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The Definitive Guide to the 802.11ac WiFi Standard

Jan 04, 2021

Accessing the internet is very convenient and easy when wireless networking is used. The number of devices and users accessing the internet grows every year. This unfortunately results in many people experiencing unreliable wireless connections and a slowdown of speed. To improve the wireless experience and address those challenges, the WiFi-Alliance has established a new WiFi standard, the IEEE 802.11ac standard.

802.11ac Definition.

IEEE 802.11ac standard is the 5th generation of WiFi and is also known as Gigabit WiFi and WiFi 5. This is an upgrade from WiFi 4 or 802.11n. 802.11ac was developed to deliver better WiFi performance and speeds, and improved range to cope with increased data consumption and the increasing number of devices and users.

802.11ac History.

The purpose of a WiFi standard such as IEEE 802.11 is to enable better user experiences with wireless local area networks, also known as Wireless LAN or WLAN. Better wireless standards are continuously being developed to cater to new technology and address shortcomings in previous versions.

During the time that the IEEE 802.11n standard was generally used, there was a substantial upsurge in the volume of devices and users that used wireless internet. This caused increased latency and a marked drop in connection speeds. To improve WLAN's performance to cater for this, the Institute of Electrical and Electronic Engineering (IEEE) developed the 802.11n standard to version 802.11ac between 2008 and 2013. This ultimately resulted in a better Wireless LAN experience with less latency, increased bandwidth, and faster speeds. This update was released in December 2013.

Products implementing the 802.11ac standard were introduced in two waves. Wave 1 was launched in 2013, while the second made its appearance in 2015.

At What Speed Does the WiFi 5 Standard Run?

As maximum internet speeds are based on ideal conditions, they are theoretical. They don't factor in potential interference. In theory, the maximum speed of 802.11ac is between 1.3 Gbps (1,300 Mbps) and 2.3 Gbps (2,300 Mbps). It is the first WLAN standard that can achieve gigabit speeds theoretically, rather than speeds of megabits per second. In comparison, 802.11n's theoretical speed is 0.45 Gbps (450 Mbps). This means WiFi5 may be up to 3 times faster than WiFi 4 under ideal conditions.

Data rates in reality are however susceptible to interference caused by the environment. The speed is slowed down by obstacles such as furniture, building materials, doors, walls, and floors can reduce the signal strength.

According to Forbes, the fastest 802.11ac speed was measured at about 0.72 Gbps (720 Mbps), whereas the maximum speed measured for 802.11n was 0.24 Gbps (240 Mbps). Although 802.11ac is 3 times faster than 802.11n, actual speeds are much slower than the speeds indicated in theory.

Key Features of 802.11ac.

802.11ac expanded on the features available on 802.11n to provide improved speed, bandwidth, and throughput.

Multi-User Multiple-Input Multiple-Output (MU-MIMO).

MIMO technology uses several receivers (antennas) and transmitters to send data to several WiFi devices at the same time.

802.11n routers originally used Single-User Multiple-Input Multiple-Output (SU-MIMO), which meant that the router was only able to communicate with one connected device at a time. When the first wave of 802.11ac was launched, the SU-MIMO technology had not yet been improved. These improvements only come to light with the second wave.

802.11ac routers in Wave 2 adopted MU-MIMO, resulting in routers being able to transmit information to multiple devices simultaneously. The new technology only supported downlinks, i.e. data being sent from the router to wireless devices. The data packets that were sent to the router (uplink) from the devices could only be sent one at a time. This new technology supports more connected devices and improved speeds.

Wider WiFi Channels.

Wireless devices and routers send and receive data to and from each other via two frequency bands – 2.4 GHz & 5 GHz. Most WiFi devices have two bands and they can therefore use both frequencies. The two bands differ from each other in terms of bandwidth, speed, and range. The 5GHz band provides less coverage at faster speeds, while the 2.4 GHz band works at slower speeds but provides more coverage.

Within each frequency band, there are minor bands that are used as WiFi channels. Wireless devices use WiFi channels to receive and send data. The width of the channel determines how much data it can pass through and at which speeds. A traditional channel is 20 MHz wide, and channel widths can be increased by using channel bonding. Wider channels generally provide faster speeds and bigger data transfers, providing the channel does not experience interference and is not crowded.

