Quasi-Zenith Satellite Research Articles

위성항법시스템을 위한 항재밍 기술 분석

위성항법시스템을 위한 항재밍 기술 분석

Time Comparison Experiments Between the Qzs-1 and its Time Management Station

The National Institute of Information and Communications Technology (NICT) developed the time management system of the first Quasi-Zenith Satellite (QZS-1) in order to monitor the onboard clock as a part of the satellite navigation system. While an onboard clock is usually estimated together with the orbit of the satellite, the system described here enables the direct measurement of an onboard clock by comparing it with a ground clock by making use of a two-way time and frequency transfer which removes most of the propagation errors. Our system achieves a measurement precision of about 25 picoseconds which is an order of magnitude better than the precision of the clock parameters obtained from the combined orbit and clock estimation. Copyright © 2013 Institute of Navigation

Dissemination of UTC(NICT) by Means of QZSS

The Japanese Quasi-Zenith Satellite System (QZSS) offers the possibility to transmit information with an unprecedented bit rate of 2000 bps via the L-band experimental signal. This feature can be used to disseminate Japan Standard Time, i.e., Universal Time Coordinated (UTC)(NICT), to any user capable of receiving the new QZSS signal. Various timing transmission modes as well as a dedicated ionosphere correction model allow users to instantaneously realize UTC(NICT) across Japan with an uncertainty of a few nanoseconds. However, a sophisticated real-time ionosphere correction model also needs to be transmitted to the user to compensate for dispersive ionosphere delays which are the largest contributor to the total error budget of the system.

PERFORMANCE ANALYSIS OF DOPPLER AIDED GPS/QZSS PRECISE POSITIONING FOR LAND VEHICLES

ABSTRACT For ITS (Intelligent Transport Systems), especially for land vehicles, precise position is the prime information. GNSS is the most popular navigation system. Generally, ITS demands lane distinguishable positioning accuracy. However urban area is most environments of land vehicles and the signal blocks of satellite with low elevation angle, multipath error and etc. make unreliable positioning results. Especially, lack of number of visible satellites (fewer than 4 satellites) cannot provide positioning results. QZSS (Quasi-Zenith Satellite System) which operated by Japan has high interoperability. In addition, its elevation angle is very high in long time in Korea. It means QZSS signal can be received in urban area and it can be great advantage for land vehicles. The most positioning errors are occurred by multipath, cycle slip, and etc. For example, multipath error is unexpected momentary error. In order to reduce position error, smoothing technique in position domain is needed. In this paper, precise positioning for land vehicles was evaluated. First, by using QZSS, probability of navigation solution was enhanced. Second, the reliability is improved by smoothing positioning result using Doppler measurement. The analysis was performed by trajectory analysis using precise map data.

Demonstration Experiments of a Remote Synchronization System of an Onboard Crystal Oscillator Using “MICHIBIKI”

Two kinds of demonstration experiments have been performed for the Remote Synchronization System of the Onboard Crystal Oscillator (RESSOX) for the first Japanese Quasi-Zenith Satellite System (QZSS) “MICHIBIKI.” In Experiment One, a RESSOX control signal that includes information of the standard time is sent from ground stations and the onboard crystal oscillators (VCOCXO) are controlled to synchronize the arrival of the RESSOX control signal. The maximum synchronization error is 50 ns. In Experiment Two, on the basis of the results of the time comparison between VCOCXO and ground standard time, the voltage applied to VCOCXO is calculated at the ground station and transmitted. The synchronization error of the time comparison is less than 0.3 ns for six days. Moreover, switchover experiments between Okinawa and Tokyo stations were successfully conducted. Although the QZSS is loaded with two rubidium atomic standards, RESSOX is used in future QZSSs. Copyright © 2013 Institute of Navigation.

