CCQ this unknown

I have a little question,
why when I use a lot of bandwidth, the CCQ down?
In a normal condiction I have a 90% of CCQ, but when I saturate the bandwidth, it down to 4%. Depending on what?
Can someone explain how to improve it? Thanks

p.s. Excuse me for my poor english

Hi,

your observation is expected - wireless is a shared broadcast network medium, so as percent of airtime utilisation increases, so too does your chance of collisions and interference. When you ‘saturate’ your network, congestion is self-perpetuating: the more collissions you get, the more retries, and those additional retransmissions contribute to more congestion.

Cheers.

That answer is correct, but I think overcomplicated for the question.

If a link shows 90% ccq until you start moving traffic, you have a problem.

If you have an overloaded AP that does the same, the answer above applies, and could have a bad client (poor signal, bad radio, etc).