Definition
IEEE 802.11af is an amendment to the IEEE 802.11 family of standards that specifies the operation of wireless local area networks (WLANs) in the television broadcast “white‑space” spectrum (typically 470 MHz to 790 MHz). The amendment is commonly referred to as “Super Wi‑Fi.”
Overview
The 802.11af amendment enables WLAN devices to access unused channels in the TV broadcast bands by employing cognitive‑radio techniques, primarily a geolocation database to identify permissible frequencies at a given location. By operating at lower frequencies than conventional Wi‑Fi (2.4 GHz and 5 GHz), 802.11af can achieve longer propagation distances and better penetration through obstacles, making it suited for rural broadband, community networks, and IoT deployments where coverage area is a priority. The standard was ratified by the IEEE 802.11 Working Group in 2013 and subsequently published in the IEEE 802.11af-2014 specification.
Etymology/Origin
- IEEE: Institute of Electrical and Electronics Engineers, the standards‑development organization responsible for the 802.11 family.
- 802.11: The identifier for the WLAN (Wi‑Fi) working group within IEEE.
- af: The alphabetical suffix assigned by the working group to denote this particular amendment; earlier amendments include “a” (802.11a), “b” (802.11b), etc.
The suffix “af” does not carry a specific linguistic meaning beyond its role as a sequential identifier.
Characteristics
| Characteristic | Description |
|---|---|
| Operating Spectrum | TV white‑space channels in the 470 MHz–790 MHz band, depending on regional allocation. |
| Channel Bandwidth | Typically 6 MHz, 7 MHz, or 8 MHz, matching the channel spacing used by terrestrial TV services. |
| Modulation & PHY | Orthogonal Frequency‑Division Multiplexing (OFDM) with optional use of higher‑order constellations (e.g., 64‑QAM) and Multiple‑Input Multiple‑Output (MIMO) techniques. |
| Maximum Data Rate | Up to approximately 350 Mbps using 2 × 2 MIMO and 64‑QAM; actual rates depend on channel width, coding, and environmental conditions. |
| Range & Propagation | Longer range than 2.4 GHz/5 GHz Wi‑Fi, often exceeding 1 km in line‑of‑sight conditions, owing to lower frequency and favorable propagation characteristics. |
| Regulatory Mechanism | Devices must query a certified geolocation database (or, where permitted, perform spectrum sensing) to obtain a list of available channels and transmit power limits for their current location. |
| Transmit Power | Typically limited to a few tens of milliwatts ERP (Effective Radiated Power), with exact limits set by national regulators (e.g., FCC in the United States, Ofcom in the United Kingdom). |
| Compatibility | Not directly backward‑compatible with other 802.11 amendments; however, devices may support multiple radios (e.g., 802.11n/ac on 5 GHz and 802.11af on TVWS) within a single chipset. |
Related Topics
- IEEE 802.11 – The broader family of Wi‑Fi standards covering various frequency bands and technologies.
- IEEE 802.11ah (HaLow) – An amendment targeting sub‑1 GHz operation for low‑power IoT devices, distinct from 802.11af’s use of TV white spaces.
- TV White Spaces (TVWS) – Unused portions of the television broadcast spectrum made available for secondary services.
- Cognitive Radio – Radio systems that adapt their transmission parameters based on environmental awareness, a core principle of 802.11af.
- Geolocation Database – A regulatory tool used by 802.11af devices to determine permissible channels and power levels based on location.
- OFDM (Orthogonal Frequency‑Division Multiplexing) – The modulation scheme employed in most modern Wi‑Fi standards, including 802.11af.
- MIMO (Multiple‑Input Multiple‑Output) – Antenna technology that increases throughput and robustness, supported in 802.11af implementations.
Note: The above information reflects the current understanding of IEEE 802.11af as documented in IEEE publications and regulatory guidelines. Accurate information is not confirmed for any unpublished or future revisions of the standard.