Also known as: 802.11, IEEE 802.11, WLAN PHY, Wi-Fi PHY
Wi-Fi (802.11) is the wireless local-area-network air interface defined by the IEEE 802.11 family, which carries data over unlicensed radio in the 2.4, 5, and 6 GHz bands using OFDM subcarriers and, in later generations, MIMO spatial streams and OFDMA.1 This page covers the physical layer and radio interface; for the everyday networking concept see Wi-Fi.
Overview
Wi-Fi began in 1997 as a 1–2 Mbit/s spread-spectrum system, but its modern form dates to 1999 when 802.11a/g adopted OFDM: instead of one fast carrier, the channel is split into dozens of slow, orthogonal subcarriers, each modulated with QAM. This makes the link robust to the multipath echoes that plague indoor radio. Successive generations — marketed by the Wi-Fi Alliance as Wi-Fi 4 (11n), 5 (11ac), 6 (11ax), and 7 (11be) — widened channels, added MIMO spatial streams, denser constellations, and OFDMA multi-user scheduling.
Technical characteristics
| Property | Value |
|---|---|
| Standard | IEEE 802.11 a/b/g/n/ac/ax/be |
| Bands | 2.4, 5, 6 GHz (unlicensed) |
| Channel width | 20, 40, 80, 160, 320 MHz |
| Access | CSMA/CA; downlink/uplink OFDMA in 11ax+ |
| PHY (legacy) | DSSS/CCK (11b), OFDM (11a/g) |
| PHY (modern) | OFDM + MIMO, up to 4096-QAM (11be) |
| Subcarrier spacing | 312.5 kHz (legacy) / 78.125 kHz (HE) |
Peak rates rose from 54 Mbit/s (11g) past 1 Gbit/s (11ac) to multi-gigabit (11ax/be) by combining wider channels, more spatial streams, and denser QAM. Actual throughput depends heavily on signal-to-noise ratio, interference, and contention.
History
The 802.11 working group formed under the IEEE in 1990 and published the first standard in 1997. 802.11b (1999) popularised the 2.4 GHz band; 802.11a/g brought OFDM; 802.11n (2009) introduced MIMO; and 11ac, 11ax, and 11be pushed into 5 and 6 GHz with ever-larger channels. The Wi-Fi Alliance certifies interoperability and coined the numbered generation names.
Deployment
Wi-Fi is the dominant wireless-LAN technology worldwide, in homes, offices, and public hotspots, and increasingly in IoT devices. It shares the crowded 2.4 GHz ISM band with Bluetooth, microwave ovens, and other unlicensed users, which is one reason the 5 and 6 GHz bands matter.
Decoding it with GopherTrunk
GopherTrunk does not decode Wi-Fi. It is a narrowband land-mobile and aeronautical trunking decoder; 802.11’s 20–320 MHz OFDM channels sit far outside its receiver bandwidth and protocol scope, and general-purpose SDRs like the RTL-SDR lack the sample rate to capture a full Wi-Fi channel anyway. Wi-Fi matters to GopherTrunk mainly as a source of 2.4 GHz interference to avoid when siting an antenna, and as a convenient backhaul for a remote node.
Sources
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IEEE 802.11 — Wikipedia, on the 802.11 wireless-LAN family, its OFDM/MIMO physical layers, bands, and generations. ↩