Wireless Data Blaster

With a crackling sound like that of frying eggs, an undulating thread of intense, blue-white light dances across the small space between the tips of two metal rods. Using his spark-gap transmitter, a mild-mannered 31-year-old physics professor demonstrates electromagnetic phenomena to students in a dimly lit classroom at the University of Karlsruhe in Germany. The year is 1887, and Heinrich Hertz is generating radio waves. Seven years later a young Italian named Guglielmo Marconi reads a journal article by Hertz while vacationing in the Alps and abruptly rushes home with a vision of a wireless telegraph in his head. Soon Marconi's own spark-gap transmitters are sending Morse-code pulse streams across his lab without wires. After boosting power and building much larger antennas, the radio pioneer eventually uses the device to transmit coded wireless signals across the Atlantic Ocean in 1901.

Fast-forward a century, and researchers are once again beaming short electromagnetic pulses across their labs. But the technology has changed. Hertz's and Marconi's bulky coils and capacitors have been replaced by tiny integrated circuits and tunnel diodes. Likewise, the ragged and erratic spark streams emitted by early transmitters have now been refined into precisely timed sequences of specially shaped pulses lasting only a few hundred trillionths of a second each. And whereas Marconi's devices could convey the equivalent of about 10 bits of data per second, today's short-range, low-power descendant of the original spark-gap systems--called ultrawideband (UWB) wireless technology--can send more than 100 million bits of digital information in the same amount of time.

The high-speed data-transfer capabilities of UWB systems have spurred a group of inventors and entrepreneurs to promote this short-range technology as a nearly ideal way to handle the burgeoning flow of wireless information among networks of portable (battery-powered) electronic devices. These stand-alone networks could include personal digital assistants, digital cameras and camcorders, audio/video players, cell phones, laptop computers and other mobile electronic gear. To exchange the large digital files needed to support increasingly sophisticated broadband applications, these devices require high-bandwidth wireless communications links.

The growing presence of wired connections to the Internet is another driver of short-distance wireless technology. Many in the developed world already spend most of the day within 10 meters of some kind of wired link to the Internet. This proximity opens up the possibility of using short-range wireless technology to communicate between portable electronics and the Internet. As a result, the industry has responded by developing narrowband communications techniques that can "get me to the jack on the wall." These include the IEEE 802.11b and Bluetooth standards, which operate in an unlicensed frequency band from 2.400 to 2.483 gigahertz (GHz), and IEEE 802.11a, which operates indoors on frequencies from 5.150 to 5.350 GHz.

Bluetooth is the best known of what are commonly called wireless personal-area networks (PANs). Wireless PANs were designed to replace the (physical) serial and USB cables used to pass data among closely located electronic equipment. Although specific implementations differ, the low-power Bluetooth standard is expected to offer users a maximum data-transmission speed of about 700 kilobits per second over distances of up to about 10 meters.

The IEEE 802.11a and 802.11b standards were established for wireless local-area networks (LANs), which emphasize faster speeds and longer range but require higher-power consumption. Typically these wireless LANs provide links from laptops to wired LANs via access points. Users of IEEE 802.11b can expect maximum transmission speeds of about 5.5 megabits per second (Mbps) across open-space distances of up to 100 meters. Its companion standard, IEEE 802.11a, will provide users with maximum data speeds of between 24 to 35 Mbps over open spaces of about 50 meters. In practice, all short-range radio systems "downshift" their speeds to compensate for long distances, walls, people and other obstacles.

At present, it appears that semiconductor-based UWB transceivers will be able to provide very high data transmission speeds--100 to 500 Mbps across distances of five to 10 meters. These high bit rates will give rise to applications that are impossible using today's wireless standards. What is more, engineers expect these UWB units to be cheaper, smaller and less power-hungry than today's narrowband radio devices.

UWB is superior to other short-range wireless schemes in another way. Growing demand for greater wireless data capacity and the crowding of regulated radio-frequency spectra favor systems that offer not only high bit rates but high bit rates concentrated in smaller physical areas, a metric that has come to be called spatial capacity. Measured in bits per second per square meter, it is a gauge of "data intensity" in much the same way that lumens per square meter determines the illumination intensity of a light fixture. As increasing numbers of broadband users gather in crowded spaces such as airports, hotels, convention centers and workplaces, the most critical parameter of a wireless system will be its spatial capacity, a capability in which UWB technology excels. SPATIAL CAPACITY, a gauge of operational efficiency important when comparing short-range wireless systems, favors UWB technology. Measured in kilobits per second per square meter (kbps/m2), spatial capacity focuses not only on bit rates for data transfer but on bit rates available in the confined spaces defined by short transmission ranges.

