Coming Soon: Ultra Wide Band

JScarpace writes: "Robert X. Cringely has a new article in which he talks about Ultra Wide Band (UWB), a new wireless communications technology which may allow wireless networking speeds up to a gigabit per second. Read the article."

Comments

of course....

[fluxrad]

if you have a 48" waist...this technology has been out for years.

Why didn't he mention...

[zoid.com]

TimeDomain? They are the leader in the UWB development and hold a bunch of key patents.

http://www.timedomain.com/

Cheers!

more info

[Syre]

Here's a FAQ from the Ultra Wideband Working Group.

It's not clear that it will be allowed to be deployed widely, since it may in fact interfere with the spectrum allocated for other uses. As the U.S. Governmetn's Ultrawideband (UWB) Signal Characterization Project says:

Many claims have been made that UWB communication transmitters can effectively share spectrum with existing users. Some of these claims have not been independently verified.

We'll have to wait and see...

Re:Positioning

[chill]

More likely UWB will compliment GPS nicely. GPS will be used for wilderness, nautical and aviation. UWB will be used to supplement GPS by giving much more accurate measurements in the urban and sub-urban areas -- where 80% of the population lives.

+/- 6 meters isn't good enough for things like parking cars; locating stores/kids in malls; densely populated areas and it really sucks for vertical distances. Yes, differential GPS with ground stations really helps, but UWB could make location-based information and services pervasive.

UWB has a lot of potential.

Seti Etc.

[Alien54]

The biggest losers, though, would appear to be the radio astronomers. Just as the light pollution from street lamps made work harder for astronomers with optical telescopes, UWB will raise the noise threshold for the radio astronomers.

Not only that, but what if all of the Alien Civilizations are already using the equivalent of UWB for all of their interstellar communication? This is going to be really hard for SETI to deal with.

;-)

Re:Security, not bandwidth

[hpa]

because its broad frequency range includes the ultra-low frequencies used to communicate with submerged submarines, UWB can be used easily in buildings and even underground.

Bullshit.

There is so little bandwidth in those low frequencies that you can hardly talk about "ultrawideband"! If it wasn't clear that he doesn't know what he was talking about beforehand, that statement should have made it clear.

"Ultrawideband" is really not anything other than a marketing name for direct-sequence spread spectrum (DSSS). It has been rebranded in no small part in order to attempt to get the FCC and similar regulatory agencies to allow it to be spread across already allocated radio bands (where they become part of the noise floor) rather than confined in between narrowband applications.

All of this really isn't anything particularly earth-shattering. The standard electromagnetic spectrum frequency domainis given by a Fourier transform of the electromagnetic wave using sine waves as base functions. Spread-spectrum technologies simply create a new "frequency domain" use a different set of base functions. They are resistant to interference or jamming only because most sources of interference or jamming operates in the standard frequency domain, not in the "alternate" one. 802.11b actually uses direct-sequence spread spectrum (spread across a fairly wide 2.4 GHz band officially used for industrial applications and microwave ovens) already -- the security added by DSSS is automatically removed by the fact that you can buy 802.11b-compatible waveform correlators for a few hundred dollars at any electronics store. Sorry guys, you still need encryption.

Re:*That* was interesting

[Mike Monett]

>I have questions though:

>- Can an enthusiast make one of these "impossibly cheap" devices?

Yes. Schematics and parts are readily available.

>- Are as the article suggests these devices really going to take off within the next year or will they be suppressed as the article suggests other technologies will be.

There is a patent conflict. Thoma McEwan of Lawrence Livermore Labs copied Time Domain's ideas and patented them. Manufacturer's will face litigation expense and could end up paying royalties on both.

>- Is it really that resistant to interference? We're using so many frequencies at one time, can they really not clash?

Yes. Spread Spectrum works now by switching frequencies in a pseudorandom sequence. Receivers that are not on the same sequence cannot hear the transmission.

UWB works on the same principle except it uses time slots instead of frequency slots. Receivers that are not on the same time sequence cannot hear the transmission. As mentioned, UWB is highly secure and difficult to detect for this reason.

>- Will it interfere with traditional radio signals? I.e, it seems to clobber other reserved EM frequencies to make use of high bandwidth. Would this mess up our telly or radio?

Probably, but only if the transmitter is very close (several feet) and you are trying to listen to a very weak signal.

