Phase modulated DGPS transmitter implemented with a clamped-mode resonant converter

A clamped-mode resonant converter (CMRC) is proposed to be used as a transmitter which broadcasts correction signals in a differential Global Positioning System (DGPS). The digital information of the DGPS modulates the carrier with different modulation methods minimum shift keying (MSK) (recommended for the marine radiobeacon band), stepped binary phase shift keying (S-BPSK) and BPSK. The first two methods allow keeping the converter's operation in soft switching mode. Extensive trials under impedance mismatch and modulation conditions confirm that the soft switching mode is preserved.     

Reduction of interference from DGPS transmissions in the MF bandusing a GMSK modulation scheme

The accuracy of the Global Positioning System (GPS) can be improved by differential techniques. For maritime applications a DGPS service with transmissions by maritime radiobeacons in the MF band is provided. It offers a position accuracy of approximately 5 m. For the data link a minimum shift keying (MSK) modulation scheme has been recommended. The adjacent channel interference at the maximum transmission rate might not be consistent with existing frequency plans     

用于SAR运动补偿的DGPS/SINS组合系统研究

使用考虑位置误差相关项的伪距率观测模型 ,研究了用于合成孔径雷达运动补偿的差分 GPS/ SINS伪距率组合系统。结果表明 ,组合系统的长期位置精度能达到 1 m左右。 GPS数据更新率低于 INS,在 GPS测量时间间隔内 ,组合系统的性能仅由 INS决定。虽然 INS误差随时间积累 ,在 GPS数据更新率为 1 s的情况下 ,即使采用中等精度的惯性仪表 ,其相对位置精度为厘米级 (这里相对位置精度指组合系统在 GPS测量时间间隔内位置误差的变化范围)。     

Differential GPS/inertial navigation approach/landing flight testresults

In November 1990, a differential GPS/inertial flight test was conducted to acquire a system performance database and demonstrate automatic landing using an integrated differential GPS/INS with barometric and radar altimeters. Flight test results obtained from postflight data analysis are presented. These results include characteristics of DGPS/inertial error, using a laser tracker as a reference. In addition, data are provided on the magnitude of the differential correlations and vertical channel performance with and without radar altimeter augmentation. Flight test results show one sigma DGPS/inertial horizontal errors of 9 ft and one sigma DGPS inertial vertical errors of 15 ft. Without selective availability effects, the differential corrections are less than 10 ft and are dominated by receiver unique errors over the time period of an approach. Therefore, the one sigma performance of the autonomous GPS (8-ft horizontal and 20-ft vertical) is very similar to the DGPS/inertial performance. Postprocessed results also demonstrate significant improvements in vertical channel performance when GPS/inertial is aided with radar altimeter along with a low-resolution terrain map     

RESEARCH ON THE METHODS OF IMPROVING DGPS POSITIONING PRECISION

A DGPS positioning model is described, and the elements that influence DGPS positioning precision are analyzed in detail. On this basis, the methods of improving DGPS positioning precision are proposed which include increasing updating rate of DGPS correction, building extended DGPS system and improving quality of DGPS correction signal. In the intelligent monitor and control system of the public transport in Beijing, these methods improve the vehicle positioning precision to 2～5m.     

Medium frequency broadcast of differential GPS data

The broadcast performance of DGPS (differential global positioning systems)/radio beacons is studied. It is found that a combination of receiver limiting and forward error corrections is very effective against the atmospheric noise which characterizes the MF band. This combination significantly reduces the probability of bit error and the average time between differential updates. The authors compute the probability of link outage versus range, and find that forward error correction significantly increases DGPS/radio beacon coverage. It is found that groundwave/skywave interference slightly increases the probability of outage at moderate ranges. An estimate is made of the expected duration of outage for the DGPS/radio beacon signal. All results are based on analytical and experimental results     

Aircraft traffic management on the airport surface using VHF datalink for CNS

Aircraft traffic management on the airport surface will require the effective utilization of communications, navigation and surveillance (CNS). This paper describes an experiment which provides a glimpse of future automation. The experiment combines precision surface radar, high-accuracy differential GPS (DGPS) position determination, automatic dependent surveillance (ADS), and ground and airborne automation systems able to intercommunicate via a VHF data link. In particular, this paper describes the air/ground communications provided by the VHF Data Link. Two classes of messages are processed: continual and ad hoc. The former include DGPS corrections, ADS messages and target data. The latter include graphical taxi clearances and hold bar set-reset information. The work described in this paper is the result of a cooperative venture among NASA, Westinghouse-Norden Systems and ARINC     

Relative navigation for multi-spacecraft system with GPS

A type of multi-spacecraft system with kinematical restraint but no structural restraint and force action is considered. Both the absolute and relative navigation information is required for this multi-spacecraft system, but the relative information is more critical and the accuracy requirements for relative information will be much higher than those for the absolute information. In this paper, the Global Positioning System (GPS)/Differential GPS (DGPS) are introduced and used for relative navigation. Relative motion of space vehicles is modeled. Relative position, relative velocity and relative attitude are represented and solved by GPS/DGPS measurements. Using a type of commercial GPS receiver onboard spacecraft and relative differential GPS technique, the relative navigation of space vehicles can be implemented in real-time     

