Wireless local area network channels using IEEE 802.11 protocols are sold mostly under the trademark WiFi.
The 802.11 workgroup has documented use in five distinct frequency ranges: 2.4 GHz, 3.6 GHz, 4.9 GHz, 5 GHz, and 5.9 GHz bands. Each range is divided into a multitude of channels. Countries apply their own regulations to the allowable channels, allowed users and maximum power levels within these frequency ranges.
2.4 GHz (802.11b/g/n)
Most countries
United States
Fourteen channels are designated in the 2.4 GHz range, spaced 5 MHz apart from each other except for a 12 MHz space before channel 14.
For 802.11g/n, it is not possible to guarantee orthogonal frequency-division multiplexing (OFDM) operation, thus affecting the number of possible non-overlapping channels depending on radio operation.
Interference concerns
As the protocol requires 16.25 to 22 MHz of channel separation (as shown above), adjacent channels overlap and will interfere with each other. Leaving three or four channels clear between used channels is recommended to avoid interference. The exact spacing required depends on the protocol and data rate selected as well as the electromagnetic environment where the equipment is used.
When two or more 802.11b transmitters are operated in the same airspace, their signals must be attenuated by -50 dBr and/or separated by 22 MHz to prevent interference. This is because the DSSS algorithm transmits data logarithmically along a 20 MHz bandwidth. The remaining 2 MHz gap is used as a guard band to allow sufficient attenuation along the edge channels.
Note: The 40 MHz bands in the diagram above are labelled with their centre channel numbers, but the management interface of many Wi-Fi devices labels one of these bands with the centre channel of one of the 20 MHz bands it overlaps plus an Up or Down notation to specify the other half of the band. For example, channel 3 in the diagram is called channel 1+Upper or Channel 5+Lower, and Channel 11 in the diagram is called Channel 9+Upper or Channel 13+Lower.
Countries apply their own regulations to the allowable channels, allowed users and maximum power levels within these frequency ranges. Network operators should consult their local authorities as these regulations may be out of date as they are subject to change at any time. Most of the world will allow the first thirteen channels in the spectrum.
^B In the U.S., 802.11 operation in the channels 12 and 13 is allowed under low powered conditions. The 2.4 GHz Part 15 band in the U.S. allows spread-spectrum operation as long as the 50 dB bandwidth of the signal is within the range of 2,400â€"2,483.5 MHz which wholly encompasses both channels 12 and 13. A Federal Communications Commission (FCC) document clarifies that only channel 14 is forbidden and that low-power transmitters with low-gain antennas may operate legally in channels 12 and 13. Channels 12 and 13, however, are not normally used in order to avoid any potential interference in the adjacent restricted frequency band, 2,483.5â€"2,500 MHz, which is subject to strict emission limits set out in 47 CFR § 15.205. Per recent FCC Order 16-181, "an authorized access point device can only operate in the 2483.5â€"2495 MHz band when it is operating under the control of a Globalstar Network Operating Center and that a client device can only operate in the 2483.5â€"2495 MHz band when it is operating under the control of an authorized access point"
In Canada, 12 channels are available for use, 11 of which at full power and the other (channel 12) is transmit power limited. Few devices, however, have a method to enable a lower powered channel 12.
^C Channel 14 is valid only for DSSS and CCK modes (Clause 18 a.k.a. 802.11b) in Japan. OFDM (i.e., 802.11g) may not be used. (IEEE 802.11-2007 §19.4.2)
3.65 GHz (802.11y)
Except where noted, all information taken from Annex J of IEEE 802.11y-2008
This range is documented as only being allowed as a licensed band in the United States. Please see IEEE 802.11y for details.
Countries apply their own regulations to the allowable channels, allowed users and maximum power levels within these frequency ranges.
A 40 MHz band is available from 3655â€"3695 MHz. It may be divided into eight 5 MHz channels, four 10 MHz channels, or two 20 MHz channels, as follows:
4.9 GHz (802.11j) public safety WLAN
50 MHz of spectrum from 4940 MHz to 4990 MHz (WLAN channels 20â€"26) are in use by public safety entities in the United States. Within this spectrum space, there are two non-overlapping channels allocated, both with a width of 20 MHz. The most commonly used channels are 22 and 26.
5 GHz (802.11a/h/j/n/ac)
Countries apply their own regulations to the allowable channels, allowed users and maximum power levels within these frequency ranges. Network operators should consult their local authorities as these regulations may be out of date as they are subject to change at any time.
