Direct-Ranging Loran Model Identification and Performance Predictions

With the availability of modern data processing techniques and lowcost stable time references, the use of Loran in a direct-ranging mode offers certain potential advantages. In order to generate reliable direct-ranging Loran (DRL) performance projections and system designs, however, accurate system error models are required. This paper first describes the processing of airborne flight data from a DRL receiver to identify models for significant DRL system errors. These models are then used in a Kalman filter covariance simulation to generate performance predictions for an optimally integrated DRL system. Comparisons with conventional hyperbolic Loran are also given. DRL is shown to be capable of substantially improved position accuracy over that of conventional hyperbolic Loran, especially in regions of poor geometry. A stationary ground-align technique for improving DRL performance is also discussed.     

Using GPS to calibrate Loran-C

Various techniques for using simultaneous Global Positioning System (GPS)/Loran data to estimate the propagation uncertainties that limit the absolute accuracy of Loran-C are discussed. Significant improvements in the absolute accuracy of Loran can be achieved with very simple calibrations. The absolute accuracy of Loran in the Gulf of Maine without calibration is presented. The maximum and RMS absolute errors are between 700 and 500 m, depending on the choice of land model. Simple calibrations greatly improve the absolute accuracy of Loran. As shown, if the land conductivities are fixed a priori and a single parameter is optimized, the maximum and RMS absolute errors fall to around 250 and 60 m, respectively. Alternatively, land can be treated as a single conductivity which can be adjusted to reduce offshore additional secondary phase factor errors. The performance of this practice is summarized in tables which show maximum and RMS errors of around 300 to 100 m, respectively     

一种基于FFT/IFFT技术的罗兰C天地波识别新算法

罗兰C天、地波到达时间间隔小于50μs时,对天、地波到达时刻的估计误差大。为了准确估计时间间隔小于50μs的天、地波到达时刻,在FFT/IFFT技术基础上采用了天、地波分别识别算法,并证明了该方法可行性。仿真结果表明：利用该算法,天地波自动识别的准确率分别可达99．6％和98．6％以上,相对USCG标准可改善信噪比4．4dB,对数字化罗兰C接收机的研究与设计具有重要意义。     

J.A. Pierce: pioneer award winner, 1961

A biography of John Alvin Pierce is given, starting with his early interest in radio. Pierce received his amateur license and operated a spark transmitter at the age of twelve. His amateur activities led to work at the Cruft Laboratory of Harvard University under the supervision of Professor H.R. Mimno. This association with the Cruft Laboratory has continued to the present day with few interruptions. Pierce's work with different groups and in various areas is sketched, focusing on his work with Loran     

The Effect of Aircraft Lateral Dynamics on Aircraft Positioning Accuracy When Using Loran-C

The dynamics of an aircraft following a fixed course line using Loran-C for position fixing are shown to interact with Loran-C receiver dynamics to result in cross-track aircraft positioning errors that are smaller than cross-track Loran receiver errors. In a particular case considered, this error reduction is on the order of 50 percent.     

EBAA：An efficient broadcast authentication scheme for ADS-B communication based on IBS-MR

Automatic dependent surveillance-broadcast （ADS-B） systems can broadcast satellitebased aircraft position, identification, etc., periodically, and are now on track to replace radar to become the backbone of next-generation air traffic management （ATM） systems. However, ADS-B systems suffer severe cyber-security problems due to the broadcast-type data link and the lack of designed-in security measures. Especially, since ADS-B messages are unauthenticated, it is easy to insert fake aircraft into a system via spoofing or insertion of false messages. Unfortu- nately, the authentication for ADS-B messages has not yet been well studied. In this paper, based on identity-based signature with message recovery （IBS-MR）, an efficient broadcast authentication scheme for ADS-B messages is proposed. The security analysis demonstrates that the scheme can achieve authenticity and integrity of ADS-B broadcast messages, as well as adaptive evolution of broadcasters＇ private keys. The performance evaluation shows that the scheme is computationally efficient for typical avionics devices with limited resources. Furthermore, the scheme achieves low communication overhead since broadcast messages can be recovered from signatures, and thus it is suitable for low-bandwidth ADS-B data link.     

