IEEE 802.11

IEEE 802.11 (also: Wireless LAN (WLAN ), Wi- Fi) denotes an IEEE standard for communication in wireless 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 wireless networks.

For the physical layer two spread spectrum ( transmission via radio waves) and a method for transmitting data via infrared light are specified in the original standard, with a transfer rate of up to 2 Mbit / s (gross ) is provided. For data transmission via radio waves, the royalty-free ISM band is used at 2.4 GHz. The communication between two nodes can be done directly in the so -called ad -hoc mode, infrastructure mode using a base station (Access Point ) or as a mesh network.

1999 was followed by two expansions: 802.11a specifies a further variant of the physical layer operating in the 5 GHz band and allows transmission rates up to 54 Mbit / s. 802.11b is also an alternative specification of the physical layer, which works with the previously used 2.4 GHz band and allows transmission rates up to 11 Mbit / s. Adopted in 2003 802.11g extension, which also operates in the 2.4 GHz band, increases the maximum transfer rate of 54 Mbit / s The newest addition to 802.11n provides a transfer rate of up to 600 Mbit / s at different frequency bands and new channel organizations.

The fact that the 2.4 GHz band in most countries may be used royalty- free products according to the standard 802.11b / g have gained wide acceptance. Products that work standards compliant and ensure interoperability with other manufacturers' products can be certified by the Wi -Fi Alliance.

For use it should be noted that the latency times that elapse until a channel is established or an access point has changed, can lead to significant waiting times for moving objects under these access points. Further, the same potential population of active participants is closely limited by the residence time in the individual channels. A new participant can only be active if the previous user releases the channel. This transfer of the concept of wired networks is more of a hindrance.

• 5.1 802.11b / g
• 5.2 802.11a
• 5.3 802.11ad

802.11

Generally

802.11 is a family of standards for wireless local area networks (WLAN). The definition of the IEEE 802 standards, the general first describe the network access, began in February 1980, hence the name was chosen 802.

Currently the family consists of 12 standards: 802.11, 802.11a, 802.11b, 802.11c, 802.11d, 802.11e, 802.11f, 802.11g, 802.11h, 802.11i, 802.11j, 802.11n.

• Adopted the original 802.11 standard in 1997 Data Rate: 1 or 2 Mbit / s gross ( for user data and protocol overhead )
• Frequency band 2.400 to 2.485 GHz (license free)
• Acceptance: outdated, no longer used widely

• 802.11a expansion of the physical layer 1999 Data rate: 6, 9, 12, 18, 24, 36, 48 or 54 Mbit / s gross, up to ~ 22 Mbit / s net
• The frequency band 5 GHz ( released in Germany since 13 Nov. 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 from 2.400 to 2.4835 GHz (license free)
• Acceptance: outdated, no longer used widely

• 802.11g of the 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 2.4835GHz ( RF)
• Modulation method: OFDM (Orthogonal Frequency Division Multiplexing)
• Supports 802.11 and 802.11b as a fall-back
• Acceptance is widespread but increasingly displaced by 802.11n.

• 802.11-2007 summary of the standards of 8 March 2007 Summary of the version of the 1999 8 extensions ( 802.11a, b, d, e, g, h, i, j ) to a single standard.
• Posted on 8 March 2007 under the name IEEE 802.11-2007.

• 802.11n ratification on September 11, 2009 happened Data rate: 6.5 to 72.2 Mbit / s (20 MHz bandwidth), 13.5 to 150 Mbit / s ( 40 MHz bandwidth), 4x4 MIMO to 600 Mbit / s
• Frequency band: 2,400 2.4835GHz (20 MHz bandwidth), 5 GHz ( 40 MHz bandwidth) as an additional band
• Acceptance of new devices and most have 802.11n, so older standards are superseded.

• Known 802.11p enlargement 802.11a for use in vehicle - to-vehicle networks, 2010 under DSRC Data rate: 27 Mbit / s gross
• Frequency Band: 5.850 to 5.925 GHz planned (in the U.S. already reserved for use in the transport sector )
• Acceptance favored technology of car-to- car Communication Consortium (C2C -CC), ISO TC204 WG16 essential basis CALM M5.

• 802.11-12 Summary of the standards of 29 March 2012 Summary of the extensions 10 ( 802.11k, R, Y, n, W, p, Z, V, U, S ) to the base 2007 standard to a single standard.
• The original extensions of the PHY (physical layer ) are found in each chapter ( " Clauses " ) again ( see table below)
• Posted on 29 March 2012 under the name IEEE 802.11-2012.

• 802.11ac planned expansion to 802.11n ( from 2013 ) Data rate: 6.5 to 96.3 Mbit / s (20 MHz band ), from 13.5 to 200 Mbit / s ( 40 MHz band ), from 29.2 to 433 Mbit / s (80- MHz band, ), 58.5 to 867 Mbit / s ( twice 80 MHz or 160 MHz band ), 8x8 MIMO to 6933 Mbit / s
• Frequency band: only 5 GHz
• Initial Router ( eg AVM FRITZ! 7490 ), Macs (eg MacBook Air 2013) and the first smartphones (eg HTC One, LG Nexus 5 and Samsung Galaxy S IV ) already have this standard.

