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

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.

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.)

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).

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.