全球卫星导航系统自主导航完好性隔离算法

全球卫星导航系统在自主导航工作模式下,为了保持星座系统的稳定,保证系统的完好性,需要对故障卫星进行及时可靠的隔离。因此提出一种基于星间链路的全球卫星导航系统(GNSS)自主完好性隔离算法,分析全球卫星导航系统故障判别方式,设计了基于星间链路的故障隔离流程,提出了基于星间测距误差和判别的故障检测及隔离算法。仿真结果表明,基于星间链路的GNSS自主完好性隔离算法,可以有效隔离故障卫星,保持星座自主导航精度,并且算法实现复杂度较小,易于工程实现。     

基于星间链路GNSS自主完好性加权算法

全球卫星导航系统在自主导航工作模式下,传统的地面支持完好性系统无法满足用户的完好性要求。因此提出一种基于星间链路的全球卫星导航系统(GNSS)自主完好性加权算法,通过改进稳健估计理论中的M-估计对星间链路测距加权的计算方法,降低故障卫星星间测距值的影响,以保持星座自主时间同步和精密定轨处理的连续、稳定与精度。仿真结果表明,在一颗及两颗故障卫星情况下,基于星间链路的GNSS自主完好性加权算法,可以有效地消除故障卫星对自主导航精密定轨的影响,星座具有与无故障时相当的自主定轨精度。     

基于脉冲星观测的导航星座自主导航数据融合方法

为解决完全依赖基于星间观测的导航星座长期自主导航的基准秩亏问题,提出基于脉冲星和星间链路的组合导航方法。给出了该方法的基本原理。为合理分散计算,采用简化和改进后的广义联邦滤波算法来对两种观测数据进行融合。仿真试验对该方法的合理性和可行性进行了验证。     

基于星上天线仰角约束的星间可视卫星集解析算法

星座自主导航需要对星间可视性规律做定量分析,可为进一步研究星间自主组网策略以及星间网络拓扑设计提供理论依据,同时星上自主建立星间链路需要卫星已知其可视卫星集合,因此有必要研究星间可视性解析算法.建立了基于星上环带天线仰角约束的星间可视性判定模型,结合星座几何特性以及卫星运动规律,以时间为变量,推导了卫星在运动过程中对同...     

高动态导航接收机直扩信号捕获方法研究

针对高动态导航接收机中,多普勒频移带来的伪码速率和伪码相位变化造成积累损失、捕获精度下降的问题,提出了一种改进的FFT快速捕获算法。该算法根据搜索频点实时更新本地再生伪码,并基于定时器和捕获的多普勒频率对捕获伪码相位进行实时校正。理论分析和计算机仿真结果表明,提出的改进算法在几乎不增加实现资源的前提下,提高了高动态导航接收机直扩信号的捕获性能。     

卫星导航系统星间链路发展的关键影响因素分析

建设有星间链路支持的导航星座已经成为新一代卫星导航系统的发展趋势之一。各国发展卫星导航系统的战略意图、综合国力、技术水平、国土分布等情况不同,导致导航系统对星间链路有不同的需求和约束,各系统发展论证的星间链路技术方案也各有不同。通过梳理国外卫星导航系统星间链路的发展论证过程,归纳出国外建设卫星导航系统星间链路考虑的3个共性关键因素:需求、技术与经济,并分析了以上因素对星间链路发展的影响。     

星间链路方案的设计与评价方法

星间链路技术降低了卫星通信网络对地面站的依赖,使得基于星间链路的卫星通信与组网具有地面网络难以比拟的优势。传统研究集中于星间链路的可行性分析和构建方法,对星间链路方案设计缺乏评价。从实际应用的系统性和构建流程的完整性出发,提出一种基于星座特性分析的星间链路方案设计方法,并为方案性能检验和选择提出了基于路由性能的评价方法。最后,通过对实际系统星间链路方案的设计和评价,验证了所提方法能够针对任务需求构建可行方案并通过路由性能比较选出最优方案。     

