翼伞精确定点着陆归航方法研究

文章介绍一种翼伞精确定点着陆归航的方案 ,按高度将归航过程划分为 6个阶段 ,给出了每个阶段的制导算法 ,讨论了系统的稳定性并给出结论。     

一种外环水平结构双轴光纤惯导系统旋转方案设计方法

目前国内外长航时高精度自主惯导系统多采用双轴旋转调制自动补偿技术,而旋转方案设计对系统导航精度影响至关重要.双轴惯导系统按结构可分为外环水平结构和外环航向结构两类.分析了外环水平结构双轴惯导系统在旋转方案设计中的局限性,考虑到光纤陀螺输出特性,指出外环水平结构双轴光纤惯导系统不宜采用传统旋转方案,并提出了一种该类双轴光纤惯导系统的旋转方案设计方法,最后对所设计旋转方案与十六位置旋转方案进行试验对比,试验表明此设计方案导航精度提升了71％.     

Mid-latitude amplitude scintillation of GPS signals and GPS performance slips

Degradation of transionospheric radio signals and operation failures during ionospheric disturbances constitute a crucial factor of space weather influence on radio engineering satellite systems performance. We found that during the main phase of strong magnetic storms in 2000–2003 when the auroral oval expands into mid-latitudes, its southern boundary develops a region with intense small-scale electron density irregularities. Such irregularities may cause strong amplitude scintillations of GPS signals at both GPS operating frequencies. The another consequence of it was significant random GPS signal phase fluctuations, breaking-down of signal tracking, and sharp increasing of GPS positioning errors as a result.     

New field of application of the IRI modeling – Determination of ionosphere transfer characteristic for radio astronomical signals

We suggest a new field of application of IRI modeling – determination of ionosphere transfer characteristic (ITC) for radio astronomical signals (RAS). VHF and HF RAS are widely used for observations of the Sun and pulsars. It is necessary to take into account possible distortions of RAS in the Earth ionosphere. However, in contrast to modern navigation systems (GPS, GLONASS, GALILEO), where very accurate reconstruction of ionosphere parameters is a built-in function, in present-day radio astronomy a retrieve of ITC has not been appropriately worked out yet. It collides with increasing requirements to accuracy of the analysis of RAS amplitude profile and to the angular and polarizing resolution of radio telescopes of new generation. We have developed a method and software for calculation of the ionosphere measure of rotation (RM) and the measure of dispersion (DM). We used the ionosphere model IRI-2001, magnetic-field model IGRF-10 and values of ionosphere total electron content as deduced from GPS measurements. The obtained values of the ionosphere DM and RM were recalculated into characteristics of phase delay, Faraday amplitude modulation and polarization changes. We made calculations for different levels of geomagnetic activity and for different angular position of radio sources as well.     

LDPC码在卫星导航系统中的应用

作为一种接近香农极限的信道编码,近年来LDPC码被广泛采用,例如欧洲第二代数字视频广播卫星标准DVB-S2和空间数据咨询委员会(CCSDS)遥测信道编码标准就分别采用了LDPC码。文章将讨论LDPC码在卫星导航系统中的应用,内容涵盖星上编码与接收机解码。GPS联合项目办公室在接口规范(Draft IS-GPS-800,Navstar GPS Space Segment/User Segment L1C Interfaces,19 April 2006)中展现了L1电文结构中的LDPC码。子帧2和子帧3将分别用一个独立的24bit循环冗余检验(CRC)算法。加入CRC比特之后每一子帧将进一步被长度为1200/548码率为1/2的LDPC码编码。文章将给出同等长度同等码率的不同类型的LDPC码。它们表现出了优异的译码性能、简单的编码结构和较低的译码复杂度。另外一个优点是其校验矩阵无需用一系列的冗余表格来表示。这种LDPC码的构造方法可以被扩展到其它卫星导航系统,比如欧洲的伽俐略(Galileo)系统和中国的北斗(Compass)系统。     

对GPS区域映射系统中比例优化的研究

GPS区域映射系统通过对分布式转发器的时延控制,实现定位区域上的映射关系,使由GPS制导的武器错误定位,从而偏离原有的目标,实现对重要目标的保护^[1]。文章首先给出了求解区域映射系统中虚拟点邻域的迭代算法,在此基础上分析了虚拟点与真实点的位置关系以及转发器的分布对映射比例的影响,并在有效干扰区域内,对如何选择虚拟点的位置和转发器的分布以达到映射比例的优化进行了研究,得出的结论为实际应用提供了参考。     

