利用GNSS实现高轨卫星自主导航的新方案

针对GNSS应用于GEO卫星导航存在的导航信号弱、可见卫星少、定位几何差等突出问题,探讨了一种在GPS导航星冲天面安装导航天线并辐射导航信号的新方案,设计了冲天面天线和GEO接收天线的波束宽度和增益以及讨论了冲天天线所需发射功率,分析了新方案中GEO卫星对GPS卫星可见性、GDOP和定位精度。分析表明,新方案仅需从现有导航星引出一部天线,即可实现以小于10W的功率代价使得GEO卫星80%以上的时间里可以利用GPS系统定位,且定位精度约77m。通过仿真验证了本方案的可行性。     

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。     

GPS小波去噪的误差方差建模技术与试验

如何消除GPS观测数据的噪声以提高定位精度并估算消噪信号的误差方差对工程测量具有重要意义。在介绍小波多尺度分析的基础上,推导了在小波多尺度分析巾平滑信号误差的理论方差模型。并通过实际的GPS单点静态定位试验给予验证。试验结果表明,该方法在有效消除噪声的同时,计算得到的各尺度平滑信号的误差方差与理论方差模型基本一致。     

原子钟性能对卫星导航系统定位精度的影响分析

星载原子钟是卫星导航系统的关键设备,原子钟主要通过影响卫星钟差对定位精度产生影响,分析了GNSS星载原子钟性能对定位精度的影响.通过原理分析,建立了原子钟稳定度与卫星导航系统定位精度的关系.在不考虑控制段对星钟校准误差的前提下,将原子钟噪声与星上工作环境因素作为主要因素,分析了GPS-IIF铷钟和铯钟对钟差/定位误差的影响,并给出了分析结果.最后,利用iGMAS提供的钟差产品数据,对比了北斗和GPS部分原子钟的稳定度及其对定位精度的影响,为后续星载原子钟的发展与选择提供了一定参考.     

天线整流罩对GNSS观测值与定位精度影响研究

当前大部分城市为保护卫星连续运行参考站(CORS)系统基准站天线安装了整流罩,但天线整流罩对观测值以及基准站坐标影响的研究仍显不足。为解决基于广州CORS(GZCORS)的网络RTK高程测量存在较大偏差的问题,基于2016—2021年观测站数据,以及拆除基准站天线罩前后的观测数据质量与定位效果相关分析,对天线整流罩对GNSS观测值与高程定位精度的影响进行了深入探究,并分别进行了静态仿动态和城市车载动态定位测试验证。研究结果显示,天线整流罩在一定程度上会增加原始观测值的多路径效应影响,降低约10%的数据可用率,并对基准站高程定位结果产生1～14 cm的系统性偏差,进而影响用户RTK高程定位效果。定位结果显示,拆除基准站天线罩后,基于GZCORS的RTK水平定位均方根误差(RMS)为1 cm左右,高程定位精度RMS为2 cm左右;城市场景下车辆动态定位精度RMS为15～20 cm,满足车道级定位性能。     

星载AIS收发机的关键技术初探

研究了现有的VHF频段的船用自动识别系统在超小或微型卫星应用中的若干关键技术。阐述了大气层、降雨、多径失真、多普勒频移对星载AIS通信的影响,接收到的星载AIS信号的载噪比以及星上天线的设计等。研究结果表明,多普勒频移对于星载AIS通信的影响是最主要的,而大气和气侯情况对星载AIS通信的影响则较小。     

4种DGPS模块动态定位精度测试与分析

采用RTK-DGPS为参照,对GARMIN GPS15L、Ublox LEA-4S、Gstar GS-87和Gstar GS-89m-J共4种DGPS模块在单机模式、地面伪距差分模式和卫星差分模式下的动态定位精度进行了测试和分析.结果表明:(1)对于GARMIN GPS15L 和Ublox LEA-4S,单机定位精度为米级,使用地面伪距差分定位可分别提高动态定位精度20%和87%;(2)总体上看,DGPS模块的地面伪距差分定位精度优于卫星差分定位,卫星差分定位精度优于单机定位;(3)在视野狭窄地段,无论单机定位、伪距差分定位还是卫星差分定位,动态定位精度都受到一定影响,和视野开阔地段相比,精度明显下降.     

