用于检测双星故障的RAIM算法分析与研究*

随着GPS等卫星导航技术的广泛应用,在实际导航中对接收机的导航定位精度,尤其对定位的有效性提出了越来越高的要求。目前对此较为有效的方法就是利用接收机自主完好性监视(RAIM, Receiver Autonomous Integrity Monitoring)进行保障,而且该方法日益凸显出其优越性,但目前对该方法的研究多基于单星故障的假设。随着新一代导航系统的完善以及组合导航技术的发展,双星甚至多星同时出现故障成为不可避免的话题。本文分析和比较了用于检测两颗卫星故障的偏差完好性风险(BIT, Bias Integrity Threat)法和保护限值(PL, Protection Level)法两种RAIM算法。通过数据仿真,对用不同方法检测卫星故障的可用性及故障检测率进行比较,并分析了两种方法存在差异的理论依据。通过分析比较,说明在未来接收机处理多颗卫星同时出现故障的情况时,如何更精确地描述统计检测量与定位偏差的关系以及如何处理不同测量噪声的影响是RAIM算法可用性及有效性的关键。     

导航系统全球完好性仿真分析的设计与实现

完好性分析是导航系统分析的重要组成部分,完好性的仿真验证和测试可以降低系统研制的技术风险,是导航领域仿真的一个重要问题.提出了基于用户接收机格网的完好性仿真分析涉及的PAlM算法和RAIM可用性算法等相关算法模型,基于此,设计和实现了导航系统完好性仿真分析系统,最后针对格网分辨率为10°×10°的中国区域格网(24个网格点)进行了完好性的仿真试验分析,验证了相关RAIM算法,讨论了失效卫星对导航系统完好性的影响和基于保护级别概念的完好性计算的不足.     

GPS+BD双模接收机自主完好性监测算法研究

在高动态导航中,卫星接收机自主完好性监测(RAIM)越来越受到重视.假如在单一模式下监测,RAIM系统至少需要接收到5颗卫星的信息才能监测出异常卫星,而如果需要辨识出故障卫星,则至少需要接收到6颗卫星的信息,这就使得单一的接收模式很难保证在全球范围内进行全天候的完整性检测.而随着北斗(BD)系统的迅速发展,使得采用GPS+BD导航模式进行监测成为可能.文中讨论了GPS和BD组合接收机中,在某时刻假设只有一颗卫星出现故障的情况下,怎样使用加权方法进行自主完好性监测.并通过仿真GPS、BD单模式和GPS+BD模式下的故障识别率和RAIM完好性可用率,证明了GPS+BD模式RAIM算法要优于任何一种单系统模式的RAIM算法.     

GPS+BD双模接收机自主完好性监测算法研究

在高动态导航中,卫星接收机自主完好性监测(RAIM)越来越受到重视。假如在单一模式下监测,RAIM系统至少需要接收到5颗卫星的信息才能监测出异常卫星,而如果需要辨识出故障卫星,则至少需要接收到6颗卫星的信息,这就使得单一的接收模式很难保证在全球范围内进行全天候的完整性检测。而随着北斗(BD)系统的迅速发展,使得采用GPS+BD导航模式进行监测成为可能。文中讨论了GPS和BD组合接收机中,在某时刻假设只有一颗卫星出现故障的情况下,怎样使用加权方法进行自主完好性监测。并通过仿真GPS、BD单模式和GPS+BD模式下的故障识别率和RAIM完好性可用率,证明了GPS+BD模式RAIM算法要优于任何一种单系统模式的RAIM算法。     

ARAIM算法应用于LPV-200服务

传统的接收机自主完好性监测(RAIM)技术仅支持LNAV航路,而无法满足有更严格完好性需求的LPV-200进近。近些年来国际上开始兴起的高级RAIM(ARAIM)算法因其垂直导航能力而凸显优势,并且可以通过优化配置危险误导信息概率,进一步降低垂直保护级别(VPL),提高可用性。通过Spirent GSS 8000信号模拟器设置针对LPV-200的场景,利用生成的数据对优化前后的算法进行仿真比较,结果证明双频GPS下的ARAIM技术在局部地区可以达到LPV-200服务的要求。     

