5GHz Interference Issues
Unlike 2.4GHz bands, there are no overlapping channels in 5GHz range, like it was with 1, 2 and 3 channels. For example, within the context of U-NII-1 (see a list of WLAN channels below) only channels 36, 40, 44 and 48 can be selected; by default, each of them occupies 20MHz and nominally does not interfere with neighboring channels. The channel bonding procedure can be used to increase throughput that allows expanding the bandwidth up to 40, 80 and 160 MHz due to aggregation of neighboring channels. In this scheme, one of the channels begins to perform the function of the control channel (primary) and the rest will act as secondary channels. It should be noted that in generally recognized standards the channels corresponding to wider bands are indicated as an arithmetic mean of the connected channels.
The table of channels in 5GHz range
However, a network scan will show only the primary channel:
The illustration of the scanned 5GHz channels
To overcome this inconsistency, we prepared a compliance table between the actual and standardized channels for different bandwidths.
U-NII-2A and U-NII-2C frequency sub-bands are used as ranges for DFS (Dynamic Frequency Selection) channels in most countries. This means that Wi-Fi devices should dynamically change channels in case of a radar impact. Both AP and STA should support this feature. Advantage: increasing the number of non-overlapping channels reduces the CCI (Co-channel interference). Disadvantage: Wi-Fi devices should not interfere with radars which means longer scanning and roaming. Moreover, some vendors do not allow you to use this spectrum out of the box.
It should also be mentioned that the nominal characteristics of non-overlapping channels can be violated by a spectral leakage between neighboring channels, therefore, this condition must be taken into consideration when ranking devices in frequencies.
Based on the theoretical assumptions and experimental data provided in:
Zankiewicz, Andrzej. "Experimental analysis of susceptibility of IEEE 802.11 ac Wave 1 networks to adjacent and co-channel interference" Przegląd Elektrotechniczny 94, no. 2 (2018): 88-91.
And shown in the picture results:
The following method for interference definition was approved:
the CCI has the largest ratio (1.0)
spectral intersections during the connection of the channels will be considered as CCI
neighboring channels can affect each other (similar to ACI) and will be taken into account with a ratio of 0.5 weighted in accordance with the formula