If many transmitters are in use nearby, it may affect GPS by raising the general noise level. GPS works on very weak signals.

- Does anyone have experience to say whether this stuff is really as good as it proclaims to be?

A lot of people have worked on it with good results. Yes, it works.

The antennas have to be specially designed for broadband. They may be larger than practical for handheld phones, but fractal antennas may reduce the size.

- Finally, there must be more downsides than just messing up radio astronomers

It can raise the general background noise level and affect reception of weak signals. However, in an urban environment, there are plenty of signals that already raise the noise level. Radiation from Local oscillators in superhet receivers (probably hundreds of thousands used at different frequencies), cellular phones and other mobile transmitters (this really is bad for radio astronomy), industrial process like arc welding and power conversion, motor starting transients, automobile ignition noise, temperature controllers using bimetallic sensors, light switches, ad infinitum.

Electrical noise pollution is a part of modern society. The noise added by UWB may well be lost in the background noise that already exists.

Mike Monett
mrmonett@yahoo.com

Re:I Think I'm Missing Something

[Kwil]

I'm no engineer, but what little reading on it I've done suggests it works like this:

Think about your normal physical line. It sends data in a sequential form.. first a 1, then a 0 , then a 1, then a 0 and so on. Now admitted, it does this ridiculously fast but it's still sequential. (This is a huge simplification, btw, but it's the general gist)

Now UWB is using a whole bunch of frequencies to send those ones and zeros, but each frequency carres a different bit. So the first frequency carries a 0, the second carries a 0, the third carries a 1, the fourth carries another 1, and so on. The trick is, it sends these all at the same time and it's up to the receiver to not only know exactly WHEN those frequencies will be carrying information to it, but put them together into the proper sequence of bits.

It's the difference between getting hit by a steady, narrow stream of water, and getting hit by a single tidal wave. They'll both get you wet, but one will do it a lot faster.

So that's the faster.

The cheaper is that a physical line requires a way to code and decode the information and.. well.. a physical line. Which means you have to pay for the line, you have to pay for running line through cities and into people's houses, you have to pay for when a bad weatherstorm comes and a tree busts the line, you have to pay licensing fees to lay all this line, etc.

UWB requires a more sophisticated coder and decoder, but since it doesn't require a line and microchips are so cheap these days, this comes out to be a much lower cost - especially if the FCC lets it go unregulated.

Now as to how it avoids interfering with each other, I really don't know, because if you have enough of these devices, you would think that sooner or later *some* of them in the same area will be sending at the same time.

School Glue GEL

[Graymalkin]

Ultra wide band communication isn't so damn fancy conceptually. The problem is is practically difficult. It works on the same principals as regular sized band radio transmission with the small difference of not splitting the band into channels. Channels are just time slots you set your transciever to listen to or send on which arej ust portions of a band. With UWB there's no channel designations so reception and transmission frequencies can be all over the specified band. It sounds like a good idea because there are not channels to occupy or share with others and your beeps all over a band can be construed as static rather than interference. A random beep in the middle of a frequency used for aviation radio isn't going to crash a plane as it is catagorized as static.

The problem with implimenting UWB is getting the electronics to move fast enough. In order for me to send lets say my voice over UWB I need electronics in my transmitter that can switch really quickly between enough frequencies in order to give me the aggregate bandwidth to send my voice signal. Easy you say modern CDMA cells phones already do that. Granted they make the most of their radio spectrum by splitting up data over the entire band but they are splitting up big chunks of data over a limited band. UWB transceivers will have to switch fast enough where a single radio blip might only be half a word or a quarter of a word and switch over a much higher range of frequencies.

In order to have a gigabit of bandwidth your transceiver would have to switch frequencies in excess of a billion times a second (not merely transmit at a billion hertz). It takes x electronic clock cycles to switch the electronics to switch frequencies you'd have to have electronics working at xgigahertz in order to send a gigabit of data. In a handheld unit? Not likely in the next couple years no matter how fast microprocessors get. Companies have just recently been able to build circuits that can switch at 10GHz it will still be a little while before actual logical circuits can be mass produced and run on batteries. Handheld devices are going to have the same amount of information throughput as they have now even if the radio band they work on is a good portion of the radio spectrum. There is alot of engineering left before UWB is really a viable solution to any problem but it is still a cool concept and I hope these problems get worked out sooner than later.

