Page 161 - DCAP311_DCAP607_WIRELESS_NETWORKS

Unit 10: Wireless MAN Technologies

rather than the 2.4 GHz ISM frequency band, where adjacent channels overlap - see list of WLAN Notes
channels. Better or worse performance with higher or lower frequencies (channels) may be
realized, depending on the environment.
The segment of the radio frequency spectrum used by 802.11 varies between countries. In the US,
802.11a and 802.11g devices may be operated without a license, as allowed in Part 15 of the FCC
Rules and Regulations. Frequencies used by channels one through six of 802.11b and 802.11g
fall within the 2.4 GHz amateur radio band. Licensed amateur radio operators may operate
802.11b/g devices under Part 97 of the FCC Rules and Regulations, allowing increased power
output but not commercial content or encryption.
10.1.1 Wi-Fi Standards

The 802.11 standard is defined through several specifications of WLANs. It defines an over-the-
air interface between a wireless client and a base station or between two wireless clients.
There are several specifications in the 802.11 family:

z z 802.11: This pertains to wireless LANs and provides 1- or 2-Mbps transmission in the 2.4-
GHz band using either frequency-hopping spread spectrum (FHSS) or direct-sequence
spread spectrum (DSSS).
z z 802.11a: This is an extension to 802.11 that pertains to wireless LANs and goes as fast as 54
Mbps in the 5-GHz band. 802.11a employs the orthogonal frequency division multiplexing
(OFDM) encoding scheme as opposed to either FHSS or DSSS.

z z 802.11b: The 802.11 high rate Wi-Fi is an extension to 802.11 that pertains to wireless LANs
and yields a connection as fast as 11 Mbps transmission (with a fallback to 5.5, 2, and 1
Mbps depending on strength of signal) in the 2.4-GHz band. The 802.11b specification uses
only DSSS. Note that 802.11b was actually an amendment to the original 802.11 standard
added in 1999 to permit wireless functionality to be analogous to hard-wired Ethernet
connections.

z z 802.11g: This pertains to wireless LANs and provides 20+ Mbps in the 2.4-GHz band.
Here is the technical camparsion between the three major Wi-Fi standards.

Source: http://www.tutorialspoint.com/wi-fi/wifi_ieee_standards.htm

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