Wi-Fi / WLAN Channels, Frequencies, Bands & Bandwidths

- Wi-Fi / WLAN / 802.11 channels, their channel frequencies and bandwidth allocations around the globe, spectral mask and summary of which channels can be used together for WLAN solutions.

The IEEE 802.11 Wi-Fi / WLAN standards set the attributes for the different channels that may be used.

These attributes enable different Wi-Fi modules to talk to each other and effectively set up a WLAN.

To ensure that WLAN solutions operate satisfactorily, parameters such as the RF signal centre frequencies, channel numbers and the bandwidths must all be set..


ISM bands

Wi-Fi is aimed at use within unlicensed spectrum. This enables users to access the radio spectrum without the need for the regulations and restrictions that might be applicable elsewhere. The downside is that this spectrum is also shared by many other users and as a result the system has to be resilient to interference.

There are a number of unlicensed spectrum bands in a variety of areas of the radio spectrum. Often these are referred to as ISM bands - Industrial, Scientific and Medical, and they carry everything from microwave ovens to radio communications. Many of these bands, including he two used for Wi-Fi are global allocations, although local restrictions may apply for some aspects of their use.

The main bands used for carrying Wi-Fi are those in the table below:


Lower Frequency
MHz
Upper Frequency
MHz
Comments
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.

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 WLAN standards specify a bandwidth of 22 MHz and a 25 MHz channel separation, although nominal figures for the 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 Wi-Fi to provide WLAN 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.

Channel Number Lower Frequency
MHz
Center Frequency
MHz
Upper Frequency
MHz
1 2401 2412 2423
2 2404 2417 2428
3 2411 2422 2433
4 2416 2427 2438
5 2421 2432 2443
6 2426 2437 2448
7 2431 2442 2453
8 2436 2447 2458
9 2441 2452 2463
10 2451 2457 2468
11 2451 2462 2473
12 2456 2467 2478
13 2461 2472 2483
14 2473 2484 2495


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:

Wi-Fi channels, how they overlap and sets that can be used together
Wi-Fi Channel overlap and which ones can be used as sets.

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.

IEEE 802.11n Wi-Fi channels can occupy 40 MHz to provide the additional data throughput. This only gives space for two channels
802.11n 40 MHz channel capacity

The diagram above shows the 802.11n 40 MHz signals. These signals are designated with their equivalent centre channel numbers.


2.4 GHz WLAN / 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.


Channel Number Europe
(ETSI)
North America
(FCC)
Japan
1
2
3
4
5
6
7
8
9
10
11
12 No
13 No
14 No No 802.11b only

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.

Channel Number Frequency (MHz) 5 MHz Bandwidth 10 MHz Bandwidth 20 MHz Bandwidth
131 3657.5    
132 36622.5    
132 3660.0    
133 3667.5    
133 3665.0    
134 3672.5    
134 3670.0    
135 3677.5    
136 3682.5    
136 3680.0    
137 3687.5    
137 3685.0    
138 3689.5    
138 3690.0    

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.


Channel Number Frequency MHz Europe
(ETSI)
North America
(FCC)
Japan
36 5180 Indoors
40 5200 Indoors
44 5220 Indoors
48 5240 Indoors
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
149 5745 SRD No Access
153 5765 SRD No Access
157 5785 SRD No Access
161 5805 SRD No Access
165 5825 SRD No Access

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.


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 WLAN and Wi-Fi technology develops further new bands will be added to enable sufficient interference bandwidth to be available to ensure the ever increasing requirement for the transfer of high speed data.

By Ian Poole


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