802.11n is an amendment to the IEEE 802.11-2007 wireless-networking standard. Its purpose is to improve network throughput over the two previous standards—802.11a and 802.11g—with a significant increase in the maximum net data rate from 54 Mbit/s to 600 Mbit/s (slightly higher gross bit rate including for example error-correction codes, and slightly lower maximum throughput) with the use of four spatial streams at a channel width of 40 MHz.
MIMO is a technology that uses multiple antennas to coherently resolve more information than possible using a single antenna. One way it provides this is through Spatial Division Multiplexing (SDM), which spatially multiplexes multiple independent data streams, transferred simultaneously within one spectral channel of bandwidth. MIMO SDM can significantly increase data throughput as the number of resolved spatial data streams is increased.
Channels operating with a width of 40 MHz are another feature incorporated into 802.11n; this doubles the channel width from 20 MHz in previous 802.11 PHYs to transmit data, and provides twice the PHY data rate available over a single 20 MHz channel.
In the 5.8 GHz band 802.11n can achieve increased real bandwidth due to the larger number of available charnels.
There are 76 channels in 2.4 and 5.8 GHz bands with channel 77-127 being reserved. Each channel has varying encoding to support backwards compatibility. Channels can be 20 MHz or 40 MHz depending on other users in the channel space.
The Wi-Fi Alliance was established in mid 2007 to help make sure that draft n implemented interopérable equipment to prevent problems. The Intel Centrino Wi-Fi uses 802.11a to achieve broadband operation with 802.11n wave 2 access points.
The second wave of 802.11n has improved the channel size to 20 or 40 MHz which made for better bandwidth. Mass produced 150 Mbps and 300 Mbps USB adapters are very inexpensive. 802.11n was replaced in the market rather quickly by 802.11ac which is a refinement that provides more bandwidth in mainstream consumer equipment.