Researchers push transmission rate of copper
cables
11/14/2007 12:00 am
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Researchers push transmission rate of copper
cables
Wednesday, November 14, 2007
Atlanta – You may not be able to get blood out of a turnip, but
according to Penn State engineers, you can increase the data transmission
of Category-7 copper cables used to connect computers to each other and
the Internet.
"Working with NEXANS, the company that manufactures
the cable, we have examined the possibility of sending digital data at a
rate of 100 gigabits per second over 100 meters of Category-7 copper
cable," says Mohsen Kavehrad, the W.L. Weiss Endowed Chair professor of
electrical engineering. "These are the current, new generation of Ethernet
cables."
These cables are used to connect computers within a room
or a building or to create parallel computing systems. While the long
distance lines of most Internet systems are glass fiber optic cables,
which are very fast, copper cable is generally used for short
distances.
"In home networks, for example, it is expensive to use
fiber optic cabling," says Ali Enteshari, graduate student in electrical
engineering who presented the team's methods to the IEEE High Speed Study
Group today (Nov. 14) in Atlanta.
All transmission cables are
limited by the distance they can transmit data without degradation of the
signal. Before errors and interference make the signals non-recoverable,
cable systems use repeaters – which are 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.
"What we are offering is a less expensive solution
and one that is easier to build," says Jarir Fadlullah, graduate student
in electrical engineering.
Using information on specifications and
characteristics of the cables from NEXANS, the researchers modeled the
cable with all its 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.
Ethernet cable like the Category 7 is made
up of four pairs of twisted wires shielded to reduce crosstalk. Category 7
is heavier weight wire with better shielding than Category 5 cable.
Kavehrad's group did similar analysis on the Category 5 cables in
2003.
"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 Enteshari. "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 roadmap to design a high speed modem for 100
gigabits."
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
they expect in the next two generations to get to what is required, says
Kavehrad.
The amount of data encompassed by 100 gigabits is
amazing. The entire Encyclopedia Britannica contains 1 gigabyte of
information. A byte is equivalent to 8 bits, so 1 Gigabyte is equal to 8
gigabits. A rate of 100 gigabits per second over 100 meters is the
transmission of 12.5 Encyclopedia Britannica sets per second.
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