Lately there have been tremendous improvements in the Global Navigation Satellite Systems (GNSS). Going with the current trends, future demands for efficient and stable positioning, navigation and timing services are escalating globally. Unfortunately, applications of these systems have been limited by a number of drawbacks. For instance, the long initialization times in precise point positioning are attributed to lack of accurate atmospheric delay corrections. Consequently, they require dense network references that in most cases are not available in some areas such as deserts and oceans. This has led to the development of several approaches to enhance the orbit quality and precision of the satellites. Currently more than eighty satellites are available in service globally. However, the slow change in satellite geometry with respect to the ground station deteriorates the instantaneous initialization of the precise positioning. To this end, researchers have been looking for alternatives and have identified positioning, navigation, timing, remote sensing and communications (PNTRC) concept with different types of satellites based on the global navigation satellite systems constellations as well as low Earth orbit (LEO) constellations as a promising solution.
To this note, Tongji University researchers: Professor Bofeng Li, Yunzhong Shen, Dr. Haibo Ge, M.S. Liangwei Nie from the College of Surveying and Geo-Informatics in collaboration with Dr. Maorong Ge and Professor Harald Schuh at German Research Centre for Geosciences (GFZ) proposed a LEO enhanced global navigation satellite system (LeGNSS) comprising of low, medium and high orbital satellites. Specifically, they extended the GNSS system based on LEO constellation. They managed to provide efficient and accurate real-time precise point positioning services. The work is currently published in the research journal, Remote Sensing.
In brief, the research team first cross-examined the data collected from 14 BeiDou navigation satellite system, 24 global positioning system (GPS) satellites and 66 Iridium satellite constellations. Next, the data processing system entailed both server-end that functioned to estimate the orbit and clock for the satellites and user-end that functioned to investigate the signal-in-space ranging error and geometry dilution of precision. It was necessary to balance the precise orbit determination (POD) accuracy and complex calculations using two different approaches including low Earth orbit precise orbit determination comprising of ground tracking stations and GNSS precise orbit determination comprising of a LEO satellite subnet. Eventually, simulations were carried out to determine the influence of the low earth orbit on the clock and orbit quality and general performance of the LeGNSS.
The authors observed that both of the methods produced desired orbit and clock accuracy and particularly for LEO clocks. Consequently, LEO constellation significantly enhanced the positional geometries in isolated areas like polar regions achieving centimeter level, attributed to the precision positioning capacity of the LeGNSS.
In summary, the study successfully demonstrated the real-time precise point positioning application using the LeGNSS system by introducing various operations techniques. Therefore, this is expected to pave the way for enhancing the real-time precise point positioning performance of LeGNSS.
Ge, H., Li, B., Ge, M., Zang, N., Nie, L., Shen, Y., & Schuh, H. (2018). Initial Assessment of Precise Point Positioning with LEO Enhanced Global Navigation Satellite Systems (LeGNSS). Remote Sensing, 10(7), 984.Go To Remote Sensing