Access to the EGNOS signal in space over mobile-IP

The EGNOS service will provide better positioning availability and accuracy than that from the standalone GPS solutions. However, in order to access the EGNOS service, the end user needs to access the corresponding GEO satellites that broadcast the augmentation information for the region. This is not a problem normally for aviation and maritime applications because an open sky is always available for such applications. However, an open sky is not always available for land applications because of the obstacles in the vicinity of the end users, for example, in the city canyons. The situation gets worse for the regions at high latitudes because the elevation angles to the GEO satellites are rather low (e.g. 4–22° in Finland). This article describes briefly the SISNeT technology, designed and developed by the European Space Agency, which allows accessing the EGNOS SIS via the Internet. It will describe in detail the handheld SISNeT receiver, designed and developed by the Finnish Geodetic Institute under ESA contract. The SISNeT data server is an IP-based server that acquires the EGNOS messages from an EGNOS receiver, and broadcasts them over the Internet in real-time. The handheld receiver consists of a GPS PC-card receiver, a GPRS (or GSM) card phone, and a pocket PC as the host platform. The receiver software is a Windows CE-based package with a multi-process and multi-thread architecture. It simultaneously receives: (1) the EGNOS SIS over a GPRS wireless connection and the Internet and (2) the NMEA messages from a serial connection to a GPS receiver. It decompresses and decodes the EGNOS messages, and utilizes the information in the messages to estimate the EGNOS-corrected coordinates, which are finally delivered to the end user via a virtual COM port. The virtual COM port has been implemented as a stream interface driver in the Pocket PC. It can be accessed in the same way as the physical COM port in a GPS receiver is accessed. Therefore, it is easy to interface to any third-party applications. The test results show that the handheld SISNeT receiver can provide a positioning accuracy of about 1–2 m for the horizontal components, and 2–3 m for the vertical component in real time. Due to the poor performance of the wireless connection, 10–30% of the EGNOS messages can be lost depending on the services provided by the wireless network operators. The impact of the messages lost on the positioning accuracy is about 0.5 m in both the horizontal and vertical components. Electronic Publication     

基于RTCA标准的WAAS和EGNOS广播星历差分完好性服务性能研究

为了提高GPS卫星导航系统服务性能,很多国家和地区建立了独立的星基增强系统(SBAS),通过提供广播星历差分与完好性增强信息,满足高精度高完好性用户使用需求。本文介绍了美国WAAS和欧洲EGNOS等星基增强系统的广播星历差分完好性信息电文编码格式,并对实际星基增强系统的广播星历差分与完好性电文进行解析。由于不同的星基增强系统采用的信息处理模式不同,针对WAAS和EGNOS两个不同地区建立的星基增强系统,对广播星历差分慢变改正／快变改正的变化特征进行了比较分析。研究了星基增强系统广播星历差分完好性信息用户使用算法,基于国际GNSS服务组织(IGS)提供的GPS实测数据,对WAAS系统和EGNOS系统的广播星历差分服务精度和完好性性能进行了对比分析。结果表明,WAAS系统的伪距单点定位精度约为1.2 m, EGNOS系统的伪距单点定位精度约为1.8 m,与GPS基本导航服务相比,伪距单点定位精度可提高约22％和16％。两个星基增强系统利用完好性电文计算的完好性保护限值大致相当,均在16 m以内,能够对定位误差进行包络。      

SBAS orbit and satellite clock corrections for precise point positioning

The quality of real-time GPS positions based on the method of precise point positioning (PPP) heavily depends on the availability and accuracy of GPS satellite orbits and satellite clock corrections. Satellite-based augmentation systems (SBAS) provide such corrections but they are actually intended to be used for wide area differential GPS with positioning results on the 1-m accuracy level. Nevertheless, carrier phase-based PPP is able to achieve much more accurate results with the same correction values. We applied SBAS corrections for dual-frequency PPP and compared the results with PPP obtained using other real-time correction data streams, for example, the GPS broadcast message and precise corrections from the French Centre National d’Etudes Spatiales and the German Deutsches Zentrum für Luft- und Raumfahrt. Among the three existing SBAS, the best results were achieved for the North American wide area augmentation system (WAAS): horizontal and vertical position accuracies were considerably smaller than 10 cm for static 24-h observation data sets and smaller than 30 cm for epoch-by-epoch solutions with 2 h of continuous observations. The European geostationary navigation overlay service and the Japanese multi-functional satellite augmentation system yield positioning results with biases of several tens of centimeters and variations larger by factors of 2–4 as compared to WAAS.     

