802.16a wireless links the last mile

First-generation proprietary technology for broadband fixed wireless networks had lackluster non-line-of-sight performance, and the equipment was relatively expensive. Both of these drawbacks delayed widespread deployment of broadband wireless networks. However, the advent of the Institute of Electrical and Electronics Engineers (IEEE) 802.16a standard for wireless metropolitan-area networks is likely to accelerate adoption.

Approved in January, 802.16a provides wireless, last-mile broadband access over the frequency bands below 11 GHz to connect homes, businesses and wireless LAN hot spots. 802.16a also is known as WiMAX because the Worldwide Interoperability for Microwave Access Forum industry group is working to promote the standard's deployment.

802.16a greatly improves non-line-of-sight performance, and it is the most appropriate technology available when obstacles such as trees and buildings are present. Stations can be mounted on homes or buildings rather than towers on mountains.

Just as important, standards-based products are less expensive to manufacture, and interoperability reduces the risk to carriers that wish to roll out service. Both of these factors should help spur deployment. Equipment manufacturers are expected to start implementing 802.16a in systems in the second half of next year.

With throughput up to 75M bit/sec, the wireless standard gives companies another way to get business-quality broadband service. While it could take several months for a carrier to provision a T-1 line, service providers could provision wireless service in a matter of days.

802.16a provides flexibility not possible with wired services, such as high-speed backhaul for events such as trade shows, with hundreds or even thousands of 802.11 hot-spot users. On-demand connectivity also could benefit businesses such as construction companies that have sporadic or nomadic connectivity needs. The 802.16e extension to 802.16a introduces nomadic capabilities that let users connect while roaming outside their home service areas.

The technology also offers privacy and Triple-DES encryption features to support secure transmissions and authentication.

In a typical enterprise deployment, laptop and desktop computers are connected via wired Ethernet or 802.11 Wi-Fi access points located throughout the campus. An 802.16a directional antenna provides the connection from the business to a service provider's cell tower. Even if there is no line of sight between the antenna and the tower, signal still can be received after it reflects off buildings or other obstructions and reaches the tower indirectly. At the base station, 802.16a technology correctly interprets the information even though reflections distort the radio frequency signal. Backhaul to the Internet is then provided via wireless 802.16 point-to-point links or by traditional wired backhaul such as DS3 and OCX.

Technical aspects of 802.16a that are instrumental in powering robust performance include:

- Support for licensed and license-exempt band operation below 11 GHz.

- High spectral efficiency, which reduces carriers' costs and improves users' experience.

- Forward error correction, for more reliable transmission.

- Support for advanced antenna techniques to improve range and capacity.

- Space/time coding to enhance performance in fading environments.

- Adaptive modulation support, which allows for trade-off of bandwidth for range to reach customers up to 30 miles away.

802.16a technology also provides low latency for delay-sensitive services such as circuit-switched voice traffic or voice over Internet Protocol, optimized transport for video, and prioritization of data traffic. This is especially important for businesses that want voice in addition to data services from their broadband service provider.

With the IEEE 802.16a standard in place, it is expected that carriers will be able to offer enterprise and individual customers more options for broadband connectivity at a lower cost. For the millions of people worldwide who cannot get access to broadband connectivity via cable or Digital Subscriber Line, the new 802.16a wireless technology will enable a "third pipe" to connect to the many benefits of the Internet.

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