Re:School Glue GEL

[Graymalkin]

You make a good point about antennas which I didn't mention but is very pertienent because not all antennas send or receiver well at all frequencies. The sky high expectations of UWB technologies providing gigabit upon gigabit of data throughput is a bit ridiculous when you figure in the actual physics of the system. UWB is most effective when you use predetermined bands but widen them considerably over conventional channel arrangement techniques. This limits the amount of interference a prevelance of these devices WOULD actually make. It would be rare for a handful of devices ever to send enough bit pulses to cause perceptable interference in electrical equipment but millions and millions of devices all doing the same thing will statistically cause enough interference on one band that narrowband equipment or electrical devices will register it and it will cause problems. Cringly also talks about antennas that need no tuning, millions of tiny antennas all broadcasting radio pulses with no concern for tuning out harmonics is a crappy idea.

As for 2.4GHz phones being made from 1.9GHz parts that is mostly due to the similar antenna and electrical requirements of transmitting on the two different bands. The phones are also operating under the same principals so they have the same bandwidth requirements whether they are transmitting on 2.4 or 1.9GHz. The digitalized voice signal needs a certain amount of throuput no matter what frequency it is eventually transmitted over. Adapting current technologies for UWB is a bit more difficult because it requires VERY high precision electronics in order to make the whole thing feasible. A PCS or GSM cell phone can miss out on a small chunk of data without the phone HCF. An UWB receiver needs to have pretty incredible reception and timing characteristics because the natual SN ratio is just enormously high. I think we're still several years away from marketable products using UWB.

Re:School Glue GEL

[BeBoxer]

I was going to mod the parent down, but I figured it is better to correct misinformation. You need to go read up on how UWB actually works. It absolutely does not require the transmitter to "switch frequencies". It does not attempt to transmit a little bit of information on lots of different frequencies. Rather, it transmits little bits of information on all frequencies at once. Doing this is not hard. Rather, it is trivial.

You see, in many ways UWB is just like the very first radio tranmissions. The first radios were "spark gap" transmitters, which basically generated RF by creating a little arc of electricity. Doing this creates a little burst of energy which is spread across most of the RF band. You can still hear this effect by trying to listen to AM radio during a lightning storm. Each lightning strike sends out a burst of RF which you can hear on any AM modulated radio. It wipes out all the AM stations, and I guarantee you that the lightning is not using any fancy electronics to "change frequencies". You don't notice the interference as much other radios, such as FM, because they use more advanced modulation techniques. So, the noise from lightning doesn't usually manage to turn into actual audible interference. But if you are listening to a weak signal and the lightning is close, it will still fade out when the noise from the lightning overpowers the signal from the radio station.

Back to UWB, the basic 'unit' of transmission is not unlike the signal generated by a spark gap transmitter or a lightning strike. In order to transmit a bit, the transmitter sends the wide-band pulse either a little bit early or a little bit later than expected. The receiver knowns exactly in time when the next pulse should show up. It has a bit of circuitry which can detect whether the pulse shows up early or late, and spit out a 1 or a 0 accordingly. If the pulse never shows up, nothing gets output. The circuits involved are actually fairly simply. Certainly simpler than a frequency-hopping radio which does work the way you described. Actually, I think you've gotten your wish for "these problems get worked out sooner than later." I say this because I think they have working hardware now. It's not on the market, but it would be if the FCC approval came thru.

Of course, the claims that UWB won't interfere with existing RF users, or with itself, is pretty close to BS. UWB definitely creates interference for other radios, it just a question of whether or not it's enough interference to be noticable. But it will definitely raise the noise level for pretty much every other RF band, so it's safe to assume that the potential of problems exists.

UWB will also interfere with itself. If you are the only user, your fine. But as soon as more than one person is using it, you are going to start finding out that pulses from other transmitters are showing up times which set your receivers correlator off erroniously. If a lot of people are using it in the same area, you are going to get more and more errored bits showing up at the receiver. These can be worked around by using error correcting codes at a higher layer, but it's still interference. Folks who think it can't be jammed are full of it too. One of the papers mentioned that the radios might have a duty cycle as low as 1% or less. If I build a radio that starts spitting pulses out at a 50% duty cycle or some such, I can probably get everyone elses receiver to go nuts trying to deal with all of my extraneous pulses. Maybe I'll need 100 radios running at 50% duty cycles, but it can be done.

