GEO卫星测距系统设计

随着卫星测定轨精度的提高,现有测距系统难以满足要求.文中着重介绍了GEO卫星采用三点测距为实现高测距精度的方案,给出了三点测距系统的结构和功能,并分析测距系统模型,以及提高测定轨精度的因素,最后对测距性能进行了分析.     

Relating to the efficiency of utilization of the geostationary orbit/spectrum in the fixed-satellite service

Rapidly growing radio-telecommunications needs, only partially satisfiable by the use of new frequency bands, demand greater, more efficient, use of traditional frequency bands. The development of geostationary fixed-satetlite communications systems is a prime example of the pressures towards more efficient spectrum utilization. It is investigated in which manner the geostationary orbital spectrum may be utilized to produce more capacity. The major means to achieve this derive from 1) technical factors which affect the frequency reuse potential of the geostationary satellite orbit; 2) technical factors which affect the amount of information which may be transmitted in a given bandwidth; and 3) other factors which facilitate or enhance the application of the technical factors with a view towards conserving and increasing orbit and spectrum utilization. Each of the individual factors is discussed in some detail, and estimates of their impact on orbit/spectrum utilization efficiency are provided in parametric form.     

Analyzing GPS signals to investigate path diversity effects of non‐geostationary orbit satellite communication systems

The concept behind path diversity is that a user who can access several satellites simultaneously will be able to communicate more effectively than a user who could only access one. The success of this method depends on the environment, the satellite constellation, and diversity combining technology. This paper explores the path diversity effects of non‐geostationary orbit (NGO) satellite personal communication services, for different degrees of user mobility, under various scenarios, using the constellation of the global positioning system (GPS). Measurements are taken near downtown Taipei. Three types of mobilities (fixed‐point, pedestrian, and vehicular) are examined, and the switch diversity and maximum ratio combining method are applied to determine the path diversity gain and calculate bit error probability. The error probability performance of applying diversity schemes in coherent binary phase shift keying (BPSK) and non‐coherent differential phase shift keying (DPSK) modulations over Rician fading channels are also analysed and evaluated by using the characteristic function method. The results show that fading can be significantly reduced and diversity greatly increased. A significant diversity gain and improvement in bit error rate (BER) can be expected in all cases by simply applying switch diversity scheme. Besides, for the maximum ratio combining method, the results imply that summing two satellite signals suffices to increase diversity and improve the bit error rate performance. Copyright © 2002 John Wiley & Sons, Ltd.     

Effective utilization of the geostationary orbit for satellite communication

The geostationary satellite orbit has a finite capacity for communication satellites operating in the frequency spectrum available, but saturation could be delayed for a long time if various practices and principles of system design and use were agreed internationally and applied. Three broad areas are identified where action is needed, namely system engineering for an interference-limited environment, intersystem coordination of the use of orbit and the spectrum, and the ordering of the use of orbit and spectrum so that systems with radically different characteristics do not interfere. In each of the three areas, the main factors of concern ate identified, the benefits that would be achieved are deduced in broad terms, and the practical and economic feasibility of actually securing the benefit is reviewed for each factor.     

Interference considerations in frequency sharing between low earth orbit satellites and the geostationary fixed satellite and terrestrial service

Recently many companies and consortia have considered launching LEO satellites for such projects as remote sensing, transportation and mining operations. When the multiple low Earth orbit (LEO) satellites are transmitting they can interfere with existing terrestrial microwave and satellite earth-stations in the fixed and mobile service. The interference problem is related to the number of proposed LEOs and the altitude and consequently the time to orbit the earth. These systems usually consist of many small satellites, and each satellite stays in the beam of a terrestrial station for up to 72 seconds in each 222 minute orbit. Earth coverage could be obtained by 48 (LEO) satellites 1500 km above the earth in polar orbit, and hence at least one LEO would always be interfering with terrestrial networks. A technical evaluation would then be required to determine the resultant BER (bit error rate) effecting existing terrestrial services. A determination can then be made to support such a LEO system or object via official channels such as the ITU.     