準天頂衛星による電離圏・プラズマ圏電子数の計測( GPS/GNSS研究会)

準天頂衛星による電離圏・プラズマ圏電子数の計測( GPS/GNSS研究会)

Orbit and Clock Determination of QZS-1 Based on the CONGO Network

QZS-1 is the first satellite of the Japanese QuasiZenith Satellite System (QZSS) launched in September 2010. QZSS provides regional augmentation capabilities to users of the Global Positioning System (GPS) in Asia and the Pacific. Five stations of the Cooperative Network for GIOVE Observation (CONGO) are able to track the QZSS L1, L2, and L5 navigation signals. Together with the GPS observations of these stations, QZS-1 orbit and clock parameters were estimated. Various orbit parameterizations were tested and a sub-meter accuracy of the best orbits could be achieved. Differences of orbits obtained from various linear combinations are on the decimeter level and differential code biases are on the few nanosecond level. QZS-1 is equipped with a rubidium atomic clock that is similar to the ones of the GPS Block IIF satellites. At periods up to 100 s both clocks show a very similar performance. However, short periodic variations with a peak-to-peak amplitude of about 4 cm were detected in the QZS-1 clock estimates. Three time intervals with different periods of 13.6–15.5 minutes could be identified. Three way carrier phase analysis confirmed the presence of these variations. The origin of these periodicities is unknown.

A High-Resolution, Precipitable Water Vapor Monitoring System Using a Dense Network of GNSS Receivers

This work describes a system aimed at the near realtimemonitoring of precipitable water vapor (PWV) by means of a dense network of Global Navigation Satellite System (GNSS) receivers. These receivers are deployed with a horizontal spacing of 1-2 km around the Uji campus of Kyoto University, Japan. The PWV observed using a standard GPS meteorology technique, i.e., by using all satellites above a low elevation cutoff, is validated against radiosonde and radiometer measurements. The result is a RMS difference of about 2 mm. A more rigorous validation is done by selecting single GPS slant delays as they pass close to the radiosonde or the radiometer measuring directions, and higher accuracy is obtained. This method also makes it possible to preserve short-term fluctuations that are lost in the standard technique due to the averaging of several slant delays. Geostatistical analysis of the PWV observations shows that they are spatially correlated within the area of interest; this confirms that such a dense network can detect inhomogeneous distributions in water vapor. The PWV horizontal resolution is improved by using high-elevation satellites only, with the aim of exploiting at best the future Quasi-Zenith Satellite System (QZSS), which will continuously provide at least one satellite close to the zenith over Japan.

４. 北陸地区における準天頂衛星LEX信号の受信実験による精度検証

Survey using GPS has been spreading in the world including Japan. Japanese government launched QZS (Quasi-Zenith Satellite) which is the first satellite of QZSS (Quasi-Zenith Satellite System) for the purpose to improve of GPS weak point. It can stay over Japan for 8 hours and keep the high zenith angle. Moreover, it is possible to obtain location information of high accuracy by support signal transmitted from QZS which is LEX signal. The purpose of the research is to conduct the demonstrated experiment which uses the LEX signal from QZS in Hokuriku area of Japan, and it was compared with accuracy for absolute positioning between VRS-GPS and QZSS.

６. マルチGNSS対応受信機の動向

In the past time, “GPS” was the only one available satellite system for the global positioning. During the last decade, “GNSS” has become popular as a general term of satellite based global positioning system which includes GPS and other satellite systems such as GLONASS of Russia. Recently, as deployment plans, such as QZSS (=Quasi-Zenith Satellite System) of Japan, Chinese BeiDou, Galileo of EU, and IRNSS of India, progressed steadily and two or more global positioning systems can be used simultaneously, the multi-GNSS environment became realistic. This report expounds the effect of multi-GNSS and the latest information relating to the multi-GNSS receivers, especially the surveying instruments for which the positioning results of cm order are required.

Evaluation for Vehicle Positioning in Urban Environment Using QZSS Enhancement Function

In this paper, we have evaluated the performance and availability enhancement of Quasi-Zenith Satellite System (QZSS) in urban environments. In urban environments, QZSS can be expected to be fairly effective because of the high elevation angle of satellite and enhancement functions. Therefore, we conducted performance and availability enhancement evaluation tests to verify thus. In performance enhancement evaluation test, in order to evaluate the improvement of GPS accuracy by L1 Submeter-class Augmentation with Integrity Function (L1-SAIF) broadcasted by QZSS satellite, we compared the positioning errors of only GPS positioning and L1-SAIF positioning in open sky environment. In availability enhancement evaluation test, we performed the static and kinematic observation test. In static observation test, in order to evaluate the improvement of GPS accuracy by availability enhancement, we observed GPS and QZSS statically in narrow-sky environment. And we compared the positioning errors of only GPS positioning and positioning using availability enhancement. In kinematic observation test, in order to evaluate the availability of QZSS based on the visibility of QZSS satellite in urban environment, we observed QZSS and SBAS from moving vehicle. And we compared the visibility of QZSS and SBAS satellites. From these evaluation tests, it was confirmed that the performance and availability enhancement of QZSS have high availability and effectiveness.

