The IEEE 802.11 WLAN standard defines how RF in the unlicensed ISM frequency bands is used for the physical layer and the MAC sublayer of wireless links.
Various implementation of the IEEE 802.11 standard have been developed over the years. The following highlights these standards:
- 802.11 - Released in 1997 and now obsolete, this is the original WLAN specification that operated in the 2.4 GHz band and offered speeds of up to 2 Mb/s. When it was released, wired LANs were operating at 10 Mb/s so the new wireless technology was not enthusiastically adopted. Wireless devices have one antenna to transmit and receive wireless signals.
- IEEE 802.11a - Released in 1999, it operates in the less crowded 5 GHz frequency band and offers speeds of up to 54 Mb/s. Because this standard operates at higher frequencies, it has a smaller coverage area and is less effective at penetrating building structures. Wireless devices have one antenna to transmit and receive wireless signals. Devices operating under this standard are not interoperable with the 802.11b and 802.11g standards.
- IEEE 802.11b - Released in 1999, it operates in the 2.4 GHz frequency band and offers speeds of up to 11 Mb/s. Devices implementing this standard have a longer range and are better able to penetrate building structures than devices based on 802.11a. Wireless devices have one antenna to transmit and receive wireless signals.
- IEEE 802.11g - Released in 2003, it operates in the 2.4 GHz frequency band and offers speeds of up to 54 Mb/s. Devices implementing this standard; therefore, operate at the same radio frequency and range as 802.11b, but with the bandwidth of 802.11a. Wireless devices have one antenna to transmit and receive wireless signals. It is backward compatible with 802.11b. However, when supporting an 802.11b client, the overall bandwidth is reduced.
- IEEE 802.11n - Released in 2009, it operates in the 2.4 GHz and 5 GHz frequency bands and is referred to as a dual-band device. Typical data rates range from 150 Mb/s to 600 Mb/s with a distance range of up to 70 m (.5 mile). However, to achieve the higher speeds, APs and wireless clients require multiple antennas using the multiple-input and multiple-output (MIMO) technology. MIMO use multiple antennas as both the transmitter and receiver to improve communication performance. Up to four antennas can be supported. The 802.11n standard is backward compatible with 802.11a/b/g devices. However supporting a mixed environment limits the expected data rates.
- IEEE 802.11ac - Released in 2013, operates in the 5 GHz frequency band and provides data rates ranging from 450 Mb/s to 1.3 Gb/s (1300 Mb/s). It uses MIMO technology to improve communication performance. Up to eight antennas can be supported. The 802.11ac standard is backward compatible with 802.11a/n devices; however, supporting a mixed environment limits the expected data rates.
- IEEE 802.11ad - Scheduled for release in 2014 and also known as “WiGig”, it uses a tri-band Wi-Fi solution using 2.4 GHz, 5 GHz, and 60 GHz, and offers theoretical speeds of up to 7 Gb/s. However, the 60 GHz band is a line-of-site technology and; therefore, cannot penetrate through walls. When a user is roaming, the device switches to the lower 2.4 GHz and 5 GHz bands. It is backward compatible with existing Wi-Fi devices. However supporting a mixed environment limits the expected data rates.
The figure summarizes each 802.11 standard.