SINS/GNSS组合系统在超视距空空导弹上的中制导研究

阐述了超视距空空导弹使用SINS／GNSS组合制导的必要性,研究了如何在超视距空空导弹SINS上添加GNSS实现组合制导,系统分析了SINS／GNSS组合系统的模型,并利用卡尔曼滤波进行仿真。     

惯性/卫星导航系统实际导航性能评估算法

针对惯性/卫星组合导航进行实际导航性能(Actual Navigation Performance,ANP)评估,是保证飞机所需导航性能(Required Navigation Performance,RNP)及航空运行安全的关键.提出了惯性/卫星组合导航系统实际导航性能评估算法,从卡尔曼滤波器位置协方差矩阵开展分析,...     

GNSS接收机自主完好性监测算法研究

为了满足保障生命安全以及航空航天高精度、高可靠导航的要求,GNSS接收机不但要提供精确的导航服务而且也要提供完好性服务。为此,用于故障卫星检测和隔离的不同RAIM算法已被国内外学者广泛研究。丈中首先介绍了RAIM算法的原理,然后对国内外用于单颗和多颗卫星故障检测与隔离的RAIM算法研究进展进行系统的综述和深入的分析,并对多星座GNSS接收机完好性监测算法进行了深入细致的论述。另外对GPS最新的用户接口文件在定位精度以及可靠性方面的改善进行了介绍,最后总结给出了RAIM算法的主要研究方向。     

静止轨道瞬态点源多目标闪电信号实时探测技术

闪电是具有代表性的瞬态点源多目标,与雷暴等强对流气象现象有着密切的联系,通过对闪电的观测可获取雷暴雨等强对流天气的分布、变化、定位。文中论述了在静止轨道上利用瞬态点源多目标闪电信号和缓变的云层、陆地与海洋等背景噪声之间存在时间、空间和光谱特性上的差异,采用光谱滤波、空间滤波、帧—帧背景去除三种方法的组合来实现瞬态点源多目标闪电信号的增强与探测的方案及其技术实现,进行了理论分析与试验验证。     

利用地磁/星光观测角度的飞行器自主导航方法

针对地磁场模型精度较低从而导致导航精度不高及基于轨道动力学方程的天文导航方法的局限性问题,提出了一种利用天文,地磁信息进行飞行器自主导航的方法,建立了适用于一般飞行器的动力学方程,并推导了系统的观测方程.该方法以星光与地磁矢量夹角为观测量,采用Unscenteal Kalman Filter(UKF)方法估计飞行器的位...     

Preprocessing of GNSS signals subject to interference

Increasingly, interference effects on GNSS receivers are becoming important as more safety-critical applications such as civil aviation are employing the system. The inherent interference rejection capability of the GNSS spread spectrum modulating technique is now no longer considered adequate to remove the effects of very strong jammers. These can be generated intentionally, as in jamming situations, or unintentionally by systems such as mobile satellite systems. Continuous satellite tracking through this interference is essential for high-integrity applications. This study describes a new hardware-based GNSS interference mitigation scheme which is particularly effective against CW and pulsed CW interference. Interferers with some degree of frequency or amplitude modulation can also be reduced. The core hardware can remove two CW interferers from anywhere within the GPS P code bandwidth or the GLONASS frequency spectrum and further interferers can be removed by cascading modules. Simulation and actual data are shown. Owing to the wideband nature of the signal processing, the module introduces very little additional phase distortion and thus group delay to the GLONASS band, which has been shown to be advantageous to differential GLONASS processing. © 1997 John Wiley & Sons, Ltd.     

静止轨道微波卫星热带气旋高分辨率观测仿真

热带气旋在我国沿海区域频发,造成不可估计的损失,将卫星探测数据转化成可观察的亮温显示图像使得研究人员可以实时地观察热带气旋走向.文中主要基于WinSCP工具解决了将目标亮温系统产生的亮温数据集自动传输到亮温显示模块的问题,WinSCP原为手动操作同步于不同操作系统间文件的工具,文中利用脚本来运行WinSCP工具,成功实...     

