UniFi - Selecting channel and channel width

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Paul1977

5058 posts

Uber Geek

#198545 13-Jul-2016 11:28

I have a UAP-AC-LITE, I'm not having any trouble with it but just wanting to make sure I have it as optimized as possible.

It is the only AP in a small standalone house in a suburban neighbourhood. I have a mix of 2.4GHz and 5GHz capable devices.

Below are the results of an RF scan:

2.4Ghz is set to autochannel HT20. It has set it to channel 6.

5GHz is set to autochannel VHT80. It has set it to channel 36. I intentionally changed this from VHT40 to VHT80 to increase throughput as the lower end of the 5GHz spectrum seems to be pretty empty.

Questions:

Looking at the 2.4GHz scan results, is 6 really the best channel to be on since 5 and 7 are clearly being utilized?

Would anything be gained by changing 2.4GHz to HT40? Would any throughput improvements likely be offset by increased interference? is HT40 inconsiderate to other 2.4GHz users?

Given that the low end of the 5GHz appears to be empty, is there any disadvantage in my using VHT80?

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Crowdie

228 posts

Master Geek

#1592217 13-Jul-2016 19:23

Paul1977:

Looking at the 2.4GHz scan results, is 6 really the best channel to be on since 5 and 7 are clearly being utilized?

When you say "channel 6" what you actually mean is "center channel 6". If you select center channel 6 then the 20 MHz wide channel comprises channels 4, 5, 6, 7 and 8. Therefore, there are only three 20 MHz wide center channels that do not overlap - 1 (channels 1, 2 and 3), 6 (channels 4, 5, 6, 7 and 8) and 11 (channels 9, 10, 11, 12 and 13).

This is due to the 2.4 GHz center channels only being 5 MHz apart while 802.11 2.4 GHz wireless devices utilise 20 MHz wide channels. Channel 1 has a center frequency of 2.412 GHz, channel 2 has a center frequency of 2.417 GHz, channel 3 has a center frequency of 2.422 GHz and so forth....

Therefore center channels 1 or 11 would be a better option than 6.

Paul1977:

Would anything be gained by changing 2.4GHz to HT40? Would any throughput improvements likely be offset by increased interference? is HT40 inconsiderate to other 2.4GHz users?

The answer to the first part is dependent on how many access points/wireless routers and 2.4 GHz wireless neighbours you have. If you have more than one access point and/or router then the answer is no - in fact your 2.4 GHz performance would be adversely affected. If you only have one wireless router or access point then the consideration is how many 2.4 GHz wireless neighbours you have - the more the less advantage you will get. You also need to consider non-802.11 devices that operate in the 2.4 GHz spectrum - microwave ovens, cordless phones, Bluetooth devices, baby monitors, monitored alarms, etc. Each of these will adversely affect your 2.4 GHz spectrum performance.

A not well known fact is that if you enable the "Fat Channel Intolerant" option (sometimes called 40 MHz Channel Intolerant) in your wireless driver any neighbouring wireless routers/access points with 40 MHz wide 2.4 GHz channels enabled should drop back to 20 MHz wide channels. In my personal testing the majority of consumer wireless devices ignore the request and continue operating with 40 MHz wide 2.4 GHz channels - there is nothing like that WiFi Alliance certification testing :-(

If you have a large number of neighbouring 2.4 GHz wireless networks you should operate with 20 MHz wide 2.4 GHz channels.

Paul1977:

Given that the low end of the 5 GHz appears to be empty, is there any disadvantage in my using VHT80?

You will see more RTS/CTS exchanges between your client(s) and the access point(s) and your signal propagation will reduce but apart from those no. As your U-NII-1 band (channels 36 to 48) are extremely clear I would configure your 80 MHz wide here. The U-NII-2 band (channels 52 to 64) requires DFS and this may cause issues with wireless clients that are not DFS compliant. 80 MHz wide 5 GHz channels are really only usable in residential deployments and your wireless client(s) can drop back to 40 or 20 MHz wide 5 GHz channels if required. The RTS/CTS exchanges I referenced earlier are how the wireless clients and access points determine which adjacent 20 MHz wide channels are available to make the 40 and/or 80 MHz wide channels.

Paul1977

5058 posts

Uber Geek

#1592339 14-Jul-2016 10:00

Crowdie:

Paul1977:

Looking at the 2.4GHz scan results, is 6 really the best channel to be on since 5 and 7 are clearly being utilized?

When you say "channel 6" what you actually mean is "center channel 6". If you select center channel 6 then the 20 MHz wide channel comprises channels 4, 5, 6, 7 and 8. Therefore, there are only three 20 MHz wide center channels that do not overlap - 1 (channels 1, 2 and 3), 6 (channels 4, 5, 6, 7 and 8) and 11 (channels 9, 10, 11, 12 and 13).

This is due to the 2.4 GHz center channels only being 5 MHz apart while 802.11 2.4 GHz wireless devices utilise 20 MHz wide channels. Channel 1 has a center frequency of 2.412 GHz, channel 2 has a center frequency of 2.417 GHz, channel 3 has a center frequency of 2.422 GHz and so forth....

Therefore center channels 1 or 11 would be a better option than 6.

Paul1977:

Would anything be gained by changing 2.4GHz to HT40? Would any throughput improvements likely be offset by increased interference? is HT40 inconsiderate to other 2.4GHz users?

The answer to the first part is dependent on how many access points/wireless routers and 2.4 GHz wireless neighbours you have. If you have more than one access point and/or router then the answer is no - in fact your 2.4 GHz performance would be adversely affected. If you only have one wireless router or access point then the consideration is how many 2.4 GHz wireless neighbours you have - the more the less advantage you will get. You also need to consider non-802.11 devices that operate in the 2.4 GHz spectrum - microwave ovens, cordless phones, Bluetooth devices, baby monitors, monitored alarms, etc. Each of these will adversely affect your 2.4 GHz spectrum performance.

A not well known fact is that if you enable the "Fat Channel Intolerant" option (sometimes called 40 MHz Channel Intolerant) in your wireless driver any neighbouring wireless routers/access points with 40 MHz wide 2.4 GHz channels enabled should drop back to 20 MHz wide channels. In my personal testing the majority of consumer wireless devices ignore the request and continue operating with 40 MHz wide 2.4 GHz channels - there is nothing like that WiFi Alliance certification testing :-(

If you have a large number of neighbouring 2.4 GHz wireless networks you should operate with 20 MHz wide 2.4 GHz channels.

Paul1977:

Given that the low end of the 5 GHz appears to be empty, is there any disadvantage in my using VHT80?

You will see more RTS/CTS exchanges between your client(s) and the access point(s) and your signal propagation will reduce but apart from those no. As your U-NII-1 band (channels 36 to 48) are extremely clear I would configure your 80 MHz wide here. The U-NII-2 band (channels 52 to 64) requires DFS and this may cause issues with wireless clients that are not DFS compliant. 80 MHz wide 5 GHz channels are really only usable in residential deployments and your wireless client(s) can drop back to 40 or 20 MHz wide 5 GHz channels if required. The RTS/CTS exchanges I referenced earlier are how the wireless clients and access points determine which adjacent 20 MHz wide channels are available to make the 40 and/or 80 MHz wide channels.

Thanks for that. It looked to me like 1 or 11 seemed a better choice as well for 2.4GHz, but I thought I may have been missing something - like maybe the AP knew something I didn't.

I'm a bit confused as to the difference between utilization and interference. Some channels with high utilization say they have less interference than other channels with very low utilization. Which is the more important to avoid?