三种卫星故障检测策略的对比研究与仿真

故障检测是保证导航系统完好性的重要途径.针对接收机自主完好性监测算法RAIM需要至少5颗可见星时才能进行故障检测的问题,在惯性/卫星组合导航系统的框架下,通过构建能反映卫星故障特征的检验统计量,并根据检验统计量的分布确定相应的检测门限,提出了解分离和残差外推两种卫星故障检测方案.仿真结果表明:解分离算法能在存在RAIM漏洞时检测故障且易于进行系统重构,但其故障检测效率不高;残差外推法适用于检测慢变故障.仿真结果表明,改进方法故障检测效率有较大提高,甚至在只有三颗可见星时仍能较快地检测出慢变故障.     

基于优选几何分组增强的假设检验RAIM方法

针对传统接收机自主完好性监测(RAIM)算法对15~50m级较小故障检测和排除率低,不易满足多测距故障场景应用问题,建立4种典型卫星分布几何结构模型,通过研究各模型对含偏差测距带来的定位误差与检测统计值间耦合性的影响,提出了一种基于几何优选分组增强的RAIM方法。该方法在假设检验方法基础上,利用分组间残差矢量建立新型检测统计量与门限值,通过检验子集一致性来检测和排除含有偏差的测距。仿真表明:该方法能够提升较小故障检测和排除率,增强接收机自主完好性性能水平,且支持联合导航系统单、多测距故障场景假设,有效降低定位估计误差,保证了定位解的精度。     

基于多假设解分离算法的BDS/SINS紧组合完好性监视

完好性是民航基于性能的导航（PBN）运行的关键性能要求,是导航安全性的重要支撑。北斗导航系统（BDS）/惯性导航系统（SINS）紧组合导航系统将SINS信息加入到完好性监视中,增加了冗余信息,通过多假设解分离算法进行故障卫星的检测与隔离,满足民航特定飞行阶段高完好性要求。论文利用BDS接收机接收到的BDS卫星数据,通过设置飞行轨迹,模拟卫星故障,对BDS/SINS组合导航系统的完好性算法进行测试验证。实验结果表明,基于多假设解分离方法的BDS/SINS紧组合导航系统可以较好地实现故障卫星的检测与隔离,保护限计算符合预期。     

基于自适应策略的权值修正累积历元RAIM算法

传统的接收机自主完好性监测(RAIM)算法对微小慢变故障的检测延迟较长,漏检率较高,不利于故障检测。针对这一问题,在奇偶矢量RAIM算法基础上,提出了一种基于自适应策略的权值修正累积历元的RAIM新方法。该算法根据单历元故障程度确定权值因子,进而调整选定“窗口”内各历元所占比例,以构造更有效的检测统计量,其中“窗口”的大小依据多次仿真实验确定。仿真结果表明,该算法相对于累积历元和传统RAIM方法检测延迟时间分别缩短了16.67%和56.52%,能更好地检测微小慢变故障。     

全球定位系统PRAIM算法研究与仿真

对于卫星导航系统而言,系统所能提供的完好性是指当导航系统处于不健康状态,不能准确导航时向用户提供及时报警的能力,目前民航运输机上主要采用接收机自主完好性监控算法实现上述功能,对于满足AC-91FS-01运行要求的民航客机还需具备预测完好性的能力。本文提出了一种基于神经网络的全球定位系统预测性接收机自主完好性监控算法,该算法相对与传统基于星座的预测算法,具有较好的可行性和有效性。     

Risk Analysis and Risk Management

Abstract

Risk management is the process that allows business managers to balance operational and economic costs of protective measures and achieve gains in mission capability by protecting business processes that support the business objectives or mission of the enterprise. Senior management must ensure that the enterprise has the capabilities needed to accomplish its mission. Most organizations have tight budgets for security. To get the best bang for the security buck, management needs a process to determine spending.     

