IEEE 802.11

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IEEE 802.11 (also: Wireless LAN (WLAN) , Wi-Fi ) refers to an IEEE standard for communication in radio networks. The publisher is the Institute of Electrical and Electronics Engineers (IEEE). The first version of the standard was adopted in 1997. It specifies the medium access ( MAC layer) and the physical layer (see OSI model ) for local radio networks.

For the physical layer, two spread spectrum methods (transmission by radio waves) and a method for data transmission by infrared light are specified in the original standard , whereby a transmission rate of up to 2 Mbit / s (gross) is provided. The license-free ISM band at 2.4 GHz is used for data transmission via radio waves . Communication between two participants can take place directly in so-called ad-hoc mode , in infrastructure mode with the aid of a base station ( access point ) or as a mesh network .

Two extensions followed in 1999: 802.11a specifies another variant of the physical layer that works in the 5 GHz band and enables transmission rates of up to 54 Mbit / s. 802.11b is also an alternative specification of the physical layer, which works with the 2.4 GHz band previously used and enables transmission rates of up to 11 Mbit / s. The 802.11g extension passed in 2003, which also works in the 2.4 GHz band, increases the maximum transmission rate to 54 Mbit / s. The 802.11n extension provides for a transmission rate of up to 600 Mbit / s with changed frequency bands and new channel divisions.

Because the 2.4 GHz band can be used license-free in most countries, products based on the 802.11b / g standard have become widespread. Products that conform to standards and ensure interoperability with products from other manufacturers can be certified by the Wi-Fi Alliance. Other frequency bands are currently being used: the 802.11ac standard uses the 5 GHz band, 802.11ad opens up the 60 GHz band and 802.11ah is intended for the 900 MHz band.

Standard 802.11


802.11 is a family of standards for wireless local area networks (WLAN). The definition of the IEEE 802 standards , which initially describe network access in general, began in February 1980. The number 802 is sometimes associated with the start of the project in February 1980, but it was simply the next free IEEE identification number.

Some important standards of the IEEE 802.11 family:
802.11, 802.11a, 802.11b, 802.11g, 802.11n, 802.11ac, 802.11ad, 802.11ah.

