@Jan-Pieter 

Hey and Welcome

1. The channel numbers used are not as expected according to the 80MHz channels (see image below). I know that some manufacturers use the 20MHz-start-channel as number for the 80MHz start channel, and some manufacturers use the center-20-number. Can anyone clarify what TPlink uses for numbering the 80MHz channels? The start-20-number or the center-20-number?

According to WiFi Analyser in my testing Tp Link use the channel as the CENTRE.    I am on 108 and it spans 100-116 approx

2. It seems that also overlapping channels are being set by AI optimization. 40 is in the same overlap as 36. 48 is also overlapping with 40 and 36. 100 is overlapping with 108. Etc. Any clue why the AI WLAN optimization does not select only non-overlapping channels?

Non overlapping channels are not an issue unless the signal strengh is high between the APs.   Take the Hall B you mentioned, 36 and 48 are overlapping but this may not be an issue.   The APs could be far enough apart that one doesn't cause issues for the other, it may also be adjusting the power to compensate if you actually have too many APs for that area.    The only way to say for sure is a heat map of that area and look to see the results as its not something you can guestimate from the channels alone.  

Personally, unless its causing you an issue I personally wouldnt get too hung up on this

3. Any idea why the AI WLAN optimization tool does not use and channels between 52-64 and between 132-165 ? I ran the AI-optimization multiple times, and they never got selected.

These are DFS channels and can be interfered with by Radar.   If Radar is detected it will cause all APs in that range to switch to 36-48 for safety (this is an actual law requirement).  The change could cause a massive drop in connections as all APs move at once, you will have dozens of re-authentications, lost packets, dropped packets, congestion etc etc..  for that reason most AI is slow to use the DFS channels.   

In short if you have 4x APs in DFS and it detects radar.. you now have 4x APs no longer serving clients for 30+ seconds while they scan and negotiate a new channel to hop to!

That was Huawei's answer to that question when i asked it a few years ago :)

  @Philbert 

Thanks for your reply. I did some Wifi Analyzing with the Android Wifi-Analyzer tool from Kevin Yuan, version 3.11.2.

In Hall B the latest AI optimization selected channels 36 + 48 + 100 + 128. The Wifi Analyzer tooling measured the signal strength below.

To my big surprise the channels selected by the TPLink AI enging for this hall uses only 3 frequencies! Channel 36 and channel 48 are in fact using the same frequencies and are therefore fully overlapping! So although the 5G wifi space has room voor 6 independent and non-overlapping 5G channels, but the AI algorithm of Omada is not able to select 4 non-overlapping channels in the same physical hallroom. And note the maximum distance between AP's is less than 10 meters (30 feet) with no walls between them.

To be complete: the AI optimization was ran against all 8 AP's in the same building and the algorith selected in the other hall channels 36-100-124 and in the entrance 112. Channel 100 and 112 also use the same frequency spectrum according to Wifi Analyzer, so in total the AI engine selected for 8 AP's only 3 frequencies (36+48 5170-5250MHz , 100+112 5490-5570,  124+128 5570-5650)

So again 2 questions:

1. Are indeed channel 36 and 48 using exactly the same frequency-spectrum (and 100+112, and 124+128)?

2. Do we have a bug here in the AI algoritm? Does it not work correctly with 80MHz channel bandwith or something like that??

  @Jan-Pieter The EAP610 & 620 do not have radios that can use the UNII-2 radio space (aka DFS).  Without DFS channels on these APs, there are only 2 non-overlapping 80mhz segments of channels to be used.  The AI is setting the base channel different on each AP because, not all clients can use 80mhz but will use the smaller sections, and those will be non-overlapping.

With APs only 10m appart in an open hall, it will be difficult to reduce transmit power on the APs enough to reduce congestion.  But if most of the laptops have Wifi 6, your setup should work pretty well, just make sure to have fast roaming turned on.  Wifi 6 is desinged for these types of installations where there is a lot of overlap on APs.  They use the BSSID color scheme to ID the different APs to the client.  Also if most of the users are connecting with Wifi 6, think about going down to 40mhz bandwidth.  This will give you 4 non-overlapping segments, and is alomst as fast a 80mhz Wifi 5 link.

Another option is turn on the 2.4ghz radios and setup the load balancing.  With stone walls there is probably not much outside interference, and you could run a 40mhz broadcast from each hall.

  @JoeSea 

That is a pretty much PERFECT answer, kudos!

  @JoeSea Thanks for your answer. This helps a bit, but not completely.

The EAP 610 and 620-HD do not offer all DFS channels, but they offer (with my Europe location set) UNII-1, UNII-2a and UNII-2c until channel 128. I am not able to select channels 132-144 (upper UNII-2c) and also no UNII-3.

This leads to the ability to use 4x non-overlapping 80MHz channels.

The AI optimization only uses/selects 3 of those 4. In my setup the AI optimization skips the UNII-2a channels 52-64. And that's in my opinion still a bug in the AI optimization...

And for me this is very important as I have 4 AP's in tha same hall. With 4 non-overlapping this should work. Of course I can set channels manually, but because of DFS channels are changed once in a while, and I need something as the auto-AI-optimizations periodically to reset all 4 AP's in a single hall back to non-overlapping channels...

Does support read those forums also or do I have to report a case with them to get this solved?