A Poisson multi-Bernoulli mixture filter with spawning based on Kullback–Leibler divergence minimization

In the classical form, the Poisson Multi-Bernoulli Mixture (PMBM) filter uses a PMBM density to describe target birth, surviving, and death, which does not model the appearance of spawned targets. Although such a model can handle target birth, surviving, and death well, its performance may degrade when target spawning arises. The reason for this is that the original PMBM filter treats the spawned targets as birth targets, ignoring the surviving targets’ information. In this paper, we propose a Kullback–Leibler Divergence (KLD) minimization based derivation for the PMBM prediction step, including target spawning, in which the spawned targets are modeled using a Poisson Point Process (PPP). Furthermore, to improve the computational efficiency, three approximations are used to implement the proposed algorithm, such as the Variational Multi-Bernoulli (VMB) filter, the Measurement-Oriented marginal MeMBer/Poisson (MOMB/P) filter, and the Track-Oriented marginal MeMBer/Poisson (TOMB/P) filter. Finally, simulation results demonstrate the validity of the proposed filter by using the spawning model in these three approximations.     

卫星姿控发动机高空羽流场工程分析

发展卫星姿控小推力发动机高空羽流场的工程估算方法,计算分析其主要燃气组分的分布特征.采用网格技术将发动机喷管出口截面剖分形成多独立点源,建立了非均匀出口流动条件下的分析模型.与自由分子单一点源模型相比,该模型的计算结果更接近实验值.对MBB 10 N双组元发动机多组分羽流场的研究表明,压强场和内能场的变化较剧烈;不同于轻分子组分,重分子组分主要集中于轴线附近,其密度场呈较强方向性.     

环境因子的定义及其统计推断

利用不同环境下寿命之间的折算原则，导出了不同寿命分布类环境因子的定义，得到了环境因子的点估计和区间估计。     

Modeling and initial assessment of the inter-frequency clock bias for COMPASS GEO satellites

The COMPASS system is a project established by China to develop an independent global satellite navigation system, which has five GEO (Geostationary Orbit) satellites and thirty Non-GEO satellites. An apparent inter-frequency clock bias (IFCB) for COMPASS GEO satellites is investigated using the real data. The bias also is modeled by the different models. Based on the 15 months (DOY 121, 2011–214, 2012) single-day-estimated results, the periodic variation of IFCBs of the COMPASS GEO satellite is studied using a harmonic analysis. The notable periods of 12 h and 8 h are noted. The harmonics-based models with different periods and different orders and quadratic function based model are used to describe the IFCB. The performances show that the 4-order harmonics-based model with the periods of 24, 12, 8 and 6 h is most optimal than others for describing the IFCB of COMPASS GEO satellite. Its amplitudes and phases estimated from a least square fit are used to study the features of the IFCB. The results show that the current amplitudes and phases do not present special features. Although the irregular amplitudes and phases of the model are disadvantageous for the long-term prediction of IFCB, it is obvious that the modeling IFCB can simple its service and a few of coefficients can replace the IFCB series. The performance of the model in short-term prediction IFCB is tested using the ten-day data (DOY 215-224, 2012).     

A real-time ionospheric model based on GNSS Precise Point Positioning

This paper proposes a method of real-time monitoring and modeling the ionospheric Total Electron Content (TEC) by Precise Point Positioning (PPP). Firstly, the ionospheric TEC and receiver’s Differential Code Biases (DCB) are estimated with the undifferenced raw observation in real-time, then the ionospheric TEC model is established based on the Single Layer Model (SLM) assumption and the recovered ionospheric TEC. In this study, phase observations with high precision are directly used instead of phase smoothed code observations. In addition, the DCB estimation is separated from the establishment of the ionospheric model which will limit the impacts of the SLM assumption impacts. The ionospheric model is established at every epoch for real time application. The method is validated with three different GNSS networks on a local, regional, and global basis. The results show that the method is feasible and effective, the real-time ionosphere and DCB results are very consistent with the IGS final products, with a bias of 1–2 TECU and 0.4 ns respectively.     

用线性曲线拟合判断固态功率放大器饱和点

在自动化测量系统中,软件需要根据测量数据自动寻找并判断功率放大器的饱和点。在受噪声影响较大的在轨测试中,这是个难点。本文根据固态功率放大器AM/AM特性曲线的特点,提出一种使用多项式线性曲线拟合测量数据建立增益曲线预测关系式,并通过增益趋势线准确判断饱和点的方法。经过真星在轨测试验证,该方法与实际特性吻合很好。     

基于结构光的空间大目标特征重构与位姿测量

针对因缺少空间非合作大目标的全局特征而难以实现相对位姿测量的问题,提出利用点状光源与单目光学相机组成点结构光视觉测量系统进行特征重构与位姿测量的方法。以非合作大目标上尺寸未知的局部矩形特征为测量对象,首先建立点结构光视觉测量系统相对位姿测量模型;接着利用相对约束关系给出特征重构方法并获得隐性特征点;然后利用特征点计算测量系统与非合作大目标之间的相对转移矩阵得到相对位置和姿态。通过数字仿真校验该方法的有效性并对测量误差因素进行分析,仿真结果表明该测量方法是有效的。     

An improved approach to model ionospheric delays for single-frequency Precise Point Positioning

PPP with low-cost, single-frequency receivers has been receiving increasing interest in recent years because of its large amount of possible users. One crucial issue in single-frequency PPP is the mitigation of ionospheric delays which cannot be removed by combining observations on different frequencies. For this purpose, several approaches have been developed, such as, the approach using ionospheric model corrections with proper weight, the GRAPHIC (Group and Phase Ionosphere Calibration) approach, and the method to model ionospheric delays over a station with a low polynomial or stochastic process. From our investigation on the stochastic characteristics of the ionospheric delay over a station, it cannot be precisely represented by either a deterministic model in the form of a low-order polynomial or a stochastic process for each satellite, because of its strong irregular spatial and temporal variations. Therefore, a novel approach is developed accordingly in which the deterministic representation is further refined by a stochastic process for each satellite with an empirical model for its power density. Furthermore, ionospheric delay corrections from a constructed model using GNSS data are also included as pseudo-observations for a better solution. A large data set collected from about 200 IGS stations over one month in 2010 is processed with the new approach and several commonly adopted approaches for validation. The results show its significant improvements in terms of positioning accuracy and convergence time with a negligible extra processing time, which is also demonstrated by data collected with a low-cost, handheld, single-frequency receiver.     

筛选时间的确定

本文研究在威布尔分布下筛选时间的点估计和置信上限估计,分别包括图估计和数值估计。推导了为确定筛选时间的置信上限而建立的方程式。确定了IC高温动态老化的筛选时间。为制定筛选技术条件和确定整机老练时间提供理论依据。