Orbital design of LEO navigation constellations and assessment of their to BDS

Navigation augmentation based on Low Earth Orbit (LEO) satellites has become a hot topic in recent years. The orbital design of LEO augmentation constellations and the analysis of their performance are essential issues for the development of LEO augmentation systems. In this paper, LEO constellations for navigation are designed with the constraint that they augment the BeiDou Navigation Satellite System (BDS) in independent and combined modes. First, the calculation of the dilution of precision (DOP) values in different augmentation work modes is derived. Second, some numerical simulations of LEO constellations with different altitudes and inclinations are carried out. Based on the designed constellations, the coverage performance in typical regions and the global DOP values are analyzed, the suitable constellations with the orbital altitude of 500 km, 1000 km, 1500 km and 2000 km are derived. Finally, the suitable LEO constellations combined with the BDS in a time synchronized scenario and a non-synchronized scenario are demonstrated. The results show that 320/16/1:500 km, 80 degrees, 144/12/1:1000 km, 70 degrees, 100/10/1:1500 km, 70 degrees and 80/8/1:2000 km, 60 degrees are the suitable constellations, and the average GDOP values of these constellations are all below 5. In the combined work mode, the amplitude and stability of the DOP are improved significantly in the time-synchronized scenario of LEO navigation system and the BDS compared with only applying the BDS. The GDOP and TDOP values are improved by up to 22.46-44.41% and 29.06-60.62% respectively. When the nonsynchronized scenario is considered, i.e. the LEO navigation system and the BDS are independent systems, the improvement of the DOP value is relatively limited because a new LEO clock error parameter has to be introduced in the positioning estimation. In that case, the improvement of the GDOP values is only 3.11-22.28%, and the TDOP values become worse at medium and low latitudes. (c) 2020 COSPAR. Published by Elsevier Ltd. All rights reserved.