As another poster mentioned, eavesdropping will still be quite possible for most applications. It might be hard to detect UWB if you know nothing a priori about the signal. But, anybody who is using it already has a receiver which knows everything it needs to know to pick up signals! It's just like 802.11. It might be hard to pick up a FHSS 802.11 radio if you know nothing about the signal. But if you go out and buy an 802.11 receiver for $100, you can pick up the signal just fine. To some extent this can be worked around by using cryptographically secure PRNG's to generate your timing signals. Then only folks who know the 'key' will be able to pick up the signal. But I can guarantee you that consumer UWB gear will not under any circumstances use secure PRNG's if for no other reason than it would make it a real pain in the ass to set the stuff up to work properly.

Re:I don't normally say this.. but really.

[scoove]

No, it's not going to happen any time soon, for what should be obvious reasons.

For those who the reason isn't obvious, much of the controversy with UWB comes from its unlimited use of other people's licensed frequencies, allegedly under the "we don't think it'll interfere too much" rationale. UWB, in that respect, represents the largest theft of frequency since the auctions of the late 90s - stealing pretty much any frequency they want.

There has been substantial analysis of UWB and quite critical findings (see the ARRL's opinion submitted to the FCC - hams in many bands are secondary users and are used to coexisting with primary users, so there's a good reason the ARRL is very concerned about UWB), but instead of addressing it, the UWB lobbyists keep on pushing it forward and getting publicity (quite similar to it showing up on slashdot every once and awhile... who's on the lobby here?).

Unfortunately, the RIAA and peers have done a good job showing how easy it is to steal public or other peoples property when you pay off congress.

But hey, most of the public is technologically illiterate or unconcerned...

*scoove*

Bah! TANSTAAFL.

[phliar]

This keeps coming up every so often.

UWB is ... a series of very short electrical pulses ... on ALL frequencies simultaneously.

UWB requires ultra-low power... [it is] a signal that can't be detected and doesn't interfere.

Here goes: Bullshit!

He (or whoever he got this story from) needs to read a little bit of signal processing. Yes, it sounds very nice, and you can build it, and it's all true... if there's only one such device. You see, what this does to other users of spectrum is raise the noise floor just a bit. No big deal.

But what happens if there's a whole bunch of these devices? Well, let's say you're an FCC licensed user of spectrum. You've been allocated a certain bandwidth. Your channel capacity depends on the bandwidth and the noise floor. If your noise floor goes up, your channel capacity goes down.

Where did that lost channel capacity go? It's being used by these "UWB" devices. As evil as the FCC is, we do need some arbiter of the EM spectrum.

TANSTAAFL, folks. Go read Shannon.

Cringely is an idiot.

More UWB articles - Tech and Regulatory

[billstewart]

There's an article on UWB on Dave Farber's Interesting-People List, posted from The451.com with content from Janos Gereben and Dewayne Hendricks.

There's a longer article on Hendricks's work in This month's Wired, talking about UWB, unwiring Tonga, and using Indian Reservations to try out radio technology because their sovereign nation status may be a useful regulatory hack as well as because they need better communications on the rez.

Re:I don't normally say this.. but really.

[isdnip]

I hardly think the "property" argument jibes with the "public interest, convenience and necessity" traditional mandate of FCC regulation. Older "narrowband" (and CDMA) licensed services are sensitive to interference from each other. UWB promises not to interfere, so what's the beef? That they didn't pass a Morris Code exam? That allowing phone patches (old amateur radio tradition predating even Carterphone) will take away "the phone company's" guaranteed revenue? That my radio waves can't "overfly" your land without paying your for the privilege?

The debate over UWB centers on the difference between intentional and unintentional transmission. UWB advocates want to be allowed to intentionally transmit at levels *below* those autorized in Part 15 for unintentional radiators. Sounds fair, except of course that the sum of lots of them might seriously raise the noise floor in some portions of the spectrum. That's a valid technical debate, but not a property debate, unless it degrades performance of licensed services.

Cringely, of course, did make major mistakes in his article. UWB doesn't use "ALL" frequencies (the proverbial "DC to daylight"), just a lot more than "traditional" spread spectrum. And its power/range tradeoff is about the same as other spread spectrum. And PCS goes a LOT farther than 1 km, outside of the densest urban enviroments, if its towers are high enough.

