Growing demands on the wireless LAN (WLAN) are creating increased pressure to provide more bandwidth at higher rates. To address congestion and the need for higher throughout speeds, the IEEE is developing the new 802.11ac standard, which is expected to be ratified by February 2014 and will be backwards compatible with 802.11n.
802.11ac moves wireless traffic to the 5 GHz band, instead of 2.4 GHz, and claims to provide ‘faster throughput at greater distance’ through:
- wider channels
- higher modulation and coding
- multi-user MIMO
- more spatial streams.
One of the key ways 802.11ac gains speed is by using 80 MHz wide channels. In a second phase this will increase to 160 MHz channels (although these will be optional). However, this means fewer available channels in the 5 GHz band. In Europe, 802.11ac has four available 80 MHz channels, and will have two available 160 MHz channels. In comparison, there are 19 non-overlapping 20 MHz channels available.
Note that without using DFS, in Europe the available 80 MHz channels drops to 1 so DFS support in APs and clients is going to be a necessity to deploy 802.11ac effectively.
Table 1 — Available 802.11ac channels. *DFS = Dynamic Frequency Selection — for avoiding interference with weather radar.
Higher modulation and coding schema
802.11ac introduces higher order modulation using 256QAM. This increases the number of bits that can be encoded in a single symbol and can provide up to a 33 per cent improvement in bit rates. However, it requires a change in transmitter and receiver design, making RF system design more challenging.
Beamforming allows 802.11ac routers to deliver a wireless signal straight to a device. Although supported in 802.11n, the new standard is more efficient — in part because it only includes one method of beamforming.
Multi-user MIMO – more spatial streams via more antennae
802.11ac will use multi-user MIMO (Multiple Input Multiple Output) to support simultaneous transmissions to multiple clients,