舰载惯导传递对准仿真系统设计及实现

构建了舰载惯导系统传递对准计算机仿真系统,利用轨迹发生器产生主子惯导系统的惯性器件的输出,送入主子惯导系统的惯导解算模块,产生不同匹配模块的惯导参数输出,进而进行滤波估计。仿真系统可以对所建立的舰载惯导系统的误差模型和滤波算法进行计算机仿真验证,提高误差模型的精确性和滤波算法的可靠性,并对后续的半实物仿真和实际装备实验验证提供理论依据和支撑。     

GNSS global real-time augmentation positioning: Real-time precise satellite clock estimation,prototype system construction and performance analysis

Lots of ambiguities in un-differenced (UD) model lead to lower calculation efficiency, which isn’t appropriate for the high-frequency real-time GNSS clock estimation, like 1 Hz. Mixed differenced model fusing UD pseudo-range and epoch-differenced (ED) phase observations has been introduced into real-time clock estimation. In this contribution, we extend the mixed differenced model for realizing multi-GNSS real-time clock high-frequency updating and a rigorous comparison and analysis on same conditions are performed to achieve the best real-time clock estimation performance taking the efficiency, accuracy, consistency and reliability into consideration. Based on the multi-GNSS real-time data streams provided by multi-GNSS Experiment (MGEX) and Wuhan University, GPS + BeiDou + Galileo global real-time augmentation positioning prototype system is designed and constructed, including real-time precise orbit determination, real-time precise clock estimation, real-time Precise Point Positioning (RT-PPP) and real-time Standard Point Positioning (RT-SPP). The statistical analysis of the 6 h-predicted real-time orbits shows that the root mean square (RMS) in radial direction is about 1–5 cm for GPS, Beidou MEO and Galileo satellites and about 10 cm for Beidou GEO and IGSO satellites. Using the mixed differenced estimation model, the prototype system can realize high-efficient real-time satellite absolute clock estimation with no constant clock-bias and can be used for high-frequency augmentation message updating (such as 1 Hz). The real-time augmentation message signal-in-space ranging error (SISRE), a comprehensive accuracy of orbit and clock and effecting the users’ actual positioning performance, is introduced to evaluate and analyze the performance of GPS + BeiDou + Galileo global real-time augmentation positioning system. The statistical analysis of real-time augmentation message SISRE is about 4–7 cm for GPS, whlile 10 cm for Beidou IGSO/MEO, Galileo and about 30 cm for BeiDou GEO satellites. The real-time positioning results prove that the GPS + BeiDou + Galileo RT-PPP comparing to GPS-only can effectively accelerate convergence time by about 60%, improve the positioning accuracy by about 30% and obtain averaged RMS 4 cm in horizontal and 6 cm in vertical; additionally RT-SPP accuracy in the prototype system can realize positioning accuracy with about averaged RMS 1 m in horizontal and 1.5–2 m in vertical, which are improved by 60% and 70% to SPP based on broadcast ephemeris, respectively.     

GNSS water vapour tomography – Expected improvements by combining GPS,GLONASS and Galileo observations

The German Research Centre for Geosciences (GFZ) operates a GNSS water vapour tomography system using about 350 German GNSS stations. The GNSS data processing at the GFZ works in near real-time and provides zenith total delays, integrated water vapour and slant delay data operationally. This large data set of more than 50,000 slant delays per hour is used to reconstruct spatially resolved humidity fields by means of tomographic techniques. It can be expected that additional observations from the future Galileo system provide more information with improved quality. A simulation study covering 12 h at 14 July 2009 was therefore started to estimate the impact of GPS, Galileo and GLONASS data on the GNSS tomography. It is shown that the spatial coverage of the atmosphere with slant paths is highly improved by combining observations from two or three satellite systems. Equally important for a reliable tomographic reconstruction is the distribution of slant path intersections as they are required to locate the integrated delay information. The number of intersection points can be increased by a factor of 4 or 8 if two or three systems are combined and their distribution will cover larger regions of the atmosphere. The combined data sets can be used to increase the spatiotemporal resolution of the reconstructed humidity fields up to 30 km horizontally, 300 m vertically and 15 min. The reconstruction quality could not be improved considerably using the currently available techniques.     

组合导航系统实验平台的设计与实现

随着科学技术的发展,人们对导航定位的要求越来越高,单一的导航方式已无法满足导航技术发展的需要,组合导航已成为导航技术发展的必然趋势.本文根据组合导航系统的概念,设计出一种通用的组合系统模型.该组合导航系统实验平台可以直接应用于目前的组合导航研究和实验,成为组合导航系统研究方面的有效工具,促进组合导航研究的发展.