Virtual differential GPS based on SBAS signal

In order to access the satellite-based augmentation system (SBAS) service, the end user needs access to the corresponding geostationary earth orbit (GEO) satellites that broadcast the augmentation information for the region. This is normally not a problem for aviation and maritime applications, because an open sky is typically available for such applications. However, it is difficult to access the GEO satellites directly at high latitudes for land applications because of the low elevation angles to the GEO satellites (e.g., 4–22° in Finland to the European geostationary navigation overlay services [EGNOS] GEO satellites). Results from a driving test of 6,100 km in Finland show that the EGNOS GEO satellites can be accessed in only 51.8% of the driving routes. Furthermore, it is also difficult to access the GEO satellites from city canyons, because the high buildings block the GEO signals. This article presents a solution to solve this problem by creating virtual differential GPS (DGPS) reference stations using the SBAS signal in space (SIS). The basic concept is to convert the SBAS signal to Radio Technical Commission for Maritime Services (RTCM) signals, and broadcast the converted RTCM signals over the wireless Internet using the Internet radio technology. Therefore, access to the SBAS service will not be limited by low elevation angles to the GEO satellites because the converted RTCM data streams are disseminated over the wireless Internet. Furthermore, the SBAS service can then be accessed via a legacy DGPS receiver. Two test cases have been carried out with the prototype system developed by the Finnish Geodetic Institute. The test results showed that the positioning accuracy of the virtual DGPS solution was about 1–2 m at 95%, which was similar to that of the standard WAAS/EGNOS solution. The positioning accuracy was not degraded, compared to that of the standard wide area augmentation system–European geostationary navigation overlay services (WAAS/EGNOS) solution, as long as the distance between the rover receiver and the virtual DGPS reference station was less than 150 km. A preliminary driving test of 400 km carried out in southern Finland showed that the availability of the virtual DGPS solutions was 98.6% along the driving route.     

基于数理统计学的手持GPS测量精度测定

手持GPS是一种依靠GPS卫星进行定位、导航、数据采集的测绘仪器,以其操作简单、便于携带,具有一定的测量精度,在油田的井位踏勘、道路巡检、井位导航、距离量算、概略坐标采集等勘探开发工作中,得到了十分广泛的应用。本文以数理统计学原理和测量误差理论为基础,对手持GPS实际采集的坐标数据进行了分析、处理、计算,求取了手持GPS接收机的定位精度和实际定位误差,为手持GPS的适用范围提供了参考。      

Measured performance of the application of EGNOS in the road traffic sector

European Geostationary Navigation Overlay Service (EGNOS) is a satellite-based system developed to improve the performance of GPS in the European region. It not only enhances the estimated positioning accuracy but also provides an integrity solution. We assess the EGNOS performance through analysis of real measurements, performed in different road user environments. We investigate the use of the integrity concept in future Global Navigation Satellite System (GNSS)-based applications in the road environment, considering both suburban and dense urban areas. The analysis is motivated by the fact that there is an increasing number of road applications, such as billing system, transportation of dangerous goods, remote tracking of trucks and snow plows, fleet management and “pay as you go” car insurances, where the system liability has to be guaranteed. The scope of the analysis is to investigate to which extent the use of the integrity concept can be used for such purpose; the assessment is based on real measurement campaigns in representative environments, providing statistical results in terms of accuracy and integrity, and in a wider sense of the feasibility of the use of EGNOS for augmenting the reliability of GNSS positioning for road applications.     

Windows CE下手持电脑对GPS OEM板设置与通讯

简要介绍了手持电脑和Windows CE操作系统的特点。以CMC SuperStar GPS OEM板为例,讨论了在二进制和NMEA-0183两种格式下对GPS OEM板设置时的指令格式,详细介绍了利用Windows API函数对手持电脑的串口进行操作的方法,实现了在Windows CE环境下对GPS OEM板进行设置和导航定位数据及时间信息的提取与处理等功能。     

