802.11n – the one they called Wi-Fi 4

IEEE Std 802.11n-2009, Amendment 13, was the moment Wi-Fi got serious. developed by **Task Group n** and released in 2009, it was officially titled “Enhancements for Higher Throughput” – and it delivered exactly that. the goal? push past 100 Mbps at the MAC service access point (SAP), and make wireless fast enough to compete with wired LANs. mission accomplished.

802.11n introduced **MIMO – Multiple Input Multiple Output** and **MIMO-OFDM**, which meant devices could send and receive multiple streams in parallel using multiple antennas. this didn’t just boost speed – it improved range and reliability too. instead of praying for a clear signal, now the system could work with reflections and spatial paths.

channel-wise, 11n supported both **20 MHz and 40 MHz** bandwidths. using 40 MHz (especially in 5 GHz) meant double the spectrum and double the throughput – when available. in crowded 2.4 GHz bands, that was hit or miss, but still a big deal for flexibility.

for efficiency, 11n brought in **frame aggregation**: **A-MPDU** (Aggregate MAC Protocol Data Unit) and **A-MSDU** (Aggregate MAC Service Data Unit). instead of sending one small packet at a time and dealing with tons of overhead, you could bundle several into one bigger transmission. less airtime wasted, more data moved.

it also defined a full set of new **Modulation and Coding Schemes (MCS)** under the **High Throughput (HT)** banner – including different rates for different antenna configs, guard intervals, and channel widths. the result? top speeds of up to **600 Mbps** on paper with four spatial streams, short guard interval, and 40 MHz channels. in practice, 150–300 Mbps was already a game-changer.

802.11n got baked into **802.11-2012**, and has been part of every standard since – 2016, 2020, and beyond. more importantly, it became the first Wi-Fi standard to earn a consumer-friendly label: **Wi-Fi 4**. and yeah, it was everywhere – homes, offices, phones, routers, embedded devices. this was the moment Wi-Fi stopped being a backup and became the default.

historically? huge. 802.11n made fast, reliable wireless a standard expectation. it killed the Ethernet cable for most people. everything that came after stood on its shoulders.