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WLAN Frame Structure

What is wlan?
WLAN standards-11a,11b,11g,11n,11ac
11a WLAN Physical layer
11b WLAN Physical layer
11n WLAN Physical layer
WLAN MAC layer
WLAN 802.11-ac
WLAN 802.11-ad
Difference between 11a,11b,11g,11n
WLAN router providers
WLAN providers

This page covers WLAN frame structure as per IEEE 802.11 standards. It covers 11a,11b,11n and 11ac frame structures.

WLAN stands for Wireless Local Area Network. The system has two main components viz. STATION(STA) and ACCESS POINT(AP). Though the frame exhange between AP and STA are different they have common frame structure as shown below for different variants. WLAN has been evolved since 1997 with various standards to cater for different data rate/distance specifications.

802.11a WLAN frame structure

11a WLAN frame structure

The figure depicts 802.11a WLAN frame which consists of three parts viz. preamble,header and data. Preamble is about 12 symbols in length and referred as PLCP preamble. It is used for synchronization purpose. Header is mainly used to carry modulation-code rate of data,length and service bits. It is always BPSK1/2 so that after synchronization is done device can demodulate the header and obtain necessary information to further decode the data part. Data part carry MAC frames and CRC is appended for error checking purpose. Type and subtype fields transmitted in SERVICE field defines various frames required to establish and maintain WLAN link between AP and STA.

802.11b WLAN frame structure

11b wlan frame structure long PLCP 11b wlan frame structure short PLCP

Based on the rate supported by 11b compliant devices viz. 1,2,5.5 and 11 Mbps there are different modulation techniques and preambles are supported as mentioned below:

1Mbps Data rate- DBPSK modulation,DSSS scheme,long preamble, 1bis/symbol
2Mbps Data rate-DQPSK modulation,DSSS scheme,long/short preamble,2 bits/symbol
5.5Mbps Data rate-CCK modulation,CCK scheme,long/short preamble,4 bits/symbol(first 2bits DQPSK modulated and next 2bits CCK modulated)
11Mbps data rate-CCK,long/short preamble supported,8 bits/symbol,first 2bits DQPSK and next 6 bits QPSK

802.11n WLAN frame structure

11n legacy mode frame structure 11n mixed mode frame structure 11n green field mode frame structure

WLAN 11n devices have support for three modes viz. legacy mode,mixed mode and green field mode. As per this modes 11n devices follow different frame structure to communicate with legacy devices(compliant to 11a/11b/11g) as well as other 11n devices.

L-STF, L-LTF and HT-LTF are used as preamble for synchronization purpose. L-SIG and HT-SIG are used as header which carry length and rate of data part carried in the frame. Data part is used to carry mac control/management frame as well as information to be exchanged between WLAN devices.

802.11-ac WLAN frame structure

11ac frame structure

802.11ac frame consists of L-STF,L-LTF,L-SIG, VHT-SIG-A,VHT-STF,VHT-LTF,VHT-SIG-B and Data part. To know each fields in detail refer 11ac frame format.

Frame structure of wireless standards, technologies

Frame structure of various wireless standards/technologies are mentioned below. It include WiMAX, WLAN, Zigbee, GSM, GPRS, UMTS, LTE, TD-SCDMA, GPS, SDH, 11ac WLAN, AMPS, Ethernet, VLAN etc.

WiMAX physical layer Frame Structure as per 802.16d and 802.16e standards
WiMAX MAC layer Frame Structure as per OFDM 802.16d standard
Zigbee RF4CE Frame Structure
Zigbee physical layer Frame Structure
Zigbee MAC layer Frame Structure
GPRS Frame Structure
GPS Frame Structure
LTE Frame Structure
TD-SCDMA Frame Structure
UMTS Frame Structure
SONET Frame Structure
SDH Frame Structure
802.11ac PHY Frame Structure
802.11ac MAC layer Frame Structure
WLAN Frame Structure as per 802.11a,11b,11n,11ac standards
AMPS Frame Structure
Ethernet Frame Structure
VLAN Frame Structure
GSM Frame Structure

RF and Wireless Terminologies

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