基于平均可工作概率的星间链路整网抗干扰性能评估方法

导航战条件下的全系统自主导航运行是卫星导航系统星间链路建设的重要目标之一。对星间链路在导航战情况下的工作性能进行准确评估具有非常重要的意义。星间链路的整网抗干扰性能与单星抗干扰能力、星间信号体制、建链策略、网络体制等多种因素均有关系,比较复杂,从而为其准确评估带来很大困难。为准确评估导航战条件下星间链路的整网抗干扰性能,对影响星间链路整网抗干扰性能的各种因素进行分析,并在此基础上对整网抗干扰性能评估场景进行建模设计。提出了以干扰场景遍历条件下的平均可工作概率为指标的星间链路抗干扰性能评估方法,定义了可用率评估指标体系,从而使准确、定量评估星间链路整网抗干扰性能成为可能。     

广播星历参数星上自主拟合算法

导航星座自主导航要求卫星能自主生成导航电文,针对星载计算机的处理能力有限,引入基于遗忘因子的递推最小二乘估计算法实现快速拟合广播星历。针对导航卫星轨道偏心率近似为0,在数据拟合过程中会导致法矩阵(HTH)奇异的问题,提出基于无奇异变换的广播星历参数拟合算法,引入无奇异轨道根数代替经典开普勒根数,迭代拟合得到改进广播星历参数,再将结果归一化到基于开普勒根数的广播星历参数。利用仿真算例验证了广播星历星上自主拟合算法的合理性。     

基于相关系数谱的宽带跳频信号时延估计

结合目前跳频信号带宽越来越宽、跳频点越来越多的特点,提出了一种基于相关系数谱的宽带跳频信号时延估计方法,实验表明该方法能够有效实现宽带跳频信号的时延估计,估计精度不受限于采样间隔.并且该算法具有较好的实时性和数据扩展性,易于工程实现.     

Putin – the masked nemesis of the strategy of ambiguity

Recent events demonstrate the complex and adaptive approach employed by Russia to reassert influence in Europe. The changing face of Russia’s strategy commenced in 2007 when it launched a crippling cyber-attack against Estonia. This was followed by a large Russian conventional attack against Georgia in 2008, occupying two large areas of the nation. 2014 witnessed the Russian annexation of Crimea where in just a week, Russia seized control of Crimea “without firing a shot.” The annexation of Crimea was rapidly followed by a Russian inspired and led subversive war in eastern Ukraine. The common thread among these diverse Russian operations is its use of ambiguity to confound and confuse decision makers in the West.     

India's counter-insurgency experience: the ‘trust and nurture’ strategy

The Indian Army, a force trained primarily for conventional warfare, has been engaged in internal counter-insurgency operations since the 1950s. Despite such a long innings on a counter-insurgency mode, little attention has been accorded within military circles to doctrinal innovation for waging sub-conventional warfare in India's democratic political context. At best, the Army continues to view counter-insurgency duty as secondary to its primary duty of defending India from external conventional threats. By conceptualizing a counter-insurgency strategy of ‘trust and nurture’, this article aims to fill this critical doctrinal gap in India's military policy. The author argues that a counter-insurgency strategy of ‘trust and nurture’ based on democratic political culture, measured military methods, special counter-insurgency forces, local social and cultural awareness and an integrative nation-building approach will result in positive handling of India's internal security problems. The author utilizes India's counter-insurgency experiences in Assam, Mizoram, Nagaland, Punjab, and Operation ‘Sadhbhavana’ in Jammu and Kashmir as illustrative empirical indicants in order to validate the ‘trust and nurture’ strategy.     

