I saw you left a message after my question. I did some research about artificial potential field(APF) method path planning and cross entropy optimization for APF. And I planned to use fractional order potential field to let the approach more reliable. Currently, I am surveying the UAS traffic management(UTM) system. 

I talked with Prof. Chen about what research to do about UAS, and he suggested me to focus on sense-and-avoid and UTM.

I think it is a good idea to keep contact with scholars in this area and take part in the international conferences such as ICUAS if possible.

http://www.aviationsystems.arc.nasa.gov/utm/index.shtml

Thank U for ur valuable suggestion.