星载全空间可见GPS接收系统定位精度分析及验证

针对低轨空间科学卫星在轨任意姿态无固定对天面造成的无法连续GPS(Global Positioning System,全球定位系统)定位的问题,在HXMT(Hard X-ray Modulation Telescope,硬X射线调制望远镜)卫星中提出了星载全空间可见的GPS接收系统,并指出了双天线多径干扰对定位精度的影响。建立模型,对双天线下主瓣直达信号和后瓣镜像干扰信号叠加合成的信号进行定位精度分析,结果表明,空间中83.3%以上的GPS卫星信号对该系统带来的定位误差影响不大于单天线的定位误差影响。通过半物理动态仿真验证以及外场试验进行验证,实际工程测试数据结果表明采用剔星策略后定位精度提高约13.4%。从而证明了星载全空间可见的GPS接收系统方案的正确性,并可广泛应用于工程实际。     

GPS Program Status

The Navstar Global Positioning System (GPS) Program is composed of three segments ? Space, Control, and User Equipment. The Space segment is responsible for the development and launch of the GPS satellite constellation. The Control segment is responsible for monitoring the satellite telemetry and providing updated navigation information to the satellites. The User Equipment (UE) segment is responsible for the development and procurement of the GPS receivers for a variety of host vehicle platforms. Recently, approval was given to the User segment to enter Low Rate Initial Production (LRIP). This approval marks the beginning of Phase III (production and deployment) of the GPS program. This paper will discuss the overall status of all three segments with an emphasis on the User Equipment segment as it enters the production phase of the program.     

Integrating BDS and GPS for precise relative orbit determination of LEO formation flying

Low-Earth-Orbit(LEO) formation-flying satellites have been widely applied in many kinds of space geodesy. Precise Relative Orbit Determination(PROD) is an essential prerequisite for the LEO formation-flying satellites to complete their mission in space. The contribution of the BeiDou Navigation Satellite System(BDS) to the accuracy and reliability of PROD of LEO formation-flying satellites based on a Global Positioning System(GPS) is studied using a simulation method. Firstly, when BDS is added to GPS, the mean number of visible satellites increases from9.71 to 21.58. Secondly, the results show that the 3-Dimensional(3 D) accuracy of PROD, based on BDS-only, GPS-only and BDS + GPS, is 0.74 mm, 0.66 mm and 0.52 mm, respectively. When BDS co-works with GPS, the accuracy increases by 29.73%. Geostationary-Earth-Orbit(GEO) satellites and Inclined Geosynchronous-Orbit(IGSO) satellites are only distributed over the Asia-Pacific region; however, they could provide a global improvement to PROD. The difference in PROD results between the Asia-Pacific region and the non-Asia-Pacific region is not apparent. Furthermore, the value of the Ambiguity Dilution Of Precision(ADOP), based on BDS + GPS, decreases by 7.50% and 8.26%, respectively, compared with BDS-only and GPS-only. Finally, if the relative position between satellites is only a few kilometres, the effect of ephemeris errors on PROD could be ignored. However, for a several-hundred-kilometre separation of the LEO satellites, the SingleDifference(SD) ephemeris errors of GEO satellites would be on the order of centimetres. The experimental results show that when IGSO satellites and Medium-Earth-Orbit(MEO) satellites co-work with GEO satellites, the accuracy decreases by 17.02%.     

Characterization of NAVSTAR GPS and GLONASS on-board clocks

Investigation into navigation satellite on board clock frequency references and performance are reported. The focus is on the stability of the clocks aboard the NAVSTAR GPS (Global Positioning System) and GLONASS satellites as well as those used by their respective maser control stations and associated time scales. Allan-variance techniques have been applied to determine the long-term time-domain behavior of satellite clocks in an attempt to identify different regions of power spectral density. Coupled with analysis of relative-frequency drift over a period of many weeks, this behavior allows the type of satellite onboard standard to be tentatively identified. The known nature of the GPS clocks has shown that the different types of clocks aboard the satellites (crystal, rubidium, and cesium) are distinguishable given a sufficient sample time. The same approach has been applied to the GLONASS satellites, and a comparison of the results obtained from GPS has allowed conjecture on the type of clock used by the GLONASS satellites. It appears that GLONASS has used clocks of the quality of rubidium atomic oscillators since at least 1986, and that the quality and performance of onboard standards have increased steadily with time. Some current satellites perform well enough in terms of frequency drift, flicker FM noise floor, and long-term stability to compare favorably with the cesium beam standards carried on NAVSTAR GPS satellites launched in 1983-84     

Enhanced space integrated GPS/INS (SIGI)

Safe, reliable, and low cost space-based navigation is being provided with embedded INS/GPS systems such as the space integrated GPS/INS (SIGI). The SIGI is being used for various space vehicle applications such as launch vehicles, orbital vehicles, and re-entry vehicles. This paper describes current space vehicle navigation capabilities. The SIGI is being enhanced to provide additions to these existing capabilities with such items as higher processing and a commercial-off-the-shelf operating system. This will allow hosting of various software applications such as advanced navigation functions, flight control, guidance and vehicle management algorithms. The SIGI can host redundancy management functions by incorporating a cross channel data link card (CCDL) using a high speed firewire bus. The SIGI can then be used as a redundancy management platform which has application to current space vehicle avionics topologies incorporating distributed processing architectures     

