turn off wifi power manager

Open this file with your text editor, let's use nano for example:

sudo nano /etc/NetworkManager/conf.d/default-wifi-powersave-on.conf

By default there is

    wifi.powersave = 3

Just change it to a value of 2.

The change will be active upon the next reboot.

The values for the powersave field are:

NM_SETTING_WIRELESS_POWERSAVE_DEFAULT (0): use the default value
NM_SETTING_WIRELESS_POWERSAVE_IGNORE (1): don't touch existing setting
NM_SETTING_WIRELESS_POWERSAVE_DISABLE (2): disable powersave
NM_SETTING_WIRELESS_POWERSAVE_ENABLE (3): enable powersave