Abstract
Low Earth orbit (LEO) satellites located at altitudes of 500 km~1500 km can carry much stronger signals and move faster than medium Earth orbit (MEO) satellites at about a 20,000 km altitude. Taking advantage of these features, LEO satellites promise to make contributions to navigation and positioning where global navigation satellite system (GNSS) signals are blocked as well as the rapid convergence of precise point positioning (PPP). In this paper, LEO-based optimal global navigation and augmentation constellations are designed by a non-dominated sorting genetic algorithm III (NSGA-III) and genetic algorithm (GA), respectively. Additionally, a LEO augmentation constellation with GNSS satellites included is designed using the NSGA-III. For global navigation constellations, the results demonstrate that the optimal constellations with a near-polar Walker configuration need 264, 240, 210, 210, 200, 190 and 180 satellites with altitudes of 900, 1000, 1100, 1200, 1300, 1400 and 1500 km, respectively. For global augmentation constellations at an altitude of 900 km, for instance, 72, 91, and 108 satellites are required in order to achieve a global average of four, five and six visible satellites for an elevation angle above 7 degrees with one Walker constellation. To achieve a more even coverage, a hybrid constellation with two Walker constellations is also presented. On this basis, the GDOPs (geometric dilution of precision) of the GNSS with and without an LEO constellation are compared. In addition, we prove that the computation efficiency of the constellation design can be considerably improved by using master–slave parallel computing.
Highlights
With the completion of the construction of China’s BeiDou navigation satellite system (BDS) in 2020, all global navigation satellite systems will be capable of offering global service [1]
Simulation results show that the swifter motion of low Earth orbit (LEO) satellites significantly reduces by 70%~90% the convergence time of the precise point positioning (PPP), and the tracking data of global navigation satellite system (GNSS) satellites from LEO satellites improves the accuracy of the precise orbit determination of GNSS by 70% [4,5,6]
For any LEO-augmented constellation with a specific altitude, the single objective is the global average of visible satellites; the genetic algorithm (GA) is adopted for the augmented constellation design
Summary
With the completion of the construction of China’s BeiDou navigation satellite system (BDS) in 2020, all global navigation satellite systems will be capable of offering global service [1]. Due to the weak signals of these satellites, the positioning, navigation and timing (PNT) services, on which many critical infrastructures are heavily dependent, are disrupted in a deeply attenuated environment or can be interfered with by a jammer [2] To avoid this limitation, the low Earth orbit (LEO)-augmented global navigation satellite system (GNSS) has attracted increased attention. Aiming at LEO-based even global coverage augmentation systems, Ma et al designed an optimal hybrid configuration of 100 LEO satellites. For any LEO-augmented constellation with a specific altitude, the single objective is the global average of visible satellites; the GA is adopted for the augmented constellation design. The paper is organized as follows: Section 2 describes the problem and the methodology, the results and analysis are presented in Section 3; and the conclusions and discussion are presented in the last section
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