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November 19, 2007 -- Working with cable manufacturer Nexans, a team of
researchers at Penn
State University "has examined the possibility of sending
digital data at a rate of 100 Gbit/sec over 100 meters of Category 7
copper [Ethernet] cabling," according to Mohsen Kavehrad, the
university's W.L. Weiss Endowed chair/professor of electrical
engineering.
The Penn State researchers presented their system to the IEEE
High Speed Study Group last week in Atlanta.
The university's technology seeks to enable copper cables within
a room or building (perhaps being used to interconnect servers) to
handle data rates typically reserved for fiber-optic links. The
researchers say the key is to develop a transmitter/receiver that
uses error correcting and equalizing methods to cancel interference
better than traditional systems.
Using information on specifications and characteristics of the
cables from Nexans, the researchers say they modeled their Cat 7
cable with all attributes including modeling crosstalk. They then
designed a transmitter/receiver equipped with an interference
canceller that could transfer up to 100 Gigabits using error
correcting and equalizing approaches.
"A rate of 100 Gigabit over 70 meters is definitely possible, and
we are working on extending that to 100 meters, or about 328 feet,"
says Ali Enteshari, a graduate student in electrical engineering at
Penn State. "However, the design of a 100 Gigabit modem might not be
physically realizable at this time, as it is technology limited. We
are providing a road map to design a high-speed modem for 100
Gigabits."
The researchers note that all transmission cables are limited by
the distance they can transmit data without degradation of the
signal; and that before errors and interference make the signals
non-recoverable, cable systems can use repeaters - similar to
computer modems - to capture, correct or recover data, and resend
it. The distance between repeaters depends on the cable and the
approach used by the modem to correct errors, say the engineers.
The researchers believe that "two or three generations in the
future," the technology of chip circuitry will allow these modem
designs to be built. Currently, chip design is at about 65
nanometers, but the researchers expect "in the next two generations
to get to what is required," according to professor Kavehrad.
Consisting of four pairs of twisted wires shielded to reduce
crosstalk, Cat 7 cable is of heavier weight than Cat 5 cable;
Kavehrad's group did similar work on Cat 5 cable four years ago.
"What we are offering is a less expensive solution and one that
is easier to build," concludes graduate student Jarir Fadlullah,
another member of the Penn State research team.
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