IEEE 802.11n
Unit: 12
Lesson: 1
aliases:
802.11nWifi 4
this is a lot of yap for a wifi standard
802.11n increased bandwidth over it's predecessors by multiplexing the signals from 2-4 separate antennae (a radio chain) using MIMO.
Radio Chain
Radio chains are identified using the $A$x$B$:$C$AxB:C notation, where:
- $A$ is the number of transmit (Tx) antennae
- $B$ is the number of the receive (Rx) antennae
- $C$ is the number of simultaneous Tx and Rx streams
Spatial Multiplexing
The maximum possible is 4x4:4, but common configurations include 2x2:2 and 3x3:2. Why? Well if I have a 4x4:4 access point, I could allocate two streams carrying data to two different 2x2:2 clients, increasing bandwidth.
Spatial Diversity
Where multiple Rx antennae can derive a stronger signal, even if there's only one Tx stream, or where multiple Tx antennae can be combined to boost range to improve signal reliability, even if there's only one Rx antennae. For example, 2x2:2 and 2x3:2 have the same throughput, but 2x3:2 can use more Rx antennae to increase range.
Channel Bonding
802.11n products can use both the 2.4 and 5 GHz band. 802.11n also allows for link aggregation for combining 2 20 MHz channels into one 40 MHz channel, called channel bonding. However, channel bonding is only viable in the 5 GHz band due to the highly limited bandwidth on the 2.4 GHz band.
Performance (Raw Lesson Content)
The data rate for 802.11n is 72 Mbps per stream. Assuming the maximum number of four spatial streams and optimum conditions, the nominal data rate could be as high as 600 Mbps for a 40 MHz bonded channel. 802.11n can work in high throughput (HT)/greenfield mode for maximum performance or HT mixed mode for compatibility with older standards (801.11a, 802.11b, and 802.11g). Mixed mode reduces overall WLAN performance, as it involves the transmission of legacy identification and collision avoidance frames (HT protection) but not to the extent that 802.11n devices are reduced to, for example, 802.11g data rates. Operating in greenfield mode is likely to cause substantial interference if there are legacy WLANs operating nearby on the same channel(s).
In recent years, Wi-Fi standards have been renamed with simpler digit numbers. 802.11n is now officially designated as Wi-Fi 4.
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