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Copper Wire Competitive
With Fiber Optic Cable For LANS
Penn State engineers 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 10 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, said, "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,
Dec.4 at the IEEE GLOBCOM Conference. His co-authors are: Dr. John
F. Doherty, associate professor of electrical engineering; Jun Ho
Jeong, doctoral candidate in electrical engineering; Arnab Roy, a
master's candidate in electrical engineering; and Gaurav Malhotra, a
master's candidate 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 sec," Kavehrad explained. "At
these higher speeds, some energy penetrates into the other wires and
The Penn State scheme eliminates crosstalk by using a new error
correction method they developed that jointly codes and decodes the
signal and, in decoding, corrects the errors.
Kavehrad said, "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
wires." The Penn State 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," added the Penn
State researcher. "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 work is continuing.