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。      

基于移动GIS的南疆天然气利民工程管道巡检系统设计与实现

设计的管道巡检系统由手持终端、无线服务网络、监控管理中心组成。在管道巡检工作中,巡检人员配置手持终端,手持终端将实时接收卫星发送的经度、纬度、时间等信息,且每隔3 min将定位信息及巡检时发现的事件状况信息通过GPRS无线服务网络发送给监控管理中心的数据库服务器中。监控管理中心的监控人员通过管道巡检系统平台对实时数据进行分析,对巡检工作及巡检事件进行处理,实现对巡检工作实时的管理。     

Development and testing of a new ray-tracing approach to GNSS carrier-phase multipath modelling

Multipath is one of the most important error sources in Global Navigation Satellite System (GNSS) carrier-phase-based precise relative positioning. Its theoretical maximum is a quarter of the carrier wavelength (about 4.8 cm for the Global Positioning System (GPS) L1 carrier) and, although it rarely reaches this size, it must clearly be mitigated if millimetre-accuracy positioning is to be achieved. In most static applications, this may be accomplished by averaging over a sufficiently long period of observation, but in kinematic applications, a modelling approach must be used. This paper is concerned with one such approach: the use of ray-tracing to reconstruct the error and therefore remove it. In order to apply such an approach, it is necessary to have a detailed understanding of the signal transmitted from the satellite, the reflection process, the antenna characteristics and the way that the reflected and direct signal are processed within the receiver. This paper reviews all of these and introduces a formal ray-tracing method for multipath estimation based on precise knowledge of the satellite–reflector–antenna geometry and of the reflector material and antenna characteristics. It is validated experimentally using GPS signals reflected from metal, water and a brick building, and is shown to be able to model most of the main multipath characteristics. The method will have important practical applications for correcting for multipath in well-constrained environments (such as at base stations for local area GPS networks, at International GNSS Service (IGS) reference stations, and on spacecraft), and it can be used to simulate realistic multipath errors for various performance analyses in high-precision positioning.     

Single receiver phase ambiguity resolution with GPS data

Global positioning system (GPS) data processing algorithms typically improve positioning solution accuracy by fixing double-differenced phase bias ambiguities to integer values. These “double-difference ambiguity resolution” methods usually invoke linear combinations of GPS carrier phase bias estimates from pairs of transmitters and pairs of receivers, and traditionally require simultaneous measurements from at least two receivers. However, many GPS users point position a single local receiver, based on publicly available solutions for GPS orbits and clocks. These users cannot form double differences. We present an ambiguity resolution algorithm that improves solution accuracy for single receiver point-positioning users. The algorithm processes dual- frequency GPS data from a single receiver together with wide-lane and phase bias estimates from the global network of GPS receivers that were used to generate the orbit and clock solutions for the GPS satellites. We constrain (rather than fix) linear combinations of local phase biases to improve compatibility with global phase bias estimates. For this precise point positioning, no other receiver data are required. When tested, our algorithm significantly improved repeatability of daily estimates of ground receiver positions, most notably in the east component by approximately 30% with respect to the nominal case wherein the carrier biases are estimated as real values. In this “static” test for terrestrial receiver positions, we achieved daily repeatability of 1.9, 2.1 and 6.0 mm in the east, north and vertical (ENV) components, respectively. For kinematic solutions, ENV repeatability is 7.7, 8.4, and 11.7 mm, respectively, representing improvements of 22, 8, and 14% with respect to the nominal. Results from precise orbit determination of the twin GRACE satellites demonstrated that the inter-satellite baseline accuracy improved by a factor of three, from 6 to 2 mm up to a long-term bias. Jason-2/Ocean Surface Topography Mission precise orbit determination tests results implied radial orbit accuracy significantly below the 10 mm level. Stability of time transfer, in low-Earth orbit, improved from 40 to 7 ps. We produced these results by applying this algorithm within the Jet Propulsion Laboratory’s (JPL’s) GIPSY/OASIS software package and using JPL’s orbit and clock products for the GPS constellation. These products now include a record of the wide-lane and phase bias estimates from the underlying global network of GPS stations. This implies that all GIPSY–OASIS positioning users can now benefit from this capability to perform single-receiver ambiguity resolution.     

