Raspberry PI random connection interruptions

i am running a raspberry pi B+ headless and losing network connection irregulary.
I am living with that since a few years, but now want to fix the problem.
What would be a good approach to find out the reason?

Problem

• ssh connection to PI not possible sometimes (today failing nearly constantly, otherwise every few days)
• Active ssh connection aborted
• PI cannot get internet data (pinging google fails)

Setup

• Raspberry PI B+
• WIFI USB Adapter EDIMAX EW 7811Un
• My own app (digital picture frame) is running on python 3 and QT5.7

My countermeasures so far

• self implemented software wachdog that checks some connection parameters and reboots if necessary (i would say works in 95% of the cases)
• Auto PowerOff deactivated for the Wifi adapter by setting rtw_power_mgnt=0 and rtw_enusbss=0 in /etc/modprobe.d/8192cu.conf

Comments

• My WIFI connection at home sometimes gets interrupted as well. But far less often than the connection to the PI fails
• I know that similar questions have been asked before, but i was not able to adapt them to my specific problem, sorry.

Thanks for any directions

Ben