Using the 5Ghz Wireless LAN (WiFi) Band
Most Wireless LAN (WiFi) products sold in the past 10 years have used the 2.4Ghz band, which includes every wireless router, access point, smartphone and tablet as well as other device types which share the band (DECT cordless phones, Bluetooth etc.). If you live or work in a built-up area, you can see this when you try to connect - 10, 20 or even more access points appear on your device's selection screen. You select 'your' access point, but it's still sharing the same wireless channels as all of the other access points. Due to the bandwidth of 802.11n, there are only 4 distinct (non-overlapping) channels you can select.
The 5Ghz band provides more channels and is far less widely used (at present), so you are far less likely to have many other adjacent access points to interfere with yours. The main advantage, therefore, of using the 5Ghz band vs. the 2.4Ghz band is less congestion. In certain scenarios, the 5Ghz band also permits higher power devices, thus longer range.
To make use of the 5Ghz band, you must have both a wireless router or access point and wireless clients (laptops, smartphones, tablets) which support that band. Many devices are dual-band, so can operate in either the 2.4Ghz or 5Ghz bands. Some wireless routers support, one band, either band (but not concurrently), or both bands concurrently (simultaneous). If your router or access point supports simultaneous/concurrent dual-band then devices using either of the two bands can all connect at the same time.
The 5Ghz 'Band Plan'
5Ghz Wireless has four 'bands', offering up to 19 distinct channels (assuming a 20Mhz bandwidth - see later):
|Band||Frequency Range||Channel Nos.||DFS/TPC Required||Max Power||Application|
|A-Lower||5150-5250Ghz||36||-||200mW / 23dbM EIRP||Indoor|
|A-Upper||5250-5350Ghz||52||Yes||200mW / 23dbM EIRP||Indoor|
|B||5470-5725Ghz||100||Yes||1W / 30dbM EIRP||Indoor/Outdoor|
|C||5735-5850Ghz||147||Yes||4W / 36dbM EIRP||Outdoor/FWA
Note that the channel numbers increase by 4 each time; this is because each channel is 5Mhz wide, but to avoid overlapping, each usable channel is spaced 20Mhz apart (4x5 = 20!) If you use a 40Mhz wide channel (or two bonded adjacent 20Mhz channels) you reduce you number of distinct channels further. Band C is permitted for point-to-point applications (fixed wireless access), not general AP-Client usage. Band C requires a licence; that can be easily obtained from your local wireless authority, for example Ofcom in the UK for a nominal cost).
DFS (Dynamic Frequency Selection)
Some of the 5Ghz radio space is shared with other services, notably military and other radar services. In order to reduce the chance of interference with these services, DFS is mandated in the shared bands. DFS selects a channel within the requested band and must scan for any activity before it can enable transmission (Channel Availability Check, CAC). If it detects other band activity, it must select a different channel, having checked that too. DFS must then be repeated every 24 hours of operation, during which time operation of the wireless LAN device is suspended for 60 seconds (Channel Observation Time, COT). The use of DFS is mandatory in bands A-Upper, B and C so in order for your access point or router to use these bands, you must also use DFS. The router specification will list if DFS is supported, if it's not then bands A-Upper, B and C would not be available for selection in the configuration.
TPC (Transmission Power Control).
This is a secondary method to avoid interference with other nearby equipment. With TPC, the transmission power of a device is reduced to the minimum required for an adequate connection. The use of TPC is mandatory in bands A-Upper, B and C.
One of the ways that 802.11ac achieves higher data rates than 802.11n is by using channel bonding. Each channel, as standard is 20Mhz wide - i.e. it occupies frequencies 10Mhz either side of its centre frequency. If you use two channels, you get double the bandwidth (40Mhz), four channels (80Mhz) and even 8 channels (160Mhz), so theoretically 8 times the data capacity.
The problem is that as you bond channels, there are less distinct channels available, which means you are sharing your bandwidth with any other devices or neighbours using the same band. Using a 160Mhz channel width means that you only have 2 distinct channels to use (in Europe) and that assumes the DFS/TCP channel is available. So, if you want to have (say) 3 access points, they cannot have a distinct channels - they'd overlap and performance may end up being worse than if you'd stuck to 80Mhz channels, or 40Mhz and so on. In most environments, you will have other wireless networks nearby, so there will be clashes.
Therefore, don't enabled 80Mhz or higher channel widths and just assume it will give the best peformance, and bear in mind the limitation to channel allocation using wider channels will provide. Wide channels work well on gree-field sites or point-to-point links where shared airspace is unlikely. We like this 3rd party article, which goes into much more detail.
This page is provided as a guide only and is not intended to provide specific guidance on the permitted band usage in all geographic areas; licensing requirements vary around the world. It is the users' responsibility that they comply with all local regulation and this document should not be used as the basis for confirming compliance - please check your own local and up-to-date regulations for permitted band-plans, equipment certification, permitted power output and licensing.
- First Published: 18/03/2013
- Last Updated: 13/01/2017