Engineers at Penn State University in University Park,
Pennsylvania, have developed and simulation-tested a copper wire
transmission scheme for distributing a broadband signal over local
area networks (LANS) with a lower average bit error rate than fiber
optic cable that is ten times more expensive.
Dr. Mohsen Kavehrad, the W. L. Weiss professor of electrical
engineering and director of the Center for Information and
Communications Technology Research who led the study, says, "Using
copper wire is much cheaper than fiber optic cable and, often, the
wire is already in place. Our approach can improve the capability of
existing local area networks and shows that copper is a competitor
for new installations in the niche LAN market."
Kavehrad presented the Penn State team's results in a paper,
10Gbps Transmission over Standard Category-5, 5E, 6 Copper Cables,
at the IEEE GLOBCOM Conference in San Francisco, California, in
December. His coauthors are Dr. John P. Doherty, associate professor
of electrical engineering; Jun Ho Jeong, doctoral candidate in
electrical engineering; and Amab Roy and Gaurav Malhotra, master's
candidates in electrical engineering.
The Penn State approach responds to the IEEE challenge to specify
a signaling scheme for a next generation broadband copper Ethernet
network capable of carrying broadband signals of 10 gigabits per
second. Currently, the IEEE standard carries one gigabit over 100
meters of category 5 copper wire which has four twisted pairs of
wire in each cable.
"In the existing copper gigabit systems, each pair of wires
carries 250 megabits per second. For a 10 gigabit system, each pair
will have to carry 2.5 gigabits per second," Kavehrad explains. "At
these higher speeds, some energy penetrates into the other wires and
produces crosstalk." Crosstalk is eliminated by using a new error
correction method they developed that jointly codes and decodes the
signal and, in decoding, corrects the errors.
Kavehrad says, "Conventional wisdom says you should deal with the
wire pairs one pair at a time but we look at them jointly. We use
the fact that we know what signal is causing the crosstalk
interference because it is the strongest signal on one of the
The approach also takes account of the reduction or loss of
signal energy between one end of the cable and the other that can
become severe in 100 meter copper systems. "We jointly code and
decode the signals in an iterative fashion and, at the same time, we
equalize the signals," he adds. "The new error correction approach
acts like a vacuum cleaner where you first go over the rough spots
and then go back again to pick up more particles."
A MATLAB simulation has shown that the scheme is possible and can
achieve an average bit error rate of 10 to the minus 12 bits per
second. Fiber optic cable typically achieves 10 to the minus nine.
The project is receiving support from Cisco, Tyco, Nexan, and the
International Copper Association.
For more information, contact Dr. Kavehrad at email@example.com
or (814) 865-7179.
Copyright Seven Mountains Scientific, Inc. Mar/Apr 2004
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