, or SONET, or the vertical and horizontal sync bars in a TV signal.
The more bandwidth you sacrifice, the faster your receiver's clock syncs up when reception starts. If you're transmitting bursts you can put most of the sync at the start of the burst to get things locked quickly (and identify the signal and its start), then use just enough to keep the receiver locked for the rest of the burst.
Re:Not just the noise floor... (Score:2)
Wow, talk about a technical response! Thank you! Please see my previous comment [slashdot.org] which talks about what I meant by being "in favour" of the technology.
There is only so much spectrum. The faster you change the signal, the broader the chunk of spectrum you use.
Yes of course. This is what I had meant. My thought process was "It doesn't use a specific chunk of the spectrum" rather than "It doesn't take up any space in the spectrum." I apologize for the confusion.
Want to send data a hundred miles? Imagine you were doing this with VISIBLE light. You're modulating an arc light at your transmitter, bright enough that the output of a solar cell a hundred miles away has more signal from your arc light than from all the other light sources (including any other arc lights) combined. Now imagine somebody on your block trying to read morse-code flashes from a distant colored lightbulb, using his own solar cell and a color filter.
This is actually a bad example as light is very directional and unless that arc light is pointed to your neighbour, he should be able to see his coloured light. (perhaps in a haze of white light.)
Run a protocol so the radio versions of your "arc lights" take turns and you can run a network. (Think of running "Ethernet" in the real aether.) But that's ALL you'll be able to run. Goodbye TV, goodbye AM and FM radio, goodbye aircraft band, police band, CB, ...
What about using this technology for all communications. Pie in the sky, yes definately... but would it work any better?
Time-domain and frequency-domain signals don't play well together. And the time-domain kids got to the playground first. Do you want ANOTHER war with broadcast media? Remember, if they lose it's their death, so they'll fight REAL HARD.
You mean Frequency Domain, no? :-) But yes, I see what you are saying and this is the single biggest threat to UWB -- being shut down because of the interference.
Each one of those "arc lights" raises the noise floor - by a bunch. More noise means you can't measure the signal from the desired "arc light" as accurately - which means you get less bits-per-second from it.
As I'd stated in the message I posted at the start of this reply, I was only in favour for low-power applications: PANs basically. I don't seriously think you can get an antenna with enough dynamic range to effictively limit the splatter of a long-range signal. As you said, you can have speed, but it costs bandwidth. And wide-bandwidth antennae are hard to design.
You sacrifice a part of your bandwidth to send a pre-defined, typically repetitive, synchronization signal, to keep the receiver synchronized with the transmitter. Think of the start/stop bits on a serial line, the framing bits in T1, T3, or SONET, or the vertical and horizontal sync bars in a TV signal.
Ahh yes, this would work perfectly. I had not thought of that... (the most obvious answer of course.)
Thanks for that lengthy response. I see from my comment history that I did not make myself clear enough; my mistake but I am sort of glad I did. I got some really great responses. :-)
Re:Not just the noise floor... (Score:2)
This is actually a bad example as light is very directional and unless that arc light is pointed to your neighbour, he should be able to see his coloured light. (perhaps in a haze of white light.)
What I had in mind was an arc light without a reflector. A bare gas-discharge lamp or a pair of carbon rods at the top of a pole.
Don't stand under it, epsecially the latter, unless you want a sunburn. Don't look if you don't want to burn out your own personal "light detectors". B-)
What about using this technology for all communications. Pie in the sky, yes definately... but would it work any better?
Switch everything over to this technology and it works. But you end up with the same amount of communication as if you didn't switch. And if you want simultaneous transmissions rather than taking turns you still end up with a hybrid where you pulse-shape to band limit and have to assign channels.
You mean Frequency Domain, no?
I mean Frequency Domain, yes. B-)
Re:Not just the noise floor... (Score:2)
This is actually a bad example as light is very directional and unless that arc light is pointed to your neighbour, he should be able to see his coloured light. (perhaps in a haze of white light.)
What I had in mind was an arc light without a reflector. A bare gas-discharge lamp or a pair of carbon rods at the top of a pole.
Oh, yes. And no telescope reflector, focusing lens, or directional light shade on the solar cell, either. (I was making an analogy to omnidirectional antennas on both ends of the link.)
Re:Gotta pick one or the other... (Score:1)
EM energy will have a spectrum. It always takes
up space (pretty much by definition -- sort of
like saying matter has mass). Any opinion
otherwise requires a redefinition of one or
another of the terms, i.e., marketspeak.