QZS-1 Yaw Attitude Estimation Based on Measurements from the CONGO Network

The first satellite of Japan’s Quasi-Zenith Satellite System (QZSS) has been launched in September 2010, and its signal transmission has been activated at the end of the same year. The satellite transmits five signals from its L-band main antenna, including C/A code and L1C on L1, and the SAIF signal from a dedicated antenna mounted with an offset to the main antenna. Using differential pseudorange and carrier-phase measurements, it is possible to compute the phase center offset vector, or baseline vector, between these two antennas, if the satellite’s attitude is known. Using this vector as a priori information, it is furthermore possible to compute the yaw attitude of the spacecraft. This is a unique feature of the QZSS satellites and particularly interesting since their attitude mode is switched between yaw-steering and orbit-normal orientation during certain periods. Precise knowledge and consistent modeling of the satellite’s attitude is essential when processing carrier-phase measurements or satellite laser ranging measurements. This paper introduces the algorithm for baseline vector and yaw attitude estimation and presents results based on real measurements collected with five QZSS-capable receivers of the CONGO network. The observability of the baseline vector and the accuracy of the yaw angle estimates are discussed. The analysis for the yaw attitude estimation includes a switch from yaw-steering to orbit-normal orientation as well as changes of the attitude mode during an orbit maintenance maneuver.

Initial assessment of the COMPASS/BeiDou-2 regional navigation satellite system

An initial characterization and performance assessment of the COMPASS/BeiDou-2 regional navigation system is presented. Code and carrier phase measurements on up to three frequencies have been collected in March 2012 with a small regional network of monitoring stations. The signal and measurement quality are analyzed and compared with the Japanese Quasi Zenith Satellite System. A high level of stability is demonstrated for the inter-frequency carrier phase biases, which will facilitate the application of triple-frequency undifferenced ambiguity resolution techniques in future precise point positioning applications. The performance of the onboard Rubidium frequency standards is evaluated in comparison to ground-based hydrogen masers and shown to be well competitive with other GNSS satellite clocks. Precise orbit and clock solutions obtained in post-processing are used to study the presently achievable point positioning accuracy in COMPASS/BeiDou-2-only navigation. Finally, the benefit of triple-frequency measurements and extra-wide-lane ambiguity resolution is illustrated for relative positioning on a short baseline.

CIRCULARLY POLARIZED MICROSTRIP ARRAY ANTENNA FOR GROUND SEGMENT IN QUASI-ZENITH SATELLITE SYSTEM

In satellite communication system, antenna plays an important role. Therefore, the antenna must meet some requirements, such as high gain, circular polarization, and good directivity. In this paper, a four element linear array triangular patch microstrip antenna with cross slot is designed to be used for Quasi-Zenith satellite system. A simulation study as well as experimental study was carried out. The simulation showed that the 3 dB axial ratio bandwidth of 87 MHz (2.569-2.656 GHz) is achieved while the measured results showed 96 MHz (2.556-2.652 GHz). The linear array of 4 element antenna has a gain of 13.73 dB and maximum radiation pattern at 40° and -40°. Simulation and experiment results show that this antenna has met the characteristic requirements of Quasi-Zenith satellite.

Overview of Initial Observation Data of Technical Data Acquisition Equipments on the First Quasi-Zenith Satellite

TEchnical Data Acquisition equipments (TEDA) on the first Quasi-Zenith Satellite (QZS-1) MICHIBIKI was launched by the H-IIA Launch Vehicle No.18 on September 11, 2010 from the Tanegashima Space Center. The TEDA consists of sensors of three types; Light Particle Telescope [LPT, including Alpha particle and Proton Sensor-B (APS-B) and Electron Sensor-A (ELS-A)], Magnetometer (MAM), and Potential Monitor (POM). The TEDA on the QZS-1 has collected these data of space environment from September 21, 2010, these data will help us to identify the cause of the satellite anomaly. This paper describes some results from these data analysis on the QZS-1 orbit.

