So, I was wondering. Is it feasible to setup multiple Wi-Fi access points on the same channel when they are far apart, but can still hear each other? Will they be able to reliably cooperate with each other in sharing the same channel, or will the interference just be horrendous? It appears that with Wi-Fi, things are destined toward the later.
On the other hand, I found a great article with a lot of information and design considerations for setting up multiple access Wi-Fi points on the same network. I’ll summarize some of the noteworthy design considerations:
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Water is a strong attenuator of Wi-Fi signals. Therefore, humans are a strong attenuator of Wi-Fi signals because they are water rich. Also, wood is a significant attenuator of Wi-Fi signals because it absorbs water vapor from the air, -6db, -20db, or more depending on the thickness of the wood. Notably, this also means that when the humidity is higher, like in the summer, the Wi-Fi signal attenuation is stronger, but when the humidity is lower like in the winter, the Wi-Fi signal attenuation is less.
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Glass is actually also a fairly significant attenuator of Wi-Fi signals, -4db per pane. Double-paned and triple-paned glass respectively result in double and triple the attenuation. Likewise, fiberglass insulation is a significant attenuator of Wi-Fi signals.
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Sheetrock drywall is not a very significant attenuator of Wi-Fi signals, -2db.
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Brick walls basically totally block off Wi-Fi signals, of course. -28db!
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Metal and steel likewise basically totally block off Wi-Fi signals, -50db! Concrete is a likewise strong attenuator of Wi-Fi signals.
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If you need more than 3 or 4 Wi-Fi access points within proximity of sharing essentially the same collision domain, it will not bee possible to have them all on separate channels with 802.11n. 802.11ac will be required since it has many more channels, and because of this, it is the Wi-Fi technology of choice for high-density installations. Go for equipment capable of 802.11ac Wave 2.
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Outside neighbor Wi-Fi interference can degrade performance on your network too, of course.
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Use specific outdoor Wi-fi access points for outdoor use, if applicable. Because of many of the reasons listed previously, the exterior walls of a building will be strong attenuators of Wi-Fi signals.
So, armed with this knowledge, is it really necessary to have one Wi-Fi access point per floor in a house, even if the straight line distance is not all that great? In the old days, the answer was “no” simply because the air was relatively clean of Wi-Fi signals when very few people had Wi-Fi. But nowadays, in a neighborhood where almost everyone has Wi-Fi, and the average person has more than one Wi-Fi device, the signal noise from the neighbors and from inside the same residence is going to be too great for that to work well anymore. So you need smaller cells to boost Wi-Fi signal strength, and because of the thickness of wood, concrete, or steel in the floors of buildings, the floor itself is a pretty good attenuator of Wi-Fi signals, which means you do generally need one access point per floor, even when the straight line distance is short.
20190719/DuckDuckGo wi-fi access points on same channel
20190719/https://www.madebywifi.com/blog/multiple-wifi-aps-on-the-same-network/