Getting Familiar with Wi-Fi Channels? WLAN Back to Basics
For all its simplicity to the end user, Wi-Fi is really an incredibly complex technology. In this series, we “get back to the basics” of the technology.
In the 4th installment of my “WLAN Back to the Basics” blog series I discussed the standards organizations within the wireless industry. This week we will take a look at a basic overview of the spectrums and channels over which Wi-Fi operates.
2.4 GHz Band
The 2.4 GHz band is 100 MHz wide and spans from 2.4 GHz to 2.5 GHz. The following wireless radios use this band: 802.11 (FHSS or DSSS radios), 802.11b (HR-DSSS radios) , 802.11g (ERP radios), and 802.11n (HT radios).
In addition to its use by 802.11 WLAN equipment, the 2.4 GHz band is also used by microwave ovens, cordless home phones, baby monitors, and wireless video cameras. It is also used in Bluetooth communications. Because of all its uses, 802.11b/g/n 2.4 GHz radios have to deal with the potential for high interference.
The IEEE standard divides the 2.4 GHz band into 14 separate channels. Channels are designated by their center frequency and how wide the channel is depends on the technology used by the 802.11 transmitter. Unfortunately, the distance between channel center frequencies in the 2.4 GHz spectrum is only 5 MHz (and each channel is 22 MHz wide), which means that the channels have overlapping frequency space.
Only channels 1, 6, and 11 are separated from each other by enough frequencies that they do not overlap. Enterprise deployments of three or more access points in the 2.4 GHz band should normally only use channels 1, 6, and 11 which are shown below (these are the most commonly used nonoverlapping channels in North America).
5 GHz Band
802.11 a, n, and ac radios transmit in the 5 GHz U-NII bands. A total of twenty-five 20 MHz channels in the 5 GHz bands can be utilized when designing a WLAN with a channel reuse pattern— but the channels you can actually use depend on regulations enforced in each country.
Because there are more channels available in the 5 GHz spectrum there is often less interference in this band as opposed to 2.4 GHz band and more room for bonding. 802.11n technology introduced the capability of bonding together two 20 MHz channels to create a larger 40 MHz channel in the 5 GHz spectrum. And more recent 802.11ac technology introduces the possibility of bonding even more channels together – including 80 MHz (4 channels bonded together) and 160 MHz (8 channels bonded together), but this is more difficult even with a total of twenty-five available channels.
The FCC has proposed two more U-NII bands with 195 MHz of frequency space for unlicensed use by 802.11 radios. If all the proposals are implemented and all the 5 GHz space be made available, there would be as many as thirty-seven 20 MHz channels that could be used by Wi-Fi radios.
All Posts In The Back To Basics Series: