For example, signal strength for some client is -70dBm, and Tx/Rx CCQ is 70-90% if there isn’t any activity download/upload.
But when he start download or upload signal strength stay good (-70dB) but CCQ is very low sometimes 8%..
When CCQ is 10% or less for one client.. that start affecting all other users on that AP.. ( bad ping etc. to all of them)
How to solve this, or at least how to not affect all clients if there are some problems with one of them..
I you use legacy mode 802.11a or b/g then you should set Hw. Protectionmode on the clients to RTS/CTS and set the value to 256. This way it is always on.
Fragmentation threshold is not so important for the link quality.
If this is not helping we need more info on both AP and client settings and also about real situation of the antenna’s (LOS, distance, interference of other AP’s etc) to give you a bit more advices..