GNSS satellite-based augmentation systems for Australia

We provided an overview of various satellite-based augmentation systems (SBAS) options for augmented GNSS services in Australia, and potentially New Zealand, with the aim to tease out key similarities and differences in their augmentation capabilities. SBAS can technically be classified into two user categories, namely SBAS for aviation and “non-aviation” SBAS. Aviation SBAS is an International Civil Aviation Organization (ICAO) certified civil aviation safety-critical system providing wide-area GNSS augmentation by broadcasting augmentation information using geostationary satellites. The primary aim was to improve integrity, availability and accuracy of basic GNSS signals for aircraft navigation. On the other hand, “non-aviation” SBAS support numerous GNSS applications using positioning techniques such as wide-area differential-GNSS (DGNSS) and precise point positioning (PPP). These services mainly focus on delivering high-accuracy positioning solutions and guaranteed levels of availability, and integrity remains secondary considerations. Next-generation GNSS satellites capable of transmitting augmentation signals in the L1, L5 and L6 frequency bands will also be explored. These augmentation signals have the data capacity to deliver a range of augmentation services such as SBAS, wide-area DGNSS and PPP, to meet the demands of various industry sectors. In addition, there are well-developed plans to put in place next-generation dual-frequency multi-constellation SBAS for aviation. Multi-constellation GNSS increases robustness against potential degradation of core satellite constellations and extends the service coverage area. It is expected that next-generation SBAS and GNSS will improve accuracy, integrity, availability and continuity of GNSS performance.     

EGNOS电离层延迟改正数分析

EGNOS是一个广域增强系统,向用户提供电离层改正数是其服务内容的一部分。本文分析了EGNOS电离层改正数的结构,介绍了用户的电离层改正数算法流程。结合EGNOS在中国测试的实际数据,对EGNOS电离层改正数进行了分析。通过对EGNOS的电离层改正数分析可以为我国的广域增强系统提供技术参考。     

SBAS监测站构成及部署方法分析

星基增强系统(SBAS)可以增强全球卫星导航系统（GNSS）的定位精度和完好性服务等性能,满足以民航用户为主的服务需求．地面监测站是SBAS的重要组成部分,其构成、布局、数据质量等对星基增强系统的服务性能具有重要的影响．因此,本文以美国WAAS和欧洲EGNOS实测数据为基础,对地面监测站的构成及分布,监测站天线分布、监测站数据质量以及多路径相关性进行了详细的分析,总结出适用SBAS系统地面监测站构成及部署的通用方法,为SBAS监测站建设的实施途径提供参考．      

Improving BeiDou precise orbit determination using observations of onboard MEO satellite receivers

In recent years, the precise orbit determination (POD) of the regional Chinese BeiDou Navigation Satellite System (BDS) has been a hot spot because of its special constellation consisting of five geostationary earth orbit (GEO) satellites and five inclined geosynchronous satellite orbit (IGSO) satellites besides four medium earth orbit (MEO) satellites since the end of 2012. GEO and IGSO satellites play an important role in regional BDS applications. However, this brings a great challenge to the POD, especially for the GEO satellites due to their geostationary orbiting. Though a number of studies have been carried out to improve the POD performance of GEO satellites, the result is still much worse than that of IGSO and MEO, particularly in the along-track direction. The major reason is that the geostationary characteristic of a GEO satellite results in a bad geometry with respect to the ground tracking network. In order to improve the tracking geometry of the GEO satellites, a possible strategy is to mount global navigation satellite system (GNSS) receivers on MEO satellites to collect the signals from GEO/IGSO GNSS satellites so as that these observations can be used to improve GEO/IGSO POD. We extended our POD software package to simulate all the related observations and to assimilate the MEO-onboard GNSS observations in orbit determination. Based on GPS and BDS constellations, simulated studies are undertaken for various tracking scenarios. The impact of the onboard GNSS observations is investigated carefully and presented in detail. The results show that MEO-onboard observations can significantly improve the orbit precision of GEO satellites from metres to decimetres, especially in the along-track direction. The POD results of IGSO satellites also benefit from the MEO-onboard data and the precision can be improved by more than 50% in 3D direction.     

