IEEE802.11ac is the next generation WLAN and follow-on to the family of 802.11 standards. IEEE802.11ac was approved as a standard in December of 2013 after five years of work. The goal is to deliver multi-station throughput at least 1 GBps and a single link throughput of 500 Mbps. The technology accomplishes this through wider channel bandwidth (160 MHz), more MIMO spatial streams, and extreme density modulation (256-QAM). 802.11ac exists only in the 5 GHz band, yet will coexist with previous standards (IEEE802.11a/n).
Specifics and differences of IEEE802.11ac than IEEE802.11n are:
- 80 MHz channel width minimum with 160 MHz maximum channel width
- Eight MIMO spatial streams:
- Introduced downlink MU-MIMO with up to four downlink clients
- Multiple STAs with multiple antennas can now transmit and receive independently on multiple streams
- 256-QAM optional modulation with the ability to use 1024-WAM
- Standardized beamforming ability
Multi-user MIMO is worth further detail. 802.11ac extends 802.11n from four spatial streams to eight. One of the largest contributing factors to 802.11ac speed is Spatial Division Multiplexing (SDM), referred to earlier. When combined with multi-user or multiple client aspects of 802.11ac, this technique goes by the name Spatial Diversity Multiple Access (SDMA). Essentially, MU-MIMO in 802.11ac is a wireless analog of a network switch. The following illustration depicts an 802.11ac 4 x4: 4 MU-MIMO system with 3 clients.
80211.ac also extends the modulation constellation from 64-QAM to 256-WAM. This implies there are 16 amplitude levels and 16 phase angles, requiring very precise hardware to implement. 802.11n represented six bits per symbol, while 802.11ac represents a full eight bits per symbol.
Beamforming methods have been formally standardized by the IEEE committee. For example, the committee has agreed that explicit feedback is the standard approach to beamforming association. This will allow beamforming and the performance benefits to be available from multiple vendors.
The increased bandwidth per channel (up to 80 MHz with the option of 160 MHz or two 80 MHz blocks) provides a substantial increase in throughput in the 5 GHz space. Theoretically, using an 8 x 8: 8 device, 160 MHz wide channels, and 256-QAM modulation, one could sustain 6.933 GBps throughput in aggregate.