Using a WorldCall EVDO with a wireless router

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 me

That is a strange problem as if it connect initially then it should not disconnect. I think factory restore the router and then make re-enter the settings.
Reset the router to factory settings, any issues or settings will be gone and it should start working like it used to. Make sure you have the correct IP address and settings entered.