Successful development of UWB wireless technology should make possible an entirely new class of electronic devices and functions that would change the way we live. For example, rather than picking up recorded movies at the video store, we may end up downloading films using a portable mass-storage unit and UWB wireless transmission while filling the car up at the fuel pump. UWB could permit bulky PDA calendars and e-mail directories to be flash-synchronized or messages to be sent or received in public places such as coffee shops, airports, hotels and convention centers. While traveling on planes or trains, people could enjoy streaming video input or interactive games on three-dimensional-vision eyeglasses and high-fidelity audio sets equipped with UWB. Photoenthusiasts could download digital images and video from their cameras to computers or home theaters via UWB wireless, eliminating the rat's nests of cables we often use today.

UWB technology has other significant, noncommunications applications as well. It relies on razor-thin, precisely timed pulses similar to those used in radar applications. These pulses give UWB wireless the ability to discern buried objects or movement behind walls, capabilities that could be important for rescue and law-enforcement missions.

UWB's precision pulses can also be used to determine the position of emitters indoors. Operating like a local version of the Global Positioning System (GPS) or the LoJack anti-auto-theft technology, a UWB wireless system can triangulate the location of goods tagged with transmitters using multiple receivers placed in the vicinity. This ability might be very useful to department store personnel for doing "virtual inventories"--keeping track of high-value products on the shelves or in the warehouse, for instance. This location-finding feature could also be used to enhance security: UWB receivers installed in "smart" door locks or ATM machines could permit them to operate only when an authorized user--carrying a UWB transmitter--approaches to within a meter or less.

Ultrawideband wireless is unlike familiar forms of radio communications such as AM/FM, short-wave, police/fire, radio, television, and so forth. These narrowband services, which avoid interfering with one another by staying within the confines of their allocated frequency bands, use what is called a carrier wave. Data messages are impressed on the underlying carrier signal by modulating its amplitude, frequency or phase in some way and then are extracted upon reception [see box for modulation techniques].

UWB technology is radically different. Rather than employing a carrier signal, UWB emissions are composed of a series of intermittent pulses. By varying the pulses' amplitude, polarity, timing or other characteristic, information is coded into the data stream. Various other terms have been used for the UWB transmission mode--carrierless, baseband, nonsinusoidal and impulse-based among them.

Because of their extremely short duration, these ultrawideband pulses function in a continuous band of frequencies that can span several gigahertz. It turns out that the shorter the pulse, the broader the frequency spectrum that the pulse will occupy [see box for an explanation of this phenomenon]. Image: JOHHNY JOHNSON RADIO-SIGNAL TECHNICALITIES

Because the UWB pulses employ the same frequencies as traditional radio services, they can potentially interfere with them. Marconi's spark-gap stations used high power because they needed to bridge great distances. In today's regulatory environment, systems like Marconi's would be intolerable because they would interfere with almost everybody else on the air. Ultrawideband communications systems would share the same problem except that they deliberately operate at power levels so low that they emit less average radio energy than hair dryers, electric drills, laptop computers and other common appliances that radiate electromagnetic energy as a by-product. This low-power output means that UWB's range is sharply restricted--to distances of 100 meters or less and usually as little as 10 meters. For well-chosen modulation schemes, interference from UWB transmitters is generally benign because the energy levels of the pulses are simply too low to cause problems.

As with emissions from home appliances, the average radiated power from UWB transceivers is likewise expected to be too low to pose any biological hazard to users, although further laboratory tests are needed to confirm this fully. A typical 200-microwatt UWB transmitter, for example, radiates only one three-thousandth of the average energy emitted by a conventional 600-milliwatt cell phone.

On February 14 the Federal Communications Commission gave qualified approval to UWB usage, following nearly two years of commentary by interested parties. Most of the more than 900 comments on the proposed ruling concerned whether UWB might interfere with existing services such as GPS, radar and defense communications, and cell-phone services.

Taking a conservative tack, federal regulators chose to allow UWB communications applications with full "incidental radiation" power limits of between 3.1 and 10.6 GHz. Outside that band, signals must be attenuated by 12 decibels (dB), with 34 dB of attenuation required in areas near the GPS-frequency bands. More liberal restrictions were permitted for law-enforcement and public safety personnel using UWB units to search for earthquake or terrorist attack victims.

Despite the imposed limitations, UWB developers are confident that the wireless technology will be able to accomplish most of the data-transfer tasks its proponents envision for it. The FCC regulators indicated that they will examine easing the constraints once operational experience has been gained and further studies have been conducted.

Ironically, the more challenging technical problem appears to be finding ways to stop other emitters from interfering with UWB devices. This area is one in which narrowband systems have a decided advantage--all such systems are fitted with a front-end filter that prevents transmitters operating outside their reception bands from causing trouble. Unfortunately, a UWB receiver needs to have a "wide-open" front-end filter that lets through a broad spectrum of frequencies, including signals from potential interferers. The ability of a UWB receiver to overcome this impediment, sometimes called jamming resistance, is a key attribute of good receiver design. One approach to improving jamming resistance is to install so-called notch filters that attenuate those narrow parts of the spectrum where interference is known to be likely. Another protective measure that has been developed would be to use automatic notch filters that seek out and diminish the signals of particularly strong narrowband interferers.

