Standard procedure

The 802.11 standard was primarily intended for wireless LANs, but vendors have designed antennas and added bridging functions to adapt the use of 802.11 products for point-to-multipoint applications for end users in fixed locations.

Many wireless Internet service companies, such as Weblinks and Wave2Wave, base their products on Wi-Fi (IEEE 802.11b) standards, which operate using direct sequence spread spectrum in the 2.4-GHz frequency band. Each channel accommodates an 11M bit/sec signal, and it's possible to have up to three channels operating in the same area without interfering with each other. However, the actual throughput for each channel is often less than 6M bit/sec because of the effects of protocol overhead.

Some wireless Internet providers use frequency hopping spread spectrum (FHSS) components that operate in the 2.4-GHz band. Experts generally agree that FHSS operates better in outdoor applications, such as fixed wireless Internet, because of FHSS's resiliency to impairments such as radio frequency interference and multipath propagation. A version of the 802.11 standard defines FHSS operation, but it only supports data rates of 1M and 2M bit/sec, which is much lower than 802.11b performance.

On the horizon is an IEEE standard focusing on fixed wireless metropolitan-area networks. The IEEE 802.16 Working Group on Broadband Wireless Access is developing a standard for reliable, high-speed network access in the 'last mile' that extends to homes and companies. Recently, the 802.16 standards group made a decision to create a unified air interface document, with a common, flexible media access control platform supporting multiple physical layers. They also approved, pending comment resolution, a draft 10-66 GHz air interface standard with the expectation of publication by year-end. The working group will base a 2-11 GHz air interface standard (referred to as 802.16a) on both single carrier and using orthogonal frequency division multiplexing physical layers.

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Geier provides consulting services to companies implementing wireless Internet systems and in-building wireless LANs. He is the author of Wireless LANs (2nd edition). His Online Guide to Wireless Networking is located at www.wireless-nets.com/guide.htm. He can be reached at jimgeier@wireless-nets.com.

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