check advanced settings on the wireless adpter in yhour laptop to ensure they are set for maximum performance not power saving.
Maybe the settings for the modem have a disconnect time setting.
Using an ethernet cable, connect to the router (into the 'modem'
port), open your browser & type '192.168.1.1' into the address bar. That should give you the modem setup. Look for 'connection' topic tab and select the 'always connected' choice, or disable the 'disconnect after x minutes'. Don't forget to save the settings before closing the window.