And I doubt the noise floor is raised uniformly
(that's really bulky and expensive) -- just using
cheap pulses is a lot like using a PC with no
shielding or case. And the number of such items
does affect the total noise (not quite linear,
but nearly, if I remember my physics courses back
in the 60's). And reradiation is rarely as
broadband as the incident radiation, so in the
real world we may see things like FM radios that
generate FM band noise internally (not good).
I would like to see more information on the actual
tests done in Austin before I am convinced.
Intel (Score:3, Informative)
And not inly in the US. (Score:3, Interesting)
This is not unimportant. Prices drop and rapid adoption increases when a standard is worldwide (like 802.11b on 2.4 GHz).
The 5 GHz equivalent of 802.11b (.a) will be approved at the world radio freqeuency conference in 2003 (light speed for governments) - and I was already told by the British govt Radio Agency [radio.gov.uk]
that the UK frequency will differ slightly from the US frequency. And that the 5 GHz standard wil be approved for commercial use (unlike the current 2.4 GHz standard).
That's just for one country, the UK. Imagine when all others (Japan, Europe, etc) also get in on the act. Result: nothing moves.
So, nice as all these new 'standards' are, I am afraid they will slow down wireless adoption.
TANSTAAFL (Score:2)
Re:TANSTAAFL (Score:2)
There ain't no such thing as a free lunch.
The analogy doesn't work for me either. Car exhaust diffuses over large areas where it can add to the general level of pollution produced by all the other cars in that area. If this is limited in power so that it naturally dissipates after 150 feet, then the potential to build up RF noise would seem rather limited since it's unlikely for there to be too many other transmitters in that area. (I realize the article says you could go to higher power, but that's what the FCC is there for to make sure it doesn't cause too many problems, right?)
Besides are you looking for patterns in the static on your TV or what? It's not like most of us are interested in listening to our Pentium chips. Before you get upset, could you mind showing me why this source of RF noise is going to be especially bad? Afterall if we want new types of RF applications then we have to take spectrum from somewhere. Stuff that isn't being used right now seems a good place to start.
Re:TANSTAAFL (Score:1)
Extraneous RF noise is bad. Air, light, and noise pollution are bad. RF noise is just as bad to the RF spectrum as those are to the "human spectrum". If it causes interference with other legitimate uses, such as GPS and cell phones, then it is polluting the RF spectrum. Either use an area that is not in use, or fix it so it does not cause interference.
Of coure, if it were to interfere enough with cell phones, and still be approved, I might just have to get one in my house. Want to drive pst, my house? Get off the damned phone!
Re:TANSTAAFL (Score:1)
Just an observation from a non-too-keen-on-radio-stuff geekoid.
Re:TANSTAAFL (Score:2)
Re:TANSTAAFL (Score:2)
In a respect, UWB seems to be a clever marketing way to steal other people's licensed frequencies.
Get your own frequency or play above 6 GHz, time domain...
*scoove*
Interference? (Score:2)
Anyone know what kind of fault tolerance is built into this thing? How do they deal with the interference that's already there?
I smell several contradictions. (Score:1)
For one thing, because UWB pulses don't actually use a traditional radio signal, called a carrier, UWB transmissions don't take up any of the radio spectrum.
Third, because UWB operates in the electronic "noise" area of the spectrum, it requires little power.
So, it's just like a regular spread spectrum technology. Yay, let's everyone use this! We'll just add loads of background noise to wherevere we use this technology. "We're not using any radio spectrum" is pure bollocks. Of course they are using it, just for an extremely wide range of frequencies, so it seems like background noise. Fine as long as you only have one or two transmitters. How do you think it would work with existing system when there are many more users?
I just find it strange that CNN buys the hype.
SETI? (Score:2)
I know this is not the most practical question, but I have been wondering for a while whether it would is possible to do a Search for ExtraTerristrial Intelligence (or a sky survey for whatever reason) for ultrawide band signals. I've heard that it is very difficult to detect UWB if you don't know exactly what you're looking for, but perhaps someone who knows a lot about ultrawideband could comment on its general detectability.
Re:SETI? (Score:1)
Deploying UWB signals here on earth will be really bad for SETI. It will cause interference in the protected bands where the various projects are looking for very weak signals.