An Unlikely Alliance: Portuguese and South African Airpower in Angola, 1968–1974

The war that Portugal was obliged to fight in Africa began in 1961 and immediately stretched the resources of its armed forces. Nowhere was this thinness more apparent than in policing the vast territory of Angola. The east and southeast of Angola were particularly vulnerable, as the area was a vast, sparsely populated region characterised by enormous featureless plains or chanas covered in tall grass and broken by an extensive river system and mountainous forests. The only military solution to policing these immense spaces was aviation and specifically the helicopter that could carry troops into battle, protect them with a gunship and bring them home when the operation was concluded. The immediate problem for the Portuguese Air Force (Força Aérea Portuguesa or FAP) in Angola and elsewhere was a scarcity of helicopters. The solution was an alliance with South Africa, which had a strong inventory of Alouette IIIs, to help in policing the east. This move was likewise in the interest of South Africa, as its threat came from Zambia through south-eastern Angola. This article examines the strategic and tactical development of this unusual, cross-cultural alliance and the symbiotic relationship that resulted in destruction of the enemies of both in Angola.     

国内外结构钢焊条研究的现状与发展

本文主要介绍了国外焊条的现状和发展趋势,包括焊条的高韧性、高效率、低尘低毒和耐吸潮性能,为国内的焊条研究提供了参考依据。     

A Sign of Victory?: ‘Scottish Swords’ and Other Weapons in the Possession of the ‘Auld Innemie’

Many late medieval documents, notably inventories of arms and armour, of Englishmen contain references to ‘Scottish swords’ and other weapons. What did the compilers of these documents mean when they described a weapon as ‘Scottish’? How did such weapons come to be in the possession of these men? This article will attempt to explain this phenomenon drawing on primary documentary sources and surviving material culture from Glasgow Museums’ collections and others, as well as artworks from the period.     

Helping hands: civil–military cooperation and Italy's military operation abroad

In the Post-Bipolar Era the growing complexity of the military operations requires a new approach for the resolution of international crises. Since the end of the Cold War, peace support operations (PSO) have become the mainstay and principal occupation of most Western armies. At the same time, Italy has been one of the most important actors in such an area. The article focuses on the cooperation between military and civil components (a process called CIMIC) as a key variable in the Italian PSOs. We will analyse in detail the main lessons learned from past military interventions as well as the general context in which new tendencies are taking place. The maintaining of a minimum security frame becomes essential to fulfil activities ‘collateral’ to the mission: reconstructing services and infrastructure, food distribution, water and medication, law and order, de-mining, training of local forces, and supporting local institutions. These are the main tasks to obtain thrust and support from the population.     

Terrorism,insurgency, kidnapping,and security in Africa's energy sector

Energy continues to serve as the bedrock of modern economies and the main driver of modern society. For Africa, the production and supply of energy resources such as crude oil, natural gas, uranium, coal, biomass, biofuels and other renewables are an important source of employment, rents, taxes, royalties and profits. This sector brings in several tens of billions of dollars of revenue annually. The production and delivery of such resources, however, depend on critical infrastructures such as pipelines, refineries, processing plants, terminals, rigs, electrical energy pylons, substations, pump stations, vessels, and tankers. These infrastructures have been attacked by terrorists, insurgents, vandals and saboteurs, all of whom see them as targets against which to register their grievances and extract concessions from the state. This paper is a chronological account of some of the documented incidents of terrorism, insurgency, kidnapping, destruction, sabotage, and human casualties suffered in the oil and gas sectors in Africa between 1999 and 2012. It is based on data extracted from the databases of the RAND Database of World Terrorism Incidents and the University of Maryland's Global Terrorism Database (GTD).     

Cyberpower in Strategic Affairs: Neither Unthinkable nor Blessed

Abstract

This article explores the effect of connectivity on strategic affairs. It argues that the effect on war's character is potentially, although not yet shown in practice, considerably large. Its effect upon the distribution of power among states in the international system is small, contrary to the claims of ‘cyberwar’ alarmists. All told, however, its effect upon strategic affairs is complex. On the one hand, it represents a significant advance in the ‘complexification’ of state strategies, understood in the sense of the production of intended effects. On the other hand, strategists today – still predominantly concerned with the conflicts and confrontations of states and organised military power – are generally missing the power which non-traditional strategic actors, better adapted to the network flows of the information age, are beginning to deploy. These new forms of organization and coercion will challenge the status quo.