Online INS/GPS integration with a radial basis function neural network

Most of the present navigation systems rely on Kalman filtering to fuse data from global positioning system (GPS) and the inertial navigation system (INS). In general, INS/GPS integration provides reliable navigation solutions by overcoming each of their shortcomings, including signal blockage for GPS and growth of position errors with time for INS. Present Kalman filtering INS/GPS integration techniques have some inadequacies related to the stochastic error models of inertial sensors, immunity to noise, and observability. This paper aims to introduce a multi-sensor system integration approach for fusing data from INS and GPS utilizing artificial neural networks (ANN). A multi-layer perceptron ANN has been recently suggested to fuse data from INS and differential GPS (DGPS). Although being able to improve the positioning accuracy, the complexity associated with both the architecture of multi-layer perceptron networks and its online training algorithms limit the real-time capabilities of this technique. This article, therefore, suggests the use of an alternative ANN architecture. This architecture is based on radial basis function (RBF) neural networks, which generally have simpler architecture and faster training procedures than multi-layer perceptron networks. The INS and GPS data are first processed using wavelet multi-resolution analysis (WRMA) before being applied to the RBF network. The WMRA is used to compare the INS and GPS position outputs at different resolution levels. The RBF-ANN module is then trained to predict the INS position errors and provide accurate positioning of the moving platform. Field-test results have demonstrated that substantial improvement in INS/GPS positioning accuracy could be obtained by applying the combined WRMA and RBF-ANN modules.     

无人机下滑着陆DGPS/INS导航及引导系统的仿真与试验研究

介绍了一种采用输出校正方式DGPS/INS组合导航系统引导无人机下滑着陆的方案。给出了该方案的数学模型,对组合导航系统进行了数字仿真,并在数字仿真的基础上进行了动态跑车试验,验证了所设计的输出校正方式DGPS/INS组合导航系统能够满足引导无人机自动下滑着陆的精度要求。     

差分GPS在飞行试验中的应用

ＧＰＳ是美国正在大力发展的高精度卫星导航系统。主要叙述差分ＧＰＳ在飞行试验中的应用，首先介绍ＧＰＳ的伪距测量定位原理和测速原理，ＤＧＰＳ提高定位精度的原理。     

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。     

地磁辅助的无缝INS/GPS组合导航研究

INS/GPS组合导航已经成为当前无人机导航系统的主要实现形式,由于GPS信号容易受到干扰,在恶劣的电磁环境下信号易丢失,从而导致GPS卫星信号失锁而无法使用。地磁导航作为一种无源导航方法,其难以受到外界干扰且具有较强的自主性,从而为克服GPS在干扰情况下无法对INS误差实现持续无缝修正的不足提供了很好的途径。针对INS/GPS组合导航中GPS卫星信号失锁的情况,设计提出了使用地磁匹配导航进行辅助实现无人机无缝导航的实现方案,设计了基于地磁特征的地磁匹配算法和地磁匹配辅助的INS/GPS组合无缝自主导航算法,并通过仿真验证了采用地磁匹配辅助导航方法,可以在GPS无效的情况下,实现对INS导航误差的持续无缝修正,从而提高导航系统性能。     

A GPS/GLONASS/INS test program

Under contract of different German Ministries a test program investigating the combinations of GPS, GLONASS, and Inertial Navigation has been carried out since 1991. Besides other goals, the aim of the project is to investigate the capabilities of GLONASS in comparison to GPS, to realize a combined GLONASS/INS solution and to perform joint processing of GPS and GLONASS raw data. The paper describes the test procedures and presents some of the results. This includes the comparison of DGPS with stand-alone GLONASS and GLONASS/INS under different dynamic situations, e.g., driving tests, flight tests, and also the presentation of results of combined GPS/GLONASS data processing, which was successfully achieved in March '93 for the first time. The results show the potential of the non-SA-degraded GLONASS and the advantage of using both, GPS and GLONASS for combined solutions     

I: PRECISE ORBIT DETERMINATION AND GRAVITY FIELD MODELLING: Strategies for Precise Orbit Determination of Low Earth Orbiters Using the GPS

Considerable experience accumulated during the past decade in strategies for processing GPS data from ground-based geodetic receivers. First experience on the use of GPS observations from spaceborne receivers for orbit determination of satellites on low altitude orbits was gained with the launch of TOPEX/POSEIDON ten years ago. The launch of the CHAMP satellite in July 2000 stimulated a number of activities worldwide on improving the strategies and algorithms for orbit determination for Low Earth Orbiters (LEOs) using the GPS. Similar strategies as for ground-based receivers are applied to data from spaceborne GPS receivers to determine high precision orbits. Zero- and double-differencing techniques are applied to obtain kinematic and/or reduced-dynamic orbits with an accuracy which is today at the decimeter level. Further developments in modeling and processing strategies will continuously improve the quality of GPS-derived LEO orbits in the near future. A significant improvement can be expected from fixing double-difference phase ambiguities to integer numbers. Particular studies focus on the impact of a combined processing of LEO and GPS orbits on the quality of orbits and the reference frame realization. This revised version was published online in August 2006 with corrections to the Cover Date.     

