This is the smart battery saving Settings of the phone.
To keep wifi connected when your Android screen is off: Turn your phone on and tap the Settings icon.
Select the \"WiFi Options\" bar.
Click \"Options\".
Select the \"Advanced\" option bar.
Click the \"Keep WiF connected while hibernating\" bar and select \"Always\"; Or set it to Never Sleep.
How to set up the iphone to maintain wifi connection: First find the connected wifi network. The wifi page is displayed. Slide down, there is an \"automatic\" at the bottom of the page, click to complete, WiFi will always be connected, and the phone can download things in the background screen. But being constantly connected to WiFi can cause your phone to consume more power.