IEEE 802.11ac is a wireless networking standard in the 802.11 family (which is marketed under the brand name Wi-Fi), developed in the IEEE Standards Association process, providing high-throughput wireless local area networks (WLANs) on the 5 GHz band. The standard was developed from 2008 (PAR approved 2008-09-26) through 2013 and published in December 2013 (ANSI approved 2013-12-11).
The specification has multi-station throughput of at least 1 gigabit per second and single-link throughput of at least 500 megabits per second (500 Mbit/s). This is accomplished by extending the air-interface concepts embraced by 802.11n: wider RF bandwidth (up to 160 MHz), more MIMO spatial streams (up to eight), downlink multi-user MIMO (up to four clients), and high-density modulation (up to 256-QAM)
New technologies introduced with 802.11ac include the following:
- Extended channel binding
- Optional 160 MHz and mandatory 80 MHz channel bandwidth for stations; cf. 40 MHz maximum in 802.11n.
- More MIMO spatial streams
- Support for up to eight spatial streams (vs. four in 802.11n)
- Downlink multi-user MIMO (MU-MIMO, allows up to four simultaneous downlink MU-MIMO clients)
Multiple STAs, each with one or more antennas, transmit or receive independent data streams simultaneously.
- Space-division multiple access (SDMA): streams not separated by frequency, but instead resolved spatially, analogous to 11n-style MIMO.
- Downlink MU-MIMO (one transmitting device, multiple receiving devices) included as an optional mode
256-QAM, rate 3/4 and 5/6, added as optional modes (vs. 64-QAM, rate 5/6 maximum in 802.11n)
Some vendors offer a non-standard 1024-QAM mode, providing 25% higher data rate compared to 256-QAM
Beamforming with standardized sounding and feedback for compatibility between vendors (non-standard in 802.11n made it hard for beamforming to work effectively between different vendor products)
MAC modifications (mostly to support above changes)
Coexistence mechanisms for 20, 40, 80, and 160 MHz channels, 11ac and 11a/n devices
Adds four new fields to the PPDU header identifying the frame as a very high throughput (VHT) frame as opposed to 802.11n’s high throughput (HT) or earlier. The first three fields in the header are readable by legacy devices to allow coexistence
The single-link and multi-station enhancements supported by 802.11ac enable several new WLAN usage scenarios, such as simultaneous streaming of HD video to multiple clients throughout the home, rapid synchronization and backup of large data files, wireless display, large campus/auditorium deployments, and manufacturing floor automation.
With the inclusion of USB 3.0 interface, 802.11ac access points and routers can use locally attached storage to provide various services that fully utilize their WLAN capacities, such as video streaming, FTP servers, and personal cloud services. With storage locally attached through USB 2.0, filling the bandwidth made available by 802.11ac was not easily accomplished.