802.11 Overview

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IEEE 802.11 is an industry standard set of specifications for WLANs developed by the Institute of Electrical and Electronics Engineers (IEEE). IEEE 802.11 defines the physical layer and media access control (MAC) sub-layer for wireless communications.

At the physical layer, IEEE 802.11 defines both direct sequence spread spectrum (DSSS) and frequency hopping spread spectrum (FHSS) transmissions. At the MAC sub-layer, IEEE 802.11 uses the carrier sense multiple access with collision avoidance (CSMA/CA) MAC protocol.

The IEEE 802.11 standard currently has four specifications: 802.11, 802.11a, 802.11b, and 802.11g. Windows Embedded CE supports the 802.11, 802.11 a, 802.11 b, and 802.11g specifications.

IEEE 802.11a operates at a data transmission rate as high as 54 megabits per second (Mbps) and uses a radio frequency of 5.8 GHz. Instead of DSSS, 802.11a uses orthogonal frequency-division multiplexing (OFDM). OFDM allows data to be transmitted by sub-frequencies in parallel. Compared to IEEE 802.11, this modulation mode provides better resistance to interference and improved data transmission.

This higher-speed technology improves WLAN networking performance for video and conferencing applications. Because they are not on the same frequencies as Bluetooth devices or microwave ovens, OFDM and IEEE 802.11a devices provide both a higher data rate and a cleaner signal. The bit rate of 54 Mbps is achievable in ideal conditions. In less-than-ideal conditions, the slower speeds of 48 Mbps, 36 Mbps, 24 Mbps, 18 Mbps, 12 Mbps, and 6 Mbps are used.

IEEE 802.11b, an enhancement to IEEE 802.11, provides standardization of the physical layer to support higher bit rates. IEEE 802.11b uses 2.45 GHz, the same frequency as IEEE 802.11, and supports two additional speeds, 5.5 Mbps and 11 Mbps. It uses the DSSS modulation scheme to provide higher data transmission rates. The bit rate of 11 Mbps is achievable in ideal conditions. In less-than-ideal conditions, the slower speeds of 5.5 Mbps, 2 Mbps, and 1 Mbps are used.

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