GPS ground updates correct for clock skew and disturbances in orbits. The Japanese system also seems to upload the differential measurements of their entire gro

GPS ground updates correct for clock skew and disturbances in orbits. The Japanese system also seems to upload the differential measurements of their entire ground reference points to rebroadcast to individual receivers. In some senses, the technique is just an augmentation/expansion of WAAS [0] to Japan (WAAS is strictly North American). [0] http://en.wikipedia.org/wiki/Wide_Area_Augmentation_System http://en.wikipedia.org/wiki/Wide_Area_Augmentation_System EDIT: And to the OP, you would need some sort of GPS+ device.