Technical Verification Status of Quasi-Zenith Satellite System

M. Kishimoto, E. Myojin, K. Kawate, M. Miyoshi, S. Kogure, H. Noda

Abstract:	QZSS (Quasi-Zenith Satellite System) is a Japanese satellite navigation system that consists of space segment and ground segment. In space segment, there are several QZS (Quasi-Zenith Satellite) whose orbit is designed that one QZS out of several satellites always exists near zenith over Japan at least. QZSS also has slightly elliptical and highly inclined orbits in different orbital planes. The eccentricity is about 0.075 and inclination is about 41 degrees which optimized for the middle latitude area like Japan. The benefit of QZSS is that QZSS can provide a seamless service from a high elevation angle to improve the positioning availability in downtown and mountainous areas. Users in Japan, therefore, can observe one QZS at more than 60 degrees elevation angle, and especially, users in main island of Japan can receive a QZS signal from more than 70 degrees. QZSS signals from high elevation angle can provide substantially better positioning availability than that of GPS alone. QZS transmits 6 signals on 4 frequencies, and has 2 types of the GPS interoperable and GPS augment. There are L1C, L1-C/A, and L1-SAIF (Sub-meter class Augmentation with integrity function) signals on L1-band, L2C signal on L2-band, L5 signal on L5-band, and LEX signal on E6-band. L1C, L1-C/A, L2C, and L5 signals are the GPS interoperable signals. These signals are designed to have full interoperability and compatibility with current and future GPS civil signals. L1-SAIF and LEX signals are the GPS augment signals. L1-SAIF signal has full compatibility with GPS-SBAS and will transmit WDGPS (wide area differential GPS) correction data with integrity message. LEX is the experimental and augment signal with much higher data rate (2kbps) message than other SBAS and has compatibility with Galileo E6-CS signal. QZS-1, which is called MICHIBIKI, was launched on September 11, 2010 by Japanese H2A launch vehicle no.18. After the 5 times of AEF (Apogee Engine Firing) and 5 times phase adjustment maneuvers, the satellite reached to the operational inclined elliptic geosynchronous orbit (Quasi-Zenith Orbit) on September 27. On-Orbit Checkout (OOC) was completed for 3 months successfully. From middle of December, 2010, JAXA changed the navigation signals to the standard code and technical verification and application demonstration started. The technical verification such as SIS (Signal-in-Space) accuracy improvement by various parameter tuning, data screening, and so on was performed. After we confirmed the system performance such as accuracy, integrity, and availability met the Interface Specification for QZSS (IS-QZSS), the MICHIBIKI navigation signals were set to be the healthy status. L1-C/A and L2C signals were set healthy in June 22nd 2011, L5 and L1C signals were set healthy in July 14th 2011. Since then, QZSS system performance met continuously. After the GPS interoperable signals of MICHIBIKI were set healthy, we continuously improve the system performance, especially POD (precise orbit determination). We are also improving the PPP (Precise Point Positioning) accuracy using LEX signal (JAXA-LEX). JAXA is to establish Multi-GNSS (Global Navigation Satellite System) network for coming Multi-GNSS era. This paper describes the improvement status of the precise orbit determination and PPP using LEX signal. In this paper, the latest status of QZSS system performance is also presented.
Published in:	Proceedings of the 2012 International Technical Meeting of The Institute of Navigation January 30 - 1, 2012 Marriott Newport Beach Hotel & Spa Newport Beach, CA
Pages:	1223 - 1227
Cite this article:	Kishimoto, M., Myojin, E., Kawate, K., Miyoshi, M., Kogure, S., Noda, H., "Technical Verification Status of Quasi-Zenith Satellite System," Proceedings of the 2012 International Technical Meeting of The Institute of Navigation, Newport Beach, CA, January 2012, pp. 1223-1227.
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