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Chapter 6
Chapter 6 - Glossary
IEEE 802.11a (54Mbits/sec)
The 802.11b standard was designed to operate in the 2.4-GHz ISM
(Industrial, Scientific and Medical) band using direct-sequence spread-
spectrum technology. The 802.11a standard, on the other hand, was designed
to operate in the more recently allocated 5-GHz UNII (Unlicensed National
Information Infrastructure) band. And unlike 802.11b, the 802.11a standard
departs from the traditional spread-spectrum technology, instead using a
frequency division multiplexing scheme that's intended to be friendlier to
office environments.
The 802.11a standard, which supports data rates of up to 54 Mbps, is the
Fast Ethernet analog to 802.11b, which supports data rates of up to 11
Mbps. Like Ethernet and Fast Ethernet, 802.11b and 802.11a use an identical
MAC (Media Access Control). However, while Fast Ethernet uses the same
physical-layer encoding scheme as Ethernet (only faster), 802.11a uses an
entirely different encoding scheme, called OFDM (orthogonal frequency
division multiplexing).
The 802.11b spectrum is plagued by saturation from wireless phones,
microwave ovens and other emerging wireless technologies, such as
Bluetooth. In contrast, 802.11a spectrum is relatively free of interference.
The 802.11a standard gains some of its performance from the higher
frequencies at which it operates. The laws of information theory tie
frequency, radiated power and distance together in an inverse relationship.
Thus, moving up to the 5-GHz spectrum from 2.4 GHz will lead to shorter
distances, given the same radiated power and encoding scheme.
