Development of a Robust Positioning Method for Unknown Radio Sources Using Satellite Constellations

Satellite geolocation uses the Time Difference of Arrival (TDOA) derived from the difference in distance between the radio source and each satellite, and the Frequency Difference of Arrival (FDOA) derived from the difference in speed in the line of sight of the satellite from the radio source. However, if the radio wave source is a radar wave source, such as pulse radar, multiple TDOAs and FDOAs are calculated, causing ambiguities in the geolocation. One way to solve this ambiguity is to equip a satellite with an array antenna and use azimuth information. However, this would increase the cost of manufacturing the satellite. Therefore, the authors previously proposed a method to solve the ambiguity and locate the target radio source without using the direction, instead using the information of signals acquired multiple times. Using this method, ambiguity can be eliminated, and the derived true target points can be extracted. However, if all the estimated points are used in the positioning process, the positioning accuracy may deteriorate owing to the relatively large Dilution of Precision (DOP) of the estimated points. In this paper, we propose a method that calculates the error ellipse followed by each estimation point, and we performed the positioning process using only the estimation points that exist in the common part of the error ellipse, thereby reducing the influence of estimation points with a large DOP and enabling more robust positioning for the relationship between the satellite and unknown radio sources.