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Fall 1999



Tech Deploys World's 1st Rural TDD Network Using LMDS Spectrum Purchased Last Year

Virginia Tech has deployed its first wireless network utilizing the high-bandwidth radio spectrum that it purchased last year. The first-of-its-kind TDD network provides several off-campus offices with wireless DS1 and Ethernet bridge service, replacing leased lines and dial-up modems.

Shown here, an outdoor unit sits atop the Virginia Tech Museum of Natural History building - one of the remote sites. Approximately 25 computers are operating on the LAN, including two servers. (Photo by John McCormick)

Virginia Tech has deployed the world's first rural broadband wireless local multipoint distribution service (LMDS) network based on time division duplexing (TDD).
The point-to-multipoint network utilizes Tech's new high bandwidth radio spectrum and provides wireless internet service to selected off-campus university office sites. The three-beam, five customer network, uses technology developed by Wavtrace, Inc. of Bellevue, Washington.

The network is the first step in developing an LMDS research testbed for advanced wireless telecommunications. Tech purchased the 1150-megahertz wireless spectrum in an FCC auction last year. The Tech spectrum includes the greater Roanoke, Martinsville, Danville, and Bristol areas.

The value of the spectrum has increased dramatically in the last year, according to Cortney Martin, LMDS director in the university's Communications Network Services (CNS). "One of the larger winners in the LMDS auction, Virginia-based WNP, resold their largely urban market licenses in just nine months for four times their original purchase price," she said.
In addition to developing a research testbed, the university is using its spectrum to support economic development of rural areas by providing citizens and communities with early access to the emerging technologies of LMDS.

"LMDS is uniquely positioned to serve nontraditional, rural areas," Martin said. "Many communities lack access to broadband media such as fiber, and may even lack cable TV or reliable phone service. There may be a dearth of competition and related high prices for telecommunications services. Broadband wireless, or LMDS, is a flexible, scalable technology that will prove to be a good fit for rural areas."

The Center for Wireless Telecommunications (CWT) is coordinating most of the research efforts involved, while the CNS group is responsible for overall deployment.
LMDS Testbed

The TDD LMDS network is based on time division duplexing, in which transmit and receive occur on the same channel. Conventional technologies employ frequency division duplexing (FDD), which simultaneously transmits and receives on separate channels.

When completed this fall, the Tech system will include one hub with three 30 degree beams, providing wireless DS1 and Ethernet bridge service to five remote sites.
The customers for the field trial include university affiliates located in off-campus leased spaces. These offices are not connected to the campus backbone network and previously relied on leased lines and dial-up modems for service. "LMDS offered a significant improvement in service, and the portability of the equipment was ideal for the remote sites," Martin said. "The radio links are performing well and the level of customer satisfaction is very high," she reported.

CWT is conducting several projects to determine the ideal applications for this type of system. Eric Johnson, a CWT graduate student, is serving as the engineer primarily responsible for the Wavtrace system installation and testing in Blacksburg. He has designed a monitoring system that measures local weather conditions along with the bit error rate, received signal strength, and carrier-to-noise ratio on the radio links. One of his research interests is in how predicted link behavior in rain compares to actual performance. For a complete overview of the project, visit http://www.lmds.vt.edu/.

The Bradley Department of Electrical and Computer Engineering
Virginia Tech

Last Updated, October 15, 1999
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