Wi-Fi (a commercial trademark) is a set of technologies for enabling the sending of data packets across a wireless local area network (WLAN), similar to the use of Ethernet cable in wired LANs. It makes use of radio frequencies that are suitable for short-distance communications, and by international agreement are not required to be licensed as (for example) the broadcasting frequencies are. However, the permitted uses of these frequencies are subject to local regulations that vary across the world, so that all Wi-Fi equipment must be sold using channels within those permitted for the country of sale.

Early equipment under the Wi-Fi standard was sold using the 2.4GHz frequency band (channels 1 to 11, and up to 13 or 14 depending on the country). More recently, new Wi-Fi standards have included the 5GHz frequency band, with generally shorter range but higher capacity for data transmission. The newer standards also improve transmission by using the available bandwidth more efficiently and changing frequencies automatically to minimize interference.

Some of these wireless ranges are intensively used, as can be seen by the number of SSIDs that nowadays can be detected in any neighborhood, but Wi-Fi is also competing with other uses of the same frequencies. In the 2.4GHz range, interference can include cordless telephones, Bluetooth devices and radiation leakage from other electronics. Radar for aeronautical and weather-forecasting use share the 5GHz range. In addition, the wireless mesh that connects a VeeaHub network operates on 5GHz, and other proprietary networks may also do so.

This article covers some VeeaHub features that mitigate these problems, Automatic Channel Selection (ACS) and Dynamic Frequency Selection (DFS).

Automatic Channel Selection (ACS)

ACS is a feature on the VeeaHub that sets the wireless access points (APs) to the best frequency channel for each, based on a number of metrics that take account of such problems as interference from external wireless sources and the communications with other VeeaHubs in the network.

ACS is the default option on the VeeaHub, whenever available. ACS then chooses the best frequency for each AP when it is started or restarted; the frequency is not changed while the AP is running. In the Control Center or VeeaHub Manager, there is the option to override this and set a specific channel from the list of available channels.

ACS frequency scan

To select the best channel, the ACS function carries out a scan of the available channels on the frequency range. This scan ranks the channels in order of preference, and the auto selected frequency is the highest ranked. The ranking is primarily based on a combination of the following measurements.

the number of Wi-Fi SSIDs detected on this channel
the Received Signal Strength Indicator (RSSI) for the SSIDs on this channel
the detected noise floor on this channel
the measured load or occupancy on the channel

These measurements are combined with additional interference statistics to select a best channel for the ACS.

Channel bandwidth

Wi-Fi channels typically employ a bandwidth that is a multiple of 20MHz. Greater bandwidths, where available, can result in higher data throughput. The VeeaHub can use 20MHz, 40MHz or 80MHz bandwidth channels when this is technically possible. The default values are 20MHz for the more congested 2.4GHz band and 80MHz in the 5GHz band. You can select these values by setting 20/40 or 20/40/80 for the Bandwidth option in the Radio tab for the access point.

If you select bandwidth wider than 20MHz when ACS is active, then you must ensure that the constituent 20MHz channels that are used are all in the Auto Channel Whitelist, otherwise the bandwidth will revert to a lower value. If in doubt, select all available channels for the whitelist.

Control Center

ACS settings appear on the Wi-Fi Radio tabs in the VeeaHub Settings section of Control Center whenever ACS is an option. ACS is in operation whenever Channel is set to Auto, and this is the default. If you do not wish to use ACS, set the value to the channel you wish to specify. The Channel in Use is the actual channel, whether auto or manually selected.

The Auto Channel Whitelist enables you to select or exclude particular channels for the automatic selection.

You can see the ACS scan results on the Scan tab for that Wi-Fi frequency range. It shows a list of SSIDs that have been detected, along with their channel, signal strength and bandwidth. You can refresh the statistics by clicking the Rescan button. This temporarily interrupts the operation of the mesh.

For further information, see the Introduction to Control Center.

VeeaHub Manager

ACS settings appear on the Wi-Fi Radio tabs in Node Manager whenever ACS is an option. ACS is in operation whenever Channel is set to Auto, and this is the default. If you do not wish to use ACS, set the value to the channel you wish to specify. The Channel in Use is the actual channel, whether auto or manually selected.

The Auto Channel Whitelist drop-down enables you to select or exclude particular channels for the automatic selection.

You can see the ACS scan results on the Scan tab by tapping the Wi-Fi Network Scan option. It shows a list of SSIDs that have been detected, along with their channel, signal strength and bandwidth. You can refresh the statistics by tapping RESCAN. This temporarily interrupts the operation of the mesh.

For further information, see the Introduction to Control Center.

Dynamic Frequency Selection (DFS)

DFS is a feature that enables Wi-Fi operation on an extended set of channels in the 5GHz frequency range, the so-called DFS channels. These channels have regulatory constraints that mean unlicensed operations such as Wi-Fi, has to give way to licensed usage such as radar. DFS functionality enables the WLAN functionality in the 5GHz band to switch frequency channels dynamically in response to detected interference from external sources, such as radar. The channels and the operation of DFS vary with location in accordance with national regulations.

If this feature is available for your VeeaHub model, then it is configured by default when DFS channels are selected. To remove DFS channels from ACS operation, select the Exclude DFS channels option (if available). When using DFS channels, whether by manual channel selection or with ACS operation, then Auto Channel Whitelist defines the set of channels to dynamically switch to if interference from radar sources is detected.

There are no DFS requirements for 2.4GHz WLAN operation, so the feature is not applicable to radios operating in this frequency band.

Note that if DFS is enabled, the automatic change of channel may cause a brief interruption in connectivity. When the VeeaHub is powered on, there is a brief period while the channels are scanned before an AP becomes available.