• 802.11ad, large bandwidth (eg for uncompressed video) in the 60 GHz band Frequency Band: 4 channels in the 60 GHz band: 57.24 to 59.40, 59.40 to 61.56, 61.56 to 63.72 63.72 to 65.88 GHz and
• OFDM ( more robust) and QAM mode (single )
• Data rate: OFDM Mode: 1540, 2310, 2695, 3080, 4620, 5390 and 6930 Mbit / s
• Data rate: QAM mode: 26 361-5280 Mbit / s
• Max. 10 m range

Extensions

In addition to these, there are proprietary extensions that allow different transmission 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, and 125 Mbit / s

But these are not the official IEEE standards.

Maximum transmission or radiation powers (Effective isotropic radiated power ( EIRP) - antenna gains are therefore to be considered ):

• 2.4 GHz 100 mW - in Germany, other countries have different rules here. Thus, (eg in the U.S.) also cards with 300 mW and more legal.
• 5 GHz: between 30 mW and 1000 mW - depending on the frequency band. In Europe, TPC / DFS is required by 802.11h for the operation of 802.11a WLANs. Without DFS and TPC only 200 mW and limited frequency band for 802.11a in Germany are allowed.

Compatibilities:

• 802.11b and 802.11g are compatible. The 802.11g devices will work in a compatibility mode, which allows 802.11b devices to recognize a space occupied by an 802.11g device channel. The effective rate will slightly reduced.
• 802.11a and 802.11h are fully compatible to each other.

Media access

To allow shared access by a plurality of devices on the medium, the CSMA / CA mechanism is required in use of the 802.11 standard. Optional CSMA / CA RTS / CTS and CSMA / CA PCF.

Since radio communication a higher error rate exists at 802.11, a separate mechanism for retransmission. For a correct transmission, the receiver confirms the data transmission in a faulty transmission, the data must be resent.

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

Advantages and disadvantages of the bands

2.4 GHz band:

• Advantages: toll- free shared ISM frequency band
• No extensive range of management functions such as TPC or DFS needed to exploit full transmit power of 100 mW can
• Widespread and therefore low unit costs

• Frequency band is shared with other devices or wireless technologies (Bluetooth, microwave ovens, baby monitors, etc.), thereby jamming and interference
• Trouble-free operation of a maximum of 4 (USA: 3) networks in the same place possible, as effectively are only 4 usable (barely overlapping ) channels available ( in Germany: channels 1, 5, 9 and 13 - U.S. 1, 6 and 11)

5 GHz band:

• Advantages: less -used frequency band, thereby often trouble poorer operation possible
• In Germany 19 non-overlapping ( at Federal Network Agency Approved) channels
• Greater ranges, as possible with 802.11h up to 1000 mW output power - which more than offset the greater attenuation of the higher frequencies

• Stronger regulations in Europe: on most channels DFS necessary; on some channels no operation allowed outdoors; If no TPC is used, the transmission power must be reduced
• Ad- hoc mode is not supported by most devices
• Less widespread, so little available devices on the market, and high equipment costs

Components / extensions

• TPC (Transmit Power Control) reduced similar to mobile phones, the transmission power depending on the need ( good contact between the devices = less power).
• DFS (Dynamic Frequency Selection): It is independently selected an unused frequency, eg to avoid the interference from radar systems.

Frequencies or channels

802.11b / g

The frequencies in the 2.4 GHz band have been divided into channels; some countries allow only certain channels. In Germany is responsible for the allocation of frequencies, the Federal Network Agency ( FNA ).

In Spain and France, all channels are now valid that are valid in the rest of Europe, while in Spain initially only the channels 10 and 11, respectively, in France, channels 10 to 13 were allowed.

Although the channel spacing (except for port 14 ) is 5 MHz, a radio connection needs a bandwidth of 20 MHz ( 22 MHz b standard ). To avoid interference, spatially overlapping radio cells must choose non-overlapping frequency ranges, according to the above scheme have a distance of at least four channel numbers. Therefore, the channel combinations ( 1,5,9,13 ) in the United States ( 1,6,11 ) are used for overlapping radio cells preferred.

Due to the low frequency range of the FCC U.S. cards are also known as "World" card. This is to emphasize that they can be used in most countries.

802.11a

With the exception of the U.S., in which the channels may be 52 to 64 used outdoors, the 802.11a standard is approved for use only in enclosed spaces worldwide. In Europe, however, extended use options are given by the 802.11h standard.

The specified FBWA channels are enabled for "Fixed Broadband Wireless Access" by the Federal Network Agency in Germany for commercial, public networks and notifiable. Allow up to 4 W output power.

Since August 2006, as defined in the 802.11a standard between 5180-5260 MHz channels (channel 36, 40, 44 and 48) may be used indoors without DFS and TPC with a transmission power of up to 200 mW in Germany.

802.11ad

The 60 GHz band is 57-66 GHz.

Bandwidth: 1760 MHz Channel spacing: 2160 MHz

Other standards in the near

Other standards for data transmission by radio in the vicinity are HIPERLAN / 1 and HIPERLAN / 2, HomeRF and Bluetooth. Of these three standards but only Bluetooth has gained practical importance.