基于GPRS的CORS网络差分模块设计

为了解决旧GPS设备在JSCORS系统下实现网络RTK的问题,基于通用无线分组业务（GPRS）设计了CORS网络差分模块。该模块采用GPRS／Internet无缝链接技术,通过Ntrip协议的顺从及分析,将其嵌入到模块中,建立了GPS差分数据传输通道。通过大量测试表明该CORS网络差分模块性能可靠。     

Time-Relative Positioning with a Single Civil GPS Receiver

Time-relative positioning is a recent method for processing GPS phase observations. The operational method undertaken in this paper consists of the following steps: first, recording phase observations at a station of known coordinates; second, moving the GPS receiver to an unknown station (which can be located up to a few hundred meters away, dependint on what type of transportation – e. g., walking, motorcycle – is available) while continuously observing carrier phases; and, third, recording phase observations at a second station of unknown coordinates with a single GPS receiver. To obtain the position of the unknown station relative to the first (known) station, the processing method uses combined observations taken at two different epochs and two different stations with the same receiver. For this reason, the errors that vary between two epochs must be taken into account in an appropriate way, especially errors in satellite clock corrections and ephemerides, and errors related to tropospheric and ionospheric delays. Ionospheric modeling using IONEX files (the ionospheric maps calculated by the International GPS Service) was also tested to correct L1 phase observations. This method has been used to calculate short vectors with an accuracy of a few centimeters (for a processing interval of 30 s) using a single civil GPS receiver. ? 2001 John Wiley & Sons, Inc.     

GPS天线阵列接收机及其配套软件

介绍GPS天线阵列接收机产生的背景,简述GPS天线阵列接收机的工作原理和系统的组成,包括PDA控制系统、GPS信号放大器、无线传输系统。重点论述配套的处理软件和在线灾害监测分析系统,指出该接收机及其配套软件具有成本低廉、实用性强、安全性高、预测模型先进等优点,展望了其在灾害监测方面很好的市场推广前景。     

Definition of a reconfigurable and modular multi-standard navigation receiver

The growth of innovative positioning-related services and applications within the wireless mass-market, and the green light for the development and modernization of Global Navigation Satellite Systems (GNSS) catalyze the research activity in the navigation field both at the system and user levels. In addition, different government institutions are working toward the definition of navigation plans and regulations which will require accurate locations of mobile users in case of emergency (US E-911 law and the European E-112 directive). From the technical standpoint, within every navigation/positioning system which will be available in the near future, the user terminal will play a central role. In fact, if navigation signals from different sources are available, the unique possibility to obtain the best navigation performance from the user perspective will be the employment of enhanced smart receivers able to fuse different data. With this aim, the Software Defined Radio (SDR) technology can be successfully employed for the design of innovative navigation receivers. The main goal of this paper is to present the overall SDR receiver architecture, focusing attention on reconfigurability and flexibility issues which are guaranteed by the use of reprogrammable high-speed hardware (FPGA–Field Programmable Gate Array and DSP–Digital Signal Processor). The direct benefit of such an implementation is the possibility to obtain a deep integration at the raw signal level between GPS and the future Galileo; the interoperability issue among different systems is then solved at the receiver level. Electronic Publication     

From GPS and GLONASS via EGNOS to Galileo – Positioning and Navigation in the Third Millennium

Positioning and navigation – as are presently possible with the American Global Positioning System (GPS) and the Russian GLONASS system – is briefly reviewed. Deficiencies, which have led to augmentations like the European Geostationary Navigation Overlay System (EGNOS), are outlined. Europe's decision to get involved in the definition and possible set-up of a Global Navigation Satellite System (GNSS) of the second generation (GNSS-2), called Galileo, is discussed in detail as well as the GPS modernization program that might take place during the sample phase. Finally, some brief thoughts on the benefit of GNSS-2 for geodesy and surveying are given. ? 2000 John Wiley & Sons, Inc.     

GBAS testbed development in Taiwan with a prototype GPS/GBAS receiver

In this paper, we present the development of a local area differential GPS testbed of the ground-based augmentation system (GBAS) as the future airport navigation facility in the Taipei Flight Information Region (FIR) in Taiwan. The testbed is mainly a GBAS ground facility, which consists of a ground station, three GBAS receivers, and a VDL (VHF data link) broadcast antenna. We also present an airborne GPS/GBAS prototype receiver in this paper. The airborne subsystem (a GPS/GBAS receiver) receives the correction messages from the ground subsystem to perform a differential GPS (DGPS) positioning. In order to provide an ILS-look-alike approach and landing, the output messages of the airborne receiver are packed in an ARINC 429 format. The proposed airborne system has a software-based global navigation satellite system (GNSS) receiver structure.     

