University the first to conduct outdoor wideband research
By Susan Trulove
Spectrum Volume 20 Issue 30 - April 30, 1998
The wideband broadcast spectrum--such as the 28 to 31 gigahertz frequency range just licensed to Virginia Tech for the Roanoke, Danville, Martinsville, and Bristol markets--has the potential to deliver the same amount of information as fiber-optic cable.
"What Virginia Tech and others want to do is provide local-area networks (LAN's) across campus, between buildings in a business location, or within an urban corridor--without using cable," said Robert Boyle, research assistant professor with the Mobile and Portable Radio Group. "A provider can broadcast the same information to everyone or different information to different people, just like ethernet. Potential applications are up to the imagination of the service provider."
The operative word here is "potential." The technology remains to be developed, tested, and fine tuned. "Companies are spending millions of dollars to development equipment to provide wireless services," Boyle said. Students and faculty members at Virginia Tech are an important part of that effort.
"The unknown is the environment," Boyle said.
Research at Virginia Tech beginning April 21 is using the university campus as a model to measure the success of wideband signals in good weather and bad--by setting up equipment in Slusher Tower and in Whittemore.
"MPRG will become perhaps the first academically based research center in the United States to conduct wideband radio wave propagation measurements at millimeter wave frequencies in an outdoor environment," Boyle said. "This research coupled with the recent Local Multi-point Distribution Service (LMDS) license, which the Center for Wireless Telecommunications helped spearhead, will establish Virginia Tech as the leader in the areas of system design, system performance analysis and wideband propagation research at millimeter-wave frequencies."
Because the researchers want to conduct measurements over the longest possible line-of-sight path on campus while keeping the prototype equipment out of the weather, "Slusher tower became an obvious candidate," Boyle said. "We found that if we operate from the stairwell on the twelfth floor of Slusher, we can establish a 500-meter line-of-sight link to an office on the sixth floor of Whittemore.
"We will send the pulse from Slusher and measure what is received at Whittemore. We will measure interference from buildings, weather, and the wind blowing the leaves on the trees."
The researchers are measuring signal loss, signal reflections (multi-path power-delay profile), signal spread and the number of echoes (delay spread), the time varying nature of the radio channel--or how signal delays change, and weather impact.
The resulting measurements will determine what kind of equalizer is required and how adaptive an equalizer will need to be to track changes in the channel. "The data from the measurements will be used to develop statistically based propagation models that can be used to provide wideband wireless services," Boyle said.
The research team, made up of Boyle, graduate students Hao Xu and Neal Patwari, MPRG director Ted Rappaport, and sponsor representative Jim Schaffner of HRL Laboratories, Inc., will move equipment into Slusher as various weather opportunities occur. They are using equipment developed by MPRG students with assistance from Professor Aicha Elshabini and Fred Barlow of the micro-electronics lab in electrical engineering. The transmitter will radiate 1 watt of power at 38 GHz using a standard 120 VAC power source from an extension cord to a dorm room.
Each measurement activity will take four to five hours.
The team expects to complete measurements by early May, process the information and make a report to the sponsors, Hughes Network Systems, by the end of June, and publish the results of the research by the end of the year. "We'll have a model by next year," Boyle said.