Copper wire shown to be competitive with fiber optic cable
for LANS December 8, 2003
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, 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, Calif.,
Thursday, Dec. 4. 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 explains. "At these higher speeds, some energy
penetrates into the other wires and produces crosstalk."
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 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 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," adds 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.
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