European standard EN 301 893 covers 5.15â€"5.725 GHz operation, and v1.8.1 is in force.
In 2007, the FCC (United States) began requiring that devices operating on 5.250â€"5.350 GHz and 5.470â€"5.725 GHz must employ dynamic frequency selection (DFS) and transmit power control (TPC) capabilities. This is to avoid interference with weather-radar and military applications. In 2010, the FCC further clarified the use of channels in the 5.470â€"5.725 GHz band to avoid interference with TDWR weather radar systems. In FCC parlance, these restrictions are now referred to collectively as the "Old Rules". On 10 June 2015, the FCC approved a "new" ruleset for 5 GHz device operation (called the "New Rules"), which adds 160 and 80 MHz channel identifiers, and re-enables previously prohibited DFS channels, in Publication Number 905462. This FCC publication eliminates the ability for manufacturers to have devices approved or modified under the Old Rules in phases; the New Rules apply in all circumstances as of 2 June 2016.
Germany requires DFS and TPC capabilities on 5.250â€"5.350 GHz and 5.470â€"5.725 GHz as well; in addition, the frequency range 5.150â€"5.350 GHz is allowed only for indoor use, leaving only 5.470â€"5.725 GHz for outdoor and indoor use.
Since this is the German implementation of EU Rule 2005/513/EC, similar regulations must be expected throughout the European Union.
Austria adopted Decision 2005/513/EC directly into national law. The same restrictions as in Germany apply, only 5.470â€"5.725 GHz is allowed to be used outdoor and indoor.
South Africa simply copied the European regulations.
Japan's use of 10 and 20 MHz-wide 5 GHz wireless channels is codified by Association of Radio Industries and Businesses (ARIB) document STD-T71, Broadband Mobile Access Communication System (CSMA). Additional rule specifications relating to 40, 80, and 160 MHz channel allocation has been taken on by Japan's Ministry of Internal Affairs and Communications (MIC).
In Brazil, the TPC use in 5.150â€"5.725 GHz band is optional. DFS is required only in the 5.470â€"5.725 GHz band.
As of 2015, some of the Australian channels require DFS to be utilised (a significant change from the 2000 regulations, which allowed lower power operation without DFS). As per AS/NZS 4268 B1 and B2, transmitters designed to operate in any part of 5250â€"5350 GHz and 5470â€"5725 GHz bands shall implement DFS in accordance with sections 4.7 and 5.3.8 and Annex D of ETSI EN 301 893 or alternatively in accordance with FCC paragraph 15.407(h)(2). Also as per AS/NZS 4268 B3 and B4, transmitters designed to operate in any part of 5250â€"5350 MHz and 5470â€"5725 MHz bands shall implement TPC in accordance with sections 4.4 and 5.3.4 of ETSI EN 301 893 or alternatively in accordance with FCC paragraph 15.407(h)(1).
New Zealand regulation differs from Australian.
Singapore requires DFS and TPC capabilities on 5.250â€"5.350 GHz above 100 mW (e.i.r.p.) and below or equal to 200 mW (e.i.r.p.), and requires DFS capability on 5.250â€"5.350 GHz below or equal to 100 mW (e.i.r.p.). In addition, 5.150â€"5.350 GHz is allowed only for indoor use.
China MIIT expanded allowed channels as of 31 December 2012 to add UNII-1, 5150 ~ 5250 GHz, UNII-2, 5250 ~ 5350 GHz (DFS/TPC), similar to European standards EN 301.893 V1.7.1.
5.9 GHz (802.11p)
The 802.11p amendment, also known as Wireless Access in Vehicular Environments (WAVE), published on 15 July 2010, specifies WLAN in the licensed Intelligent Transportation Systems (ITS) band of 5.9 GHz (5.850â€"5.925 GHz). The 802.11p standard is intended for use in vehicular communication systems.
60 GHz (802.11ad)
The 802.11ad, also known as WiGig. This operates in 60 GHz ISM band.
900 MHz (802.11ah)
802.11ah operates in sub-gigahertz unlicensed bands.
See also
- Electromagnetic interference at 2.4 GHz
- High Speed Multimedia Radio
- IEEE 802.11#Layer 2 .E2.80.93 Datagrams
- Wireless LAN
References
Further reading
- "Regulatory Database". Linux Wireless â€" An online database of allowed frequencies used by Linux 802.11 subsystem.Â
- "FCC Regulations Update". www.cisco.com â€" Dynamic Frequency Selection for 5 GHz WLAN in the U.S. and Canada.Â