Risk Conductors

Abstract

Akin to sound resonating through a piano wire, impacts from both physical (flood, vandalism/sabotage, explosions, pandemics, etc.) and logical (network/software/data) incidents resonate between and through enterprises and business hierarchies via “risk conductors.” There are two orders of risk conductor: Critical Infrastructure (CI) as the industrial risk conductors, and intra-organizational operational risk conductors in the form of Human Factors (HF) and Information and Communication Technology (ICT). Risk conductors, either industrial or operational, are the dispersal agents of geographically centered, physical, or logical impacts.

Critical infrastructures may transmit an impact from one enterprise to another throughout an economy. Operational risk conductors—HF and ICT—transmit horizontally within an enterprise from one business unit to another, potentially amplifying internal incidents from manageable to crisis/disaster proportions. Operational risk conductors may also transmit vertically, away from the enterprise up to the client base and downwards into the supply chain, transmitting impacts to both customers and partners/suppliers. Operational risk conductors are not necessarily a new phenomena, but they have taken on considerably greater significance under the rapid convergence of information and communication assets to Internet Protocol (IP), which has catalyzed a feedback-loop between HF and ICT. As an incident typically possesses both HF and ICT impacts, HF and ICT in turn impact each other, multiplying the scope and scale of the impact.

In addition to presenting a framework for understanding and managing operational risks and resiliency, this paper proposes a cause-and-effect relationship between IP convergence and the materialization of operational risk conductors.     

Risk Assessment

Before selecting a solution for any sort of problem, first identify the problem to solve. It sounds obvious but the process of problem discovery — or, in the case of security, risk assessment — is even more critical. Yet it’s surprising how often this simple concept isn’t rigorously adhered to, especially when it comes to security. It all comes down to your view of the scale and importance of security in the first place.     

Understanding Risk

Abstract

Over an extremely short period of our history, computer systems and the Internet have become a critical element in our social and economic infrastructure. Most would agree that information systems and, dare I say, information security, have evolved into the most critical elements of our economic infrastructure. Security has been charged with a simple task: to plan, implement, and manage an integrated, heterogeneous security environment across hardware, operating systems, middleware, network protocols, applications, and databases. There is just one small problem. Security technology is relatively immature. Security tools are weak or lacking. The tools that are available are product based — not enterprisewide, which leads to many uncommon and unworkable solutions.     

Revisiting Risk

Networks dominate today’s computing landscape and commercial technical protection is lagging behind attack technology. As a result, protection program success depends more on prudent management decisions than on the selection of technical safeguards. Managing Network Security takes a management view of protection and seeks to reconcile the need for security with the limitations of technology.     

Risk Concentration

Nature takes a variety of approaches regarding risk concentration. Stationary life tends to bend but not break, whereas mobile life tends toward risk concentration with stout border protection. Client and network devices tend to follow the latter model.     

Arguments for Qualitative Risk Assessment: The StAR Risk Adviser

Calculating risk is relatively straightforward when there is reliable statistical evidence on which to base a judgment. However, novel technologies are often characterised by a lack of such historical data, which creates a problem for risk assessment. In fact, numerical risk assessments can be positively misleading in such situations. We describe a decision support system – StAR – that gives quantitative assessments where appropriate, but which is also able to provide qualitative risk assessments based on arguments for and against the presence of risk. The user is presented with a summary statement of risk, together with the arguments that underlie this assessment. Furthermore, the user is able to search beyond these top-level arguments in order to discover more about the available evidence. Here we suggest that this approach is well-suited to the way in which people naturally make decisions, and we show how the StAR approach has been implemented in the domain of toxicological risk assessment.     

软件项目风险管理中风险分析方法的研究

对软件项目风险分析中的定性分析方法和定量分析方法进行了讨论，提出了定性分析与定量分析相结合的方式对软件项目中已识别的风险进行分析的方法，并且在分析过程中考虑了风险偏好性的影响。