卫星导航差分增强系统

SBAS即Satellite Based Augmentation Systems,是利用地球静止轨道卫星和其他地面设施建立的地区性广域差分增强系统。主要用于卫星导航系统信号的增强和误差修正,增加系统的覆盖面积和抗干扰性能,并进一步改进系统的定位性能,减小数据的误差。目前主要有DGPS/DGLONASS/EGNOS系统等。DGPS称为Differential GPS,是美国雷声公司的广域增强系统(WAAS),覆盖美洲大陆。预计增强后的差分GPS定位精度可以达到1～1.5m。     

卫星导航局域增强地面子系统的设计

基于差分修正的局域增强的方法可以改进卫星导航系统的精度、完好性、连续性和可用性等指标,使卫星导航系统能够满足国际民航组织对于1类精密进近的要求。本文依据局域增强的原理和具体环境的要求,给出了某机场的局域增强系统地面子系统的设计。     

双系统卫星导航增强系统研究

提出了对双系统组合定位的增强方法，详细研讨了双卫星导航增强系统方案。该方法提高了卫星导航系统信息的安全性，在特殊时期，在某一系统不能使用时（如GPS），仍能利用其它卫星导航系统提供定位服务；通过地面差分修正站播发双卫星导航系统之间的系统时差以及地面差分修正站视界内所有卫星的伪距修正量，提高了卫星导航设备的可用性和定位精度；同时增加了信号的完好性，提供的冗余信息增加，使接收机自主完好性监测（RAIM）方法更易鉴别出故障卫星。     

欧洲静止卫星导航重叠服务系统（EGNOS）

近年来，随着对全球导航卫星系统(GNSS)定位精度与可靠性要求的不断提高，具有广域差分定位性能的星基增强系统迅速发展。美国的广域增强系统(WAAS)和欧洲静止卫星导航重叠服务系统(EGNOS)是两个最具代表性的系统，其中以多国合作研究，民间管理为特色的EGNOS尤为世人所瞩目。本文就EGNOS的体系结构，基本原理，关键信号处理技术与计划进展状况作了详细阐述。     

我国广域差分GPS参考站布站选址研究

我国广域差分GPS增强系统在服务区域能够为GPS用户提供差分修正值。广域差分参考站是系统的一个重要组成部分，它负责从GPS卫星获得距离测量。这些测量值用来计算差分修正数。因此，参考站站址及数量的选择决定了GPS增强系统的覆盖范围以及对用户的GPS增强效果，为了满足所需导航性能，本文分别从卫星完好性监测、UDRE、GIVE以及覆盖率几个方面分析了我国广域差分GPS参考站布站选址的限制条件，在最优化的条件选择参考站的间距，并且分析了实际条件下布站的原则．     

地基增强系统差分处理方法的研究

地基增强系统是通过差分的方法对卫星导航系统的精度指标进行改善的,差分效果的好坏一方面决定了对系统的精度指标,另一方面也对卫星导航系统完好性、连续性和可用性的判定产生重要的影响。本文建立了一种仿真的局域差分系统平台,根据国际民航组织（ICAO）进近飞行阶段的要求的指标对采集数据的分析,从实验的角度说明了差分处理的效果。     

局域增强系统差分定位方法

局域增强系统由地面子系统和机载子系统两部分组成。地面子系统计算卫星的伪距校正量等差分数据，并将这些数据发送给机载子系统。机载子系统利用这些差分数据，精确地完成位置的解算，达到改善定位精度的目的。本文描述了在局域增强系统中进行伪距差分定位的方法。     

关于我国北斗地基增强系统发展的思考

北斗卫星导航系统正式提供服务以来．地基增强系统的建设在我国陆续展开,多个区域地基增强系统已经建立完成。地基增强系统大大提高了北斗卫星导航系统的定位精度,拓展了北斗的高精度应用领域．但国内的建设也存在缺乏统一规划．增强系统软硬件的稳定性和可靠性有待提高、高精度应用亟待拓展等若干问题。本文结合我国北斗地基增强系统的现状,分析了存在的问题．同时给出了相关建议,以期为我国北斗地基增强系统的建设和应用提供参考。     

基于EGNOS系统增强服务的广域差分校正的实现

欧洲地球同步导航重叠服务(EGNOS)是欧洲建设的第一个卫星导航系统,它通过增强美国的GPS和俄罗斯的GLONASS两个现有的卫星导航系统来向系统服务区内用户提供测距功能、差分改正数据和系统完好性信息,以满足高安全用户的需求.深刻阐明了广域差分校正的实现过程,给出了相关的算法,并推导了相应的计算公式和计算过程.     

浅谈卫星导航信号模拟器的应用

卫星导航发展现状 随着北斗卫星导航系统的“三步走”部署开始实施,卫星导航这个新兴技术越来越受到各行各业的青睐。当今世界上一共存在四大卫星导航系统,其中包括美国的GPS,俄罗斯的GLONASS,欧盟的Galileo和中国的北斗卫星导航系统。除了这四个全球导航系统,还有部分国家正在开展局域卫星导航系统或者是导航卫星增强系统,     

WAAS完好性监测结构设计

设计了与地面通信结构密切相关的WAAS完好性监测结构,在此基础上,依据WAAS原理,确定了WAAS的信号流程,为WAAS地面通信系统的设计奠定了良好的基础。     

基于GPS WAAS地面通信网的差错控制研究

GPS广域增强系统（WAAS）的地面站间通信系统是WAAS的重要组成部分，是实现WAAS的关键系统。文中在研究WAAS原理以及地面站通信特点的基础上，选择了相应的差错控制方案以确保重要数据传输的准确性．     

