CTS 133: 802.11 PHY Types
Let’s discuss the different 802.11 PHY types available for devices to use.
Meet Glenn Cate
Our featured wireless network engineer is Glenn Cate, CWNE #181. Catching up with Glenn at Cisco Live 2018 was great and we were able to get him talking about himself. Listen to the episode to hear a little bit about Glenn.
802.11 PHY Types
The 802.11 Standard defines different PHY types. Includes the data rates supported by each PHY and what band they operate in. Data rates depend on the channel width and modulation used.
Download the free 802.11 PHY Types Reference PDF
In 1997, the first iteration of the standard was released. We call this 802.11 Prime. In this standard, the PHY type available used Direct Sequence Spread Spectrum (DSSS). It was only available in the 2.4 GHz spectrum using a 22 MHz wide channel. It offered 1 spatial stream and devices were able to use from 1 to 2 Mbps data rates.
802.11 PHY Types
802.11a was ratified in 2009 and operated in the 5 GHz spectrum. With this PHY, devices were able to use up to 54 Mbps data rates. Modulation used with this PHY type was Orthogonal Frequency Division Multiplexing (OFDM) and used a 20 MHz wide channel at 1 spatial stream.
802.11b, still operating in the 2.4 GHz spectrum used a modulation of High Rate DSSS (HR/DSSS) for this PHY type. It still used a 22 MHz wide channel width but offered data rates up 5.5 and 11 Mbps.
To maintain backwards compatibility to DSSS but bring improvements to 2.4 GHz was the 802.11g PHY type. The new modulation used was Extended Rate Physical OFDM (ERP OFDM). The channel width changed to 20 MHz but still saw data rates up to 54 Mbps using 1 spatial stream.
The biggest change to Wi-Fi came with the 802.11n PHY. It was dual-band and used the High Throughput (HT) modulation. It offered up to 600 Mbps data rates and introduced channel bonding to 40 MHz channel widths. Another improvement was the introduction of MIMO and 4 spatial streams.
What we’re currently used to, as of the release of this episode, is the 802.11ac PHY type. Defined as Very High Throughput (VHT) and only operating in the 5 GHz spectrum, it introduced new channel bonding at 80 and 160 MHz channel widths. This increased channel width, along with 8 spatial streams, touts up to 6.9 Gbps data rates. But don’t hold your breath.
Next up, not ratified yet as of the time of this published episode, is 802.11ax PHY type with modulation scheme of High Efficiency (HE). This brings increased efficiency in the 2.4 GHz and 5 GHz spectrum. Specifying, in this PHY type, is 1024 QAM and up to 9.6 Gbps data rates. We shall see what this brings to the real world.
