QZSS

QZSS
Title	QZSS
Author(s)	GMV
Level	Basic
Year of Publication	2011

The Quasi-Zenith Satellite System (QZSS) is a regional navigation satellite system commissioned by the Japanese Government as a National Space Development Program.

QZSS Introduction

QZSS was authorized by the Japanese government in 2002. At the beginning the system was developed by the Advanced Space Business Corporation (ASBC) team, including Mitsubishi Electric Corp., Hitachi Ltd., and GNSS Technologies Inc. When in 2007 ASBC collapsed, the work was taken over by JAXA together with Satellite Positioning Research and Application Center (SPAC), established in February 2007 and approved by the Ministers associated with QZSS research and development.

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QZSS System description

The QZSS service area covers East Asia and Oceania region and its platform is multi-constellation GNSS. The QZSS system is not required to work in a stand-alone mode, but together with data from other GNSS satellites.

QZSS satellites groundtrack

The space segment consists of three satellites placed in periodic Highly Elliptical Orbit (HEO). The perigee altitude is about 32000 km and apogee altitude about 40000 km, and all of them will pass over the same groundtrack. QZSS is designed so that at least one satellite out of three satellites exists near zenith over Japan. Given its orbit, each satellite appears almost overhead most of the time (i.e., more than 12 hours a day with an elevation above 70°). This gives rise to the term "quasi-zenith" for which the system is named. The design life of the quasi-zenith satellites is of 10 years. The first satellite Michibiki was launched on 11 September 2010 and injected into the Quasi-Zenith Orbit on 27 September.

The ground segment is composed of a master control station (MCS), tracking control stations (TT&C), laser ranging stations and monitoring stations. The network of monitoring stations covers East Asia and Oceania region, with stations in Japan (Okinawa, Sarobetsu, Koganei, Ogasawara) and abroad: Bangalore (India), Guam, Canberra (Australia), Bangkok (Thailand) and Hawaii (USA). The MSC is the responsible of the navigation message generation that are uplinked to the quasi-zenith satellite via a TT&C station place in Okinawa.

There are 6 signals planned for the QZSS system:

• L1-C/A (1575.42 MHz): Used by combining with GNSS; increase availability of PNT services.
• L1C (1575.42 MHz): Used by combining with GNSS; increase availability of PNT services.
• L2C (1227.6 MHz): Used by combining with GNSS; increase availability of PNT services.
• L5 (1176.45 MHz): Used by combining with GNSS; increase availability of PNT services.
• L1-SAIF (1575.42 MHz): Submeter-class Augmentation; interoperable with GPS-SBAS.
• LEX (1278.75 MHz): QZSS Experimental Signal for High precision (3 cm level) service; compatible with Galileo E6 signal.

The multi-constellation GNSS interoperable signals, L1 C/A, L2C, L5 and L1C, are to be provided on the basis of no direct user fee. Compatibility is a mandatory requirement for QZSS system, working in the same frequency bands among the multi GNSS systems without harmful interference. For the GPS performance enhancement signals, L1-SAIF and LEX, a charging policy is under examination. SPAC leads the investigation for L1-SAIF(sub meter class) and LEX(centimeter class) user terminals.

Compared to standalone GPS, the combined system GPS + QZSS will improve positioning performance via correction data provided through sub meter-class enhancement signals L1-SAIF and LEX. It will also improve reliability by means of failure monitoring and system health data notifications. The specification performances are:

• The Signal-in-Space (SIS) User Range Error: less than 1.6 m (95%), including time and coordination offset error.
• Single Frequency User positioning accuracy (positioning accuracy combined GPS L1_C/A and QZSS L1_C/A): 21.9 m (95%).
• Dual Frequency User (L1-L2) positioning accuracy: 7.5 m (95%).
• L1-SAIF signal users (using WDGPS correction data) positioning accuracy: 1m (1 sigma rms) except in cases of large multipath error and large ionospheric disturbance.

For Single Frequency users the expected performances are three times better than the specified ones in nominal conditions, i.e. 7.5 m (95%).

QZSS applications are: mobile mapping, IT aided precise farming, IT aided construction, fleet management, marine and transportation applications, among others.

QZSS Development

The Initial Phase Operation started in September 2010 with the launch of the first quasi-zenith satellite, Michibiki, has been completed by summer 2011, with all functions of the satellite and the ground segment confirmed.

During the initial phase, technical verifications and applications demonstrations have been made using Michibiki. The demonstrations have shown that in a case of a car driving route inside Tokyo, time percentage when a GPS+QZSS user could get his position improved more than 10% of the GPS-only user, with a best improvement over 40% in the worst GPS DOP situation.

The next phase of the program will be the launch of the 2nd and 3rd QZSS satellites. This will be decided by the Strategic Headquarter for Space Policy of the Japanese government by the end of 2011.

In a next step, the Strategic Headquarters for Space Policy is currently considering several QZSS satellite constellation plans. These plans range from 4 to 7 satellites, including quasi-zenith and geostationary orbit satellites.