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Wi-Fi IEEE 802.11 is used by very many devices from smartphones to laptops and tablets to remote sensors, actuators televisions and many more.
There are several frequency bands within the radio spectrum that are used for the Wi-Fi and within these there are many channels that have been designated with numbers so they can be identified.
Although many channels are selected automatically, it sometimes helps to have an understanding of the Wi-Fi spectrum, bands, frequencies and the channels with their channel numbers to enable the best performance to be gained.
Wi-Fi is aimed at use within unlicensed spectrum - the ISM or Industrial, Scientific and Medical bands. These bands have been internationally agreed and unlike most other bands, they can be used without the need for a transmitting licence. This gives access to everyone to use them freely.
The ISM bands are not only used by Wi-Fi, but everything from microwave ovens to many other forms of wireless connectivity and many industrial, scientific and medical uses.
Whilst the ISM bands are available globally, there are some differences and restrictions that can occur in some countries.
The main bands used for carrying Wi-Fi are those in the table below:
|Summary of Major ISM Bands
|2400||2500||Often referred to as the 2.4 GHz band, this spectrum is the most widely used of the bands available for Wi-Fi. Used by 802.11b, g, & n. It can carry a maximum of three non-overlapping channels.|
|5725||5875||This 5 GHz band or 5.8 GHz band provides additional bandwidth, and being at a higher frequency, equipment costs are slightly higher, although usage, and hence interference is less.It can be used by 802.11a & n. It can carry up to 23 non-overlapping channels, but gives a shorter range than 2.4 GHz.|
802.11 systems & frequency bands
There are several different 802.11 variants in use. Different 802.11 variants use different bands. A summary of the bands used by the 802.11 systems is given below:
|802.11 Types & Frequency Bands
|IEEE 802.11 variant||Frequency bands used||Comments|
|802.11a||5GHz||Read more about 802.11a|
|802.11b||2.4GHz||Read more about 802.11b|
|802.11g||2.4GHz||Read more about 802.11g|
|802.11n||2.4 & 5 GHz||Read more about 802.11n|
|802.11ac||Below 6GHz||Read more about 802.11ac|
|802.11ad||Up to 60 GHz||Read more about 802.11ad|
|802.11af||TV white space (below 1 GHz)||Read more about 802.11af|
|802.11ah||700 MHz, 860MHz, 902 MHz, etc. ISM bands dependent upon country and allocations||Read more about 802.11ah|
|802.11ax||Read more about 802.11ax|
2.4 GHz 802.11 channels
There is a total of fourteen channels defined for use by Wi-Fi 802.11 for the 2.4 GHz ISM band. Not all of the channels are allowed in all countries: 11 are allowed by the FCC and used in what is often termed the North American domain, and 13 are allowed in Europe where channels have been defined by ETSI. The WLAN / Wi-Fi channels are spaced 5 MHz apart (with the exception of a 12 MHz spacing between the last two channels).
The 802.11 Wi-Fi standards specify a bandwidth of 22 MHz and channels are on a 5 MHz incremental step. Often nominal figures for the channel bandwidth of 20 MHz are often given. The 20 / 22 MHz bandwidth and channel separation of 5 MHz means that adjacent channels overlap and signals on adjacent channels will interfere with each other.
The 22 MHz channel bandwidth holds for all standards even though 802.11b WLAN standard can run at variety of speeds: 1, 2, 5.5, or 11 Mbps and the newer 802.11g standard can run at speeds up to 54 Mbps. The differences occur in the RF modulation scheme used, but the WLAN channels are identical across all of the applicable 802.11 standards.
When using 802.11 to provide Wi-Fi solutions for offices, general use hotspots, or for any WLAN applications, it is necessary to ensure that parameters such as the channels are correctly set to ensure the required performance is achieved.
2.4 GHz Wi-Fi channel frequencies
The table given below provides the frequencies for the total of fourteen 802.11 Wi-Fi channels that are available around the globe. Not all of these channels are available for use in all countries.
|2.4GHz Band Channel Numbers & Frequencies
|Channel Number||Lower Frequency
2.4 GHz WiFi channel overlap and selection
The channels used for WiFi are separated by 5 MHz in most cases but have a bandwidth of 22 MHz. As a result channels overlap and it can be seen that it is possible to find a maximum of three non-overlapping channels. Therefore if there are adjacent pieces of WLAN equipment that need to work on non-interfering channels, there is only a possibility of three. There are five combinations of available non overlapping channels are given below:
From the diagram above, it can be seen that Wi-Fi channels 1, 6, 11, or 2, 7, 12, or 3, 8, 13 or 4, 9, 14 (if allowed) or 5, 10 (and possibly 14 if allowed) can be used together as sets. Often WiFi routers are set to channel 6 as the default, and therefore the set of channels 1, 6 and 11 is possibly the most widely used.
