Wi-Fi 4
Wi-Fi · 9 specs
Direct Answer
Wi-Fi 4 (IEEE 802.11n) was ratified in 2009, introducing Multiple-Input Multiple-Output (MIMO) spatial streaming and optional 40 MHz channel bonding across both 2.4 GHz and 5 GHz bands, achieving maximum theoretical physical link rates up to 600 Mbps.
Source: IEEE 802.11n-2009 / Wi-Fi Alliance · Last reviewed Aug 28, 2026
Specs
| IEEE Standard | IEEE 802.11n-2009 |
| Wi-Fi Generation | Wi-Fi 4 |
| Ratification Year | 2009 |
| Frequency Bands | 2.4 GHz and 5 GHz (Dual-Band) |
| Max Channel Width | 40 MHz |
| Max Theoretical PHY Rate | 600 Mbps |
| Max Spatial Streams (MIMO) | 4x4 |
| Modulation Standard | 64-QAM |
| Guard Interval | 400 ns (Short GI) / 800 ns (Standard) |
MIMO Revolution
802.11n was the first Wi-Fi standard to utilize Multiple-Input Multiple-Output (MIMO) antenna arrays. By exploiting multipath propagation through Spatial Multiplexing, transmitters could split data streams across multiple antennas, multiplying throughput linearly per stream (up to 150 Mbps per spatial stream at 40 MHz with 64-QAM).
2.4 GHz vs 5 GHz Dual-Band
Wi-Fi 4 introduced widespread simultaneous dual-band routers. While 40 MHz channels were supported on 2.4 GHz, real-world deployment on 2.4 GHz was often restricted to 20 MHz due to severe interference with neighboring networks and Bluetooth devices across the narrow 83.5 MHz ISM band.