Application of GPS to space vehicles: analysis of space environmentand errors

GPS based systems become extremely competitive for space applications because of their all-weather capabilities and continual information on position, velocity, precise time and even attitude to increase mission effectiveness, reduce mission cost, minimize requirements of on-board devices. In this paper, space application environment and error sources have been systematically analyzed, including geometric location of user with GPS satellites, dynamic state, physical environment and the effects on positioning accuracy. Several special differential GPS technologies to space use are proposed     

Urban area performance of GPS receiver with simultrac capability

The theory of operation, practical applications, and technical performance of a Global Positioning System (GPS) receiver designed for urban area use are presented. The receiver tracks as many as eight satellites, or all visible satellites, and uses the signals of the four best satellites to ascertain its location. If visibility of one satellite is blocked, one of the additional satellites can be used to provide continuous navigation. Component-level system design choices are shown to support superior automotive vehicle location performance, including optimum mobile communication with satellites and ground-based relays     

GPS软件接收机的捕获与跟踪算法

研究了GPS软件接收机的捕获与跟踪算法。分析了时域串行滑动相关捕获算法和频域基于FFT的并行相关捕获算法,设计了适合GPS软件接收机的并行算法,实现了对空中可见卫星的捕获。针对GPS信号的特点,设计了基于DLL与PLL相结合方法的GPS跟踪算法。利用实测中频信号对上述捕获与跟踪算法进行了验证分析,测试结果表明,基于FFT的并行相关捕获算法能够有效增强软件接收机的捕获能力,采用DLL与PLL相结合的方法能够实现对GPS信号的有效跟踪。     

高动态GPS卫星信号模拟器电离层延迟误差模拟方法研究

电离层延迟误差是GPS测量中非常重要的一项误差源，也是高动态GPS卫星信号模拟器要解决的一项关键技术。电离层延迟误差与目标的空间位置有关，在分析地面用户和空问用户不同电离层延迟误差修正方法的基础上，研究了卫星信号模拟器电离层延迟误差产生的途径，并给出了相应的数学模型，解决了不同应用环境下导航电8个电离层修正参数的计算问题，通过仿真计算，验证了本所提出的电离层延迟计算模型的正确性。     

GPS III system operations concepts

Over the past three years, the Lockheed Martin GPS III team has analyzed potential operational concepts for the Air Force. The completed tasks support the government's objective of a "realizable and operationally feasible" US Strategic Command (USSTRATCOM) and Air Force Space Command (AFSPC) concept of operations. This paper provides an overview of the operational improvements for the command and control of satellites, the provision of safe, precise navigation and timing services to end-users. The GPS III system changes existing operational paradigms. Improved operator capabilities are enabled by a new high-speed uplink/downlink and crosslink communication architecture. Continuous connectivity allows operators a "contact one satellite - contact all satellites" concept enabling near-real-time navigation updates and telemetry monitoring. This paper describes potential improvements for the following operations: constellation monitoring, command and control, navigation upload monitoring, global service monitoring, global service prediction, civilian navigation (CNAV) messaging, and anomaly detection and resolution. This paper also describes future operational improvements as GPS applications continue to proliferate and the need for an improved infrastructure to effectively manage all the systems that affect GPS service grows     

Unmanned space vehicle navigation by GPS

In this paper, flight-path deviation in the navigation of unmanned space vehicles by global positioning system (GPS) is analyzed. A new method to calculate flight-path deviation by means of coordinate transforming is presented and the software of navigation and control is designed. This software is practical and effective for navigation by GPS with some characteristics including high-speed, high accuracy, real-time positioning and the use of digital mapping technique     

GPS/BDS组合定位精度分析

随着定位技术的不断发展及多系统导航定位技术的逐步推广,多系统组合导航定位已经成为了GNSS导航定位领域中的主要发展趋势。主要阐述了GPS/BDS组合相对定位的观测方程和数学模型,并根据实测数据对比分析,从卫星可见性、精度因子、定位精度和均方根误差等方面对GPS、BDS及GPS/BDS组合定位系统的定位性能、定位精度进行了比较。研究结果表明,较单一的GPS和BDS系统定位,采用GPS/BDS组合定位可有效提高卫星可见数目和DOP值,且稳定性更好。GPS/BDS组合定位的定位精度也明显优于单一系统,这对GNSS高精度导航定位具有重要的参考价值。     

Multipath-adaptive GPS/INS receiver

Multipath interference is one of the contributing sources of errors in precise global positioning system (GPS) position determination. This paper identifies key parameters of a multipath signal, focusing on estimating them accurately in order to mitigate multipath effects. Multiple model adaptive estimation (MMAE) techniques are applied to an inertial navigation system (INS)-coupled GPS receiver, based on a federated (distributed) Kalman filter design, to estimate the desired multipath parameters. The system configuration is one in which a GPS receiver and an INS are integrated together at the level of the in-phase and quadrature phase (I and Q) signals, rather than at the level of pseudo-range signals or navigation solutions. The system model of the MMAE is presented and the elemental Kalman filter design is examined. Different parameter search spaces are examined for accurate multipath parameter identification. The resulting GPS/INS receiver designs are validated through computer simulation of a user receiving signals from GPS satellites with multipath signal interference present The designed adaptive receiver provides pseudo-range estimates that are corrected for the effects of multipath interference, resulting in an integrated system that performs well with or without multipath interference present.     

