IEEE 802.11n is a proposed amendment to the IEEE 802.11-2007 wireless networking standard to significantly improve network throughput over previous standards, such as 802.11b and 802.11g, with a significant increase in raw (PHY) data rate from 54 Mbit/s to a maximum of 600 Mbit/s. Most devices today support a PHY rate of 300 Mbit/s, with the use of 2 Spatial Streams at 40 MHz. Depending on the environment, this may translate into a user throughput (TCP/IP) of 100 Mbit/s.
According to the book "WI-Fi, Bluetooth, Zigbee and Wimax" :
802.11n is the 4th generation of wireless LAN technology.
• First generation (IEEE 802.11) since 1997 (WLAN/1G)
• Second generation (IEEE 802.11b) since 1998 (WLAN/2G)
• Third generation (802.11a/g) since 2000 (WLAN/3G)
• Fourth generation (IEEE 802.11n) (WLAN/4G)
The distinguishing features of 802.11n are:
• Very high throughput (some hundreds of Mbps)
• Long distances at high data rates (equivalent to IEEE 802.11b at 500 Mbps)
• Use of robust technologies (e.g. multiple-input multiple-output [MIMO] and space time coding).
In the N option, the real data throughput is estimated to reach a theoretical 540 Mbps (which may require an even higher raw data rate at the physical layer), and should be up to 100 times faster than IEEE 802.11b, and well over ten times faster than IEEE 802.11a or IEEE 802.11g. IEEE 802.11n will probably offer a better operating distance than current networks. IEEE 802.11n builds upon previous IEEE 802.11 standards by adding MIMO. MIMO uses multiple transmitter and receiver antennae to allow for increased data throughput through spatial multiplexing and increased range by exploiting the spatial diversity and powerful coding schemes. The N system is strongly based on the IEEE 802.11e QoS specification to improve bandwidth performance. The system supports basebands width of 20 or 40MHz..
Note that there is 802.11n PHY and 802.11n MAC that will be required to achieve 540Mbps.
To achieve maximum throughput a pure 802.11n 5 GHz network is recommended. The 5 GHz band has substantial capacity due to many non-overlapping radio channels and less radio interference as compared to the 2.4 GHz band. An all-802.11n network may be impractical, however, as existing laptops generally have 802.11b/g radios which must be replaced if they are to operate on the network. Consequently, it may be more practical to operate a mixed 802.11b/g/n network until 802.11n hardware becomes more prevalent. In a mixed-mode system, it’s generally best to utilize a dual-radio access point and place the 802.11b/g traffic on the 2.4 GHz radio and the 802.11n traffic on the 5 GHz radio.