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 predecessor 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 optimizations. 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 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 (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 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.