802.11n, referred to in full as IEEE 802.11n, is an amendment to the IEEE 802.11 standard developed by the Institute of Electrical and Electronics Engineers (IEEE) LAN/MAN Standards Committee which governs methods of transmission over wireless networks.
For the sake of the acceleration of the 802.11n development process, as well as the promotion of a technology specification for interoperability of next-generation wireless local area networking (WLAN) products, a group called the Enhanced Wireless Consortium (EWC) was formed.
A project of the task group IEEE TGn, the 802.11n amendment has been in development since January 2004, and it is expected to be standardized in 2009. The original draft was formed by merged proposals by three competing groups: TGn Sync, WWiSE and MITMOT.
802.11n features the use of multiple-input multiple-output (MIMO). Multiple transmitter and receiver antennas are used in MIMO for the improvement of system performance.
In order to achieve the capacity of a MIMO link, the transmitter antennas use precoding techniques such as spatial beamforming, which improves the received signal quality at the decoding stage, and spatial coding, which increases data throughput with a technique called spatial multiplexing, and increases range by using a technique called Alamouti coding to exploit the spatial diversity.
The receiver antennas use postcoding techniques. In terms of the number of antennas required, the 802.11n amendment requires two receivers and two transmitters (2×2) with a maximum of two streams, although four receivers and four transmitters (4×4) are also allowed. A dual stream MIMO device is expected to reach data rates of up to 270 Mbps, which is 20 times faster than 802.11b, 4 times faster than 802.11g and 3 times faster than 802.11a.
There are three modes that an 802.11 access point can operate in. The first is Legacy mode, which only 802.11a, b and g may operate in. The second is Mixed mode, available for 802.11a, b, g and n. The third one, Greenfield, offers maximum performance, and it is available exclusively for 802.11n.
There are "pre-N," "draft N" and "MIMO-based" products based on early 802.11n specifications being released by major hardware manufacturers. As of August 2007, about 70 products have been certified for compliance with Draft 2.0 of the 802.11n amendment.