Signals of opportunity navigation methods for complex lower airspace flight

In the complex lower airspace embraced by mountain, Global Positioning System can't take action because navigation signals are easily shaded by barriers. Signals of opportunity (SOOP), i.e. other RF signals in airspace, can be used for positioning to improve availability. In this paper, for alternative TV, Cellular, WiFi, RFID, aviation data link besides GPS, physical advantages and disadvantages are analyzed, including their application. Based on requirements for complex lower airspace, proper SOOP are chosen. Navigation positioning methods of SOOP is presented, such as TDOA (time difference of arrival), AOA (angle of arrival) and RSS (ranging signal strength). Then the positioning manners can be confirmed according to the complex lower airspace. Lastly, problems for SOOP in complex lower airspace are concluded.