A scheduling strategy to inter-satellite links assignment in GNSS

By introducing inter-satellite link (ISL), the dependence of the global navigation satellite system (GNSS) on ground infrastructure can be reduced and its performance enhanced via inter-satellite ranging and communication. Owing to platform restrictions, there are usually fewer onboard Ka-band ISL antennas than the number of visible satellites, which poses a problem when optimizing the inter-satellite links assignment of the GNSS. In this study, to optimize inter-satellite ranging and communication, a multi-objective optimization model is built and a scheduling strategy is proposed for the inter-satellite links assignment scheduling problem. The position dilution of precision (PDOP) of links and the transmission time-delay of telemetry data are set as the ranging performance and communication metrics, respectively. We regard the links assignment in each slot as a general graph-matching problem, and apply the Blossom algorithm to obtain the maximum matching. We then generate and optimize the satellite sequences for whole slots using non-dominated sorting genetic algorithm II (NSGA-II). The simulation scenes include 10,080 epochs of GNSS constellation, and the simulation results show that the performance of the proposed strategy is better than that of other methods published recently, and can provide various solutions to meet the different preferences of system managers.     

NURBS曲面上的曲线精确表达

给出一种用显式方程精确表示NURBS曲面上曲线的方法,利用该方法NURBS曲面上曲线仍然用NURBS形式来表示,此外,可用显式公式来计算该曲线的控制顶点、权因子和节点矢量.基本思想是:运用代数基本定理避免通常B样条基函数复合所采用的极形式(Polar form)以及非常烦琐复杂的开花(Blossom)运算,把B样条基函数的复合、乘积运算转化为求解线性方程组.通过实例验证了该方法的有效性,可用于CAD/CAM领域中的曲面求交、剪裁以及数控加工刀轨生成等.     

An optimized strategy for inter-satellite links assignments in GNSS

Inter-Satellite Links (ISLs) can effectively enhance the Global Navigation Satellite System (GNSS) performance, such as communication and ranging performance. These performances would have been improved by disposing sparsely of ground stations and ISLs. Here, we demonstrate a topology scheduling strategy based on Signed Variance and Blossom algorithm (SV-Blossom) to promote the topology performance of GNSS. We also analyze the effect of this strategy on the robustness of the ranging information quality of the ISLs assignments system. For the domestic and overseas satellite communication Time Delay (TD) and Position Dilution of Precision (PDOP), by analyzing the relation of satellites, a set of the ISLs cost models is established, and the cost matrix is obtained. The final ISLs assignments result is obtained by processing the link cost matrix with the Blossom algorithm in the graph theory. In order to verify the rationality of the SV-Blossom strategy, a typical BDS-3 simulation scene with 10080 min is built to test these performances of ISLs. The final results show that the ranging information quality of the SV-Blossom strategy is greatly improved compared with recently published strategies, and the proposed links assignments mechanism has good robustness.