The ionospheric impact of the October 2003 storm event on Wide Area Augmentation System

The United States Federal Aviation Administrations (FAA) Wide-Area Augmentation System (WAAS) for civil aircraft navigation is focused primarily on the Conterminous United States (CONUS). Other Satellite-Based Augmentation Systems (SBAS) include the European Geostationary Navigation Overlay Service (EGNOS) and the Japanese Multi-transport Satellite-based Augmentation System (MSAS). Navigation using WAAS requires accurate calibration of ionospheric delays. To provide delay corrections for single frequency global positioning system (GPS) users, the wide-area differential GPS systems depend upon accurate determination of ionospheric total electron content (TEC) along radio links. Dual-frequency transmissions from GPS satellites have been used for many years to measure and map ionospheric TEC on regional and global scales. The October 2003 solar-terrestrial events are significant not only for their dramatic scale, but also for their unique phasing of solar irradiance and geomagnetic events. During 28 October, the solar X-ray and EUV irradiances were exceptionally high while the geomagnetic activity was relatively normal. Conversely, 29–31 October was geomagnetically active while solar irradiances were relatively low. These events had the most severe impact in recent history on the CONUS region and therefore had a significant effect on the WAAS performance. To help better understand the event and its impact on WAAS, we examine in detail the WAAS reference site (WRS) data consisting of triple redundant dual-frequency GPS receivers at 25 different locations within the US. To provide ground-truth, we take advantage of the three co-located GPS receivers at each WAAS reference site. To generate ground-truth and calibrate GPS receiver and transmitter inter-frequency biases, we process the GPS data using the Global Ionospheric Mapping (GIM) software developed at the Jet Propulsion Laboratory. This software allows us to compute calibrated high resolution observations of TEC. We found ionospheric range delays up to 35 m for the day-time CONUS during quiet conditions and up to 100 m during storm time conditions. For a quiet day, we obtained WAAS planar fit slant residuals less than 2 m (0.4 m root mean square (RMS)) and less than 25 m (3.4 m RMS) for the storm day. We also investigated ionospheric gradients, averaged over distances of a few hundred kilometers. The gradients were no larger than 0.5 m over 100 km for a quiet day. For the storm day, we found gradients at the 4 m level over 100 km. Similar level gradients are typically observed in the low-latitude region for quiet or storm conditions.     

北斗伪距码偏差对基线解算的影响分析

北斗二代系统伪距码中存在与高度角相关的系统性偏差,该偏差会影响高精度的数据处理。基于Melbourne-Wübbena（MW）组合,分别利用现有的伪距码偏差改正模型和实测基线的双差宽巷模糊度残差,分析了伪距码偏差对基线解算的影响。理论分析表明,随着基线长度的增加,伪距码偏差对MW组合确定双差宽巷模糊度的影响越来越大,对300 km基线的影响可达0.36周。实际算例表明,无论基线长短,地球同步轨道（geostationary earth orbit,GEO）卫星的双差宽巷模糊度残差中始终存在偏差;而对于倾斜地球同步轨道（inclined geostationary orbit,IGSO）和中轨（medium earth orbit,MEO）卫星而言,当基线小于300 km时,双差基本可以消除伪距码偏差,其双差宽巷模糊度固定率基本和GPS一致,但当基线超过300 km时,部分卫星的双差宽巷模糊度残差就会存在明显偏差,其双差宽巷模糊度固定率也较低,此时需考虑伪距码偏差的影响。     

GNSS技术在GEO、IGSO航天器中的导航精度与适用性分析

现阶段高轨道航天器导航主要依靠地基测控系统,为了研究全球卫星导航系统(GNSS)技术用于高轨道航天器导航的可行性,对GNSS技术在地球静止轨道(GEO)卫星、倾斜地球同步轨道(IGSO)卫星航天器中的导航精度及适用性展开了分析研究. 采用2021年11月9日的两行轨道数据(TLE)仿真GNSS星座,以不同星下点的GEO卫星和不同倾角的IGSO卫星作为目标星展开导航仿真试验. 实验结果表明:为了满足GNSS解算所需的卫星数量,须通过接收旁瓣信号来增加可见卫星数目. 对GEO目标星而言,当接收机灵敏度高于?169 dB时,导航精度可达30 m;利用GPS对7个不同的GEO或IGSO轨道目标星进行导航实验表明,GPS对目标星导航的位置误差约为35 m;北斗三号(BDS-3)、GPS、GLONASS、Galileo的导航位置误差均值分别为28.03 m、21.16 m、37.15 m、25.09 m,具有良好的内符合精度,其中GPS精度最高,GLONASS精度最低,但大部分时段也在45 m内.      