GPS频标比对系统的研制

应用GPS技术研制频标比对系统可对野外环境条件下的通信设备快速地进行时间频率校准.本文详细描述了系统中GPS频率标准源以及比相法、时差法频标比对单元的设计方案和软件设计思路,并给出了设计方案中关键技术解决的途径.该系统经校准完全能够满足要求,并在计量技术机构范围中得到应用.     

Performance evaluation of GPS augmentation using Quasi-Zenith Satellite System

The current global positioning system (GPS) provides limited availability and capability for a country like Japan where mountainous terrain and urban canyons do not allow a clear skyline to the horizon. At present, the Japanese Quasi-Zenith Satellite System (QZSS) is under investigation through a cooperative effort between the government and the private sector. QZSS is considered a multi-function satellite system, as it is able to provide communication, broadcasting, and positioning services for mobile users in a specified region with a high elevation angle. The additional GPS compatible signals from QZSS can remarkably improve the availability, accuracy, and capability of GPS positioning. This work focuses on the performance of GPS augmentation using the proposed QZSS. The QZSS satellite constellation and signal structure are briefly reviewed. Positioning with pseudo-range and carrier phase are discussed. The performance of GPS augmentation using QZSS in the Asian-Pacific and Australian area is studied using software simulations. The results are presented using the number of visible satellites as a measure of availability, GDOP as a measure of accuracy, and ambiguity success rate as a measure of capability of carrier-phase-based positioning with spatial and temporal variations. The results show that the QZSS will improve not only the availability and accuracy of GPS positioning, but will also enhance the capability of the GPS carrier-phase-based positioning in Japan and neighboring regions.     

Navigation system of pilotless aircraft via GPS

The pilotless aircraft has wide applications in measuring earth, surveying mineral sources, fireproofing in the forest, observing floods and so on. In this paper, after briefly introducing positioning and navigation technologies for pilotless aircraft-a new kind of navigation system for pilotless aircraft using GPS (Global Positioning System) is presented. An overall plan of the navigation system is discussed, and its technology cruxes are analysed. Its hardware and software are designed and implemented, and experimental results are given. The navigation system not only has autonomous navigation capability, but can also achieve navigation aided by telecontrol system. It can supervise flying by telemetering system and displaying predetermined air line and flight path maps on the computer monitor. It can run in simple GPS receiver mode or in the differential GPS mode by means of available telecontrol channel. These are, no doubt, of great value for the navigation of pilotless aircraft     

卫星导航接收机自主完好性监测算法研究

针对航空导航定位高可靠性的要求和GPS接收机观测噪声分布的特点,研究将粒子滤波算法应用于接收机自主完好性监测（RUM）中.通过粒子滤波算法对状态进行精确估计,利用对数似然比建立一致性检验统计量进行故障检测与隔离.对算法进行了数学建模,描述了完整的RAIM算法详细流程.通过实测数据对提出的RAIM算法进行验证,结果表明：粒子滤波算法在非高斯测量噪声情况下可以对GPS接收机状态进行精确的估计,利用对数似然比建立的一致性检验统计量能有效地检测并隔离故障卫星,验证了该算法应用于GPS接收机自主完好性监测的可行性和有效性.     

量化对GPS接收机捕获性能影响的研究

由于接收机输入端的信噪比对接收机的捕获性能具有很重要的意义,所以要尽量减少接收机输入端信噪比的损失。本文首先给出了含高斯白噪声的GPS信号经过不同量化位数和量化电平的量化器后的输出信噪比计算公式;然后,在此基础上分析其对接收机捕获性能的影响;最后,仿真实验表明,接收机可以在不影响捕获性能的情况下,尽量选择合适的量化位数和量化门限。实验结果也为量化器的设计提供了重要的技术参考。     

GPS 定位解的可信度研究

基于模糊数学理论的研究方法,给出了GPS定位解的可信度的定义。然后给出了可信度的解析表达式,并利用可信度的解析表达式对可信度的性质进行了研究。最后探讨了可信度可能的应用。     

Existence and uniqueness of GPS solutions

The existence and uniqueness of positions computed from global positioning system (GPS) pseudorange measurements is studied. Contrary to the claims of S. Bancroft (1985) and L.O. Krause (1987), in the case of n=4 satellites a fix may not exist, and, if a fix exists, it is not guaranteed to be unique. In the case of n>or=5 satellites, a unique fix is assured, except in certain degenerate cases such as coplanar satellites. An alternate formulation of the direct n=4 pseudorange to three-space position solutions of Bancroft and Krause is presented, and simple tests for existence and uniqueness are derived.<>