What is the 802.11ac standard for 5 GHz wireless networks?

IEEE 802.11ac is a standard for wireless networks trans­mit­ting ex­clus­ively on the 5 GHz band. When using the right devices, com­par­at­ively high speeds can be achieved.

What is 802.11ac?

Even if ‘802.11ac’ doesn’t mean much to you at first, chances are you’ve heard of WiFi 5. IEEE 802.11ac is the standard for WLAN networks with data rates in the 5 GHz band. Just like its pre­de­cessors and successor 802.11ax, it was defined by the Institute of Elec­tric­al and Elec­tron­ics Engineers (IEEE). Compared to its pre­de­cessors 802.11b, g, a and n, the 802.11ac standard, of­fi­cially published at the end of 2013, creates sig­ni­fic­antly higher band­widths and trans­mis­sion rates in the gigabit range. In theory, its maximum data rate is 6,933 megabits per second. However, this value is almost im­possible to achieve in practice due to various lim­it­a­tions.

How does 802.11ac work?

802.11ac is not a re­in­ven­tion, but is based on its pre­de­cessors. Compared to 802.11n, there are few in­nov­a­tions with IEEE 802.11ac. A sig­ni­fic­antly higher trans­mis­sion rate is achieved through several ad­just­ments and op­tim­isa­tions. For example, 802.11ac offers wider trans­mis­sion channels that can be extended to 80 MHz or even up to 160 MHz. In addition, up to eight MIMO channels (Multiple Input Multiple Output) can be used sim­ul­tan­eously. With four or more antennas, it is also possible to implement multi-user MIMO (MUMIMO), provided this is supported by the access point and the client. Higher mod­u­la­tion methods such as 256-QAM with 3/4 and 4/5 FEC are also used.

What are the ad­vant­ages of IEEE 802.11ac?

802.11ac offers some decisive ad­vant­ages over its pre­de­cessors: The tech­no­logy is more powerful and, at least in theory, faster than many con­ven­tion­al ethernet con­nec­tions. Using a 5 GHz band enables sig­ni­fic­antly higher data rates and fewer bandwidth problems than using a 2 GHz band. However, the ad­vant­ages are only apparent if all the devices used also support 802.11ac. This includes the following:

MIMO

MIMO refers to wireless com­mu­nic­a­tion via multiple trans­mis­sion and receiving antennas. 802.11ac enables this com­mu­nic­a­tion with up to eight antennas. This means that up to eight data streams can flow sim­ul­tan­eously and the trans­mis­sion rate is sig­ni­fic­antly increased as a result.

256-QAM

256-QAM (Quad­rat­ure Amplitude Mod­u­la­tion) is one of the latest and highest quality mod­u­la­tion methods. It is used in 802.11ac. The 256 stands for the 256 stages of the mod­u­la­tion process. 256-QAM is four times as powerful as the previous 64-QAM. With this method, 8 bits are trans­mit­ted per trans­mis­sion step.

Beam­form­ing

Beam­form­ing is the focusing of trans­mis­sion energy on a specific client. This sig­ni­fic­antly improves the radio con­nec­tion. A radio station sends a signal to a receiver via several antennas with a time delay. This increases the trans­mis­sion rate and boosts the mod­u­la­tion level. IEEE 802.11n already offered this pos­sib­il­ity, at least in theory. In practice, however, the results were rather sobering. IEEE 802.11ac enables sig­ni­fic­antly better beam­form­ing. The decisive factor here is that the re­spect­ive device must also support beam­form­ing.

Speed stages of 802.11ac

Generally, IEEE 802.11ac provides different stages of speed. But how high the trans­mis­sion rate is, depends on various different factors. Aside from channel width, the number of antennas and the mod­u­la­tion method, the access point and the client must support all relevant per­form­ance features. However, that’s rarely the case. Most devices have limited per­form­ance features, which is why 802.11ac’s the­or­et­ic­al maximum speed of 6,936 megabits per second is almost never reached. The maximum channel bandwidth of 160 MHz, eightfold MIMO and 256-QAM would be required for this.

Support for DFS and TPC

As mentioned, 802.11ac ex­clus­ively transmits in the frequency range around 5 GHz. In Europe and many other countries, this means that the tech­no­logy must support DFS and TPC, because trans­mis­sions would otherwise interfere with important systems such as regional weather radar. DFS (Dynamic Frequency Selection) detects radio signals from other systems. In case of an overlap, DFS makes it possible to switch to other channels. TPC (Transmit Power Control) provides dynamic control of access points or routers and enables data to be trans­mit­ted with lower trans­mis­sion power if the radio link is good.

If routers or access points don’t support DFS and TPC, they can only transmit on channels 36 to 48 and occupy them com­pletely. This not only reduces the trans­mis­sion rate con­sid­er­ably, but also access by another router cannot be ruled out, which can lead to severe impair­ments. Devices that don’t support DFS and TPC are therefore only suitable for IEEE 802.11ac to a very limited extent.