for the following reasons
1, check the wlan sleep policy setting scheme of the mobile phone, some is the problem of mobile phone setting, set to automatically break the network when the eye, you can change the setting, setting method: setting - system - WLAN-advanced -wlan sleep policy - select [never sleep].
2, may be installed in the phone some power-saving software in doing strange, some province is the software will automatically turn off the wifi, see if the phone has installed power-saving treasure or snack power-saving software, if installed, please check carefully.
3, may be the router problem, first determine whether the computer can connect to the router Internet, if the computer can be on the mobile phone should be on. However, because the router because of the brand and price are very different, so some routers will cause wifi drop, if so, please replace a try.
Because you have WIFI connected to this place, so the phone has power, it will automatically connect to WIFI