Wi-Fi
How IEEE 802.11 amendments map to Wi-Fi generations, how the contention-based MAC works, and what OFDMA in 802.11ax and multi-link operation in 802.11be change for engineers.
Overview
Wi-Fi is the wireless LAN technology defined by the IEEE 802.11 working group and certified by the Wi-Fi Alliance. The IEEE writes the standard, a base document revised every few years plus lettered amendments. The current base revision is IEEE 802.11-2024, according to the 802.11 timelines page. The Wi-Fi Alliance runs interoperability certification and, since October 2018, the generation names, such as Wi-Fi 6 for devices that support 802.11ax, according to its announcement.
Wi-Fi works in unlicensed spectrum, so every device must share the channel with its neighbours and with other technologies. That one fact explains most of its design. This hub is for engineers who need to read 802.11 captures, plan a network, or understand what a new amendment really changes.
Key ideas
Amendments and generations
The table maps the main amendments to their names. Approval years and short titles are from the IEEE 802.11 timelines page.
| Amendment | Generation name | IEEE SA approval | Main change |
|---|---|---|---|
| 802.11a and 802.11b | none | 1999 | Higher-speed PHYs at 5 GHz (a) and 2.4 GHz (b) |
| 802.11g | none | 2003 | Further higher data rates at 2.4 GHz |
| 802.11n | Wi-Fi 4 | 2009 | High Throughput |
| 802.11ac | Wi-Fi 5 | 2013 | Very High Throughput below 6 GHz |
| 802.11ax | Wi-Fi 6 (6E in the 6 GHz band) | 2021 | High Efficiency WLAN, OFDMA |
| 802.11be | Wi-Fi 7 | 2024 | Extremely High Throughput, multi-link |
| 802.11bn | not yet named in our sources | in progress | Ultra High Reliability |
At the time of writing, 802.11bn was at draft 2.10, with approval predicted for May 2028 on the IEEE timeline. Other amendments matter for specialists: 802.11ah for sub-1 GHz operation, 802.11ad and 802.11ay at 60 GHz, and 802.11az for positioning.
A contention-based MAC
Wi-Fi uses carrier sense multiple access with collision avoidance (CSMA/CA). A station listens before it transmits. If the medium is busy, it waits for it to go idle, then counts down a random backoff. A frame that is not acknowledged is assumed lost and is retried with a longer backoff. Every station competes with every other station on the channel, including the access point. This is the main contrast with cellular, where the base station schedules almost every transmission. Contention costs airtime in preambles, gaps and collisions, so the gain from a faster PHY shrinks as the number of busy stations grows.
OFDMA in Wi-Fi 6
Earlier generations sent one user’s frame across the whole channel at a time. 802.11ax brought OFDMA to Wi-Fi. The access point divides the channel into resource units and serves several stations in the same transmission, in both downlink and uplink. Uplink OFDMA needs the access point to trigger and schedule the stations, which moves Wi-Fi a step towards the cellular model. The Wi-Fi Alliance Wi-Fi 6 page also lists multi-user MIMO and target wake time, which lets a station agree when to wake and so saves battery. Khorov and co-authors give a full tutorial on 802.11ax.
Spectrum changed too. In the United States, the FCC adopted rules on 23 April 2020 that make the 6 GHz band, 5.925 to 7.125 GHz, available for unlicensed use, according to the FCC news release. Low-power indoor access points may use the whole 1,200 MHz. Standard-power access points may use 850 MHz under an automated frequency coordination system that protects incumbent links. Other countries have opened different parts of the band, so check your national regulator.
Multi-link operation in Wi-Fi 7
802.11be (approved in 2024) defines the multi-link device (MLD). An MLD is one logical device with several affiliated radios, for example on 2.4, 5 and 6 GHz. It carries one traffic flow over several links, and a frame can be retransmitted on any of them. Liu and co-authors describe two modes in their 802.11be feature summary (arXiv, 2023). A simultaneous transmit and receive (STR) MLD uses its links independently. A non-STR MLD cannot transmit on one link while receiving on another. 802.11be also adds 320 MHz channels in the 6 GHz band, 4096-QAM and the assignment of several resource units to one station.
Where to start
Read OFDM from scratch first, because Wi-Fi 6 and Wi-Fi 7 are built on OFDM and OFDMA. Fading channels explains why indoor links vary so much over a few centimetres. The OFDM and multicarrier hub and the MIMO and beamforming hub cover the PHY in depth. For the 6 GHz rules and channel sharing, see the spectrum, security and regulation hub.
Tools and platforms
| Tool | What for | Licence |
|---|---|---|
| Wireshark | Decoding 802.11 frames from a monitor-mode capture | GPL-2.0 |
| IEEE 802.11 working group | Task groups, drafts in progress and published standards | IEEE terms |
| Wi-Fi Alliance certification search | Checking what a product is certified for | Wi-Fi Alliance terms |
Chipset vendors are on the Qualcomm platform hub. Signal analysers and Wi-Fi test sets are covered on the Keysight and Rohde & Schwarz hubs.
Common mistakes
- Quoting the PHY rate as throughput. MAC overhead and contention take a large share.
- Using 160 or 320 MHz channels in a dense building, where fewer non-overlapping channels mean more contention.
- Assuming a Wi-Fi 7 label means every link uses MLO. Both ends must support it, and the mode (STR or non-STR) matters.
- Planning 6 GHz coverage with 5 GHz numbers. Path loss and allowed power differ.
- Forgetting that 6 GHz rules differ by country.
Going deeper
- The IEEE 802.11 working group and its timelines page.
- Khorov and co-authors, A Tutorial on IEEE 802.11ax High Efficiency WLANs, IEEE Communications Surveys and Tutorials, 2019.
- Deng and co-authors, IEEE 802.11be Wi-Fi 7: New Challenges and Opportunities, IEEE Communications Surveys and Tutorials, 2020.
- Liu and co-authors, IEEE 802.11be Wi-Fi 7: Feature Summary and Performance Evaluation, arXiv, 2023.
- The FCC 6 GHz news release of 23 April 2020.