The new kid on the radio block is ultrawideband, also known as UWB or digital pulse wireless. It will help deliver television programs, movies, games and multimegabyte data files throughout our wireless homes and offices. UWB is faster than current wireless LAN technologies and provides a short-range, high-bandwidth pipe that eliminates interference.
Origins of UWB
Gerald F. Ross first demonstrated the feasibility of UWB waveforms for radar and communications applications in the late 1960s and early 1970s. Originally developed by the Defense Advanced Research Projects Agency, the technology was called baseband, carrier-free, impulse communications or time-domain signaling, until the U.S. Department of Defense named it ultrawideband in 1989.
In some respects, UWB technology goes back to the dawn of radio and Guglielmo Marconi's early spark-gap transmissions. UWB is also a successor to spread-spectrum radio (also called frequency-hopping), a World War II technology that splits a broadcast across many different radio frequencies, using one at a time to avoid jamming. (Curiously enough, spread spectrum was invented -- and patented -- in 1942 by actress Hedy Lamar and composer George Antheil.) In contrast, UWB uses every frequency available to it, all at the same time.
UWB isn't a direct substitute for any other form of wireless communications, but it does some things that no other technology can match. A UWB transmitter sends billions of short-duration pulses across a wide spectrum of radio frequencies. These RF bursts come so fast -- lasting only from a few trillionths of a second to a few nanoseconds -- that each actually uses only a few cycles of an RF carrier wave.
This short duration gives UWB waveforms some unique properties. They are relatively immune to multipath cancellation effects, such as when a strong reflected wave arrives out of phase with the direct path signal, reducing the signal strength in the receiver. UWB pulses are so short that the direct signal has come and gone before the reflected path arrives, so no cancellation takes place. Because UWB pulses are so short, they can use very wide frequency spectra; this allows signals to use very low power, which minimizes interference with and from other radio frequencies, reduces health hazards and often falls below the normal noise floor, thus making it harder to detect.
Technically, UWB is defined as any radio technology whose spectrum occupies more than 20% of the center frequency, or a bandwidth of at least 500 MHz. Modern UWB systems use various modulation techniques, including Orthogonal Frequency Division Multiplexing, to occupy these extremely wide bandwidths.
In 2002, the Federal Communications Commission approved the commercial use of UWB transmissions in the range from 3.1 GHz to 10.6 GHz, at a limited transmission power. UWB systems can, in principle, be designed to use nearly any part of the RF spectrum.
Applications
In its current state of development, UWB is aimed at high data rates for personal-area networks, which have an effective operating radius of approximately 10 meters or less. Though similar to the current capabilities of Bluetooth, it uses a very different technology. UWB transmissions trade distance for bandwidth, so the greater the range, the lower the final data rate. Range can be extended up to perhaps a kilometer by using high-gain antennas and reducing performance.
One of UWB's defining characteristics is that it requires very little electrical power -- one source says it uses 0.001% as much power as a cell phone -- and thus is virtually undetectable by conventional radios, which see the UWB signal as just very quiet background noise. Thus, a UWB telephone would use so little power that it could remain on for weeks without needing to be recharged. And because it uses all available spectra, UWB may well be cheaper to design and manufacture than conventional radios that require careful tuning to a specific frequency.
A UWB transmitter and receiver must be closely coordinated and synchronized to send and receive pulses with an accuracy of trillionths of a second. The receiver responds only to a familiar pulse sequence. This makes UWB very secure, which explains why it was once used for clandestine communications by military and espionage agencies. UWB's broad frequency range includes the ultralow frequencies the U.S. Navy uses to communicate with submerged submarines.
UWB products will include radar and electronic location and positioning devices in addition to radios. UWB radar can see right through walls, ceilings and floors that would block or reflect other types of radio signals. As an electronic measuring technology, UWB is more accurate than Global Positioning System satellites, and it can be used indoors. The Navy reportedly plans to put UWB markers on almost everything it ships overseas, just to track materiel and keep it from being stolen.
Eventually, UWB networks are expected to run at speeds up to a gigabit per second and therefore should be able to handle all of the phone, television, and Internet traffic for a home or small business.
Sidebar
UWB, Bluetooth and IEEE 802.15.3
Ultrawideband will not replace Bluetooth for short-range communications, because Bluetooth is a complete, end-to-end communications standard, whereas UWB is merely a radio technology that can be used as part of an overall standard. Bluetooth defines how data is managed, formatted and physically carried over a wireless personal-area network (WPAN). However, designers expect that future Bluetooth implementations will be built on top of UWB signals.
802.15.3 is the IEEE standard for a high-data-rate WPAN designed to provide sufficient quality of service for the real-time distribution of content such as video and music. It is ideally suited for a home multimedia wireless network. The original standard uses a traditional carrier-based 2.4-GHz radio as the physical transmission layer.
802.15.3a, a follow-on standard still in the formative stages, will define an alternative physical layer. Current proposals based on UWB will provide more than 110Mbit/sec. at a distance of 10 meters and 480Mbit/sec. at 2 meters. This will allow the streaming of high-definition video between media servers and high-definition monitors, as well as the extremely fast transfer of files between servers and portable devices.
Kay is a Computerworld contributing writer in Worcester, Mass. You can contact him at russkay@charter.net.
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