I had a PCI wireless card that would drop its connection after 20 minutes or so after installing 16.04 lts. I lived with this for a few weeks and then went searching for a solution. Was it driver(s)? No. I eventually determined that it was a feature, power-saving. I found out how to turn it off using iwconfig. But how to make this permanent...
The following link managed to get me out of the weeds -
https://unix.stackexchange.com/questions/269661/how-to-turn-off-wireless-power-management-permanently
with the following answer:
Go to the directory
/etc/NetworkManager/conf.d/
and open the file
default-wifi-powersave-on.conf
By default it is wifi.powersave = 3 so just change it to wifi.powersave = 2.
Save, exit and reboot. [edit: 2 is the correct value, not 0.]
And to check this, use tlp-stat --rfkill