Performance of Singapore Integrated Multiple Reference Station Network (SIMRSN) for RTK Positioning

Conventional RTK positioning is usable, but requires the use of a local base station. It is also restricted by the effects of the de-correlate atmospheric refraction on the GPS signal, which limits the use of the RTK positioning up to distances of 10–15 km from the reference station to the user. With a multiple reference station network approach, precise RTK positioning capability may be extended for a much larger area. The Singapore Integrated Multiple Reference Station Network (SIMRSN) has been established for this purpose. Using an existing method termed linear combination method, the multiple reference station network corrections are generated for the user on an epoch by epoch, satellite-by-satellite basis. A residual-based adaptive Kalman filter is proposed to improve network correction availability. The VRS concept is used to transmit corrections to the user for RTK positioning. Field tests were conducted to demonstrate the general performance of SIMRSN. The tests confirmed that RTK positioning within a multiple reference station network can provide the user with better than 3 cm in horizontal position, the height accuracy is in the range of 1–7 cm, and the average TTF (Time To Fix) are 46 and 76 s during GLC station and LPR station tests, respectively. With this highly efficient survey technique, the user needs only to be equipped with a single GPS receiver. This reduces equipment and manpower costs compared with traditional RTK positioning using a specially set up reference station. The multiple reference station framework also paves the way for various other applications beyond the traditional surveying profession. Electronic Publication     

GPS定位系统中的几种对流层模型

对流层折射对GPS定位精度产生重要影响。着重介绍了目前卫星定位领域主要应用的一些对流层折射修正模型。     

First comparisons of precipitable water vapor estimation using GPS and water vapor radiometers at the Royal Observatory of Belgium

We compare precipitable water vapor (PWV) time series measured by water vapor radiometers (WVRs) to PWV time series estimated using global positioning system (GPS) observations in a regional network of stations in western Europe. Inside this network, we focus on the baseline Brussels – Wettzell which presents the advantage to have the collocation of a GPS receiver and a WVR at both endpoints. The comparison between our GPS and WVR estimations of precipitable water vapor shows an agreement at the millimeter level. In addition, we show that the zenith total delay (ZTD) estimations computed with our GPS processing strategy agrees with the GPS estimations of ZTD done by the CODE analysis center at the millimeter level. Electronic Publication     

Enhancing mobile applications by combination of GNSS and W-CDMA

The location requirements for emergency callers outside urban areas can hardly be fulfilled without global navigation satellite systems (GNSS). Consequently, interest in positioning techniques based on use of a GNSS such as GPS or on the cellular network infrastructure itself is growing rapidly in the mobile-telephone community. Moreover, the increasing demand for commercial location-based services (LBS) has driven cellular-phone and network manufacturers to focus on positioning solutions which are even more accurate than the regulatory mandates for positioning of emergency callers. One example of these upcoming LBS is our PARAMOUNT project, which aims at improving user-friendly info-mobility services for hikers and mountaineers by combining wireless communications (GMTS), satellite navigation (GNSS) and geographic information systems (GIS), based on a mobile client/server architecture. The availability of mobile phones or PDAs with combined GNSS and cellular network-based wireless communication on a high integration level is one primary demand of such LBS applications. Based on this, we will give some initial answers to the question of whether mobile handset architecture synergies exist for the combination of GNSS with wireless location in CDMA cellular wireless networks. In order to identify synergies, we will outline similarities and differences between wireless communication and satellite navigation. In this respect, we pay particular attention to the so-called RAKE receiver architecture employed in mobile CDMA cellular handsets. Our initial investigations will show that the RAKE receiver architecture, on which mobile CDMA cellular handsets are based, will most likely be the one most suitable for achieving synergies between the two positioning techniques within the same mobile handset architecture. Consequently, several receiver components could be used to handle both types of signals (navigation and communications), resulting in a reduction of manufacturing costs and in a decrease in energy consumption. Electronic Publication     

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。