Elevation Angle of Quasi-Zenith Satellite to Exceed Limit of Satellite Visibility of Space Diversity which consisted of Two Geostationary Satellites

The paramedic in the moving ambulance sends the moving picture data to the doctor in the hospital via the communications satellite. However, when an ambulance runs inside a city, a radio wave to the communication satellite is blocked and as a result the moving picture data sometimes freeze. A value of the satellite visibility by the space diversity which consists of two geostationary satellites was acquired by simulation based on the hemispherical urban space data measured by a fish-eye camera in each city of Japan. From these simulation results, it was found that there was a limit in the satellite visibility by the space diversity. It is known that the satellite visibility is more improved by the quasi-zenith satellite. The elevation angle condition of the quasi-zenith satellite which exceeds the limit of the satellite visibility of two geostationary satellites was acquired. This elevation angle was compared between each city of Japan. It became clear that more than 68 deg of an elevation angle of the quasi- zenith satellite is necessary to exceed the limit of satellite visibility of two geostationary satellites.

準天頂衛星システムにおける衛星故障時の隣接衛星再配置

準天頂衛星システムにおける衛星故障時の隣接衛星再配置

Signal, orbit and attitude analysis of Japan’s first QZSS satellite Michibiki

Results are presented for Michibiki, the first satellite of Japan's Quasi-Zenith Satellite System. Measurements for the analysis have been collected with five GNSS tracking stations in the service area of QZSS, which track five of the six signals transmitted by the satellite. The analysis discusses the carrier-to-noise density ratio as measured by the receiver for the different signals. Pseudorange noise and multipath are evaluated with dual-frequency and triple-frequency combinations. QZSS uses two separate antennas for signal transmission, which allows the determination of the yaw orientation of the spacecraft. Yaw angle estimation results for an attitude mode switch from yaw-steering to orbit-normal orientation are presented. Estimates of differential code biases between QZSS and GPS observations are shown in the analysis of the orbit determination results for Michibiki. The estimated orbits are compared with the broadcast ephemerides, and their accuracy is assessed with overlap comparisons.

Remote Synchronization Experiments for Quasi-Zenith Satellite System Using Multiple Navigation Signals as Feedback Control

The remote synchronization system for the onboard crystal oscillator (RESSOX) is a remote control method that permits synchronization between a ground station atomic clock and Japanese quasi-zenith satellite system (QZSS) crystal oscillators. To realize the RESSOX of the QZSS, the utilization of navigation signals of QZSS for feedback control is an important issue. Since QZSS transmits seven navigation signals (L1C/A, L1CP, L1CD, L2CM, L2CL, L5Q, and L5I), all combinations of these signals should be evaluated. First, the RESSOX algorithm will be introduced. Next, experimental performance will be demonstrated. If only a single signal is available, ionospheric delay should be input from external measurements. If multiple frequency signals are available, any combination, except for L2 and L5, gives good performance with synchronization error being within two nanoseconds that of RESSOX. The combination of L1CD and L5Q gives the best synchronization performance (synchronization error within 1.14 ns). Finally, in the discussion, comparisons of long-duration performance, computer simulation, and sampling number used in feedback control are considered. Although experimental results do not correspond to the simulation results, the tendencies are similar. For the overlapping Allan deviation of long duration, the stability of 1.23×10−14 at 100,160 s is obtained.

次世代衛星向け軽量大型複合材料セントラルシリンダの開発

Advanced design method for manufacturing large Fiber-Reinforced-Plastics structure, such as next generation satellites like quasi-zenith satellite, is developed. The design method enables high shape accuracy, strength prediction including thermal residual stresses without trial manufactures. The design, manufacturing, and tests of a satellite main structure (verification model) are reported. The verification model was used as main structure of Quasi-Zenith Satellite and successfully launched.