Re:SETI? (Score:2)
Perhaps aliens would figure a way around, or wouldn't care about the distance restrictions, and would thus use really powerful transmitters with this tech. I suppose they could aim a beam at us, but why do that when carrier beams are easier to direct and if they are listening to us, they know it's what we've been using.
In any case, space is big and the signal would be weakened. Now I ask you, how much time do you want to spend looking for a signal that looks like noise? Looking for a signal in your noise doesn't seem highly profitable when you have a limited budget, no idea where in the noise to look, and hope for an obvious signal somewhere else.
Whats the point though... (Score:1)
Re:Whats the point though... (Score:2)
Re:Whats the point though... (Score:2)
What about the "typical" home user who buys an iMac and wants to transfer some of those neat home-edited videos from one computer to another?
Simple laws of computing: you can never have enough RAM, storage, CPU power or bandwidth.
Data is like a gas -- it expands to fill all available space.
Re:Whats the point though... (Score:1)
Yes. I fully understand the more is better theory. I live by it. But my point is, I could have 10000000gb
Re:Whats the point though... (Score:2)
Transfer video from my camcorder to a T.V. without having to jack it. Watch my DVDs/videos without having to run wires.
Having a security camera with a good resolution by the front door would be nice -- without having to run coax.
Watch "cable" TV with the portable TV out on the deck. Have a TV in every room without having to run cables everywhere.
It would also do the same for sound -- allowing me speakers in every room without a wiring nightmare.
Freedom from wires.
Another article in Network World (Score:1)
http://www.nwfusion.com/news/2001/0827specialfo
Re: (Score:2)
Tell me this isn't true... (Score:5, Funny)
50 to 70 milliwatts is one ten-thousandth the power of a cell phone? That would place an average cell phone at somewhere around 600W.
Strange, I don't remember seeing huge heatsinks and 12" fans on any cell phones lately.
Re:Tell me this isn't true... (Score:1)
Considering the credibility of all the claims these guys make, at least some of them must have had their head too close to one in the past.
Re:Tell me this isn't true... (Score:1)
600W at 1.9 GHz? Could be fun to put that into a 24dBi gain antenna and see how much smoke we could create in our neighbor's houses...
Re:Tell me this isn't true... (Score:2)
My sister has a 5W bag phone -- it's the only thing that will work in Cleveland Co. (NC) as 360 only has (had) one tower just off US74 in the corner of what used to be the Wal-mart parking lot. There's now a tower in Falston (of all the places!) beside the Community Mart at the intersection of NC18 and NC182 ("the stop light")
Re:Tell me this isn't true... (Score:2)
Re:Tell me this isn't true... (Score:1)
bash$ units "70 * 10000 milliwatts" watts
* 700
/ 0.0014285714
Or if you want it more directly since you suck at math...
bash$ units "700 watts" "1/10000 milliwatts"
reciprocal conversion
* 0.014285714
/ 70
Re:Tell me this isn't true... (Score:1)
Highly secure? Sure... (Score:2)
Okay, here's my question then. If it is so difficult to distinguish the pulse signal from ambient noise, how would one device be able to hear the other device? The whole security problem with 802.11 was the fact that the card could be put into a packet dumping mode that allowed users to view the raw packets, which would then allow them to brute force crack the encryption within meer hours. No other special equipment is needed. So as long as the cards allow promiscuous mode, filtering out the signal from ambient noise is not a problem. All you really need to concentrate on is breaking the encryption scheme. Hopefully they come up with a better method than 802.11 has.
Re:Highly secure? Sure... (Score:2)
The same way spread-spectrum "hides" itself. Unless you know the sequence used in modulating it, you'll have trouble even detecting that there is a signal (and not just noise) much less decoding it.
Assume for the sake of discussion that pulse-position modulation is being used. Typical pulses are around 200ps (picoseconds) in duration. If we have an average pulse repetition rate of 200ns, that's a .2ns pulse followed by, say, 10ns
to 390ns of silence.
Unless you know where the next pulse is to
appear, you won't be able to distinguish a
real pulse from noise that looks like a pulse.
In other words, a synchronized receiver can be
1000 times more sensitive.
If you only transmit at a few times the
necessary power, an attacker will be unable
to distinguish your signal from background
noise (unless he has managed to place his
receiver much closer and thus receive hundreds
of times more power than the desired receiver).
He'll see dozens or hundreds of noise pulses
for every signal pulse; he'll have no way to sync up with your signal.