Omega

Omega is a navigation radio aid having worldwide coverage with good accuracy. By choosing among the phase-difference lines of position?much as with celestial navigation?high and uniform accuracy can be maintained. Developed and tested by USNEL and USNRL, Omega is introduced by a discussion of qualities not shared by Gee. Decca, or Loran.     

An introduction to Loran

The history of the Loran hyperbolic navigation program as an example of the efficient mass production of research and development under the National Defense Research Committee is described. The fundamental concepts of hyperbolic navigation are addressed, and some details regarding the kinds of equipment employed for transmission, reception, and interpretation of pulse signals for this service are given. The potential usefulness of hyperbolic navigation is discussed, and some devices that will simplify the navigation of the future and enhance its reliability are suggested. The immediate organizational problems facing the program are indicated     

A Concept of Position Fixing by a Passive Mode Navigation Satellite System

A position fix in a passive mode using satellites usually necessitates an expensive computer or lengthy hand calculation. This is the largest drawback of passive navigation and it would be more desirable if the user could find his position by a mere glance at a chart and table, as one uses Loran. The first step toward this goal is to use a synchronous satellite because it simplifies the problem. The next step is to find the position of the user by a Loran type of chart, which is universal, and correct this apparent position by looking at a special table which is made according to the amount of perturbation of both the satellite and the user's position. An example of the position fix along the route between Yokohama to Hawaii is shown. The concept can be extended to orbiting satellites due to the rules which govern the motion of satellites, if the fix accuracy is in the order of 2 to 5 miles. This method should be more accurate than the common sextant and more practical due to the fact that the satellite can be used at any time and in any weather. As a total system, it will be better than Omega because it could provide additional navigation information such as communication or traffic control by using satellites.     

一个基于移动数据库的动态缓存失效算法

基于失效报告的缓存失效技术解决了数据一致性问题,但其消耗了大量的无线网络带宽。为了解决这一问题,提出了一种自适应动态缓存失效（ADCIA）算法。该算法根据当前状态自适应动态调节服务器广播模式,由制定的时间阈值和请求更新的客户数量来选择广播模式。通过模拟实验,该方法能减少带宽消耗及降低查询延迟。     

A New Approach to Geometry of Range Difference Location

Loran, as an example of a ?hyperbolic? range difference location system, provides hyperbolic lines of position on which the target must lie. It is shown in this paper that lines of position need not be hyperbolic, i.e., an exact straight line of position on the plane or the surface of a sphere (where the solution is a great circle) is derived and computer-generated error maps are given.     

基于卫星共视的罗兰C导航系统原子频标时间同步

介绍了CV技术的基本原理和罗兰C系统原子频标资源的使用状况,并通过引入系统融合和CV技术,对比对数据进行检测校验,最终实现了罗兰C导航系统原子频标与UTC时间基准同步。     

New Developments in Radar and Radio Sensors for Aircraft Navigation

Recent developments in airborne Doppler and ground mapping navigation radars and ground and satellite based radio systems are described. Simultaneous lobing and slope tracking techniques can remove the well-known Doppler sea bias error in fast and slowly moving vehicles. Doppler velocity information can be extracted from coherent forward-looking mapping radars, and high position fixing accuracy can be achieved by synthetic aperture radars. In radio navigation systems, such as Loran, Omega, and satellite systems, direct-ranging and differential techniques greatly reduce the geometric dilution and propagation effects which have plagued conventional radio navigation systems. The advantages gained by mixing of the data from these and other navigation sensors in a digital multisensor system are discussed and approaches for processing these data are suggested.     