RLG INS/GNSS极区组合导航方法

针对航空飞行器跨极区飞行,导航坐标系转换导致滤波器结构变化,进而影响导航精度的问题,提出了基于协方差变换的环形激光陀螺惯导/全球导航卫星系统算法(Ring Laser Gyroscope Inertial Navigation System/Global Navigation Satellite System,RLG ...     

卫星导航信号抗干扰能力分析

导航信号干扰是影响接收机稳定处理信号的关键因素之一,文章通过数学仿真,对BPSK信号和BOC信号在解调和跟踪阶段针对窄带干扰和匹配谱干扰下的工作性能进行了分析比较,为卫星导航信号抗干扰编码设计提供了参考。     

基于北斗导航信号的高轨卫星定位性能分析

随着我国自行研制和发展的北斗卫星导航系统的日益成熟,利用北斗导航系统对高轨卫星定位正逐渐成为研究的热点。对基于北斗导航信号的高轨卫星定轨性能展开研究,首先对高轨卫星建立动力学模型,然后对北斗信号传播链路建模,对导航卫星的接收功率、可见性、定位精度因子(DOP值)、多普勒性能建立相应的模型并开展仿真研究。仿真结果表明:高轨卫星GEO、HEO星载接收机接收功率分别为-174d BW和-180d BW时,可见星数至少4颗,满足导航定位需求;GEO的平均几何精度因子(GDOP)的均值为31.9535,HEO的平均几何精度因子(GDOP)为25.2012;GEO的多普勒频移范围约为8k HZ,HEO的多普勒频移范围约为31k HZ。该研究为后续弱信号捕获跟踪提供了理论依据和数据支撑。     

Providing differentiated service to TCP flows over bandwidth on demand geostationary satellite networks

The elasticity of transmission control protocol (TCP) traffic complicates attempts to provide performance guarantees to TCP flows. The existence of different types of networks and environments on the connections' paths only aggravates this problem. In this paper, simulation is the primary means for investigating the specific problem in the context of bandwidth on demand (BoD) geostationary satellite networks. Proposed transport-layer options and mechanisms for TCP performance enhancement, studied in the single connection case or without taking into account the media access control (MAC)-shared nature of the satellite link, are evaluated within a BoD-aware satellite simulation environment. Available capabilities at MAC layer, enabling the provision of differentiated service to TCP flows, are demonstrated and the conditions under which they perform efficiently are investigated. The BoD scheduling algorithm and the policy regarding spare capacity distribution are two MAC-layer mechanisms that appear to be complementary in this context; the former is effective at high levels of traffic load, whereas the latter drives the differentiation at low traffic load. When coupled with transport layer mechanisms they can form distinct bearer services over the satellite network that increase the differentiation robustness against the TCP bias against connections with long round-trip times. We also explore the use of analytical, fixed-point methods to predict the performance at transport level and link level. The applicability of the approach is mainly limited by the lack of analytical models accounting for prioritization mechanisms at the MAC layer and the nonuniform distribution of traffic load among satellite terminals.     

北斗卫星导航系统服务性能指标分析

北斗卫星导航系统服务性能指标是北斗卫星导航系统的关键技术指标,表示北斗导航卫星所能提供的服务水平。主要从覆盖性、精度、可用性、完好性和连续性几个方面来构建其指标体系;然后依据各个指标之间的相互关系,初步构建二级性能指标;最后通过软件仿真,对其性能进行了分析。     

特定频段导航系统信号分析

以塔康系统为例对特定频段导航系统信号进行了分析和模拟。通过分析干涉场随入射波的擦地角、反射系数、双路径干涉波程差、散射系数、直射波仰角、双路径干涉因子及系统传输损耗，分析和模拟了反射波对直射波的干涉情况。     

Performance Metrics for Positioning Terminals Based on a GNSS in Autonomous Vehicle Networks

Wireless Personal Communications - In autonomous vehicles networks, information is transferred through vehicle-to-vehicle and vehicle-to-infrastructure communication channels. We have added a new...     

航海保障通信业务服务属性的研究及思考

文章从航海保障通信业务现有管理架构、公约法规、事业属性等几个方面,对航海保障通信业务服务属性进行研究和分析。