Now, you might object that a pulse doesn't look like noise at the same amplitude, and this is indeed the case. But any advantage an attacker might gain by "knowing what to look for" in terms of the pulse spectrum can also be used to make the intended receiver more sensitive. In fact, this adds another way to add security -- an attacker who doesn't know the exact pulse shape he's looking for is put at further disadvantage. In addition, timing accuracy much smaller than the 200ps pulse width -- perhaps 10ps or less -- can be required to detect a pulse by its shape, allowing many more possible positions for the pulse, which in turn can be made so weak that it cannot be detected unless its shape and timing are known to that accuracy. Thus the receiver might have another 10 or 100 to one advantage, perhaps 100,000 to one overall.
Of course, the same techniques that are used in cryptography (which this is really an extention of) can be used to brute-force (or perhaps crack more intelligently) the encoding sequence -- the attacher can just try one sequence after another, varying the timing, until one "matches" and a stream of recognizable pulses emerge. But becuase of the time element, this can be much harder than straight cryptography . And cryptographic techniques can be used to strengthen it.
This is all a bit of a simplification, and the numbers are there for the sake of example. But you should be able to see some of the basic issues involved, here (including why you might want to be very careful how you place your transmitting antenna if an attacker may be in the area).
Re:Highly secure? Sure... (Score:1)
They could make cards that didn't have a promiscuous mode, but at the end of the day, you could create a receiver and decoder yourself to defeat that since it's all just blips in the spectrum. If the receiver can hear it and it's transmitted unidirectionally it's crazy to think that no one else could hear it.
This whole thing sounds like a marketing droid cooked it up.
OFDM? (Score:3, Interesting)
I wasn't one of the engineers working on it (I was actually a high school co-op who worked on higher-level code in the same dept), so some of my facts may be off. 802.11a (or at least the variant we were working on) used a modulation scheme called OFDM. OFDM was "invented" in the 1960s if I remember, but the technology is finally catching up with the math to allow for mass production and the data precision required in the algorithm.
OFDM would fit with the articles blurb about it being in the "noise" area. Basically, a baseband signal is multiplexed into multiple low-power subcarriers, which are aligned in such a way that the intersymbol/intercarrier interference (ISI/ICI) is minimized. Basically, this means orthangonally (at 90 deg angles), so that the peak distabution of one carrier occurs at the zero points of the carriers on either side of it. So it's a particulary advanced form of FDM. All that low power shit comes from this fact, and that the nature of noise is amplitude-related, not frequency related. Plus, data interleaving and error detection coding (described below) goes on during baseband processing I think. I forget the symbol length and all that in detail crap, but there is QAM coding and FFTs/IFFTs going on in the process. (I remember 64-QAM being a popular initial choice.) Error correction/detection might be left open in the specs (i.e. it could be this or that), but the one I was familiar using was reed-soloman (a convolutional encoding method used with CDroms) and/or turbocoding (a very advanced convolutional encoding method which gets pretty close to the limit imposed by the Shannon theorem).
OFDM has been defined as packing the data as close as physics will allow, and it whoops 802.11b in both range and bandwidth. I think it will be both in the 2GHz and the 5.4GHz bands.
Sounds exciting. The race is on.
I have seen a good intro paper on OFDM before, but I lost the URL, here is a more indepth one on it: http://www.eng.jcu.edu.au/eric/thesis/Thesis.htm
Sorry about the spelling, I'm not using a spell checker.
Re:OFDM? (Score:1)
Robby
There are really no free lunches (Score:1)
First of all, I'd like to say that I'm not a radio engineer. However it seems to me that with any device intended for communications there are just two options:
The conclusion from this is that one cannot have an endless number of channels. And wherever there's a limit, it will be reached, since spectrum is expensive and people will like more channels for less. So I don't think we have a panacea here.
Hard drive (Score:1)
All I need now is a hard drive that will do that.
This is simply Spread Spectrum radio (Score:5, Informative)
UWB is a clever form of spread spectrum technology. Spread spectrum (SS) is defined as any radio communications system in which the occupied bandwidth is much wider than the baseband (information rate) signal. The most common forms of SS include FM broadcast radio, where 200kHz is used to transmit about 50kHz of signal, and CDMA - cellular phone spread spectrum invented by Qualcomm. Spread spectrum was actually invented by the actress Heddy Lamar for use during World War II and was used for secure communications between Roosevelt and Churchill.
