Wireless - Wi-Fi 2.4GHz frequency band and channels
The 2.4GHz frequency band used by Wi-Fi technologies defines a specific range of frequencies that can be leveraged for wireless communications. This frequency range is separated into specific channels as illustrated in the following table:
| Channel | Frequency Range (GHz) | Center Frequency (GHz) |
|---|---|---|
| 1 | 2.402 - 2.422 | 2.412 |
| 2 | 2.407 - 2.427 | 2.417 |
| 3 | 2.412 - 2.432 | 2.422 |
| 4 | 2.417 - 2.437 | 2.427 |
| 5 | 2.422 - 2.442 | 2.432 |
| 6 | 2.427 - 2.447 | 2.437 |
| 7 | 2.432 - 2.452 | 2.442 |
| 8 | 2.437 - 2.457 | 2.447 |
| 9 | 2.442 - 2.462 | 2.452 |
| 10 | 2.447 - 2.467 | 2.457 |
| 11 | 2.452 - 2.472 | 2.462 |
| 12 | 2.457 - 2.477 | 2.467 |
| 13 | 2.462 - 2.482 | 2.472 |
Note that these are the defined ranges when using OFDM and are valid for most regions of the world. The older Direct Sequence Spread Spectrum (DSSS) also includes channel 14 which was only used in Japan.
There are a couple of things to keep in mind when looking at the above table:
- Each channel is defined by its center frequency. This is the frequency at the very center of the channel width.
- The channel width is the range of frequencies that each channel encompasses. From the Frequency Range column, you can see that each channel is 20 MHz in width.
- Notice that the frequency ranges of each channel overlap each other. This must be taken into account when designing wireless networks to avoid interference.
The following is a graphical representation of the channels:
Based on the above diagram, you can see that you can only achieve the use of three non-overlapping channels. 1, 6 and 11 are an example of such channels. A fourth channel will not fit.
Some technologies, such as 802.11n are able to bind two 20 MHz channels into a single channel, thus increasing the available bandwidth. This is called a bonded channel. The following diagram illustrates this:
This however is highly restrictive in the 2.4GHz frequency range, since only two such bonded channels can be used without overlapping other neighboring channels.
The limitations introduced with the 2.4 GHz frequency band has led to the adoption of the less crowded and broader frequency ranges delivered by the 5GHz frequency band and channels.
Links:
https://networklessons.com/cisco/ccna-200-301/introduction-to-wireless-networks