Modulation parameters for OFDM -based IEEE 802.11a / g / n / ac
  • 802.11 original standard, adopted in 1997
    • Data rate: 1 or 2 Mbit / s gross (for user data and protocol overhead)
    • Frequency band 2.400-2.485 GHz (license-free)
    • Modulation method : FHSS or DSSS
    • Acceptance: outdated, no longer widely used
  • 802.11a Physical Layer Extension, 1999
    • Data rate: 6, 9, 12, 18, 24, 36, 48 or 54 Mbit / s gross, up to ≈22 Mbit / s net
    • Frequency band 5 GHz (released in Germany since November 13, 2002, for more details see 802.11h )
    • Modulation method: OFDM
  • 802.11b Physical Layer Extension, 1999
    • Data rate: 5.5 or 11 Mbit / s gross (maximum 50% net)
    • Frequency band 2.400–2.4835 GHz (license-free)
    • Modulation method: DSSS with CCK (Complementary Code Keying)
    • Acceptance: outdated, no longer widely used
  • 802.11g Physical Layer Extension, 2003
    • Data rate: 6, 12, 18, 24, 36, 48 or 54 Mbit / s gross, up to ≈22 Mbit / s net
    • Frequency band: 2.400–2.4835 GHz (license-free)
    • Modulation method: OFDM (Orthogonal Frequency Division Multiplexing)
    • Supports 802.11 and 802.11b as fall-back
    • Acceptance: widespread use, but is increasingly being replaced by 802.11n.
  • 802.11-2007 Summary of Standards dated March 8, 2007
    • Summary of the version from 1999 with the 8 extensions ( 802.11a , b , d , e , g , h , i , j ) to a single standard.
    • Released March 8, 2007 under the name IEEE 802.11-2007 .
  • 802.11n ratification happened on September 11, 2009
    • Data rate: 6.5–72.2 Mbit / s (20 MHz channel width), 13.5–150 Mbit / s (40 MHz channel width), with 4x4 MIMO theoretically up to 600 Mbit / s
    • Frequency band: 2.400–2.4835 GHz (20 MHz channel width), 5 GHz (up to 40 MHz channel width) as an additional band
    • Acceptance: New devices mostly have 802.11n, which replaces older standards.
  • 802.11p extension to 802.11a for use in vehicle-to-vehicle networks , in 2010, also under DSRC known
    • Data rate: 27 Mbit / s gross
    • Frequency band: planned 5.850–5.925 GHz (in the USA already reserved for use in traffic)
    • Acceptance: favored technology of the Car to Car Communication Consortium (C2C-CC), essential basis of ISO TC204 WG16 CALM-M5.
  • 802.11-12 Summary of Standards dated March 29, 2012
    • Combination of the 10 extensions ( 802.11k , r , y , n , w , p , z , v , u , s ) with the basic standard 2007 into a single standard.
    • The original extensions of the PHY (Physical Layer) can be found in individual chapters ("Clauses") (see table below)
    • Published on March 29, 2012 under the name "IEEE 802.11-2012".
  • 802.11ac extension to 802.11n, released December 18, 2013
    • Data rate: 6.5–96.3 Mbit / s (20 MHz channel width), 13.5–200 Mbit / s (40 MHz channel width), 29.2–433 Mbit / s (80 MHz channel width ), 58.5 to 867 Mbit / s (two 80 MHz or 160 MHz channel widths). Devices with 3x3 MIMO, 80 MHz channel width and theoretical 1299 Mbit / s can often be found. In purely mathematical terms, up to 6936 Mbit / s are possible with 8x8 MIMO.
    • Frequency band: only 5 GHz
    • The first routers (e.g. AVM FRITZ! Box 7490), laptops (e.g. MacBook Air 2013) and the first smartphones (e.g. HTC One, LG Nexus 5 and Samsung Galaxy S IV) came onto the market at the end of 2013 .
  • 802.11ad , large bandwidth (e.g. for uncompressed video) in the 60 GHz band
    • Frequency band: 4 channels in the 60 GHz band (57.24-59.40; 59.40-61.56; 61.56-63.72 and 63.72-65.88 GHz)
    • OFDM (more robust) and QAM (easier) mode
    • Data rate: OFDM mode: 1540, 2310, 2695, 3080, 4620, 5390 and 6930 Mbit / s
    • Data rate: QAM mode: 26, 361 to 5280 Mbit / s
    • Max. 10 m range
  • 802.11ah (Wi-Fi HaLow), released January 4, 2016
    • Frequency band: 750 to 930 MHz, frequency range depends on region
    • USA: twenty-six 1 MHz channels, thirteen 2 MHz channels, (six 4 MHz channels, three 8 MHz channels)
    • EU: five 1 MHz channels, two 2 MHz channels, (one 4 MHz channel)
    • OFDM from a total of 64 subcarriers with a spacing of 31.25 kHz
    • BPSK, QPSK, and 16 to 256 QAM
    • MU-MIMO and single user beamforming

In 2018, the Wi-Fi Alliance simplified the names that are meaningless to end customers: 802.11n, ac and ax become Wi-Fi 4 , Wi-Fi 5 and Wi-Fi 6 .

A table of theoretically and practically possible data transmission rates for the various standards can be found in the section on data transmission rates in the article Wireless Local Area Network .


The table is taken from the book Data and Voice Transmission in Wireless Local / Personal Area Networks .

802.11c - 2001 Wireless bridging: connector between different radio networks
802.11d b, g, a, h 2001 World Mode: Adaptation to the regulatory provisions of different countries
802.11e g, a, h 2004 Quality of Service and Streaming: Quality of Service support
802.11f g, a, h 2003 Handover: interoperability between base stations
802.11h a 2006 DFS ( Dynamic Frequency Selection ) and TPC ( Transmitter Power Control )
802.11i b, g, a, h 2004 Security WPA2: Enhancements for security and authentication
802.11j a, h 2004 4.9-5 GHz operation in Japan
802.11k g, a, h 2007 Better options for radio parameters (e.g. signal strength)
802.11m b, g, a, h 2006 Maintenance: additions and fault selection
802.11p a 2010 Vehicle to vehicle communication
802.11r g, a, h 2008 Fast Handover: Extension for VoIP
802.11s g, a nb Meshed networks: For MAC level
802.11t b, g, a nb Measurement method: line parameters
802.11u b, g, a 2011 Internetworking: Binding to non-802 networks
802.11v b, g, a nb Network management
802.11w b, g, a nb Security extension for management frames
802.11y - 2008 3.6 GHz adjustment for the US
nb = not known, as still in planning

In addition to these, there are proprietary extensions that allow other transfer rates:

  • PBCC with up to 22 Mbit / s in the 2.4 GHz band,
  • 802.11b + with up to 44 Mbit / s through channel bundling,
  • 802.11g ++ depending on the manufacturer with up to 108 Mbit / s or 125 Mbit / s.

