WiFi turned off when the screen turns off

Hi

when the screen turns of or my iPad turn Locked, after ~5minutes when i just turned the screen on(not unlock the ipad just turned the screen on)no WiFi sign appears at the top of my iPad and and this cause not updating and showing Telegram or other messaging systems notifs and new messages.How can i solve it?I want to for example when i dont use from my device for 1h, if anyone massages me in this 1h,notifications come and aware me of the telegram massages