IP网络设备典型故障分析及其对策

针对IP网络设备在使用过程中产生的广播风暴、传输数据丢包、MP-group(Multilink-group,复用链路组)接口链路层运行PPP(Point to Point Protocol,点对点协议)异常等问题,结合华为S9300交换机设备、NE40E路由器设备的工作原理,对策略路由机理、STP(Spanning Tree Protocol生成树协议)、广播数据帧复制过程进行了研究和分析。并通过分析问题产生的机理,发现了目前网络数据配置存在的不足,提出了在核心层交换机上配置流过滤策略等应对措施和快速处理故障的方法,对系统进行了完善与改进,并优化了相关领域的应用,为维护人员在任务中迅速、合理地实施应急处置提供了参考。     

Microminiature Loran-C Receiver/Indicator

A Loran-C Receiver is used as an example to show how an analog system could be converted to a digital one to take advantage of the expanding integrated circuit technology. The digital equivalents of the analog servo elements are described. Criteria for the design of a phase-tracking servomechanism is developed in detail. The Loran performance requirements are used to illustrate their application. The noise performance of a critically damped Type II servomechanism is derived in detail. Since the system will be employed in aircraft, tracking velocity becomes an important consideration. An analysis is made showing that an adaptive control is desirable.     

北斗空间信号误差统计特征及描述方法研究

通过对比北斗卫星导航系统(BeiDou Navigation Satellite System,BDS)广播星历与事后精密星历,提取了轨道和卫星时钟误差。基于北斗轨道误差及北斗卫星时钟误差统计特征分析,构建区别于全球定位系统(Global Positioning System,GPS)的BDS空间信号用户测距误差(Signal-In-Space User Range Error,SISRE)描述方法,对BDS广播星历中用户测距精度(User Range Accuracy,URA)进行了验证。6个月的北斗数据测试结果表明,北斗GEO、IGSO和MEO卫星的URA分别为3.0m、1.9m和1.6m。     

Timekeeping at the US Naval Observatory

No one can stop time, but time can stop a system. Users need to be aware of the different flavors of time, depending upon their needs. Most systems require that all their components be on common time (synchrony), but they cannot keep them on time unless they are also on a common frequency (syntony). Other systems simply require syntony. The US Naval Observatory (USNO) is the timing reference for GPS. Its master clock (MC) is based upon 72 HP5071 cesium and 17 hydrogen maser frequency standards in three buildings at two sites, and their data are used to generate UTC (USNO). The USNO disseminates and distributes the time not only via GPS, but also with Loran, network time protocol (NTP), and two-way-satellite time transfer (TWSTT). Our emphasis is on robustness through repeated calibration and multiplicity of systems, and we recommend this for our users as well. Further details and explanations of our services can be found on: http://tycho.usno.navy.mil, or by contacting the author directly.     

Optimum Reset of Ship's Inertial Navigation System

Optimum linear filter and control theory is applied to the practical problem of supplementing an inertial navigation system with discrete reference information. The information takes the form of position obtained from Loran C or Decca, for example, and occasional azimuth fixes obtained from star sightings. In particular, optimum use of this information is discussed for the Ship's Inertial Navigation System (SINS) installations intended for missile carrying submarines and warships. A model representative of the SINS dynamics is formulated appropriate for application of optimum filter and control theory. Interpretation of the optimum control dictated in part by the augmented SINS model is discussed. Simulation studies that show the relative transient behavior and the stabilizing effect of the closed-loop filter and control processes are also presented.     

Digital Cartographic Data: A Case for Electronic Delivery

The demand for digital cartographic data and information is expanding rapidly, most dramatically in navigation. Electronic chart and map display systems are now reaching the market for land, sea and air navigation and rapid delivery of the latest data is absolutely essential. Commercial aviation is moving rapidly toward the automated cockpit with the new generation Flight Management Computer System. Marine navigation is experiencing a similar growth in integrated navigation systems and every major automobile manufacturer has plans for digital map navigation systems. The largest, most complete data bases to meet these requirements are Government held and difficult to access, thus most private sector firms re-digitize and agencies maintain near duplicate data. Present inefficiencies, introduced errors, and delays stem from lack of rapid access and delivery of digital data. Use of newly developed satellite data broadcast technology offers a solution.     

作息时间与广播自动控制系统的研制

采用PLC控制与CMMS4040制成的时钟脉冲发生器相结合的方式，研制开发了作息时间与广播自动控制系统，成功地应用于烟草行业作息时间与广播的控制中。