Galileo卫星星钟故障前后信号质量分析

星载原子钟是卫星导航系统的核心器件,是影响导航信号质量的重要因素。2016年11月,Galileo系统利用一箭四星发射升空4颗新一代Galileo卫星。根据观测显示,截至2017年7月,仅能接收到其中1颗卫星发射的导航信号。在2017年1月,欧洲航天局通告称多颗卫星原子钟大规模故障。针对此,40m 大口径高增益天线系统设备对不同批次和星钟故障情况的3颗Galileo卫星E5频点信号进行了数据采集处理,对各信号分量的功率谱、星座图、码片波形、相关损失、相关峰、S曲线偏差等信号质量指标进行了分析评估。结果表明,此次星载原子钟的大面积故障并未影响Galileo卫星信号的可用性,足够的星载备份钟避免了信号质量的严重恶化。     

基于分布式地面站天线的空间功率合成

卫星导航系统(GNSS)地面站天线对卫星进行上行注入时,信号到达卫星时较弱,容易受到干扰,故地面站注入天线需同时具备平时多目标注入和干扰时单目标功率增强的能力。利用卫星导航系统中地面站之间能够实现精密时间同步的特点,提出了一种基于分布式卫星导航地面站抛物面天线的空间功率合成方法,使用相位预补偿实现分布式天线阵到达目标卫星信号的相位粗同步;分析了相位误差、辐射功率误差对空间功率合成效率的影响,得到了阵元初始相位标定精度与相对定位精度的约束关系;并对合成信号的抗干扰能力和信号质量进行了研究。理论和仿真结果表明,当相位精度因子小于0.2时,4个等辐射功率天线在10°仰角以上波束扫描范围内的功率合成效率均在75%以上,且可以通过控制初始相位标定精度与相对定位精度实现更高的合成效率;而在合成效率要求75%以上时,天线辐射功率误差对合成效率的影响基本可以忽略。采用分布式波束扫描天线能够对地面站上行注入进行功率增强,可实现注入波束和功率的灵活配置,有效解决制约机动式和小型化地面站功率提升的瓶颈问题。     

Argos海洋浮标多普勒定位原理与方法

通过对海洋浮标进行定位,Argos系统在海洋科学方面得到较为广泛的应用。但Argos系统卫星过顶弧段甚短,加之信号发射周期较长,测量资料甚为稀疏,给海洋浮标的定位造成很不利的影响,容易出现矩阵奇异情况,造成定位失败。文章给出了有效的基于多普勒测量的用于数据收集发射平台的定位算法,并利用参考椭球面约束定位目标,从而改进定位算法,计算结果显示如果能有效的使用约束条件,可以使：①原先定位失败的情形成功解算;②原先定位成功的情形定位精度得到改进。文章还给出了针对海洋目标信标运动以及卫星星历误差等因素对定位结果造成的误差影响的统计分析。     

Blind GPS receiver with a modified despreader for interference suppression

The global positioning system (GPS) was designed to provide location estimates for various civilian and military applications using at least four satellites. Since GPS signals have a low signal-to-noise ratio (SNR), they also have a low signal-to-jammer ratio so that the accuracy of location estimates is influenced by cochannel interference and intentional jammers. We propose a low-complexity blind adaptive receiver that is based on a novel modified despreader and the constant modulus (CM) array. This system is capable of ing directional interference and capturing the GPS signal of interest without requiring explicit angle-of-arrival (AOA) information. We also consider the multiple satellite problem and extend the proposed receiver to capture several GPS signals of interest. Representative computer simulation examples are presented to illustrate the performance of the multicomponent system for the suppression of different jammer types.     

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.     

Preliminary Evaluation of GPS Performance for Low-Cost General Aviation

Preliminary results of a simulation effort to evaluate the requirements and feasibility of the global positioning system (GPS) as a civil air navigation system are presented. Evaluation is made of GPS requirements, from operational considerations, such as application to nonprecision approaches. The conceptual low-cost GPS receiver simulated here does not correct for the ionospheric or trophospheric delay, is sequential in nature, tracks only four satellites, and is not mechanized to make independent range rate measurements based on the Doppler shift of the GPS carrier frequency. The proposed GPS system has significantly different performance characteristics from the presently used VHF omnidirectional range (VOR) solidus distance-measuring equipment (DME) system. The GPS is a low signal level system and many have a relatively slow data rate due to the low-cost sequential receiver design. The results indicate that although the conceptual low-cost GPS receiver/ navigator is potentially more accurate than a VOR, the accuracy may degrade during aircraft turns and satellite shielding periods.     

