802.11n is standard for 4th generation of the WiFi. Check more about it.
802.11n with the official name IEEE 802.11n-2009 is the fourth generation of the WiFi family. It can work in the 2.4 GHz or 5 GHz frequency bands. The wireless networking standard uses multiple antennas to increase the speeds. The maximum data rate is up to 600 Mbps – with the use of four spatial streams at a channel width of 40 MHz. The standard supports MIMO – multiple-input multiple-output and a frame aggregation.
MIMO – Multiple-input Multiple-output and Speeds
The 802.11n speeds depend on the number of simultaneous data streams. The number of concurrent data streams is restricted by the number of used antennas on both sides.
The maximum data rate of 600 Mbps is achieved only with the maximum of four spatial streams on 40 MHz channel width.
Types of Modulations Used in 802.11n
The n standard uses the different types of OFDM modulation. The OFDM modulation type depends on the number of spatial streams and the data rate. From the one spatial stream with BPSK and speed of 15 Mbps to the four spatial streams with a 64-QAM modulation and speed of 600 Mbps.
Reducing the Layer Overhead
802.11n has introduced new methods for increasing the overall speed with the reduction of overhead.
- Block Acknowledgement
- Frame Aggregation Mechanism
The block acknowledgement reduces the number of ACKs that a receiver must send to a transmitter for confirming the frame delivery. The older standards (a, b and g) would send 9 ACKs for confirming the frames, 802.11n receiver can do the same job with only one ACK.
The frame aggregation is a process of packing multiple frames in one frame. With this aggregation is accomplished the layer overhead and increasing the packet rate.
Compatibility with the Previous Standards
Wi-Fi Alliance and 802.11n
WiFi Alliance has started certifying n products since 2007. They tested set of features and level of interoperability among vendors. The certification program involved both 20 MHz and 40 MHz channels, with up to two spatial streams. The maximum speeds were 144 Mbps for 20 MHz and 300 Mbps for 40 GHz.
More about the standard read on IEEE 802.11n-2009.
To find out more about the WLAN and other 802.11 networks check What Does WLAN Stand For.