IEEE Standard WLAN-ac basics

This tutorial section on WLAN-11ac basics covers following sub topics:
Main page  frame  PHY layer  MAC layer  data rates  spectral mask  beamforming  radio planning

This page of WLAN tutorial covers ieee802.11ac technology features,references and 11ac solution providers/vendors.

IEEE WLAN 802.11-ac is 802.11 family of standard for WLAN ( Wireless Local Area Networks) currently under development which will provide high throughput below 6 GHz. Compare to its predecessor 802.11n it has following additional features in addition to features already supported in 11n.

1. RF Bandwidth of 80 and 160 MHz incorporated.
2. MIMO spatial streams increased up to 8
3. High density modulation schemes up to 256QAM incorporated
4. Multi user MIMO(MU-MIMO) concept incorporated, where more than one Stations(STAs) having multiple antennas uses same radio channel to transmit/receive separate data streams at the same time. This technique uses more than one antenna in most of the cases.

Similar to its predecessors 802.11a,802.11n, it also uses OFDM as modulation technique to map symbols on multiple subcarriers. Frequency spacing between two subcarrier is 312.5 KHz, that leads to symbol duration of about 3.2 micro-second similar to 802.11 a symbol period(Ts). It supports 20 MHz and 40 MHz bandwidths. Supports MCS 0 to MCS 7 for single stream. To keep spacing constant as 312.5KHz between subcarriers, number of subcarriers across channel bandwidth is kept proportional. Hence for 20 MHz 64 subcarriers, for 40 MHz 128 subcarriers, for 80 MHz 256 subcarriers and for 160 MHz 512 subcarriers are mapped. Accordingly IFFT and FFT is used.

In 802.11ac multi user transmit path supports upto 4 users.Each user supports upto 4 STS(space time streams). STS should not be greater than 8 as mentioned.

PPDU transmission

For transmission PSDU from MAC layer is appended with PLCP preamble to form PPDU. PPDU i.e. Physical layer convergence procedure(PLCP) Protocol Data Unit transmitted by WLAN 11ac compliant Station(STA) follows various frame structures, such as Non HT mode, HT mixed mode,HT green field mode and VHT mode. Figure 1 depicts VHT(Very High Throughput) frame format.

WLAN 802.11ac VHT mode frame format

To know more on these type of frame formats refer our article on 11n Physical layer. For more details on VHT mode frame format, refer published standard or draft standard by IEEE on the website link mentioned below.In 11ac Physical layer LDPC tone mapper is used in addition to constellation mapper.

WLAN 802.11ac tutorial links

802.11ac physical layer

Refer WLAN 802.11ac Tutorial➤ for more information.

What is Difference between

Difference between 802.11 standards viz.11-a,11-b,11-g and 11-n
Difference between 11n,11ac and 1ad
difference between FDM and OFDM
Difference between SC-FDMA and OFDM
Difference between SISO and MIMO
Difference between TDD and FDD

Major WLAN-ac Test and Measurement Solution providers:

Test solutions for 802.11ac device measurements from R&S, Website-
Agilent test and Measurement solutions for 802.11ac compliant devices, Website-


RF and Wireless Terminologies