Status of QZSS Navigation System In Japan

摘要

Quasi-Zenith Satellite System (QZSS) is a satellite navigation system in Japan which is the constellation consisted of several satellites orbiting different high inclined orbital planes with geosynchronous period. Each satellite is allocated on the orbit so as to pass over the same ground track at constant intervals. Eccentricity and inclination are selected so that minimum elevation angle through 24 hours in service area is to be larger than about 70 degrees. As a baseline, we are now planning to launch first QZS whose orbit parameters are eccentricity as about 0.1 and inclination as about 45 degrees, respectively. From the viewpoint of users, they can receive the signal from at least one of the satellite of QZSS where it is around zenith direction, with high elevation angle, every time. This is the origin of the name, "Quasi-Zenith Satellite System". "More stars" is a primary essential requirement for GNSS applications from geodesy to navigation use of handheld equipment. The constellation design of the QZSS leads the improvement of availability effectively as less as number of satellite. Especially, the satellite with high elevation angle is highly important for land mobile users in the urban canyon and mountainous terrain. In Japan, there are many mountainous and urban areas with dense buildings and narrow roads. Under these conditions, it is expected that the augmentation of GPS by QZSS will improve the performance of GPS in such areas where we cannot see a sufficient number of GPS satellites due to some obstacles. Moreover, the effect of acceleration to Initial Operational Capability (IOC) of modernized civil signals in Asia Oceania region is considered in the paper as well as fundamental benefits such as availability and GDOP improvement. Since a couple of QZS can be observed in the region, we can obtain higher availability for new modernized signals earlier than other area in the world. The result of simulation, which it could be one or two years earlier to reach 100% availability of new modernized signals, is shown in this paper. Japan and US have been discussed how to implement full interoperability and compatibility between GPS and QZSS since GPS-QZSS Technical Working Group (TWG) was established in the 2nd US-Japan GPS plenary meeting in 2002. Both parties have agreed that GPS and QZSS have complete compatibility and interoperability in the 5th TWG meeting on January 26,2006.