But these are not official IEEE standards.

Maximum permissible transmission or radiation power ( equivalent isotropic radiation power (EIRP) - antenna gains must therefore be taken into account):

  • 2.4 GHz: 100 mW - in Germany, other countries have different regulations here. For example, cards with 300 mW and more are also legal (e.g. in the USA).
  • 5 GHz: Between 25 mW and 4000 mW - depending on the frequency band . In Europe, TPC / DFS according to 802.11h is prescribed for the operation of WLANs according to 802.11a. Without DFS and TPC, only 200 mW and a restricted frequency band for 802.11a are permitted in Germany.


  • 802.11b and 802.11g are compatible with each other. The 802.11g devices then operate in a compatibility mode that allows 802.11b devices to discover a channel occupied by an 802.11g device. This will reduce the effective speed somewhat.
  • 802.11a and 802.11h are fully compatible with each other.

Media access

The CSMA / CA mechanism is mandatory within the 802.11 standard to enable joint access to the medium by several devices . CSMA / CA RTS / CTS and CSMA / CA PCF are optional .

Since a higher error rate occurs in radio communication, 802.11 has its own mechanism for retransmission. If the transmission is correct, the recipient confirms the data transmission; if the transmission is incorrect, the data must be sent again.

The individual networks are identified by their network names (Extended Service Set Identifier (ESSID), see Service Set Identifier ).

Advantages and disadvantages of the tapes

2.4 GHz band :

  • Advantages:
    • overcomes shielding materials with less loss
    • free, approved ISM frequency band
    • no complex spectrum management functions such as TPC or DFS required in order to be able to utilize the full transmission power of 100 mW
    • wide spread and therefore low device costs
  • Disadvantage:
    • The frequency band has to be shared with other devices or radio technologies ( Bluetooth , microwave ovens , baby monitors , cordless phones , and so on), causing interference and interference
    • Trouble-free operation of only a maximum of 4 (USA: 3) networks in the same location possible, since effectively only 4 usable (hardly overlapping) channels are available (in Germany: channels 1, 5, 9 and 13 - USA 1, 6 and 11)

5 GHz band :

  • Advantages:
    • significantly higher transfer rate possible
    • Less-used frequency band, which often means less interference is possible
    • In Germany 19 (with BNetzA approval) non-overlapping channels
    • greater range, since up to 1000 mW transmission power is possible with 802.11h - this overcompensates for the greater attenuation of the higher frequencies
  • Disadvantage:
    • stronger regulations in Europe: DFS required on most channels ; outdoor operation is not permitted on some channels; if no TPC is used, the transmission power must be reduced
    • Most devices do not support ad hoc mode
    • Signal is quickly shielded by walls

Components / extensions

  • Similar to cell phones, TPC (Transmit Power Control) reduces the transmission power depending on the necessity (good contact between the devices = lower transmission power).
  • DFS (Dynamic Frequency Selection): A free frequency is selected independently, e.g. B. to avoid disturbing radar systems.

Frequencies and channels

See the section Frequencies and Channels in the article Wireless Local Area Network .

Other standards at close range

Further standards for data transmission by radio in the short range are HIPERLAN / 1 and HIPERLAN / 2, HomeRF and Bluetooth . Of these three standards, only Bluetooth has achieved practical importance.


Web links

Individual evidence

  1. Standards and Industry Groups - Standards & Initiatives . In: Helping Define 802.11n and other Wireless LAN Standards . Early 2010. Accessed January 4, 2011.
  2. Overview and Guide to the IEEE 802 LMSC. September 2004, p. 3 , accessed on October 20, 2017 (English): "The project number, 802, was simply the next number in the sequence being issued by the IEEE for standards projects"
  3. IEEE Ratifies 802.11n, Wireless LAN Specification to Provide Significantly Improved Data Throughput and Range . IEEE Standards Association. September 2009. Retrieved January 25, 2010.
  4. 802.11 timelines
  5. Press release of the Wi-Fi Alliance of January 4, 2016 (English) , accessed on January 8, 2016.
  6. Wi-Fi Alliance®: Generational Wi-Fi User Guide from October 2018 , accessed on March 13, 2019.
  7. ^ Andreas Walter: Data and voice transmission in wireless local / personal area networks . Generally usable radio technologies and their application. In: Handbook of Telecommunications . 140. Supplement. German Economic Service, 2010.