Tech Chat | A Way to Enhance GNSS Signal Tracking - Regional Satellite Systems 

When it comes to satellite navigation systems, the first thing that comes to mind are the 4 GNSS (Global Navigation Satellite System) that are well known to end users and are generally supported by GNSS products on the market, including GPS of the United States, GLONASS of Russia, BDS of China and Galileo of Europe.

With these main GNSS systems, we can receive satellite signals in every corner of the world for our daily needs. However, on the one hand, the tracking satellites in some areas are fewer, and on the other hand, some countries have a deeper demand for satellite systems, so they have begun to build their own regional satellite systems to cover their area. Such as QZSS (Quasi Zenith Satellite System) in Japan, IRNSS (India's Regional Navigation Satellite System) in India.

QZSS 

The first phase of Japan's quasi zenith satellite navigation system, QZSS, consists of three tilt synchronous orbit satellites and one geosynchronous orbit satellite, and four satellites have been deployed so far. 

The QZSS orbit design ensures that the service area covers East Asia and Oceania, within which four satellites are visible 24 hours a day, with one satellite always positioned at a high elevation over Japan. 

QZSS system transmits 6 service signals: L1C /A, L1C, L2C, L5, L1 SAIF and LEX. It can be seen that the frequency and shape of the signals transmitted by QZSS are similar to THAT of GPS and Galileo. The functions of QZSS system can be summarized into three categories: GPS system supplement, GPS system precision enhancement and alarm service.  

1. GPS system supplement

Due to Japan's mountainous environment and narrow urban streets, some GPS satellite signals with low elevation Angle are easily blocked by mountains and buildings, affecting users' reception, so a satellite with high elevation Angle is needed. After the completion of the entire QZSS system, GPS availability in the Japanese territory can be improved from 90% to 99.8% of GPS+QZSS.

2. GPS system precision enhancement

QZSS 'L1 SAIF service provides enhanced positioning accuracy at the meter level.  Like WAAS, the U.S. wide Area Enhancement system, QZSS broadcasts satellite ephemeris, clock errors and ionospheric corrections to improve the positioning accuracy of users in Japan from 10 meters with GPS alone to about 1 meter.  
QZSS broadcasts L-Band Experiment signal in addition to the meter-level positioning accuracy improvement service. The signal rate is up to 2000bps, while the information rate of GPS signal is 50bps and L1 SAIF signal is 250bps. L-Band signal can provide more error correction information, enabling the user to achieve centimeter-level positioning accuracy, which can be used in unmanned driving, mapping, precision agriculture and other industries.  

3. Alarm service

QZSS will also provide information service on L1 SAIF signal. Due to the frequent occurrence of earthquakes and tsunamis in Japan, early warning information will be broadcast through QZSS satellite to draw the attention of the public. The L1 SAIF signal also provides GPS and other satellite health information, and timely notifies users not to use the abnormal GPS satellite when it is abnormal, so as to avoid incorrect positioning results.  

IRNSS 

India's IRNSS can meet its own satellite navigation needs.  It can ensure that the number of all-weather visible satellites within the territory of India is no less than 4, realizing India's independent and controllable satellite navigation requirements. It can provide precise positioning, navigation and timing services for users within 1,500km of India and its borders, providing positioning accuracy of better than 10 meters in India and better than 20 meters in the vicinity of India.

IRNSS systems can provide standard location services (SPS), precision location services (PPS), and government licensed User (RS) services.  The space segment adopts three carrier bands, C band, S band and L band.  Among them, C-band frequency is mainly used for measurement and control, while S-band and L-band mainly provide navigation and positioning services for users. 

Characteristic

1. The system is independent and can provide independent navigation and positioning services for local users in India without relying on GPS, but the scope is mainly limited to the Indian subcontinent and the Indian Ocean. 

2. The carrier frequency of the system is different. The IRNSS system is distributed in the S band and L band, with a wider frequency range. Therefore, in the future, it will have stronger compatibility, interoperability and wider adaptability with GPS, Galileo and other systems.  

Usually tracking 4 satellites can get positioning information. Why do we need to use multiple satellite systems? Receiving more satellite signals can speed up GNSS device initialization. At the same time, the anti-noise and anti-multipath performance will also be improved, and the user experience will be better. As technology advances, we will have more choices and more convenience.

When choosing your GNSS device, also take a look if it supports your local area system.

Learn more about the SingularXYZ Y1 GNSS receiver supporting QZSS and IRNSS.
https://www.singularxyz.com/Y1_Land_Surveying_Solution.html