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802.11a
one of the original 802.11 wireless standards
released October 1999
operates in 5 GHz range
54 Mbit/s
smaller range than 802.11b
not commonly seen today
802.11b
also an original 802.11 standard
released October 1999
operates in 2.4 GHz range
11 Mbit/s
better range than 802.11a
more frequency conflict
not commonly seen today
802.11g
an upgrade to 802.11b
released in June 2003
operates in 2.4 GHz range
54 Mbit/s (similar to 802.11a)
backwards compatible with 802.11b
same 2.4 GHz frequency conflict problems as 802.11b
802.11n (Wi-Fi 4)
update to 802.11g, 802.11b, 802.11a
released in October 2009
operates at 5 GHz and/or 2.4 GHz (40 MHz channel widths)
600 Mbit/s (40 MHz mode and 4 antennas)
uses MIMO (multiple-input multiple-output, multiple transmit and receive antennas)
802.11ac (Wi-Fi 5)
approved in January 2014
significant improvements over 802.11n
operates in the 5 GHz band (up to 160 MHz channel bandwidth)
increased channel bonding (larger bandwidth usage)
denser signaling modulation (faster data transfers)
8 MU (multi-user)-MIMO downlink streams (2x as many streams as 802.11n, nearly 7 gigabits per sec)
802.11ax (Wi-Fi 6)
approved in February 2021
successor to 802.11ac/Wi-Fi 5
operates at 5 GHz and/or 2.4 GHz (20, 40, 80, and 160 MHz channel widths)
1201 Mbit/s per channel (8 bi-directional MU-MIMO streams)
RFID
Radio-frequency identification
everywhere (access badges, inventory tracking, pet identification)
radar technology (radio energy transmitted to the tag, RF powers tag, ID is transmitted back, bidirectional communication)
NFC
near-field communication
two-way wireless communication (builds on RFID, mostly one-way)
payment systems (credit cards, online wallets)
bootstrap for other wireless (Bluetooth pairing)
Bluetooth
removes the wires (headsets, speakers, keyboards)
uses 2.4 GHz range
short range (most consumer devices operate to about 10m)