why my MBA won't join known wifi automatically?

Every time it takes me minutes to re-join the known network as I need to turn the wifi off and on again for it to recognize my known network and it searches for a very long time. sometimes even though it found the known network, the wifi wont join automatically and the assistance window pops up every time when this happens to search for the problem. When the problem searching is in progress, the known wifi is joint, but it already took me around 4-5 mins and for joining a known wifi this is really a long wait.

Someone suggested me to turn off the bluetooth but i wont survive without the mouse, so i cant.

anyone got the solution? plz help....tons of thanks