Navigation message designing with high accuracy for NAV

Navigation message designing with high accuracy guarantee is the key to efficient navigation message distribution in the global navigation satellite system（GNSS）. Developing high accuracy-aware navigation message designing algorithms is an important topic. This paper investigates the high-accuracy navigation message designing problem with the message structure unchanged.The contributions made in this paper include a heuristic that employs the concept of the estimated range deviation（ERD） to improve the existing well-known navigation message on L1 frequency（NAV） of global positioning system（GPS） for good accuracy service; a numerical analysis approximation method（NAAM） to evaluate the range error due to truncation（RET） of different navigation messages; and a basic positioning parameters designing algorithm in the limited space allocation. Based on the predicted ultra-rapid data from the ultra-rapid data from the international GPS service for geodynamic（IGU）, ERDs are generated in real time for error correction.Simulations show that the algorithms developed in this paper are general and flexible, and thus are applicable to NAV improvement and other navigation message designs.     

Ranging airport pseudolite for local area augmentation

This paper discusses the integration of an airport pseudolite (APL) into a local area augmented differential GPS based precision approach system. A prototype architecture is described that is being used to develop requirements for the local area augmentation system. Key features of this prototype system are presented along with its current performance. Key features discussed include the use of a multipath limiting antenna, APL signal structure factors, a unique APL automatic gain control, and GPS blanking technique to maximize APL tracking performance, while minimizing the electromagnetic interference to nominal DGPS performance     

基于自适应遗传算法的DGPS整周模糊度快速解算

 鉴于遗传算法(GA)所具有的全局搜索特性,也为了更快速准确地解算差分全球定位系统(DGPS)整周模糊度,将自适应遗传算法(AGA)引入DGPS整周模糊度的搜索中。首先根据全球定位系统(GPS)载波相位双差方程求解出双差整周模糊度的浮点解,并以基线长度作为约束条件确定整周模糊度的搜索范围;然后利用白化滤波的方法对整周模糊度进行降相关处理,降低整周模糊度各分量之间的相关性;最后将自适应遗传算法应用在整周模糊度的解算过程中,搜索整周模糊度的最优解。仿真计算结果表明,与LAMBDA算法和简单遗传算法相比,自适应遗传算法能够快速地求解整周模糊度,也具有较好的可靠性和鲁棒性。     

低成本U-blox模块的单频GPS/BDS增强PPP定位性能分析

以U-blox单频接收机采集数据,在GPS与GPS/BDS两种解算模式下进行局域增强精密单点定位(PPP)解算,并进行模糊度固定,对其在不同环境下的定位性能进行实验研究和分析。实验结果表明:在静态环境下,GPS/BDS浮点解收敛至cm级需3min左右,较GPS缩短64%,GPS/BDS定位精度RMS在平面与高程方向分别为(3.2cm,2.7cm),较GPS提升(47%,59%);GPS/BDS在30s左右可固定模糊度,固定后定位精度为(0.4cm,1.0cm),较GPS/BDS浮点解提升(88%,63%)。在动态环境下,GPS/BDS浮点解收敛至cm级需4min左右,较GPS提升59%,定位精度为(3.1cm,5.9cm),较GPS提升(34%,43%);GPS/BDS获得固定解需2min左右,固定后定位精度为(0.7cm,1.0cm),较GPS/BDS浮点解提升(77%,83%)。     

Analysis of airborne GPS multipath effects using high-fidelity EM models

Airborne GPS systems are being upgraded to provide sufficient positioning accuracy to support automatic landing operations in low visibility conditions. This is made possible by differential GPS (DGPS), in which the errors common to the airborne receiver and ground station are removed by knowledge of the latter's precise location. However, errors specific to the airborne system remain, of which the dominant components are receiver noise and multipath. To support the assessment of the integrity of the signal in space, these residual errors are incorporated in a statistically based error model, designated as the "standard model." The standard model is defined as the standard deviation of a Gaussian distribution that overbounds the residual pseudo-range (PR) error. It relates the standard deviation of the overbounding distribution to the elevation angle of the satellite relative to the local level coordinate system. The international community is currently developing improved standards to enable DGPS systems to support landings in the worst visibility conditions (i.e., CAT III). As a part of this development, the standard model for multipath is being re-evaluated and an improved model is sought. In order to better characterize the residual multipath errors, tools for accurate calculation of the airframe scattering effects are needed. Development of such tools is the subject of this paper. A new method for accurately computing pseudo-range error, based on the use of high-fidelity EM models, is described. This approach provides new insight into the mechanisms causing multipath error.