Posted on 09/14/2002 1:14:28 PM PDT by sourcery
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 Hertz's and Marconi's bulky coils and capacitors have been replaced by tiny integrated circuits and tunnel diodes.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.
Just Get Me to the Wall
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.
Radio with No Carrier
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.
Avoiding Interference
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.
Many Paths to Take
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.
Go Low and Short
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.
Yes. Run fiber down the street. Connect each house using UWB. The only threat to this scenario would be for UWB to replace traditional broadcasting technology entirely (which is technically possible, but politically difficult). Were that to happen, fiber would go the way of copper--and so would all those currently-expensive broadcasting licences (not to mention the FCC itself).
Technological revolutions can sometimes be seen as threatening to existing businesses and investments, and therefore cause short to intermediate term devaluations of entire market sectors. Think of UWB as analogous to integrated circuits/personal computers, circa 1970.
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Good article!
Possibly this could be a contractual thing with the local cable company providing UWB to the city.
There are many possible options.
The telephone companies may even be receptive, if they could then forego the inconvenience of having to run wire/fiber optic cable to each and every residence.
Consider the cost savings for residential connection alone.
Simple running fiber optic cable down streets or alleys, and setting up transmitter stations at the corner of the block would be sufficient to provide service to a block-wide coverage area.
Interestingly, I live in an area in far North Raleigh, NC, that is "new" and.....let's just say "upscale". There is fiber to the curb here. Sprint, the local provider, offers (and we use) a high-speed Internet option that uses no modem (it isn't DSL; it isn't cable modem). They literally provide an RJ-45 jack in your home, and you connect directly to their network. They use ONU's (Optical Networking Units) to interface the "copper" from the homes to the fiber. Works like ten champs.
Of course, in the house here, I've set up a wireless network. I opted for 802.11b due to the still-rather-prohibitive cost of 802.11a gear, but mainly because the sustained data rates over "high speed" internet connections are still well within 802.11b range. Still, I love it. :)
I am looking at getting a laptop with High Rate wireless LAN PC card and the associated Gateway.
Uses the popular IEEE 802.11b wireless technology. Good to hear it works as advertised!
The FCC permits quite a few "imaging" applications (think "radar") for automotive and specialized uses. The blurb on telecomms from the FCC Press Release for the FR&O makes it clear that you're not gonna cover too much real estate with these puppies.
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While prowling for even more news, I stumbled upon a link to an 802.11b networking roundup over at PCStats. 802.11b might not be the latest and greatest, but it's still an affordable means of adding some wireless capabilities to your LAN.
Unlike a wired network, a wireless LAN, or WLAN transmits your data (personal, public, or whatever) through unlicensed airwaves that anyone within range can potentially intercept. There are ways to safeguard that data - and the first such step is enabling 64-bit or 128-bit Wired Equivalent Protocol (WEP).
The laptop owners out there will certainly find such an article of interest. People ask me why I'm still "wired" and I just reply that it probably has something to do with the amount of pepsi I drink (Sorry, that was lame). If you're currently running a wireless network, enable WEP. Read on.
Link:
I've been running 802.11b for about 8 months for my internal network. Since WEP, the security for 802.11, is badly broken, I put an OpenBSD gateway between the wireless access point and the rest of my internal network. The OpenBSD box runs IPSEC as does my laptop, creating an encrypted link across the wireless connection.
Installing the NetGear wireless card on my laptop was as easy as installing the PCMCIA card and letting autodetect find it. I set up IPSEC to start automatically on bootup, as well as the firewall software the keeps anything but IPSEC from connecting to the laptop.
It was a snap. It stays up for weeks at a time while I surf the 'net from in front of the television. Occasionaly I grab the laptop and wander out onto the porch with a beer. But I expected it would work perfectly and stay working perfectly.
You see, I run Linux on my laptop. I have come to expect stability, ease of use and security. And once again, I wasn't disappointed.
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