Only 20 MHz & 40 MHz channels were supported by the 802.11n standard. The first wave of 802.11ac products supported a channel bandwidth of up to 80 MHz, while products in the second wave took this up to 160 MHz. This 160 MHz channel bandwidth was formed by bonding 80 MHz channels, both non-adjacent and adjacent. This resulted in a significant improvement in throughput.


Traditionally, antennas on the routers transmitted signals in all directions. This resulted in signal wastage due to it being transmitted to areas where it was not required. This, in turn, led to a reduced wireless signal range, while the signal was also more susceptible to interference and loss of speed.

Beam forming improves the wireless signal between connected devices and WiFi routers. It works by focusing what is known as a smart signal in the direction of the devices that are connected, instead of transmitting it everywhere. Beam-forming improves speed and range and reduces interference.

When 802.11n was developed, beamforming technology was already available, but it had not been standardized yet. As a result, several different beamforming versions were being used. For beamforming to work, both the device and the router had to use the same beamforming technology. As there were many beamforming versions available, different 802.11n manufacturers implemented different versions.

With the 802.11ac standard, explicit beamforming was standardized, resulting in all manufacturers implementing the same version.

Spatial Streams.

Wireless devices and routers all use antennas, the number of data signals (spatial streams) that can be received and sent simultaneously is determined by the number of antennas. Spatial streams are expressed as 4x4, 3x3, 2x2, 1x1, etc. A 3x3 spatial stream for example represents three antennas supporting three data streams.

Although both 802.11ac and 802.11n devices use this technology, how many spatial streams are supported by each standard is different.

802.11n could use up to four spatial streams and 802.11ac's first wave supported three. Each type of mobile device supports a specific number of streams. While smartphones only have 1x1 spatial streams, various higher-end smartphones utilize 2x2 spatial streams, as do laptops. 3x3 spatial streams are supported by some computers, and 4x4 spatial streams aren't supported by many devices.

If you, for example, have a router supporting 802.11n and having three antennas. Although the router has 3 spatial streams, it can only allocate these to a single device at a time. Should a Mac (2x2) and an iPhone (1x1) request information from the router simultaneously, they will have to queue up to receive the data.

The router will use two of its antennas to communicate with the Mac and after that conversation is complete, it will use one of its antennas to communicate with the iPhone. With 802.11n, more than one spatial stream can never be used to talk to multiple devices, but only to one device at a time. This means the 3-antenna router could not use its potential as it can only communicate with one client at a time.

To improve communication speeds and processes, Wave 2 802.11ac routers initially supported four spatial streams, and this later increased to eight. As 802.11ac uses Multi-User MIMO, devices wanting to communicate don't have to wait as the router can allocate two antennas to the Mac and one to the iPhone simultaneously. This allows for more information to be received and transmitted at the same time. The battery life of the devices that are connected also improves as power consumption is reduced due to the signal being allocated more efficiently.

WiFi Frequency Bands.

As mentioned above, the 2.4 GHz and 5 GHz frequency bands are used to receive and send information. Both frequency bands were supported by WiFi4. WiFi 5 was however developed to use only the 5GHz band. This reduces the amount of interference within the 2.4 GHz band. When multiple devices operate using the same frequency band, this leads to signal interference. Many devices use the 2.4 GHz band, including microwaves, Bluetooth headsets, home phones, baby monitors, etc. All of these slow the data due to clogging up the band.

For the 2.4 GHz band to be used, WiFi 5 had to incorporate WiFi 4 technology.

WiFi 5 devices that use the 5GHz frequency can take full advantage of all of 802.11ac's features, but, WiFi 5 devices that use the 2.4 GHz frequency band can only utilize WiFi 4 technology.

256-QAM Enables More Data to be Transferred.

Sound frequencies are used by wireless devices to talk to each other. When data is transmitted via sound waves, the device modulates a specific radio channel's frequency. The sound wave consists of binary code (0s and 1s). The device that receives the sound waves decodes the signal to interpret it. This method is used to transfer all data used for wireless internet.

