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