Worldcall usb and TP Link 3420- wifi connection limited

Aoa.i have a problem with worldcall EC 168C USB Modem & TP Link 3420 v2.0. I works OK but after some minutes of inactivity the Internet disconnects showing wifi connection limited so I have to reboot router.i tried to change settings to connect automaticaly or connect on demand and set time out to zero which is for always active but still problem is there.Help plz One strange thing today it worked without problem whole day but now for 2-3 hours it disconnects again&again giving wifi connection limited error