Spread spectrum has a parameter called "spreading gain" which is the ratio (expressed in DB) of the occupied bandwidth to the baseband signal. UWB is a form of spread spectrum with an extremely high spreading gain - it occupies a whole lot of spectrum (contrary to some claims) to transmit a relatively small amount of information. However, because the signal is spread over a very wide frequency range, very little signal is required on any given frequency (or technically, in any given narrowband channel). Thus the signal appears to ordinary receivers as an increase in background noise, and under most circumstances will not do so in a noticeable way.
Traditional spread spectrum uses one of two modulation techniques to mix the information signal with a spreading signal: direct sequence (DSS) and frequency hopping (FH).
Direct sequence uses a bandwidth constrained random noise generator (typically a pseudo-random digital bit stream) and multiplies the baseband signal by this. It is also band limited, either/or by filters or the spectral characteristics of the pseudo-random noise. DSS is used in CDMA cellular phones.
Frequency hopping involves moving the carrier frequency frequenly, typically in a pseudo-random manner. In fact, usually the frequency changes a number of times for each bit transmitted.
Both techniques allow reception of the transmitted information by synchronous detection - the spreading signal is duplicated in the receiver, and used to recover the baseband signal. In the case of DSS, you generate a precisely timed replica of the transmitter's pseudo-random sequence, and multiply it by the input from the antenna (or in the intermediate frequency stages - dependinng on receiver design). Low pass filtering (integration) of the output yields the original signal.
Spread spectrum systems have some or all of the following characteristics:
To get back to UWB, it uses very narrow pulses as its spreading signal. The Fourier spectrum of a very narrow pulse shows a very flat distribution of energy over a very wide bandwidth. In this sense, UWB is spread spectrum. Likewise, it recovers the signal in a similar manner as other spread spectrum signals - it uses a regenerated narrow band pulse to synchronously sample (a form of multiplication) the radio spectrum, thus recovering the original pulse (minus pulse spreading caused by reflections and frequency dispersion).
AFAIK one could duplicate the behavior of a UWB system by using an extremely wide band direct sequence system. It would provide the precise ranging, see-through wall radar characteristics. It would have the low detectability. It would have the low interference to narrower-band signals. However, the UWB system appears to be much easier and inexpensive to build.
Re:This is simply Spread Spectrum radio (Score:2, Informative)
Help from a physicist? (Score:2)
There seems to be a lot of confusion about how this works. I actually don't have a clue either, but based on the little bit in the article I can speculate. Perhaps a real physicist can correct me:
A pulse in "frequency space" (thinking back to Fourier transforms) is actually composed of an infinite number of frequencies. In other words, to produce a square wave (a pulse) you have to add together a ton of sine waves at different frequencies. The more sine waves you add together, the better your approximation of the pulse. Going the other way, a pulse can be decomposed into sine waves in an analogous fashion.
So, an EM pulse would actually have some effect right accross the radio spectrum (hence the name "Ultra-Wide"), but could properly be said to not use any particular portion of the spectrum.
Is this at all correct? If so, then wouldn't a bunch of these devices pretty much screw up all other forms of radio?
Re:Help from a physicist? (Score:2)
But send MULTIPLE pulses to transmit information and it starts adding up at some frequences and canceling at others. The more redundant the information, the more concentrated the concentrations.
(Tuned receivers integrate their input over a significant time, so they add up energy from multiple pulses so that certain pulse combinations amount to a much stronger interfering signal than the energy distribution from one pulse would appear to produce.)
You can try to randomize your energy distribution by scrambling with an unrelated function. But that just makes the concentrations intermittent in time.
UWB and all that (Score:2)
The FCC has decided to regulate this by limiting unlicensed impulse devices to 2GHz and up, and mandating very low power levels. (The ground-penetrating radar devices need to work below 2GHz, so the FCC required them to have a "pointing downward" interlock switch.) So this is going to be a short-range technology.
Interference works both ways. The FCC is only concerned about unlicensed UWB devices interfering with other uses. It's the UWB manufacturer's problem to deal with interference on the receiver side. This is hard, given that these things suck up a huge chunk of spectrum. The receiver is a spread-spectrum device, with processing gain, but ignoring powerful signals anywhere within the band may be a problem.
The LLNL impulse radar systems were of very limited use for this reason. The one real product from that research is Bindicator's level indicator [bindicator.com] used in grain silos and similar tanks. The LLNL technology seems to work best inside RF-shielded spaces.
