How to make WiFi signal stronger on Ubuntu 16.04 LTS with Realtek RTL8723BE?
Run in terminal
sudo tee /etc/modprobe.d/rtl8723be.conf <<< "options rtl8723be ant_sel=1"
This will create a config file to make the setting permanent.
In case anyone comes here from google, as I did. It may help to substitute ant_sel=1 to ant_sel=2.