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Chapter 1 - Introduction

The IEEE 802.11b Specification

In 1997, the Institute of Electrical and Electronics Engineers (IEEE) adopted

the 802.11 standard for wireless devices operating in the 2.4 GHz frequency

band. This standard includes provisions for three radio technologies: direct

sequence spread spectrum, frequency hopping spread spectrum, and

infrared. Devices that comply with the 802.11 standard operate at a data

rate of either 1 or 2 Mbps.

In 1999, the IEEE created the 802.11b standard. 802.11b is essentially

identical to the 802.11 standard except 802.11b provides for data rates of

up to 11 Mbps for direct sequence spread spectrum devices. Under 802.11b,

direct sequence devices can operate at 11 Mbps, 5.5 Mbps, 2 Mbps, or 1

Mbps. This provides interoperability with existing 802.11 direct sequence

devices that operate only at 2 Mbps.

Direct sequence spread spectrum devices spread a radio signal over a range

of frequencies. The IEEE 802.11b specification allocates the 2.4 GHz

frequency band into 14 overlapping operating Channels. Each Channel

corresponds to a different set of frequencies. See the Appendix to determine

the center frequency used by each Channel.

If operating multiple 802.11b Home Gateways in the same vicinity, the

distance between the center frequencies must be at least 25 MHz to avoid

interference. Note that the Channels available to an 802.11b Home Gateway

will vary from country to country. In the United States, the 802.11b standard

allocates 11 operating Channels for direct sequence devices. Channels 1,

6, and 11 are independent and do not overlap with each other. To avoid

interference between 802.11b Home Gateways, It is recommended that you

configure the Home Gateways using only Channels 1, 6, and 11.

SpaceLink Home Gateway