So far, all successful applications of this technology are low-bandwidth. Getting high bandwidth in a noisy RF environment is hard. I suspect this is going to be one of those "up to" technologies; sometimes, in some places, you get really good bandwidth. But most of the time you don't.
I swear that there is a conspiracy. (Score:2)
Who's paying who not to give publicity to the (low) throughput of Bluetooth? I understand that people who have bought into it have adopted this marketing strategy of pushing it's features and not it's speed, but does the media have to buy into this strategy. I've seen hundreds of articles mention Bluetooth, and I've only ever seen one mention it's speed. (That was on the register, so it hardly counts as mainstream.) This especially bothers me since as far as I can tell there's nothing that Bluetooth can do that couldn't be implemented with fancy software (except for that whole low power thing...), and from what I've heard (I've never been able to get a Bluetooth device close enough to any 802.11 equipment to find out for myself) Bluetooth and 802.11 don't play nicely with each other.
Re:I swear that there is a conspiracy. (Score:1)
Re:I swear that there is a conspiracy. (Score:1)
UWB defies standard spectrum management (Score:2, Informative)
The important questions is how potential victim receivers will cope with an aggregate of many UWB emitters operating at the same time. If this technology is widely adopted, will there be an aggregate noise effect that is significant? Much work has already been done to cope with the noise properties of microwave ovens, which are centered at 2.45 GHz. See this report [bldrdoc.gov], p. 48 of the pdf. The large hump near 2.45 GHz is due to emissions from microwave ovens, and is measurable anywhere there is a sizable population (town > 20,000 people) in the U.S. Microwave ovens are very different than UWB devices -- they emit several orders of magnitude more power, and are bandwidth limited, but there are many technologies that operate within this band despite their emissions (802.11b is one of them). These technologies were designed specifically to operate in the noise environment generated by microwave ovens, and the band itself is designated to be a kind of "free for all" frequency range known as an ISM (Industrial, Scientific and Medical) band. Existing receivers in the bands where UWB devices produce emissions were not designed in such a manner.
Nevertheless, the potential increase in communication capacity offered by UWB devices demands that it be scrutinized for interoperability with these existing receivers, and given a chance to fulfill its promise.
What about price? (Score:1)
The article mentions "potentially lower costs" but doesn't give any target prices or rationale for why the costs would be lower.
The next gen 802.11 (the .a spec) will run at over 50Mb/sec, at prices
not that much higher than the original 802.11b services. Who's going to
pay for a mere 2x improvement in an untested technology unless the costs
are very significantly lower?
allocation and interference (Score:2)
Either way, the capacity is limited, and either way, as you allocate resources to one way of transmitting data, you create interference for the other way. In small numbers, UWB interference will be largely unnoticeable, but if it caches on as widely as its proponents claim it will, it may drown out traditional frequency based allocations. You get a situation roughly analogous to the interference problems between Bluetooth and 802.11.
I think UWB is basically an attempt to circumvent current frequency-based allocation schemes, and to replace our cheap, non-proprietary frequency-based infrastructure with a proprietary, patented, and more costly sequence-based scheme. Once millions of these devices are deployed and we are starting to see interference, manufacturers will whine and complain that they can't be banned anymore because the economic cost is too high.
In short, let's not fall into that trap. We already have spread spectrum technologies that are more sophisticated: they limited transmissions not only by sequence but also to a given, allocated frequency band. That works fine. We don't need UWB, and adopting UWB now would probably lead to bigger problems down the road.
You can't get something for nothing (Score:2)
UWB as a communication method depends on the time position of signals, which can be severely affected by the motion of the transmitter or reciever, especially if it is accelerating or decellerating. Traditional modulation techniques can and will be affected by UWB, though in many cases, it may just raise the noise floor.
The biggest problem with UWB right now is that it is a political football. The established users of the spectrum want to protect their "territory" from all threats, real and imagined. From what I've seen the reasoning is very much "It's different, so it must be BAD." In truth, UWB is another form of modulation. Just like FM has advantages (and disadvantages) in comparison to AM, so will we view UWB in the years to come.
Some day it will be used- it won't revolutionize communications, but it may give us a little more efficient use of spectrum- Like Turbo codes and the like, they give us an incremental increase in what we can do. Claude Shannon's "Limit" [bell-labs.com] still holds and puts bounds on what we can do.