Wireless Communications Basics --- Wi-Fi 4/5/6

Wi-Fi 4/5/6 indicate the forth-, fifth-, and sixth-generation of Wi-Fi technologies. The following table describes the differences between the Wi-Fi technologies.
Wi-Fi technologies are compatible downwards if they use the same bands. Take Wi-Fi 5 as an example. It supports only the 5 GHz band. Therefore, it is compatible with Wi-Fi 2 (802.11a) and Wi-Fi 4 (802.11n).Wi-Fi 6 supports both the 2.4 and 5 GHz bands. Therefore, it is compatible with Wi-Fi technologies that use the 2.4 or 5 GHz band.


Each generation of Wi-Fi technology has evolved features improving the transmission rate. Examples:
1.  
Wi-Fi4 (802.11n)
(1) Orthogonal frequency division multiplexing(OFDM)
(2) Forward Error Correction (FEC)
(3) Short Guard Interval (Short GI)
(4) Channel bonding/40 MHz bonding
(5) MIMO

2.
Wi-Fi5 (802.11ac)
802.11ac Wave1 (Wi-Fi 5 first release)
(1) Channel bonding/80 MHz bonding
(2) 256-QAM
(3) MIMO
802.11ac Wave2 (Wi-Fi 5 second release)
(1) Downlink MU-MIMO

3.
Wi-Fi6 (802.11ax)
(1) Rate improvement (1024-QAM)
(2) Multi-STA transmission
•  Orthogonal frequency-division multiple access (OFDMA)
•  Uplink and downlink MU-MIMO
(3) Spatial reuse (SR) (anti-interference)
•  BSS fast identification
• Dynamic CCA threshold
(4) TWT power saving management technology