Ultrafast wireless technology set to lift off
- 02 September, 2001 22:00
- This week the US Federal Communications Commission will decide whether to give the green light to so-called ultra-wideband transmission. If approved, UWB could have a dramatic impact on short-range wireless communications for the enterprise.
UWB is almost two decades old, but is used mainly in limited radar or position-location devices. Only recently has UWB been applied to business communications. It's a different type of transmission that will lead, proponents say, to low-power, high-bandwidth and relatively simple radios for local- and personal-area network interface cards and access points. At higher power levels in the future, UWB systems could span several miles or more.
Wireless technologies such as 802.11b and short-range Bluetooth radios eventually could be replaced by UWB products that would have a throughput capacity 1,000 times greater than 802.11b (11Mbit/s ). Those numbers mean UWB systems have the potential to support many more users, at much higher speeds and lower costs, than current wireless LAN systems.
There is a range of UWB vendors - not to mention academic researchers, the military, defense contractors and many others - looking to unleash UWB products. Among the best-known UWB vendors are Aether Wire and Location, Multi Spectral Solutions, Pulse-Link, Time Domain and Xtreme Spectrum. Intel has a laboratory focused on UWB research. The Ultra Wideband Working Group, a UWB advocacy organization, lists about 150 organisational members from around the world, including Compaq, Daimler Chrysler, Intersil, Lockheed Martin, Motorola and the US Air Force.
"Ultra-wideband is in its infancy in terms of speed and distance," says Frank Dzubeck, president of Communications Network Architects, a Washington, DC, consulting company, and a Network World columnist.
"The initial approval from the FCC might be, for example, for 100Mbit/s with a range of 150 feet. But there's no reason why you can't increase speed and distance. It's a matter of power and finer and finer granularity of the silicon chips."
UWB is fundamentally different from existing radio frequency technology. For radios today, picture a guy watering his lawn with a garden hose and moving the hose up and down in a smooth vertical motion. You can see a continuous stream of water in an undulating wave. Nearly all radios, cell phones, wireless LANs and so on are like that: a continuous signal that's overlaid with information by using one of several modulation techniques.
Now picture the same guy watering his lawn with a swiveling sprinkler that shoots many, fast, short pulses of water. That's typically what UWB is like: millions of very short, very fast, precisely timed bursts or pulses of energy, measured in nanoseconds and covering a very wide area. By varying the pulse timing according to a complex code, a pulse can represent either a zero or a one: the basis of digital communications. UWB energy pulses operate in the same frequency spectrum as electronic "noise" emitted by Pentium II chips, TV monitors, electric razors, automobile ignitions and fans. This is a huge swath of the spectrum, regulated only by FCC rules on how much power these devices can use.
This difference in transmission methods has several big implications.
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. Spectrum is limited, and demand for it is growing fast. That's one reason for the FCC interest: UWB would allow a whole new class, and volume, of voice and data communications that, in effect, wouldn't take up any more "space" in the crowded radio spectrum.
Second, and partly as a result of the fact that UWB doesn't use a traditional radio signal, UWB transmitters and receivers will be much simpler to build, run and maintain than those in use today, says Douglas Cummings, an engineering scientist at the Applied Research Laboratories at the University of Texas at Austin.
"For UWB, you don't need complex radio frequency converters and modulators and so on," he says. "I only need a digital method to construct the pulses and modulate them. This can all go on a single chip. One vendor already does this on a chip the size of a penny."
Third, because UWB operates in the electronic "noise" area of the spectrum, it requires little power. "These systems can use 50 to 70 milliwatts of power," says Adrian Jennings, technologist with Time Domain in Huntsville, Ala., one of the pioneer vendors in UWB. "That is one ten-thousandth the power of a cell phone." The low power limits the range, but there are features of pulse transmission and some tuning techniques that can, in effect, extend or maintain the range.
In addition, low power and the characteristic wide spread of the pulses means the pulses don't use up already crowded chunks of the radio spectrum, today occupied by 802.11b wireless LANs and Bluetooth devices.
Despite the low power, UWB also has greater capacity - higher bandwidth for more users - compared with these other technologies. In early August, Time Domain began testing its just-fabricated, second-generation UWB chipset using silicon germanium technology created by IBM. The new chipset can reach 40M bit/sec, compared with just 2.5M bit/sec for the first chipset two years ago, Jennings says. Another start-up, Fantasma Networks, which Pulse-Link acquired in May, claims to have reached 60Mbit/s .
Finally, UWB promises to be highly secure. It's very difficult to filter a pulse signal out of the flood of background electronic noise, and vendors such as Time Domain are encrypting the zeros and ones being transmitted by the pulses.
But legalising UWB, so vendors could start building network products with UWB chips, is up in the air. FCC's public comments on UWB have been generally favorable, and academics and a wide range of vendors, including Intel, are pressing for approval. 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.
The University of Texas ran a battery of tests last December looking at the UWB's impact on GPS. The data were handed over to the FCC last February with several other independent studies. UWB can have an effect, but whether it is unacceptable depends on how one defines it, Cummings says. The tests also found the effects vary widely depending on how the UWB transmitter is tuned, timed and powered.
"There are substantial disagreements [among the interested parties], especially over what are the adequate margins for protecting these bands against interference," says Julius Knapp, deputy chief of the FCC's Office of Equipment and Technology. "FCC Chairman [Michael] Powell has said to Congress that we'll address the issue before the end of this year."
Cummings says he is confident approval will be forthcoming. "There's just too much potential in this for someone to say, 'No, we're never going to use this,'" he says.