LuftVO § 21h allows the operation of drones in the special category in no-fly zones following a corresponding permit from the Federal Aviation Office (LBA) or the state aviation authority (Stuttgart Regional Council). Which authority is responsible for you depends on where you live or where your company is based.
Information on operating licenses can be found here.
LuftVO § 21i allows the operation of drones in the open category after approval by the state aviation authority in whose jurisdiction the no-fly zone is located.
In addition, you also require authorization from air traffic control to fly within a control zone. For Friedrichshafen Airport, air traffic control is DFS Aviation Services GmbH responsible.