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Wi-Fi 5 / IEEE 802.11ac / Gigabit WLAN

IEEE 802.11ac or Wi-Fi 5 is a standard for a local radio network that was passed in November 2013. It is the fifth WLAN standard based on 802.11, 802.11b, 802.11g and 802.11n.
The WLAN standard IEEE 802.11ac provides a transmission speed in the gigabit range. Strictly speaking, the standard defines a maximum data rate of 6,936 Mbit / s. IEEE 802.11ac is accelerated by optimizing the transmission protocol, wider channels in the frequency spectrum at 5 GHz and better modulation methods. Since IEEE 802.11ac is only specified for 5 GHz, the previous standard IEEE 802.11n continues to apply to the 2.4 GHz frequency range. IEEE 802.11n is therefore the lowest common denominator for all WLAN devices under IEEE 802.11ac.

Transmission speed

How fast is a WLAN with IEEE 802.11ac?

In theory, IEEE 802.11ac can transfer a total of 6,936 Mbit / s, i.e. around 7 Gbit / s. But to do this, the devices involved would have to fully support all specified performance features and also combine them with one another. In practice this is almost impossible. At this point, the WLAN standards are optimized for interoperability and not for the highest possible performance.
The theoretical transmission rate (gross data rate) depends on the following factors:

  • Number of simultaneous antennas / data streams with MIMO (maximum 8)
  • Channel width (maximum 160 MHz, normal 80 MHz)
  • Modulation method (at best 256QAM)
Frequency range5 GHz
Channel width80 MHz160 MHz
1 antennas433 Mbit / s867 Mbit / s
2 antennas867 Mbit / s1,733 Mbit / s
3 antennas1,300 Mbit / s2,600 Mbit / s
4 antennas1,733 Mbit / s3,466 Mbit / s
5 antennas2.167 Mbit / s4,335 Mbit / s
6 antennas2,600 Mbit / s5,200 Mbit / s
7 antennas3,031 MBit / s6,062 Mbit / s
8 antennas3,464 Mbit / s6,936 Mbit / s

Calculation: In practice, with a data stream with an antenna, with an 80 MHz channel and the 256QAM modulation method, you get 433 Mbit / s. With the MIMO multi-antenna technology and two spatially separated data streams, you get 867 Mbit / s. With three data streams, the data rate increases to around 1,300 Mbit / s gross.

All specified values ​​(rounded) assume that both the access point and the WLAN clients meet all technical requirements. If a WLAN client can only handle 2 data streams, then only a speed of 867 Mbit / s can be achieved. Three data streams require 3 antennas, which for reasons of space are only possible in a notebook or as an expansion card or USB with external antennas for desktop PCs.

The 8 transmitting and receiving units mentioned (8x8 MIMO) require the appropriate number of antennas and the supporting electronics. This is hardly possible in mobile and battery-operated devices. But it is precisely these device classes that rely on fast wireless technology. On the other hand, there is a lack of space and limited energy supply. This is why transmission speeds in the Gbit range will remain the exception for mobile devices.

WLAN devices with IEEE 802.11ac can only display their speed over short distances and without obstacles. Radio signals in the 5 GHz frequency band are slowed down much more strongly by walls and ceilings than in the 2.4 GHz frequency band. This is not a problem, because WLAN devices with IEEE 802.11ac can also use the IEEE 802.11n standard for 2.4 GHz.
In practice, one should expect that the gross values ​​mentioned here will be roughly halved.

WLAN standards in comparison

 IEEE 802.11nIEEE 802.11acIEEE 802.11ax
Theoretical transfer rate (maximum)600 Mbit / s6,936 Mbit / s9,608 Mbit / s
Theoretical transfer rate (typical)
per data stream (channel width)
75 MBit / s (20 MHz)
150 Mbit / s (40 MHz)
433 Mbit / s (80 MHz)600 Mbit / s (80 MHz)
Theoretical data rate with 2 antennas150 Mbit / s (20 MHz)
300 Mbit / s (40 MHz)
867 Mbit / s (80 MHz)1,200 Mbit / s (80 MHz)
Practical transfer rate
(Distance to the access point)
70 to 100 Mbit / s150 to 200 (20 m)
up to 400 Mbit / s (near)
200 to 400 (20 m)
up to 900 Mbit / s (near)
Maximum range100 m50 m50 m
Frequency ranges2.4 + 5 GHz5 GHz2.4 + 5 GHz
Maximum send / receive units4 x 48 x 88 x 8
Antenna technologyMIMO(MU-MIMO)MU-MIMO
Channel width (typ./max.)20/40 MHz80/160 MHz80/160 MHz
Modulation method64QAM256QAM1024QAM

technical features

Compared to its predecessor IEEE 802.11n, IEEE 802.11ac does not bring any significant innovations. Instead, the higher transmission rate is achieved through wider transmission channels (up to 160 MHz), more parallel send and receive units (up to 8x8 MIMO), more efficient modulation (256QAM) and multi-user MIMO.

  • Channel width: 20, 40, 80 and 160 MHz
  • Modulation method: 256QAM encodes 8 bits per transmission step
  • MIMO: up to 8 antennas that can be used simultaneously
  • Multi-user MIMO: from 4 antennas

Frequencies and channels


A WLAN with IEEE 802.11ac works in the frequency range at 5 GHz, for which there are general assignments worldwide. In the EU, the following frequency ranges are approved under certain conditions.

