In the GPS signal-blocked area, positioning is not possible since the visibility of the satellite cannot be secured and the available satellite signal information is limited. Furthermore, even if the minimum number of visible satellites for positioning can be ensured, the availability for navigation is limited due to the satellite motion (rotation). Therefore, in this paper, assuming that there is a high-altitude unmanned aircraft with pseudolite in sky over the GPS signal-blocked area, we evaluated the degree of improvement of Dilution Of Precision (DOP) and the number of the visible satellite. The simul ation was carried out by applying the virtual stratosphere flight profile of High Altitude Long Endurance (HALE) unmanned aircraft using alternative energy (such as solar power). The simulation environment was set up as urban area of Seoul, capital of South Korea, surrounded by tall buildings. Then we analyzed the DOP and satellite navigation visibility according to operation altitude of the HALE unmanned aircraft.

Keywords: pseudolite, high-altitude long-endurance UAV, DOP, satellite visibility