When you, for example, open Google on your computer, the frequency of the radio channel is modulated by the computer to transmit the signal to the router, which then decodes the signal to understand the request and uses the same process to send the relevant information back to the computer. The relevant Google page will be shown on the computer's screen once the computer has decoded the signal received from the router. This is called QAM (quadrature amplitude modulation).

As WiFi 4 uses 64-QAM, only six bits of data could be sent or received at a time. WiFi 5 has upgraded this to 256-QAM, allowing devices to send or received eight bits of data simultaneously. This change increased WiFi speeds by between 20% and 33%. Both waves of 802.11ac products supported 256-QAM.

Comparing 802.11ac Wave-1 & Wave-2

The following table shows the main features of Wave 1 and Wave 2 802.11ac products:

Key Feature Wave1 Wave2
Channel Bandwidth 20, 40, and 80 MHz 20, 40, 80, 80+80 and 160 MHz
Beamforming Only Explicit Beamforming Only Explicit Beamforming
Spatial Streams 3 4
Frequency Band 5 GHz 5 GHz
QAM 256-QAM 256-QAM


Comparing 802.11n and 802.11ac.

The following table shows the features of 802.11n and 802.11ac:

Key Feature 802.11n 802.11ac
Channel Bandwidth 20 and 40 MHz 20, 40, 80, 80+80 and 160 MHz
Theoretical Speed 450 Mbps 1,300 to 2,300 Mbps
Spatial Streams Maximum 4 Maximum 8
Beamforming Many Versions of Beamforming Explicit Beamforming Only
Frequency Bands 2.4 GHz and 5 GHz 5GHz
QAM 64-QAM 256-QAM


Backward Compatibility of 802.11ac.

As 802.11ac uses technology from 802.11n to utilize the 2.4 GHz frequency band, it is backward compatible. If 802.11ac devices only used the 5 GHz band, they wouldn't be backward compatible with previous WiFi versions.

The speed with which a device operates however depends on the WiFi generation it uses. If a computer using WiFi 5 communicates to a router using WiFi 4, the computer will only communicate at a speed the router can manage. The same will apply if a WiFi 5 router is connected to a WiFi 4 computer.

To utilize all the WiFi 5 features, all the devices connected, including the router, will have to use the WiFi 5 standard.

WiFi 5 Coverage area.

The coverage area depends on the frequency band being used and the materials that block WiFi. The 2.4 GHz frequency band can breach obstructions better and travel farther than the 5 GHz frequency band. According to Lifewire, WiFi routers using the 2.4 GHz band can reach up to 300 feet outdoors and 150 feet indoors. This range will typically be between 10 and 15 feet less when the 5 GHz band is being used.

Devices such as mesh networks and WiFi extenders have been developed to improve a router's range.

WiFi extender's a wired or wireless device that is connected to the router to extend the range of the WiFi. They should be positioned near enough to a router to receive a strong signal, yet far enough to be able to broadcast signals into the required area. Once an extender has been connected, it almost acts like a second access point. Wi-Fi extender uses its own unique SSID and password. When moving around area, the network connection to the WiFi extender or the router needs to be changed manually. Extenders are best suited for small apartments and homes.

Mesh network systems have been designed to cover an entire home or office with WiFi. They consist of several mesh nodes working together to extend the coverage of the WiFi. One node is connected directly to the router with an Ethernet cable (gigabit or fast Ethernet), while the other nodes are positioned around the building. This creates one big, continuous wireless network without RJ45 ethernet cables networked all over. Mesh networks only use one network name and password. While moving around the area, the mobile device will connect to the node it is closest to automatically. Mesh systems are mostly used in medium to big offices and homes, and huge buildings.

Which Devices Provide WiFi 5?

As WiFi 5 has been released many years ago, all later model WiFi devices including tablets, phones, routers, and computers have all implemented the 802.11ac chipset.

What is Next?

WiFi standards evolve continuously to improve the WiFi experience, especially for the host of new internet of things (IoT) devices. WiFi 6 or 802.11ax is the next WiFi generation. It will build on and improve WiFi 5 technology by offering more bandwidth, lower latency, high throughput, and faster wireless speeds.

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