一种超低频通信下行信号电磁干扰自适应抵消系统设计

超低频通信下行信号接收端受空间、地形等条件约束,难以布设远端参考线圈,因此传统的自适应干扰压制方法难以获得良好的干扰抵消性能。为解决这一难题,基于自适应相关抵消的原理,针对超低频通信下行信号的接收,提出采用多参考线圈与主接收天线本地正交布设的方案设计探测系统,并研究了一种电磁干扰自适应抵消系统的实现方法。然后,以工频谐波干扰的抵消为例进行了测试,实测结果表明:对于与干扰频谱不相重合的微弱单音信号,在不同信号强度下,采用一种基于通道相关性的多通道可变遗忘因子自适应RLS滤波算法,信干比平均改善23.51dB,其最大增益可达25.87dB,平均信噪比增益为8.13dB,说明该系统能够有效压制超低频电磁干扰。     

基于无伸缩因子CORDIC算法的DDS设计

提出一种无伸缩因子的双曲线坐标旋转数字计算(CORDIC)算法,该算法解决了伸缩因子的补偿问题,扩展了传统算法中受限的收敛域。对改进算法进行了误差分析,并通过仿真图直观比较,表明采用的算法精度满足硬件精度要求。提出了一种CORDIC算法的多级流水线结构和一种新的直接数字频率合成器(DDS)设计方法,此方案降低了硬件复杂度,易于实现。     

采用自适应简化不确定性卡尔曼滤波算法的飞行器导航控制方案

针对飞行器绕本体轴高速旋转的飞行过程出现的严重耦合干扰问题和大角加速度和大角速度测量问题,提出了一种自适应简化不确定性卡尔曼滤波算法。该算法使用超球面分布采样点和线性转移等方法简化算法采样计算和采样点的权值计算,提高算法效率;利用模型噪声和线性方程,通过一步预测进行自适应设计,计算滤波值和误差方差矩阵;使用次优噪声估计器推算过程噪声;对过程噪声进行正定判定,防止算法发散。仿真结果表明,这一改进的自适应简化不确定性卡尔曼滤波算法能够有效减少滚转角解算误差和耦合干扰,提高飞行器着陆点的精度。     

坦克炮控系统直接自适应控制器设计

应用基于CGT的直接自适应控制原理,设计了一种坦克炮控系统自适应控制器.采用并联补偿的方法,解决了被控对象的非严格正实性问题,满足了基于CGT的直接自适应控制方法的要求.该算法无需辨识系统的参数,结构简单,对参数变化的适应能力强.仿真试验表明,这种方法正确可行.     

平流层飞艇抗风场干扰约束Unscented卡尔曼滤波算法设计与应用

为了提高风场干扰环境下飞艇的导航精度,研究飞艇抗风场干扰导航算法。在建立风场干扰条件下飞艇速度误差约束模型的基础上,设计抗风场干扰的约束Unscented卡尔曼滤波算法。确定风场干扰条件下飞艇的速度误差约束量,将该约束与Unscented卡尔曼滤波算法相结合,对速度误差进行估计和补偿,以减小风场对飞艇定位精度的影响;证明该算法的状态估计量不仅是无偏的,而且协方差小于标准Unscented卡尔曼滤波的协方差;将提出的算法应用于捷联惯导/天文/合成孔径雷达组合导航系统中进行仿真验证,并与自适应扩展卡尔曼滤波和抗差自适应Unscented卡尔曼滤波算法进行比较。结果表明:提出的约束Unscented卡尔曼滤波算法的滤波性能明显优于自适应扩展卡尔曼滤波和抗差自适应Unscented卡尔曼滤波算法,能够有效抑制风场对飞艇定位精度的影响,提高飞艇的导航定位精度。     

应用极化聚类中心设计快速自适应极化滤波器

针对传统自适应极化滤波算法存在收敛速度慢、迭代步长因子选取困难等问题,采用极化聚类中心估计理论设计了一种快速自适应极化滤波器,实现了对极化雷达回波中的干扰信号逐脉冲地自适应精确对消。滤波器通过距离单元选通获取干扰信号样本,对样本极化聚类中心的直接计算能够快速估计干扰信号在当前脉冲内极化状态,依据干扰输出功率最小原则最终实现快速滤波过程,相比于传统极化滤波算法有更快的收敛速度和更稳定的干扰抑制性能。仿真对比实验结果验证了该方法的快速有效性。     

平流层飞艇抗风场干扰CUKF算法设计与应用

为了提高风场干扰环境下飞艇的导航精度,研究飞艇抗风场干扰导航算法。在建立风场干扰条件下飞艇速度误差约束模型的基础上,设计抗风场干扰的约束Unscented卡尔曼滤波算法。首先确定风场干扰条件下飞艇的速度误差约束量,将该约束与Unscented卡尔曼滤波算法相结合,对速度误差进行估计和补偿,以减小风场对飞艇定位精度的影响;然后证明该算法的状态估计量不仅是无偏的,而且协方差小于标准UKF的协方差;最后将提出的算法应用于捷联惯导/天文/合成孔径雷达组合导航系统中进行仿真验证,并与自适应扩展卡尔曼滤波和抗差自适应UKF算法进行比较,结果表明：提出的约束UKF算法的滤波性能明显优于自适应EKF和抗差自适应UKF算法,能够有效抑制风场对飞艇定位精度的影响,提高飞艇的导航定位精度。     

基于误差修正模型的自适应递推滤波算法

提出自适应滤波算法是经典Kalman滤波与最小方差自适应控制结合的成果。通过引入一个可变因子,将线性系统的状态转移方程与观测方程合并,然后平滑估计未知白噪声,使原本不相关的估计量被映射在同一线性流型中,由此获得可变因子的最优值。可变因子的最优调节保证了滤波的自适应性。最后通过仿真将此算法与经典的Kalman滤波对同一目标状态进行比较,发现由于误差修正因子的引入,此算法在滤波精度上得到显著提高。     

稳健的双基地MIMO雷达目标角度跟踪算法

针对双基地多输入多输出(MIMO)雷达变速目标角度跟踪问题,提出了基于变遗忘因子的跟踪算法。首先研究了遗忘因子对算法的收敛速率和跟踪性能的影响;其次借鉴变步长最小均方(LMS)算法的思路,提出遗忘因子的递推公式;最后将遗忘因子递推公式引入PASTd算法中,实现变速目标的收发角度跟踪。实验表明:算法的收敛速度和性能都有较大的提高,稳定性得到了增强。     

一种改进的次级通道辨识算法

为提高次级通道的辨识精度、减小辨识误差对自适应控制的影响,以横向滤波器作为估计模型,分别应用带遗忘因子的最小二乘递推算法和变步长最小均方算法来对横向滤波器的权系数进行了更新,并对两种算法的辨识精度和控制效果进行了对比。结果表明:变步长最小均方算法的性能优于带遗忘因子的最小二乘递推算法,但变步长算法仍存在收敛速度过慢、辨识残差较大的问题。为此,提出一种改进的变步长最小均方算法,并对其进行了实验验证。实验结果表明:改进之后的变步长最小均方算法的辨识精度满足控制要求,收敛速度较快。     

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.