(BTW, I have an Extra Class ham ticket, and know the Morse quite well.)

the noise can be calculated

[cats-paw]

But that doesn't mean that it's not subject to a lot of political bullshit. Here ya go :

UWB : 1uW in 5GHz BW => 200E-18 W/Hz

US Digital Cell phone BW is 30kHz

total intercepted noise in a 30kHz BW : 6E-12W => -82dBm

Assume 40dB path loss from UWB device to cell device : -122 dBm. Which is generous, if the guy standing next to you is using a UWB device the path loss is more like -30dB.

Thermal noise floor kTB = 1.38E-23 x 300 x 30kHz
That's 124E-18 W => -129 dBm

So my cell phone sensitivity just lost 7dB which will cut the range by 1/2 and that's for 1 UWB device.

Guess what happens when there is 10 of them ?
Guess what happens if I need 10uW.

Brian

Frequency Bandwidth and Information Bandwidth

[guygee]

I think several (highly modded) contributors to this discussion are confusing
the concepts of information bandwidth and frequency bandwidth. Ultra-wideband
refers to the bandwidth in the frequency domain, which is only indirectly
connected to the concept of information bandwidth, in that a wide band in
the frequency domain translates to narrow pulse in the time domain. Coding
techniques also strongly affect the ultimate information bandwidth of the
system. UWB is nothing like IEEE 802.11b,
which operates in the narrow 2.4 GHz - 2.483 GHz band.

I have been working on a project for US Army STRICOM,
in which we are using 8 UWB devices manufactured by
Time Domain Inc. to perform position location. These devices
operate at 1.9 GHz center frequency with a 2 GHz bandwidth,
which translates to a 500 ps pulsewidth.
We have a short conference paper on UWB simulation, accepted for presentation
to the 2002 IEEE Antenna and PropagationSociety Symposium,
which you can access
here. Speaking in general and rather simplistic terms, the information
bandwidth of such a system would depend of the time frame over which you
will allocate these 500 ps slots to listen for the transmission of 1 bit
of information. For example, if we choose a 5 ns time frame, then we
could theoretically obtain 200 Mb/s information bandwidth, while (ideally)
allowing for 10 channels of operation. Of course, the previous analysis
neglects the need for redundancy, and you may want to choose a time slot
over which to listen for a pulse different than the pulsewidth itself, but
I think the discussion gives one a good idea about how to relate information
bandwidth to frequency domain bandwidth in a simple communication system.

Established industries.

[Restil]

First of all, the scare that industries will vanish overnight due to newfangled technology is an unwarranted one. Granted, over time new technology will slowly replace older. Industries need to learn to adapt and grow. The market for horsedrawn carrages isn't what it used to be, but the introduction of the car wiped that industry out. But it didn't happen overnight. Even if cars are built that get 100 miles to the gallon, there will be a brief period of time when those cars cost more than the general variety. And not everybody is going to instantly trash their current cars and start buying up the new ones. The reduction in fuel requirements will be offset by the purchase of more vehicles now that people can afford it. It all works out. And if production is less, you lay off people. And natural resources last longer. Its all good.

Bandwidth is the same way. The dialup ISP will slowly go away, but "slowly" is the key word here. Business will adapt. And if they don't, they die. It happens. Tech related businesses are USED to going out of business. And the smart businesses will find a way to embrace the new technology before it destroys them. Then the next big thing will hit.

And there's always the possiblity that there are problems with the technology we aren't aware of when its more a theory than widespread in practice. Sounds cool to me. I can't wait to get 1gbps to my home! :)

-Restil

Re:I don't normally say this.. but really.

[scoove]

>I hardly think the "property" argument jibes with the "public interest, convenience and necessity" traditional mandate of FCC regulation.

Fortunately, we're beginning to have Supreme Court rulings changing that annoying trend of stealing people's property under the guise of "public interest." Look at this year's ruling on partial confiscation as an indication of a overdue correction on property rights.

Like it or not, the rules of frequency management are that transmissions in other people's bands is illegal (except in particular permitted circumstances, e.g. emergencies). UWB represents a slippery slope of property theft - allowing tresspass into anyones frequency "as long as they had good intentions."

What's next? Letting me borrow CPU cycles without your authorization because I had a nice intention and wouldn't /really/ slow your web surfing down much? (Oops... I never figured you were going to play Quake... sorry about crashing your game. Look, it's not my fault that you play annoying games that I never tested for. Maybe we ought to ban the games so we don't interfere with my borrowing cycles!).

