802.11ac is the newest wireless network standard in the 802.11 family, developed by IEEE Standards Association and is ONLY applicable for the 5GHZ frequency spectrum (Does not work on 2.4 GHz or any other frequency) and was approved in January of 2014.
There are many benefits to this new protocol of wireless network communications compared with its predecessor 802.11n, Gigabit communication on wireless networks is now possible as some factors have been improved on the protocol in order to be able to achieve these speeds. Basically the new protocol improved 3 factors that allow now this technology challenge to be conquered.
While 802.11n, which was introduced in 2009 allowed the HT (High Throughput) channels or channel bonding from 20 MHz to 40 MHz, the new 802.11ac has introduced the VHT (Very High Throughput) channels of 80 MHz (mandatory) and 160 MHz (optional). With this change the wireless equipment will be able to transmit double or quadruple the capacity by using double or quadruple the amount of spectrum compared to what was available with 802.11n, however, one disadvantage of this would be a noisier spectrum in higher populated environments.
If we consider the channels available in the 5GHz frequency without the use of DFS (Dynamic Frequency Selection), the spectrum available for 80 or 160 MHz VHT channels will become very limited, likely to 1 or 2 channels only.
One of the most important improvements of all is the modulation rates that increased from 64 QAM (Quadrature Amplitude Modulation) in 802.11n to 256 QAM with 802.11ac protocol. With this change the capacity is improved by 4 times, it’s important to clarify that in order to achieve such a modulation, good alignment between Access Point or Base Station and the Client Station is necessary. The noise floor has to be controlled, interference closely analyzed and the signal level at optimum condition of between -40 dBm to -60 dBm. With this improvement it is not necessary to use VHT (80 or 160 MHz channel size) in order to see an increase on the speed or throughput.
Antennas’ MIMO Streams
The Antennas’ MIMO (Multiple Input – Multiple Output) introduced by 802.11n is also improved by increasing the amount of maximum streams defined by the standard from 4 to 8 even though this is a feature that has not been developed from many antenna manufacturers, in the market right now we could see wireless equipment on 802.11ac that support 2X2 MIMO and 3X3 MIMO in most cases. By increasing the amount of streams, the improvement of the capacity is directly proportional to the amount of streams; meaning 3X3 MIMO wireless equipment achieves 50% more capacity than 2X2 MIMO.