基于RTS滤波的GPS+BDS非差非组合PPP/INS紧组合模型

GPS高精度定位技术在动态复杂环境中,其定位精度、可靠性和连续性因卫星信号频繁失锁而变差。为此,提出了采用基于RTS滤波(Rauch-Tung-Striebel Filter)的GPS+BDS非差非组合PPP(Precise Point Positioning)与INS(Inertial Navigation System)紧组合模型的策略来克服GPS在动态定位中的弱点。其中,采用GPS+BDS双系统观测数据,可提高PPP解算中的可用卫星数,改善星站间定位几何强度和提高PPP收敛速度;采用PPP/INS紧组合,利用INS的自主定位特性和短期高精度特性,可有效改善复杂环境下的定位精度和连续性;采用RTS滤波,可进一步提高PPP/INS紧组合性能。首先推导了GPS+BDS非差非组合函数模型、PPP/INS紧组合函数模型和RTS滤波函数模型,然后利用一组车载动态数据,对动态GPS PPP、GPS+BDS PPP、GPS/INS紧组合、GPS+BDS PPP/INS紧组合和基于RTS的GPS+BDS PPP/IMU紧组合的定位、测速和定姿性能进行分析。实验结果表明,该方案可有效提高定位(58%～72%)、测速(74%～82%)和定姿(4%～23%)精度,特别是对卫星失锁期间的定位性能改善尤为明显。     

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.     

三星定位原理研究

双星定位系统只需要两颗同步卫星便可以为用户提供定位服务,但却存在着用户位置易暴露和用户数量易饱和这两大缺陷。建议采用三颗同步导航卫星像GPS卫星那样向用户播发导航电文,用户接收机根据这些导航电文信息以及气压高度表信息,像GPS接收机那样解算用户位置,从而克服了双星定位的两大缺陷。仿真表明本定位原理行之有效。     

Basic performance of BeiDou-2 navigation satellite system used in LEO satellites precise orbit determination

The visibility for low earth orbit（LEO） satellites provided by the BeiDou-2 system is analyzed and compared with the global positioning system（GPS）. In addition, the spaceborne receivers＇ observations are simulated by the BeiDou satellites broadcast ephemeris and LEO satellites orbits. The precise orbit determination（POD） results show that the along-track component accuracy is much better over the service area than the non-service area, while the accuracy of the other two directions keeps at the same level over different areas. However, the 3-dimensional（3D） accuracy over the two areas shows almost no difference. Only taking into consideration the observation noise and navigation satellite ephemeris errors, the 3D accuracy of the POD is about30 cm. As for the precise relative orbit determination（PROD）, the 3D accuracy is much better over the eastern hemisphere than that of the western hemisphere. The baseline length accuracy is 3.4 mm over the service area, and it is still better than 1 cm over the non-service area. This paper demonstrates that the BeiDou regional constellation could provide global service to LEO satellites for the POD and the PROD. Finally, the benefit of geostationary earth orbit（GEO） satellites is illustrated for POD.     

全球导航卫星系统的测高研究

以美国全球定位系统为代表的全球导航卫星系统具有广泛的应用领域，特点是能够在全球范围和近地空间，全天候地提供飞行器的位置、速度和时间信息。     

GNSS广域差分改正数估计方法研究

随着我国北斗三号基本系统的正式运行，基于地面监测站的广域差分增强系统成为进一步提升卫星导航定位精度的手段之一。在码噪声多径误差修正（CNMC）的基础上，使用等效钟差方法实现GNSS卫星轨道与钟差误差的解耦，并依据卫星轨道运动的动力学特性，引入希尔差分方程描述卫星轨道误差变化，实现对轨道误差的实时卡尔曼滤波估计。基于GPS实测数据，对改正前后的用户等效测距误差（UERE）和定位精度进行了对比研究。实验结果表明，采用该方法，UERE标准差由改正前的0.456 m减小至0.227 m，降幅达到50.22%；整体水平定位误差（95%置信区间）由0.981 m减小至0.782 m，垂直定位误差（95%置信区间）由1.991 m减小至1.131 m，分别提升了20.29%和43.19%，差分改正效果明显。