中国GPS增强系统性能分析及技术发展

本文提出了一种GPS卫星导航增强系统技术性能分析方法,即利用IGS提供的高精度GPS星历、卫星钟差数据和电离层数据作为外符和检测标准,检验增强系统提供的卫星星历改正数据、卫星钟差改正数据和电离层改正数据的精度。通过实测数据分析表明,我国GPS卫星导航增强系统目前的服务性能与国外同类系统具有一定的差距,主要的技术薄弱环节在于GPS卫星的精密定轨与钟差解算技术。     

利用两颗退役同步轨道卫星优化中国区域定位系统导航性能的分析

中国区域定位系统（CAPS）在试验验证阶段利用两颗同步轨道（GEO）通信卫星和两颗退役的GEO通信卫星组成导航星座,结合CAPS气压测高技术实现三维定位。根据CAPS的星座特点,分析了不采用气压测高实现转发式卫星导航定位的可行性和改变退役卫星轨道参数对星座PDOP值的影响。结果表明：调整两颗退役GEO通信卫星的轨道参数后,不采用气压测高技术也可以使CAPS在一天的较长时段内实现较高精度的导航定位。     

Beidou satellite maneuver thrust force estimation for precise orbit determination

Beidou satellites, especially geostationary earth orbit (GEO) and inclined geosynchronous orbit (IGSO) satellites, need to be frequently maneuvered to keep them in position due to various perturbations. The satellite ephemerides are not available during such maneuver periods. Precise estimation of thrust forces acting on satellites would provide continuous ephemerides during maneuver periods and could significantly improve orbit accuracy immediately after the maneuver. This would increase satellite usability for both real-time and post-processing applications. Using 1 year of observations from the Multi-GNSS Experiment network (MGEX), we estimate the precise maneuver periods for all Beidou satellites and the thrust forces. On average, GEO and IGSO satellites in the Beidou constellation are maneuvered 12 and 2 times, respectively, each year. For GEO satellites, the maneuvers are mainly in-plane, while out-of-plane maneuvers are observed for IGSO satellites and a small number of GEO satellites. In most cases, the Beidou satellite maneuver periods last 15–25 min, but can be as much as 2 h for the few out-of-plane maneuvers of GEO satellites. The thrust forces acting on Beidou satellites are normally in the order of 0.1–0.7 mm/s². This can cause changes in velocity of GEO/IGSO satellites in the order of several decimeters per second. In the extreme cases of GEO out-of-plane maneuvers, very large cross-track velocity changes are observed, namely 28 m/s, induced by 5.4 mm/s² thrust forces. Also, we demonstrate that by applying the estimated thrust forces in orbit integration, the orbit errors can be estimated at decimeter level in along- and cross-track directions during normal maneuver periods, and 1–2 m in all the orbital directions for the enormous GEO out-of-plane maneuver.     

Orbit and clock analysis of Compass GEO and IGSO satellites

China is currently focussing on the establishment of its own global navigation satellite system called Compass or BeiDou. At present, the Compass constellation provides four usable satellites in geostationary Earth orbit (GEO) and five satellites in inclined geosynchronous orbit (IGSO). Based on a network of six Compass-capable receivers, orbit and clock parameters of these satellites were determined. The orbit consistency is on the 1–2 dm level for the IGSO satellites and on the several decimeter level for the GEO satellites. These values could be confirmed by an independent validation with satellite laser ranging. All Compass clocks show a similar performance but have a slightly lower stability compared to Galileo and the latest generation of GPS satellites. A Compass-only precise point positioning based on the products derived from the six-receiver network provides an accuracy of several centimeters compared to the GPS-only results.     