Actually, this whole "it's not theft if you weren't going to use it" argument you raise is rather interesting - I think it probably represents a significant rationalization used by various thieves in the tech world, though not new nor exclusive to it ("honest officer, we were just borrowing the car while it wasn't used!")

> UWB promises not to interfere, so what's the beef?

Besides the fact that it's not theirs to use? That it steals other people's frequencies? Why hell, go ahead and borrow my wife and car while you're at it, since I wasn't going to use them while I was asleep.

Seriously tho, what if the licensed owners (who paid for their right to use the frequency and received title from the government) wanted to operate similar spread spectrum apps in their allocations? Very similar to the recent partial confiscation case where the farmer could do anything he liked to his property - oh, except for build, farm, drain the wetland, etc. You're stealing this use from the frequency holders.

Also, there has been considerable debate about the "no interference" tests submitted by the applicant by their paid consultants. These tests were limited to examples that were guaranteed to pass, while other critical assessments showing interference were ignored. Which is better: a promise by a commercial interest that wants to steal the entire frequency spectrum and has a definite financial gain, or objective scientists and analysts who've demonstrated no problem in the past coexisting with other services? Can anyone say RIAA?

> That they didn't pass a Morris Code exam?

Were you making a point here, or just confused? Morris the cat? Morris what? Pathetic.

> That my radio waves can't "overfly" your land without paying your for the privilege?

Absurd points that have no bearing on the real issues, as you hopefully already knew when you posted.

> Sounds fair, except of course that the sum of lots of them might seriously raise the noise floor in some portions of the spectrum. That's a valid technical debate, but not a property debate, unless it degrades performance of licensed services.

Aha... "unless" - which is exactly the point brought up by numerous parties. Sort of like saying my theft of your vehicle "isn't a valid debate unless you actually intended on using it at a later date."

Your definition of theft - requiring intent of the entity who was robbed of later using their property - us an odd and disfunctional one. My property taken, regardless of when and how I planned on using it, is theft.

*scoove*

Faster vs. Fast Enough, Far Enough, Interference

[billstewart]

As other people have said, if you've got the wire, using wire is cheaper, but running wires costs money. The big change with some of the newer wireless technologies is that they're starting to go fast enough and far enough to be useful. 10kbps connections are fast enough to run voice on, and paging, and sometimes email, but not something you'd run real computing over. Metricom's ~30-100kbps was better - but the tradeoffs of how many users fit in a given area, how far it goes, and how many microcells it needs didn't quite work for them. But 802.11b, at "11" Mbps, is really fast enough for many networking applications, and distance-limited enough that lots of people in a city can use it without overly stepping on each other's bandwidth needs - you can use it for typical office data applications and voice phones, though you'll still need a feed to the outside world that's usually wired. Inside an office building, run by the end users, it's a win; adapting it to be a public wide-area service is a different game economically, with different competition, and perhaps folks like BAWUG or Starbuck's Coffee will succeed. But those applications still require an upstream feed, and the cost of using a wired feed is enough that the economics are still dodgy for free service, and the market for paid service hasn't taken off quite fast enough. 802.11a, at 55Mpbs, is even more useful for office LANs; we'll see if it can provide upstream feeds for WANs.

What UWB technologies can offer is that they increase the number of users and amount of bandwidth that can operate in the same space without interfering with each other, and they also have sufficiently entertaining options for directional data and longer distances that it might be possible to build a meshed distribution network that's got enough horsepower to be self-sustaining without lots of wired access points. That not only makes it more viable for wireless users to access services on each others' machines, but also to get better economies of scale sharing upstream bandwidth - N users on a 45Mps T3 connection get much more effective capacity than N/28 users on a 1.544Mbps T1 connection, plus you save the costs of running lots of small connections to lots of individual cells (the access costs for a T3 are typically about 10 times the access costs for a T1, and you get 28 times the bandwidth, plus you also have more users who'll be sending data to each other instead of to the outside world.)

UWB.ORG is a front for Time Domain, Inc.