Wide area augmentation of the Global Positioning System

The Wide Area Augmentation System (WAAS) is being deployed by the Federal Aviation Administration (FAA) to augment the Global Positioning System (GPS). The WAAS will aid GPS with the following three services. First, it will broadcast spread-spectrum ranging signals from communication satellites. The airborne WAAS receiver will add these new ranging signals to the GPS constellation of measurements. By so doing, the augmented position fix will be less sensitive to the failure of individual system components, thus improving time availability and continuity of service. Second, the WAAS will use a nationwide ground network to monitor the health of all satellites over our airspace and flag situations which threaten flight safety. This data will be modulated on to the WAAS ranging signals and broadcast to the users, thereby guaranteeing the integrity of the airborne position fix. Third, the WAAS will use the ground network to develop corrections for the errors which currently limit the accuracy of unaugmented GPS. This data will also be included on the WAAS broadcast and will improve position accuracy from approximately 100 m to 8 m. When complete, the augmented system will provide an accurate position fix from satellites to an unlimited number of aircraft across the nation. It will be the primary navigation system for aircraft in oceanic routes, enroute over our domestic airspace, in crowded metropolitan airspaces, and on airport approach     

A New System Synchronization Technique for the Switching Satellite

A new technique for achieving system synchronization to the switching satellite is described; this technique requires only three earth stations, designated as control stations, to transmit synchronization signals. The three signals are used to measure the three space delays from the control stations to the satellite. The control stations broadcast the space delays to all other stations in the system. Thus, any other earth station can obtain synchronization passively by calculating its own space delay.     

Synchronisation-burst spectra for the switching satellite

Synchronisation of Earth stations to a switching communications satellite is achieved by transmitting synchronisation-burst signals. When more than one synchronisation-burst passes through the synchronisation window, mutual interference is generated by the frequency sidelobes. This interference can be reduced, however, by amplitude modulation of the synchronisation-burst signals.     

Support infrastructures based on high altitude platforms for navigation satellite systems

In this article the use of an augmentation system based on high altitude platforms (HAPs) for supporting global navigation satellite systems is discussed. In fact, HAP-based systems are being studied and designed for several communication applications, but they can also be considered added value infrastructure if integrated with navigation systems, providing aiding services based on terrestrial stations or geostationary satellites. The article investigates the results of a feasibility study for the design of a stratospheric pseudo-satellite to provide additional ranging signal to improve the accuracy and availability of the overall navigation system, and an effective integrity service, strengthening the reliability of the positioning procedures. The work here presented discusses issues that have arisen in the design, and provides simulation performance of the proposed architecture.     

A Polarization Control System for Satellite Communications with Multiple Uplinks

Several groups have designed polarization control systems to solve the rain-crosspolarization problem in satellite communications. However, the multiple-uplink problem still exists, i.e., one system cannot receive signals from different uplink stations with different rain conditions simultaneously. In order to solve this problem, a new scheme is developed in this paper based on the assumption that an obtainable correlation exists between the uplink and downlink crosspolarizations and the concept that uplink and downlink can be compensated separately. The currently designed systems can be used directly in this scheme; only the addition of similar devices is necessary. The feasibility is checked by a practical example, and satisfactory performance is observed.     

An experimental time-compression system for satellite television transmission

We describe an experimental system for demonstrating time-compression multiplexing (TCM) of two NTSC color television signals in a satellite channel of 36 MHz. The system employs digital processing to derive line or field differentials from each picture. The television signals are then converted into interleaved lines (or fields) of unimpaired baseband video and companded line (or field) differentials. These signal components are finally time compressed and multiplexed into a combined signal for single-carrier FM transmission. With 4.5-m earth stations, the field-differential technique offers extremely good transmission quality suitable for TV distribution to cable head-ends (weighted signal-to-noise ratio, WSNR ≈ 51.5 dB), while the line-differential method provides a slightly lower WSNR ( ≈ 49 dB). We recommend the field-differential approach because of its superior overall picture quality. For larger receive stations (7m), higher picture quality (WSNR ≈ 56 dB) could be obtained. If 10-m earth stations are employed, the received video performance is practically indistinguishable from the corresponding one in the one-television-per-transponder case, and we infer that three pictures can indeed be sent with a graceful degradation as previously suggested. By choosing the parameters properly, the current TCM system can be optimized for a wide variety of applications with higher channel capacity.     

Distribution of Reference Stations:Initial Explore on the Optimal Selection Strategy

The Satellite-based augmentation system(SBAS) is intended to provide real-time differential global navigation satellite system corrections with the high accuracy,availability,and integrity required for aviation applications.Since the performance of Satellite clock and ephemeris (SCE) corrections and Ionospheric range delay(IRD) corrections can vary dramatically depending on satellites and Ground reference stations (GRSs) geometry,therefore,we present a GRSs distribution optimized crite-ria and process to improve SBAS corrections performance.The present step-by-step optimized scheme using the average satellite surveillance dilution of precision and relative centroid metric availability of grid points as fitness values to determine the appropriate GRSs distribution to sufficiently meet the corrections requirements.The results show that the statistical mean RCM availability can reach more than 0.5518 for all IGPs and the coverage depth of GRSs in China and its surrounding areas is more than 25,which fully satisfies the requirement for solving SCE and IRD corrections.