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Technology Round-Up

Wireless Optical Networks: Bridging the Last Mile

Not long ago, the expectation was that high-volume, high-speed fiber optic networks would carry bandwidth to customers everywhere. But according to the Wireless Communications Association International, of the 4.6 million commercial buildings in the U.S., 99 percent are not serviced by existing fiber optic cable. While both primary and secondary carriers have managed to implement a core infrastructure ring of fiber optic cable in most metropolitan areas, financial and time constraints as well as physical access limitations have prevented carriers from delivering high bandwidth across "the last mile." Not surprisingly then, experts project that as market demand for increased bandwidth continues, the optical wireless market will grow to a two-billion-dollar industry by 2005.

There are many reasons for a college campus to go wireless. Some schools want the luxury of a ubiquitous network for mobile accessibility, some can't afford to extend their wired network to additional buildings, and still others have buildings on campus that will not hold up structurally to fiber optic wiring.

An alternative to wired networks, optical wireless communication or laser technology, was developed in the 1960s. The concept of free space, light-based communication, however, was first described by Alexander Graham Bell in 1880.

Optical wireless transmission is the processing of digital signal transmission along narrow beams of light through the atmosphere, or "free space." Highly focused lasers transmit beams of light onto sensitive photon detector receivers. The receivers of optical wireless systems are telescopic lenses able to collect the photon stream and transmit digital data containing Internet messages, video images, radio signals, and computer files.

Optical wireless lasers operate at a wavelength in the infrared part of the spectrum, and are certified eye-safe for use in populated areas. These lasers send data through an atmospheric spectrum not regulated by federal authorities, dispensing with the need for licensing. Other advantages of optical wireless networks include rapid deployment capabilities, freedom from RF and EM interference, transmission security, and large reductions in cost.

For a campus that has wired only a few buildings, or all but a few buildings, an optical wireless solution can be a boon. There is no need to wait for the installation of additional fiber and no disruption of the campus or buildings—it can be the equivalent of plug and play technology. Once a transmitter and receiver are installed, bandwidth is immediately available in the non-wired building.

fSONA: At the Speed of Light

fSONA, which stands for Free Space Optical Networking Architecture, holds an exclusive license for optical wireless receiver technology originally developed by British Telecom Labs. The SONAbeam product line, currently completing its Beta testing phase, offers point-to-point, line-of-sight, full duplex synchronous transmission at speeds well beyond those provided by 802.11a and b, at a much smaller cost than fiber optic networks. The SONAbeam series of products are capable of carrying information at data rates from 125 Mbps (Fast Ethernet) up to 1.25 Gbps (Gigabit Ethernet, OC-24) over a propagation distance of up to 2.5 miles. Currently, installation of a mile of optical fiber access in metropolitan locations can cost as much as $500,000. In comparison, the initial SONAbeam system—including two transceivers and a backup microwave link—costs less than $25,000. Another advantage of SONAbeam systems is that they are deployable within 24 hours, once line-of-sight access is available. For longer distance connections, the dynamic beam-tracking and alignment system actually makes installation possible in less than 30 minutes. In addition, the system can be re-deployed in the event of a consolidation or move.

One of the problems with optical wireless systems over longer distances has been that they require line of sight, and the narrow beam can easily become misaligned, reducing reliability.

For links across a mile or more, or in areas where building sway could be a factor, fSona's proprietary dynamic beam- tracking system relies on a custom-designed, frictionless gimbal that takes into account building movement and inclement weather, keeping the beam on track. fSONA's products are engineered to achieve between 99 and 99.9 percent availability over their operating range—from 1.2 to 2.5 miles. For sites requiring even higher reliability, fSONA offers the option of combining a primary optical link with either a radio-frequency (RF) backup service or a lower speed wireline service for 99.999 percent availability.

The SONAbeam 155-2 transmits data at 155Mbps over 1.25 miles (2 kilometers), and will be ready to ship next month. Other SONAbeam products are differentiated by range and rate of transmission, but shipping dates are not yet available.

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