In real life no one standard has been able to maximize its theoretical performance since many factors influence the signal: electromagnetic interference from household appliances and electronics, obstacles in the signal path, signal reflections, and even magnetic storms. Because of this, manufacturers continue creating more efficient options for Wi-Fi standard, which are suitable not only for home, but also for active office use or for building extended networks. As a result of their commitment, a new version of IEEE 802.11 - 802.11ac (or simply AC standard) was recently born.

There are not too many fundamental differences from 802.11n in this new standard, but they are all aimed at increasing the throughput of the wireless protocol. Basically, the developers chose the way to improve the advantages of the 802.11n standard. The most notable is the expansion of MIMO channels from a previously maximum of three to eight. This means that soon we will be able to see wireless routers with eight antennas in stores. And eight antennas theoretically substantially increase the spatial streams.

The devices of 802.11abg standard operated in 20 MHz channels but 802.11n standard involved 40 MHz channels. The new standard presumes that AC routers have 80 and 160 MHz channels, thus doubling and quadrupling the channel width.

Also, we should mention the improved implementation of MIMO technology provided in the standard that is known as MU-MIMO technology. The old 802.11n-compliant protocols supported half-duplex device-to-device packet transmission. It means that at the moment when a packet is transmitted by one device, the other devices can only work for reception. Accordingly, if one of the devices connects to the router using the old standard, then the others will also work slower due to the increased packet transmission time to the device using the old standard. This may be the reason for the performance slowdown of the wireless network, if many such devices are connected to it. MU-MIMO solves this problem by creating a multi-stream transmission channel, which doesn’t wait for other devices to be used. At the same time, the AC router must be backward compatible with the previous standards.

However, as it can be seen from our practical studies indicated in the picture below, despite the expansion of transmission channels, it is not possible to achieve the declared speed even under perfect conditions.

Let's assume that we work with a good signal quality and therefore can use a maximum modulation order (256-QAM) and a maximum channel coding rate (⅚ LDPC). The 802.11ac OFDM frame has 4usec duration and contains 52 subcarriers. The resulting bit rate based on this PHY characteristics is 86,7 Mbps.

Currently the most common case is when user equipment has only 2 antennas. Therefore, we have usually no more than 2 parallel spatial streams.

Yes, we have the ability to use 160 MHz in 802.11ac and 802.11ax, however, this will mean more interference. Hence, 80 MHz channels are more preferable.

Finally, (assuming short guard (SG) interval and therefore SG factor = 1.11), we have 858,33 Mbps. And this is still a theoretical value! Practically, this value should be at least half as much due to interference and multipath.