Co-Channel Interference (CCI)
Living on the same floor (channel), two speakers playing a music have almost inevitable risk of hearing each other unless you have enough physical distance separation. This is the interference. As depicted in the analogy diagram above, if you and your family member or neighbor are listening to a different music using a separate loud speaker at the same time, both will hear the other music in the middle. What can you do to enjoy your own music without hearing the other speaker? One simple way is taking a turn.
In fact in the Wi-Fi world, there is a strict rule that two sources cannot transfer a data at the same time on given channel at a distance where they can hear each other because they will collide and whole data becomes unusable. The rule is called “clear channel assessment (CCA)”. It’s a simple rule. You listen first and make sure nobody else is using the channel (or playing music) then you play; otherwise, wait random time and check again.
If there is such rule, you feel the collision won’t happen unless some random, lottery winning chance two speakers hear nothing and start playing music right at the same time.
Unfortunately, there is another more frequent collision possibility. Let’s take a close look at one room with two speaker.
A person “A” sitting right next to red speaker has a control when to turn on the red speaker. In an above setting, Person A won’t hear green speakers sound because it is too far from it, so it starts playing red speaker.
If person “B” was listening to the music right in the middle between red and green speaker, he ends up hearing both. Since B does not have control of green speaker, green speaker may continue playing so does red.
Now if A is a selfish then he could continue listening his musics without any issue. However, remember in the Wi-Fi world, data transfer is bidirectional and one at a time. So if B was listening to the red speaker music instead of the green speaker, he’s having difficulty hearing the red speaker. So he’d complain/request more of his turn. This will slow down the A’s listening experience as B keeps asking for his turn.
This is an example of speaker (AP) affecting another speaker (AP) while on the same floor (channel). This is referred to as Co-channel interference (CCI). CCI, not to anyone’s surprise, will slow down overall network performance for both APs and all connected clients to those APs as illustrated by the above example case (ref).