Multipath interference, another kind of radio interference, is also an issue. In some situations, the same narrowband signal can be reflected by surrounding objects onto two or more different paths so the reflected signals arrive at a receiver out of phase, sometimes virtually canceling each other out. Most of us have experienced multipath problems when listening to FM radio in an automobile. When a car is stopped at a traffic light, for example, the signal can suddenly become noisy and distorted. Rolling forward a foot or two, however, often alters the relative timing of the received signals sufficiently to restore clear reception.

Multiple signals caused by reflections might be a liability for UWB wireless units as well, but clever design can permit them to take advantage of the phenomenon. The narrow pulses of UWB make it possible for some receivers to resolve the separate multipath streams and use multiple "arms" to lock onto the various reflected signals. Then, in near real-time, the arms "vote" on whether a received bit is a one or a zero. This bit-checking function actually improves the performance of the receiver.

Today's trend toward sending lower-power signals over shorter ranges has occurred previously in wireless communications--during the early days of radio telephony. Before 1980, a single tower with a high-powered transmitter might cover an entire city, but limited spectrum availability meant that it could not serve many customers. As recently as 1976, radio telephone providers in New York City could handle only 545 mobile telephone customers at a time--an absurdly small number by current standards. Cellular telephony was able to accommodate a greater number of customers by drastically reducing both power and distance, allowing the same spectrum to be reused many times within a geographic area. Now short-range wireless, particularly UWB, is poised to do the same.

There are still some among us who can remember, before 1920, when "spark was king." With help from semiconductors and the Internet, spark-gap radio's latter-day offspring--UWB technology--may soon emerge as a major wireless building block for advanced high-speed data communications.

WEP is better than nothing at all, but any war driver or the 13 year old next door to you can download one of several utilities on the 'net that can break into WEP in a matter of minutes. The protocol is badly broken.

Here is an article that explains WEP's weaknesses and why it shouldn't be used. Most security professionals recommend leaving WEP turned off and using IPSEC to secure your wireless connection.

Yeah, wireless networks have certainly been around for a while (we've had them at work for some time now....), but they CAN be a challenge to install in your home if you find yourself using equipment from different vendors. It's NOT supposed to matter (standards are standards, right???), but trust me........it does. I have a D-Link DI-704P wireless router, an Orinoco WAP (wireless access point), a Cisco Systems 340 Series wireless card in one laptop (the main family system.......an IntelliStation M Pro workstation, to be fairly exact........is hard wired into the router since they sit next to each other), a D-Link 650+ wireless card in another laptop, and will be picking up another wireless card (when I say cards, I'm obviously talking about PCMCIA wireless networking cards) for a third laptop here soon.

It all works like a champ, but toss in two different ISP's and a VPN that I use for work, etc., etc., it was MORE than challenging to get it all humming together.

I strongly recommend that anyone who wants to get into wireless networks pick a supplier and use their stuff across the board. D-Link, Linksys, whomever........

I was going to go with a combined wireless router/wireless hub combo unit (there are many on the market and can be had from about $160 to over $325, depending on the brand), but I "inherited" the WAP for no cost, so what the heck. :) Just got the router ($50) and another card (already had one) and off I went.

Always check out pricewatch.com for excellent prices on such things.

The very high speeds attained by this technology are offset by it's relatively short distance.

Where I see this really coming into to play is by replacing the jungle of cables that exist in a server farm. I will be able to grab a new server, install it in the rack, turn on some kind of encryption and connect it to the local LAN without running new cables all over the place.

When rack space runs out, I can install a new rack next door without having to drill holes in the wall.

If I can get 200-300 Mb/sec, then even with the overhead of encryption I can reach or surpass a 100Mb LAN and forget about the wires.

"What is the essential difference between 802.11a and 802.11b. I see them both gaining ground. Which is the VHS and which is the Betamax?"

Essential difference? Speed.

802.11b is a rated at 11 Mbps ("11 megabit"), vs. 802.11a: 54 Mbps ("54 megabit").....each is actually "megabits of data per second". Understand that at either 11 or 54 megabit, you're talking top BURST speed under ideal conditions and will rarely hit such a speed. There are now a number of manufacturers out with 802.11a gear, but it's still new and a bit pricey. Most such gear can actually support either 802.11b OR 802.11a.

For now, I just opted for 802.11b: darned sight cheaper, and my needs were simple. I didn't so much care about fast data interchange here in my home (moving data from one computer in the house to another); I basically wanted to share the high-speed Internet acceess across all of these computers (i.e. wanted a fast link to the Internet for all systems; didn't care about transferring back and forth among these same computers at blinding speed......make sense??). If you look at the data rates your high speed Internet provider can give you, 802.11b is more than enough.

The good news is that there is no "VHS vs. Beta" thing going on here; it's just "speed bumps", if you will. :)

Hope that's clear as mud.......LOL :)

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