QZSS: How the Japanese Satellite System Enhances Precise Positioning in the Asia-Pacific Region.
Knowing exactly where something is, right now, is more critical than ever. Whether it's tracking a fleet of delivery vehicles, guiding autonomous machinery, or ensuring workforce safety, real-time precise positioning is critical. But some environments can make this target challenging.
Cities in Japan are typically built up with dense high-rise buildings along narrow streets, known as dense urban canyons. In these areas, satellite signals are blocked, reflected off buildings, or distorted, leading to decreased accuracy, reduced availability, and potential loss of positioning altogether.
The Quasi-Zenith Satellite System (QZSS) is a Japanese satellite-based augmentation system designed to enhance the performance of Global Navigation Satellite Systems (GNSS), particularly GPS, in the Asia-Pacific region, especially in such challenging urban canyons.
QZSS Architecture
QZSS consists of a constellation of satellites in highly inclined, elliptical orbits, known as Quasi-Zenith Orbits. These orbits ensure that at least one satellite is nearly overhead in the Japanese sky at all times. An additional Geo-stationary satellite provides permanent coverage over the Asia-Pacific region, with more such satellites to be added in the near future. The QZSS constellation is designed to complement GPS, providing improved accuracy, availability, and reliability in regions where GPS signals may be obstructed or weak.
QZSS and GPS Integration
QZSS is designed to work seamlessly with GPS, by implementing multi-band signal and messaging structures that are very similar to those of GPS. Users with QZSS-compatible receivers can benefit from the combined signals of both systems, resulting in improved performance. The integration of QZSS and GPS provides a more robust and reliable navigation solution.
Benefits of QZSS
QZSS offers several key benefits, including:
- Improved Accuracy: By providing additional satellite signals and corrections, QZSS enhances the accuracy of positioning and navigation.
- Enhanced Availability: The unique orbits of QZSS satellites ensure better signal availability, particularly in urban canyons and mountainous regions where GPS signals may be blocked.
- Increased Reliability: QZSS provides redundancy and backup for GPS, improving the overall reliability of navigation services.
- Regional Augmentation: QZSS is specifically designed to augment GPS in the Asia-Pacific region, addressing the unique challenges of this area.
An example of improved accuracy is seen in the experiment conducted by Tupaia in a dense downtown Tokyo street. The experiment used a dual-band GNSS receiver connected to Tupaia’s Precise Positioning Cloud Service, while walking on the sidewalk. The results show that using GPS, Beidou, and QZSS satellites together achieves significantly better accuracy compared to using only GPS and Beidou. Without QZSS, the navigation led to the wrong side of the street.
Future Developments
The QZSS program is continually evolving. Future developments include the addition of more satellites to the constellation and the enhancement of signal capabilities. These advancements will further improve the performance and expand the applications of QZSS.
The QZSS constellation currently includes 4 operational satellites, with completion of the full 7 satellites expected through launch of 3 more satellites during 2024-2025, adding one satellite to the Quasi-Zenith Orbits, and two Geo-stationary satellites. The full 7 satellite system is expected to be operational by 2026.
How to access the benefits of QZSS with Tupaia’s cloud based service
QZSS is a vital satellite-based augmentation system that enhances navigation and positioning in the Asia-Pacific region. For precise positioning, additional QZSS satellites that provide improved availability and geometry are a significant boost to accuracy and reliability, especially in challenging urban areas.
The integration of QZSS with other GNSS constellations in Tupaia’s cloud-based positioning service allows users to tap into these benefits seamlessly. Adding new satellites, signals, or even new GNSS systems (like with QZSS) is seamless to the end-devices, with just a cloud software upgrade.
- Yuval Chipman, Senior Algorithms Engineer at Tupaia.
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