ore finely between signals. For external data transfer applications it can be used to greater dis- tances-up to 3 miles. Two major transmission technologies are presently used to achieve indoor wireless communication: radio and infrared. For many reasons, infrared is often preferred. Infrared links provide high bandwidth at low cost, infrared is immune to radio interference, the spectrum is freely available, and infrared components are inexpensive, small, and consume little power. The new optical antenna could help turn even more people toward infrared as an alternative to the high cost of maintaining wired networks. 4.8 KEEPING COPPER With all of the ongoing research into optical technologies, it's easy to forget that old-fashioned copper wiring remains a perfectly suitable, and cheap, technology for many telecommunication applications, particularly those that involve short distances. Penn State University engineers have developed 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. "Using copper wire is much cheaper than fiber-optic cable and, often, the wire is already in place," says Mohsen Kavehrad, a Penn State professor of electrical engineering and director of the school's Center for Information and KEEPING COPPER Communications Technology Research. "Our approach can improve the capa- bility of existing local area networks and shows that copper is a competitor for new installations in the niche LAN market." The Penn State approach was developed in response to an IEEE challenge. The organization wanted 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 specifies 1 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 sec