IEEE 802.11 is a set of standards for a wireless local area network (wlan). The standard is better known as Wi-Fi. IEEE 802.11 comprises of a number of standards.
The original 802.11 standard was published in 1997. This standard provided a data speed of 1 or 2 Mbit/s. The standard operates in the nearly worldwide available 2.4 GHz band ranging from 2400 - 2483.5 MHz. The standard uses either frequency hopping or coding (direct sequence spread spectrum) technology to make the transmissions robust.
802.11a and 802.11h
The 802.11a extension to 802.11 was developed to make use of the lower part of the 5 GHz band. The standard has a maximum bit rate of 54 Mbit/s using OFDM. The allocation in the 5 GHz band for RLAN was later extended. The 5 GHz band ranging from 5150-5350 and from 5470 - 5725 MHz can be used nowadays in most parts of the world. However, equipment has to detect and avoid radar systems that use the band and need to have transmit power control. The 802.11h standard was developed to cater for these provisions.
The IEEE 802.11 standard became popular after the publication of the 802.11b extension in 1999. This extension to the original standard provides a maximum bit rate of 11 Mbit/s. The bit rate will be decreased to 5.5, 2 or 1 Mbit/s if the link quality decreases. The 802.11b standard uses direct sequence spread spectrum coding.
The IEEE 802.11e standard provides a set of Quality of Service features including priority of data streams. This standard is mainly of relevance for time critical applications, such as voice and streaming multimedia.
IEEE 802.11f was a recommendation to ease handovers between access points of different firms. The recommendation is withdrawn.
The 802.11g standard was a further development of the standard to improve the bit rate if the link quality allows. The maximum bit rate is 54 Mbit/s. This bit rate can only be achieved if the user is in the vicinity of the access point.
IEEE 802.11i enhances authentication and encryption. The original standard included WEP (Wired Equivalent Privacy) which proved to be vulnerable. The improved version in IEEE 802.11i is commonly known as WPA2. An intermediate version called WPA (Wi-Fi Protected Access) was introduced after the security issues with WEP were shown. WPA uses a subset of IEEE 802.11i.
IEEE 802.11j is an amendment to the IEEE 802.11 standard for the Japanese market. It allows Wireless LAN operation in the 4.9 to 5 GHz band.
IEEE 802.11k is an amendment to the standard for radio resource management. It allows exchange of radio and network information. This information can be used by the client to switch to the best available access point.
IEEE 802.11n is a standard that further improves the data throughput. The throughput is increased to a maximum net bit rate of 600 Mbit/s. This througput is achieved by using more than one channel (channel bonding) and advanced antenna technology (MIMO).
IEEE 802.11r adds support for roaming to the standard. This makes seamless handovers possible in larger areas with WiFi coverage.
IEEE 802.11s defines how traffic can be delivered over self-configuring multi-hop topologies to create a WLAN mesh network.
IEEE 802.11z is a mechanism to directly transfer data between two Wi-Fi clients that are part of the same Wi-Fi network.
IEEE 802.11ac Gigabit Wi-Fi is specificaly designed to increase the bit rate in the 5 GHz band. This band offers more channels with a better seperation than the 2.4 GHz band. IEEE 802.11ac makes channel bonding possible up to a channel width of 80 MHz, and even 160 MHz under certain conditions. IEEE 802.11ac further uses MIMO and more efficient data encoding mechanisms to increase the maximum bit rate up to 6.93 Gbit/s under certain specialized conditions.
IEEE 802.11ad is specificaly designed for use in the unlicensed 60 GHz band. In this band is far more overall bandwidth available than in the 2.4 and 5 GHz band. The development of the standard started in the Wireless Gigabit Alliance (WiGig), but their work is now moved into the IEEE 802.11ad specification.
IEEE 802.11af is an amendment that uses white spaces in the TV bands. It is also known as White-Fi.