[Animats]

UWB.ORG claims to be an organization of companies that want the FCC to approve ultrawideband transmission. But when we look in the WHOIS database, we get:

Registrant:

• Time Domain Corp (UWB2-DOM)
• 
  7057 Old Madison Pike
  Huntsville, AL 35806
  US

  Domain Name: UWB.ORG
  

I thought that hype looked familiar.

the UWB landgrab

[markj02]

There is only so much bandwidth to go around. You can allocate it one way or another. We have chosen to allocate it by frequency channels. That's simple and low-tech.

UWB doesn't give you any unused spectrum, it just degrades that the spectrum there is uniformly for everybody else. In small amounts, that may not be a problem, but in big amounts it is. Think of it like trash: the occasional piece of paper on the street isn't a problem, but if everybody dumps their garbage on the sidewalk, it's a big problem.

If UWB were ever widely deployed, you can think of it as generating noise kind of like one billion light switches turned on and off many times per second. It's best to put a stop to that before it starts. Or, if we are going to throw out frequency based allocation, let's do it consciously (and let's wait for the UWB patents to run out before we do it).

Limitations of UWB

[XNormal]

Ultrawideband cannot be used to communicate from your car.

A pulse width of 1 nanosecond translates to about 1 foot. A car travels many times that distance in a second. In a free space environment such as ground-to-air communication it is possible to compensate for this, but in a typical urban environment with many reflections it is probably impractical to track so many different propagation paths that chance so rapidly.

Narrowband communication is less susceptible to this problem. Multiple paths that differ by less than one bit time do not affect the receiver too much (although they have a certain probability of fading).

The processing gain of UWB is very high, but not infinite. A cellular phone transmitting too close to a UWB receiver *will* jam it. Combining the two in a single device is probably not practical. Filtering this frequency range will not help either: the notch filter may look OK in the frequency domain but in the time domain it creates too much ringing for UWB to work correctly.

This one happens to be correct

[XNormal]

There are other inaccuracies in the article: it's spectral power density is low, not it's power.

There are many errors in the article, but this one is not entirely incorrect: in practice, USB does use lower power than narrowband. UWB is not suceptible to fading so it does not need the large fading margin required by narrowband radio.

With narrowband communication the SNR fluctuates widely because of Raleigh fading - different reflection paths interfering either constructively or destructively. You need a large fading margin (extra power) to ensure robust communication.

With ultrawideband (i.e. bandwidth approaching center frequency) there is no Raleigh fading and the signal power does not fluctuate so much, even in environments with severe multipath reflections. This translates to as much as 20db savings of real transmission power.

Almost free lunch

[XNormal]

Yes, Cringely doesn't understand 99% of the technology he writes about. That does not make the technology bullshit.

UWB is real. It's as close as it gets to a free lunch, and Claude need not turn in his grave.

you can build it, and it's all true... if there's only one such device

Not correct. UWB devices share the spectrum just fine. In fact, it's a far superior way to share the spectrum than narrowband frequency allocations.

The problems start when different devices use very different power levels: GPS uses extremely low levels, TV stations use very high levels and almost anything is at very high levels if you are close enough to the transmitter.

Spectrum sharing by frequency allocation provides very good separation between bands that use widely differing power levels. It's not too difficult to build filters that reject out-of-band interference by 100db or more. With ultrawideband, the rejection of unwanted signals cannot exceed 40-50db. UWB will work very well if all narrowband communications below 1GHz are shut down. Since that will never happen it will probably remain limited to very low power levels and certain niche applications.

Here's what might happen if all narrowband transmissions *are* shut down:

UWB cells for "last 10 miles" delivery, combined with long range fiber and satellite infrastructure could bring 100kbps to almost any person on earch and 10mbits/second to anyone living in a city. The terminals will use very little power and can have long battery life. Location tracking with 20 centimeter accuracy will be available anywhere in a city, including indoors.

How is all this possible with just 1GHz of bandwidth? The utilization efficiency of spectrum should not be measured in bps/Hz but rather in bps/Hz/square Km. Today's cellular infrastructure uses a very crude form of frequency reuse to optimize this capacity. IS-96 CDMA barely begins to utilize the real advantages of spread spectrum with a bandwidth of 1.25MHz. With 1GHz of spread spectrum things start to look different. And it's not just the bandwidth: 1GHz at a center frequency of 15GHz can only be use for line-of-sight communication. If the 1GHz band has a center frequency of 700MHz it has much better propagation and is immune to fading.

Of course, this will never happen. But not because it is mathematically or technologically impossible.