CEI对静止轨道共位卫星的轨道确定

主要考察了CEI对静止轨道共位卫星的轨道确定能力。仿真结果表明,利用CEI对共位卫星进行定轨时,需采用基线阵列。对于110°E共位卫星采用三亚-昆明基线阵列、10 km基线和2 d的数据,可使绝对轨道精度达百米级;外推至14 d时,相对轨道精度保持在m级。同样,要使绝对和相对轨道精度达到相同的量级,对于80°E共位卫星,需选用昆明-三亚基线阵列、100 km基线和1 d的观测弧段;对于140°E共位卫星,需选用上海-三亚基线阵列5、0 km基线和2 d的观测弧段。     

SBAS星历改正数及UDRE参数生成算法分析

星基增强系统(satellite based augmentation system,SBAS)通过地球同步轨道卫星实时播发导航卫星星历改正数和完好性参数,以提升用户定位精度和完好性。采用最小方差法解算GPS星历改正数,利用卡方统计进行改正数完好性检核,并依据星历改正数方差-协方差信息计算SBAS用户差分距离误差(user differential range error,UDRE)和信息类型28(message type 28, MT28)等完好性参数。利用中国区域27个监测站的实测数据,首先以国际GNSS服务组织的精密轨道和钟差产品为参考解算星历改正数,结果表明,钟差改正精度优于0.1 m,轨道改正精度优于0.4 m;然后解算广播星历改正数,并生成UDRE和MT28参数,广播星历残余误差卡方检验值均小于告警门限,保证了改正数的完好性;最后利用生成的改正数进行SBAS定位解算,得到定位结果的水平精度优于0.7 m,垂直精度优于1.0 m,对比GPS单点定位,所提算法的水平和垂直方向精度分别提升了30%和40%。     

关于建设北斗星基广域增强系统研究

鉴于GPS系统已经成熟,北斗导航系统建设尚不完善,本文考虑建设北斗卫星对GPS卫星的增强系统。一方面,采用GPS/Compass-Ⅱ组合卫星导航系统,可大大增加某一时刻的可见卫星数,增强导航定位系统的可靠性。另一方面,北斗现已发射第九颗导航卫星,其中包括5颗地球静止轨道卫星,本文重点探讨利用这5颗GEO(Geostationary Orbit,GEO)卫星对GPS系统进行外部增强,即北斗GEO卫星同时播发卫星导航电文和增强信息,提高用户定位精度。     

顾及GEO卫星约束的长距离BDS三频整周模糊度解算

长距离BDS三频载波相位整周模糊度解算受大气误差残余的影响较大,GEO卫星相对于地球静止也非常不利于载波相位整周模糊度的解算。利用GEO卫星的信号传播路径相对较稳定、大气延迟误差的影响不随卫星空间位置变化的特点,对GEO卫星进行更符合实际情况的大气延迟误差约束研究。利用GEO卫星B2和B3载波相位整周模糊度线性关系,降低测站差分电离层延迟误差残余对模糊度备选值的影响,进行B2和B3载波相位整周模糊度备选值的选择。通过三频载波相位整周模糊度间不包含观测误差影响的线性关系对模糊度备选值组合进行检测,并对模糊度搜索空间进行约束。利用历元间GEO卫星的模糊度备选值判断历元间电离层延迟误差残余的变化,对GEO卫星的参数估计进行更符合实际情况的约束。研究了顾及GEO卫星实际大气延迟变化和整周模糊度约束的长距离BDS三频载波相位整周模糊度解算方法。提出了利用历元间模糊度备选值确定电离层延迟约束值的方法,对GEO卫星历元间随机游走的约束值进行符合实际情况的调整。试验结果表明,本文的方法能够提高三频载波相位整周模糊度解算的效率和测站位置的精度。     

GEO卫星Hill方程的分析型解法

提出并实现了一种求解静地轨道GEO(geostationary orbit)卫星Hill方程摄动解的分析型方法。根据地固坐标系下GEO卫星运动的特点,在其定点处把摄动力进行泰勒展开,通过选择特定的参考轨道获得了GEO卫星的地球扁率摄动解。在此基础上,成功地将拉普拉斯变换运用于GEO卫星的Hill方程,得到了一组可用于求解摄动分析解的递推积分公式。通过逐次趋近的方法,利用这组积分公式可以有效地实现由低阶解推求高阶解。     

DGPS and RTK Positioning Using the Internet

The Internet as a basis for Real-Time Kinematic (RTK) and differential Global Positioning System (DGPS) service provides many advantages for worldwide GPS users. Among these advantages are service unification, open architecture, bidirectional communication, and scalability. The current development of this service allows users to use RTK and DGPS through the Internet with conventional accuracy over the short and medium baselines. The perspective for this service lies in the field of wide-area augmentation systems (WASS). At this stage of the Internet-based RTK and DGPS service project, the general concept, system components, draft standards, and software are developed. ? 2000 John Wiley & Sons, Inc.