Electrical engineer Robert Scholtz holds an Avtech pulse generator that creates radio energy pulses of less than a nanosecond. The pulses are emitted over a broad, or ultra-wide, portion of the radio frequency spectrum.
Photo by Irene Fertik
IN THE UltRa Lab, electrical engineer Robert Scholtz is exploring the next digital technology that could revolutionize life: ultra-wide bandwidth radio, including short-pulse radio or impulse radio.
“This is a marvelous subject for university research,” Scholtz told researchers at Hughes Research Labs in a presentation on Thursday, Sept. 16. “UWB technology forces you to rethink all of the narrow-band assumptions and premises that engineers have made since the time of [radio inventor Guglielmo] Marconi.”
Impulse radio works by sending out weak radio energy pulses that are extremely short, less than a nanosecond (a billionth of a second), millions of times each second. The pulses are emitted over a broad (ultra-wide) portion of the radio frequency spectrum.
UWB technology promises a host of fascinating applications that are being pursued by a number of companies, many of which have ties to USC. The technology also raises thorny regulatory issues.
The ability of radio to determine range is inversely proportional to its bandwidth, said Scholtz, professor and chair of electrical engineering/systems at the USC School of Engineering. Global positioning satellites span 1 megahertz of bandwidth to determine location quickly via satellite to an accuracy of roughly 10 meters. UWB radios transmit over a gigahertz or more of bandwidth.
“That’s a factor of a thousand times more bandwidth, enabling measurements that are a thousand times more accurate than GPS,” said Scholtz. “Ranging down to a centimeter or less, perhaps through walls and foliage, should be possible.”
UWB’S RADIO’S ability to propagate through many materials, along with its precise ranging, points to interesting applications such as:
• Ground-penetrating radar for land mine detection, including non-metallic mines, and underground imaging to rescue earthquake victims buried in rubble.
• Through-the-wall radar, hand-held personal radar units, home security radar systems and devices for quickly mapping the interior of buildings.
• 3D imaging systems for builders that can look into walls, floors and cement slabs to show embedded studs, wires, pipes (including plastic), rebar and other materials.
The Integrated Media Systems Center at USC’s School of Engineering is interested in using UWB positioning technology for “haptics,” the devices that impart artificial feeling and touch in virtual reality, and for in-building wireless computer networking systems.
Scholtz noted that UWB radio is completely digital. The receiver can be programmed with a code to translate pulses into digital ones and zeroes. A “zero” might be indicated by transmitting an irregularly spaced, or coded, string of pulses 100 picoseconds (trillionths of a second) early and a “one” by sending it 100 picoseconds late, relative to a known clock. A receiver without the proper code and clock would receive nothing.
UWB RADIO COULD give birth to the next generation of radio phones, which could be smaller than Dick Tracy’s wrist radio and virtually impossible to detect. The phones would have extremely long battery life because UWB radio uses very little transmitted power. Several small companies are already supplying UWB covert communications technology to government agencies.
“The average power of one of these radios is a milliwatt,” Scholtz said. “That is a hundred to a thousand times less than current cell phones.”
UWB radio transmits over a substantial portion of the radio spectrum, including frequencies reserved for military agencies and civilian aviation. The radio spectrum is governed by international treaties and is regulated in the United States by the Federal Communications Commission, which is receiving many requests for waivers from companies and proponents of UWB radio. Three such waivers have recently been granted.
Advocates of this technology contend most UWB transmissions are less powerful than the radio waves produced by microwave ovens, hair dryers, computers and a host of other electric and electronic devices. Regulatory agencies term such radio transmissions as “spurious” because they are unavoidable and are part of the normal, low-level radio noise that permeates the entire spectrum.
But UWB radio transmissions aren’t spurious; they are intentional. While a few experimental transmissions may cause no problem, what will the effect of millions of UWB devices be? Is it technically possible to chop out certain sensitive bands, such as those used for aircraft navigation or GPS satellites, and not transmit UWB pulses on them? How much concern should regulators have for those who currently hold rights to the various parts of the spectrum as UWB radio moves forward?
The answers to these questions will be found in research. Scholtz has been active in regulatory discussions about UWB radio. He presented a UWB paper at the Institute of Electrical and Electronic Engineers’ Wireless Communications and Networking Conference Sept. 21 to 24 in New Orleans, and chaired the Ultra Wideband Working Group’s technical papers session in Washington Sept. 26 to 28, where two more of his papers were presented.
“We need to get these radios out of the lab and put them in the real environment,” Scholtz said. “We are where cellular radio was in the 1960s, but with the experience and technology we’ve piled up from narrow-band radio work, we’re only three to five years away from having products.”
The main sponsor of USC’s UWB research is the National Science Foundation. Others are Advanced Micro Devices, Compaq, Sierra Monolithics, Time Domain Corp., the U.S. Army Research Office, and USC’s IMSC.
Other UWB researchers include professor John Choma, assistant professor Keith Chugg, assistant professor Antonio Ortega and associate professor Aluizio Prata, all from the electrical engineering/systems department.