As some energy spreads out further outside the nominal bandwidth, if only two channels are used, then the further away from each other the better the performance.
It is found that when interference exists, the throughput of the system is reduced. It therefore pays to reduce the levels of interference to improve the overall performance of the WLAN equipment.
With the use of IEEE 802.11n, there is the possibility of using signal bandwidths of either 20 MHz or 40 MHz. When 40 MHz bandwidth is used to gain the higher data throughput, this obviously reduces the number of channels that can be used.The diagram above shows the 802.11n 40 MHz signals. These signals are designated with their equivalent centre channel numbers.
2.4 GHz Wi-Fi channel availability
In view of the differences in spectrum allocations around the globe and different requirements for the regulatory authorities, not all the WLAN channels are available in every country. The table below provides a broad indication of the availability of the different Wi-Fi channels in different parts of the world.
|2.4 GHz Wi-Fi Channel Availability|
This chart is only provides a general view, and there may be variations between different countries. For example some countries within the European zone Spain have restrictions on the channels that may be used (France: channels 10 - 13 and Spain channels 10 and 11) use of Wi-Fi and do not allow many of the channels that might be thought to be available, although the position is likely to change.
3.6 GHz WiFi band
This band of frequencies is only allowed for use within the USA under a scheme known as 802.11y. Here high powered stations can be used as backhaul for networks, etc.
|3.6 GHz WiFi band
|Channel Number||Frequency (MHz)||5 MHz Bandwidth||10 MHz Bandwidth||20 MHz Bandwidth|
Note: the channel centre frequency depends upon the bandwidth used. This accounts for the fact that the centre frequency for various channels is different if different signal bandwidths are used.
5 GHz WiFi channels & frequencies
As the 2.4 GHz band becomes more crowded, many users are opting to use the 5 GHz ISM band. This not only provides more spectrum, but it is not as widely used by Wi-Fi as well as many other appliances including items such as microwave ovens, etc.
It will be seen that many of the 5 GHz Wi-Fi channels fall outside the accepted ISM unlicensed band and as a result various restrictions are placed on operation at these frequencies.
|5 GHz WiFi channels & frequencies
|Channel Number||Frequency MHz||Europe
|52||5260||Indoors / DFS / TPC||DFS||DFS / TPC|
|56||5280||Indoors / DFS / TPC||DFS||DFS / TPC|
|60||5300||Indoors / DFS / TPC||DFS||DFS / TPC|
|64||5320||Indoors / DFS / TPC||DFS||DFS / TPC|
|100||5500||DFS / TPC||DFS||DFS / TPC|
|104||5520||DFS / TPC||DFS||DFS / TPC|
|108||5540||DFS / TPC||DFS||DFS / TPC|
|112||5560||DFS / TPC||DFS||DFS / TPC|
|116||5580||DFS / TPC||DFS||DFS / TPC|
|120||5600||DFS / TPC||No Access||DFS / TPC|
|124||5620||DFS / TPC||No Access||DFS / TPC|
|128||5640||DFS / TPC||No Access||DFS / TPC|
|132||5660||DFS / TPC||DFS||DFS / TPC|
|136||5680||DFS / TPC||DFS||DFS / TPC|
|140||5700||DFS / TPC||DFS||DFS / TPC|
Note 1: there are additional regional variations for countries including Australia, Brazil, China, Israel, Korea, Singapore, South Africa, Turkey, etc. Additionally Japan has access to some channels below 5180 MHz.
Note 2: DFS = Dynamic Frequency Selection; TPC = Transmit Power Control; SRD = Short Range Devices 25 mW max power.
Additional bands and frequencies
In addition to the more established forms of Wi-Fi, new formats are being developed that will use new frequencies and bands. Technologies employing white space usage, etc. and also new standards using bands that are well into the microwave region and will deliver gigabit transfer speeds are being developed and introduced. These technologies will require the use of new spectrum for Wi-Fi.
|Additional Wi-Fi Bands & Frequencies
|Wi-Fi Technology||Standard||Frequencies Bands|
|White-Fi||802.11af||470 - 710MHz|
|Microwave Wi-Fi||802.11ad||57.0 - 64.0 GHz ISM band (Regional variations apply)
Channels: 58,32, 60.48, 62.64, and 64.80 GHz
As Wi-Fi technology use has increased out of all proportion and the data transfer speeds have risen significantly, so too has the way in which the bands are used.
Originally the 2.4GHz band was favoured for Wi-Fi, but as the technology for the 5GHz band fell it came into much greater use in view of its wider channel bandwidth capability.
As other Wi-Fi technologies come to the fore, many other frequencies are being used. Other unlicensed bands that are below 1 GHz as well as white space for White-Fi using the unused TV spectrum and also now increasingly higher frequencies into the microwave region where even greater bandwidths are available, but at the cost of shorter distance.
Each Wi-Fi technology has its own frequencies or bands and sometimes a different use of the channels available.
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