WiFi

  

 

 

 

PHY Frame

 

Going into very details, 802.11 Physical Frame structure gets different from each standard(e.g, b/g/a/ac etc) and it is difficult to draw a single diagram to represent the physical frame structure of every WLAN standards. However, taking a very high level view, the physical frame structure of WLAN can be represented as follows.

 

 

 

There are many different ways to represents PHY frames. Most common way would be to draw various diagram as you can easily find from specification documents or web search. I will use various diagrams as well, but I would try to put various captures from measurement equipment trying to give you more intuitive and realistic image.

 

 

Frequency Domain Structure

 

WLAN is using roughly two types of modulation method, DSSS and OFDM. DSSS is a kind of old technology which is the base technology for 802.11b and most of recent standard like 802.11a, g, n, ac are all based on OFDM. Following is summary of requency domain structure for OFDM based WLAN standard.

 

 

 

Time Domain Structure/PHY Frame Structure

 

 

< 802.11a >

 

 

 

< 802.11n >

 

 

 

 

 

 

 

< 802.11ac VHT >

 

 

 

 

< 802.11ad ControlPHY Frame >

 

 

 

< 802.11ad Single Carrier PHY Frame >

 

 

 

< 802.11ad Low Power Single Carrier PHY Frame >

 

 

 

< 802.11ad OFDM PHY Frame >

 

 

 

Spectrum Analysis Example

 

< Snapshots on 802.11g >

 

 

 

 

 

 

 

 

 

 

 

 

 

< Snapshots on 802.11n - 20 Mhz >

 

 

 

 

 

 

 

 

 

 

 

Reference :

 

[1] 802.11 OFDM Overview

[2] 802.11n Signal Structure  

[3] 802.11ac Signal Structure  

[4] WLAN 11ac frame format  

[5] WLAN - 802.11 a,b,g and n

[6] 802.11n Tutorial

[7] SIGNAL and HT-SIG