802.11
refers to a family of specifications developed by the IEEE for wireless LAN
(WLAN) technology. 802.11
specifies an over-the-air interface between a wireless client and a base
station or between two wireless clients.
The
IEEE accepted the specification in 1997.
There
are several specifications in the 802.11 family:
802.11
—
- Applies to wireless LANs.
- 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).
802.11a
—
- An extension to 802.11 that applies to wireless LANs
- Provides up to 54-Mbps in the 5GHz band.
- 802.11a uses an orthogonal frequency division multiplexing encoding scheme rather than FHSS or DSSS.
802.11b
(also referred to as 802.11 High Rate or Wi-Fi) —
- An extension to 802.11 that applies to wireless LANS and
- Provides 11 Mbps transmission (with a fallback to 5.5, 2 and 1-Mbps) in the 2.4 GHz band.
- 802.11b uses only DSSS.
- 802.11b was a 1999 ratification to the original 802.11 standard, allowing wireless functionality comparable to Ethernet.
802.11e
—
- A wireless draft standard that defines the Quality of Service (QoS) support for LANs, and is an enhancement to the 802.11a and 802.11b wireless LAN (WLAN) specifications.
- 802.11e adds QoS features and multimedia support to the existing IEEE 802.11b and IEEE 802.11a wireless standards, while maintaining full backward compatibility with these standards.
802.11g
—
- Applies to wireless LANs and is used for transmission over short distances at up to 54-Mbps in the 2.4 GHz bands.
802.11n
—
- 802.11n builds upon previous 802.11 standards by adding multiple-input multiple-output (MIMO).
- The additional transmitter and receiver antennas allow for increased data throughput through spatial multiplexing and increased range by exploiting the spatial diversity through coding schemes like Alamouti coding.
- The real speed would be 100 Mbit/s (even 250 Mbit/s in PHY level), and so up to 4-5 times faster than 802.11g.
802.11ac
—
- 802.11ac builds upon previous 802.11 standards particularly the 802.11n standard, to deliver data rates of 433Mbps per spatial stream, or 1.3Gbps in a three-antenna (three stream) design.
- The 802.11ac specification operates only in the 5 GHz frequency range and features support for wider channels (80MHz and 160MHz) and beamforming capabilities by default to help achieve its higher wireless speeds.