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The quasi-zenith satellite system (QZSS) aims to provide users over Japan with such services as broadcast/communication and improved positioning capability. These services are based on satellites at inclined geo-synchronous orbits. The QZS satellites broadcast GPS-compatible signals with which users can measure pseudo-ranges to the satellites as with GPS signals. At least one QZS satellite is always visible with higher elevation angles from the users so that, compared with the use of GPS alone, geometric strength between navigation satellites 2nd a user will be improved yielding better dilution of precision (DOP). Recently, a new satellite navigation system called Galileo has been under development in Europe. It will provide double the number of navigation satellites to users and hence improve availability and accuracy greatly. Therefore, a combined use of GPS Galileo (i.e. GNSS), with the inclusion of QZSS, is especially interesting from positioning point of view. This paper describes simulation results of evaluating positioning performances for the combined use of GPS, Galileo, and QZSS. The results are presented on the basis of the number of visible satellites and horizontal dilution of precision (HDOP) as a measure of availability and accuracy, respectively.