WLAN 802.11ac Beamforming

This page of WLAN 802.11ac tutorial covers 802.11ac beamforming.

Beamforming is the process in which transmission takes place by focusing energy towards desired direction and targeted for particular receiver. Hence in addition to power it helps increase Signal to noise power ratio and hence increase the data rate with the use of MIMO and complex modulation scheme 256QAM.

Beamforming is also referred as beam steering. Any device that shapes its transmitted frames is called a beamformer and a receiver of these frames is called a beamformee.

Prior to 11n there were proprietary standards for beamforming, in IEEE 802.11n beamforming is standardized. There are two types of beamforming i.e. implicit and explicit. In 802.11ac explicit channel measurements are performed by both the transmitter and receiver. Beamforming usually provides gain of about 2 to 5 dB. Following figure depicts beamforming process in 802.11ac.

In 802.11ac Null Data Packet sounding method of beamforming is employed. Channel sounding in 802.11ac works as follows.

• Beamformer sends NDP Announcement frame to Beamformee, which helps gain control of the channel. Beamformee responds to this frame back.
• Beamformer send Null data packet, used by beamformee to calculate channel response and hence steering matrix. For multiple users multiple NDPs are sent to receivers.
• Beamformee receives NDP and calculates feedback matrix and sends that back to beamformer.
• Beamformer calculates Steering matrix from the received FB matrix and directs the transmission accordingly towards beamformees.

There are other types of beamforming based on number of users i.e. single user beamforming and multi-user beamforming.

This tutorial also provide link to 802.11ac data rate, frame format, MAC layer, physical layer, radio network planning, spectrum mask. Refer links mentioned on the left side panel.

WLAN 802.11ac Beamforming

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