  • 5,150 to 5,350 MHz (channels 36 to 64)
  • 5,470 to 5,725 MHz (channel 100 to 140)

It looks different in other regions of the world. Usually there should be enough space for several 11ac WLANs operated in parallel.
In the frequency range of 5 GHz, channel widths of 20, 40, 80 and 160 MHz are possible. Typically a channel width of 80 MHz is used. The channel width of 160 MHz is optional and its practical use is rather questionable. The wider a channel, the fewer WLANs can work in parallel. A 160 MHz channel would occupy a large part of the available frequency spectrum. That would only make sense in exceptional cases.

DFS - Dynamic Frequency Selection

In order for access points in Europe and in many other countries to be able to use all channels in the frequency range around 5 GHz, they must be able to recognize signals from other radio systems and avoid them by changing channels. In Europe this is necessary in order not to disrupt the operation of the regional weather radar on channels 120 to 128, for example.
Without DFS (Dynamic Frequency Selection) and TPC (Transmit Power Control), WLAN devices may only use the lowest four channels from 36 to 48 (from 5,150 to 5,250 MHz), which corresponds to a channel width of 80 MHz (4 x 20 MHz).

DFS recognizes other radio systems and evades them by switching to other channels. With TPC, the access points control their transmission power dynamically. With a good radio connection, the data is sent with a lower transmission power.
Unfortunately, some WLAN manufacturers ignore DFS and TPC and save themselves the additional costs. There are devices on the market that are only incompletely capable of 5 GHz. These devices only work on channels 36 to 48. DFS is nothing new. It is already included in IEEE 802.11h. The same applies to IEEE 802.11n, which can work in both the 2.4 GHz and 5 GHz bands.

The lack of DFS is a nuisance for two reasons. A router or access point with 802.11n or 802.11ac would completely occupy channels 36 to 48 with an 80 MHz wide channel. If a neighboring router does not support DFS either, it has to use the same channels and both WLANs would have to share the bandwidth. Then there can be no more talk of fast WLAN.
The second sticking point concerns WLAN clients and adapters that cannot use the area over channel 48. If an access point has set up the WLAN on a higher channel, a smart TV without DFS / TPC support, for example, cannot establish a connection to this access point.

256QAM modulation method

Like all modern radio systems, IEEE 802.11ac uses OFDM to subdivide the frequency range into numerous, individually modulated subcarriers. In the best case, the devices support high-quality modulation methods. For example, 256QAM with 256 levels. That is 8 bits per transmission step. In comparison, 64QAM only transmits 6 bits per transmission step.

Up to 8 MIMO streams

MIMO provides for the use of several transmitting and receiving antennas. With IEEE 802.11ac up to 8 pieces. That means up to 8 simultaneous data streams. The transmission rate is increased with each data stream.
However, it is unlikely that access points with more than 4 antennas (with 5 GHz support) will come onto the market. Because the data throughput does not necessarily increase with each additional data stream. In return, the hardware effort, the number of antennas, the computing effort for signal separation and the energy consumption increase. Mobile devices in particular have to make do with one, at most two, data streams.

MU-MIMO - Multi-User MIMO

IEEE 802.11ac also provides an optional extension with multi-user MIMO (MU-MIMO), with which several antennas can send data to different WLAN clients. This requires at least 4 antennas in the access point. In addition, the clients must be MU-MIMO-capable.

Beamforming

Beamforming has been specified since IEEE 802.11n, but unfortunately too imprecise. Beamforming with devices from different manufacturers has rarely worked. Beamforming is specified in more detail in IEEE 802.11ac.
A base station can use beamforming to send the radio signal in a specific direction, thereby significantly improving the connection to a specific client. With beamforming, several antennas send the same signal with a time offset. This creates a directional effect that focuses the transmission energy on a client. This improves the quality of the radio link, which allows a higher modulation level and thus increases the transmission rate.
In order for this to work, the channel to the client must be measured before each transmission. It's about where exactly the remote station is located (outside angle) and who else is there. In addition, environmental conditions can change at any time. Finding that out costs up to 1% airtime. If the client does move, a transmission error can occur.

WLAN access point with Gigabit Ethernet port

A target data rate of over 1 GBit / s is only possible if the radio conditions are optimal. And that is very rare.
A further limitation then occurs from 1 GBit / s. With access points and WLAN routers, a Gigabit Ethernet port would then no longer be sufficient, since it is fully utilized at 1 GBit / s. A WLAN with IEEE 802.11ac in full expansion would only be possible if two Gigabit Ethernet ports are bundled with link aggregation or a 10 Gigabit Ethernet port is available. The latter is rather unlikely in consumer devices.

Conclusion

  • IEEE 802.11ac is only available in the frequency range around 5 GHz, because at 2.4 GHz only channel widths of 20 and 40 MHz are possible.
  • DFS is mandatory in the frequency range around 5 GHz. Without DFS, the use of this frequency range is limited to a few or only 20 or 40 MHz wide channels.
  • Basically we are dealing with a shared medium, which means that all WLAN clients have to share the bandwidth.
  • The specified data rates are usually significantly lower in practice.
  • Many of the standard's features are not mastered by many products (e.g. MIMO and beamforming). They require enormous computing power and thus also more energy consumption.
  • Legacy clients with IEEE 802.11n limit the access point to IEEE 802.11n, even if it and other clients can use IEEE 802.11ac.

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