I am currently doing an internal assessment evaluating the success D-day. Specifically, my topic is ‘to what extent did deficiencies in German strategic planning contribute to the success of Operation Overlord?’. Since I have a German focus, I am looking for sources about German defence systems, troop positioning etc. I am however having some trouble looking for sources about the Germans' anticipation and preparations for the allied invasion. Any suggested reads?
Hans von Luck's memior Panzer Commander has a section on his time in Normandy. It's not directly related to the planning phases, but he does give vivid accounts of the difficulties he had in implementing what plans there were (particularly due to Allied fighter-bombers).