最小冗余线阵的DOA估计

波达方向(DOA)估计是智能天线技术研究热点之一.研究了最小冗余线阵的DOA估计问题.通过引入阵列冗余度,对非均匀线阵的阵元配置进行研究,在对MUSIC算法进行分析的基础上,利用Matlab对最小冗余线阵的DOA性能进行仿真,通过与均匀线阵进行对比,结果表明,在相同阵元数目的前提下,最小冗余线阵获得了较高的空间谱分辨力和较低的估计均方误差,提高了DOA估计性能.     

基于稀疏贝叶斯学习的DOA估计

针对基于l1范数约束的稀疏表示DOA(Direction Of Arrival)估计算法对初始参数较为敏感的问题,提出了一种基于稀疏贝叶斯学习的DOA估计算法。首先通过信号来波方向的空间采样构造冗余字典,将阵列信号处理中的DOA估计信号模型转化为压缩感知中的稀疏重构信号模型。然后基于经验贝叶斯推理的方法,将待估计的稀疏系数值用方差未知的联合高斯分布描述,而未知的方差值决定了待估计系数的稀疏性。通过观测数据估计得到未知的方差,进而得到信号的DOA估计值。仿真结果表明,提出的算法有较高估计精度,并且对非相干信源和相干信源都具有较好的估计性能。     

基于空间时频分布的欠定DOA估计

波达方向（DOA）估计是阵列信号处理领域的热点问题,但经典的DOA估计方法通常要求阵元数大于源信号个数,即满足超定条件。而在实际中往往面临的是源信号个数大于阵元数目的欠定条件。提出了一种基于空间时频分布的MUSIC扩展算法,该算法通过将空间时频分布矩阵进行拓展,实现了欠定条件下的DOA估计。相比时频MUSIC算法,该算法能同时适应超定和欠定条件;相比已有的欠定DOA估计方法,该算法在保证DOA估计精度的情况下,放宽对源信号稀疏性的要求,同时降低对快拍数的要求。仿真实验结果表明了本文算法的有效性。     

基于单快拍数据的嵌套阵列DOA估计算法

针对嵌套阵列DOA估计实时性不好的问题,提出了一种基于单快拍数据的估计算法。该算法将嵌套阵分为阵元间距等于信号半波长和阵元间距大于信号半波长的两个均匀子阵。利用两子阵接收的单快拍数据分别构造Toeplitz矩阵,然后进行特征值分解结合MUSIC算法得到低精度无模糊的DOA估计和高精度有模糊的DOA估计,最后结合解模糊算法得到高精度无模糊DOA估计。在阵列孔径相同的条件下,相比于阵元间距等于信号半波长的均匀线阵,算法需要的阵元个数较少,节约了硬件成本。该算法具有较好的实时性,并且拥有较高的测向精度。仿真结果证明了算法的有效性。     

导向矢量正交分解的离格信号DOA估计

当存在离格信号时,网格失配将导致基于压缩感知理论的DOA估计算法估计性能严重下降。为解决这个问题,在对接收数据协方差矩阵进行KR积变换的基础上,提出了一种基于压缩感知理论下的导向矢量正交分解的离格信号DOA估计算法。算法利用信号导向矢量与其一阶导函数矢量间的正交性构建了新的离格信号导向矢量模型,并基于最小二乘法对离格信号的网格偏离量进行估计。在构建稀疏重建模型时,采用ILSSE方法精确估计噪声协方差矩阵,提高了稀疏重建的精度。仿真结果表明,所提算法在不同信噪比和不同的网格间距下对离格信号DOA都有较好的估计精度。     

双圆阵模式空间二维解相干

提出一种相干信号二维波达方向(Direction of Arrival,DOA)估计算法——模式空间波达方向矩阵(Mode-Space DOA Matrix,MS-DOAM)法。算法基于双圆阵,利用模式空间转换将圆阵转换为虚拟双平行线阵,计算虚拟线阵阵元间的互相关信息,构造两个等效协方差矩阵,进而构造波达方向矩阵,对该波达方向矩阵特征分解,利用得到的特征值与特征矢量求得入射信号的仰角和方位角。算法无需二维搜索,实现估计参数自动配对。仿真结果表明,算法在低信噪比和短快拍条件下,估计误差低于虚拟空间平移算法。     

一种MIMO雷达相干源波达方向估计方法

针对多径效应或智能干扰下信号高度相关,基于单基地MIMO雷达信号模型,提出一种相干源波达方向(DOA)估计方法。该文首先利用降维变换将匹配滤波后数据结构变化成低维信号空间,然后结合共轭ESPRIT(C-SPRIT)思想,通过构造数据矩阵,使得相干源之间完全解相关,获得旋转不变因子,最后利用总体最小二乘ESPRIT方法进行角度估计。仿真结果表明,该方法能够有效解算相干源DOA,在N个物理阵元下MIMO雷达比相控阵雷达能够获得更高的DOA估计精度。     

基于多尺度稀疏字典的SAR图像目标识别方法

针对合成孔径雷达目标识别问题,提出一种基于多尺度稀疏字典的SAR图像目标识别方法。稀疏字典选择是稀疏表示中的关键问题之一,该方法利用小波多尺度分析构造过完备稀疏字典,将训练样本图像在小波解析域中进行小波多层分解,充分利用小波多尺度分析突出图像局部特征的特点,并和过完备稀疏表示有效结合组成级联字典。通过求解测试样本相应的稀疏系数矢量并根据系数矢量中对应训练样本类别的重构误差判定目标类型。实验结果表明,该方法在识别前无需对SAR图像进行预处理,具有良好的识别效果。     

空间非平稳高斯噪声背景下混合信号的DOA估计

针对空间非平稳高斯噪声背景下混合信号的DOA估计问题,提出了基于四阶累积量对混合波源的DOA估计算法。该算法首先构造四阶累积量矩阵,利用类似ESPR IT方法估计出所有非相关信源的DOA,然后对四阶累积量进行修正空间差分平滑去相干,消除非相关源和空间非平稳高斯噪声的影响,从而实现了对相干源的DOA估计。此方法通过分别估计非相关和相关或者相干信号的DOA,能够以较少的阵元实现对多个信号DOA估计,最后仿真实验也验证该算法的有效性。     

一种新的特征矢量稀疏重构的DOA估计方法

针对已有的基于特征矢量稀疏重构的DOA估计方法中需要选取平衡残差项与结果稀疏性的正则化参数的问题,提出了一种新的特征矢量稀疏重构求解方法。首先在有限快拍数条件下,由特征矢量估计误差的统计分布特性,得到残差项大置信度的置信区间;再以此置信区间作为约束条件,以解矢量的l1范数作为最小化的目标函数,由此利用二阶锥规化求解时避免了正则化参数的选取。理论分析与仿真实验表明本文算法计算复杂度低;能够对非相干及相干信号的DOA进行估计,且具备很好的解相干性能;低信噪比条件下,对DOA的估计误差随着采样快拍数的增大而减小。     

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).     

Tacit support for terrorism: The rapprochement between the USSR and Palestinian guerrilla organizations following the 1967 war

This article demonstrates the inconsistent and wavering Soviet attitude towards national liberation movements in general and the Palestinian organizations in particular. Until the late 1960s, the Soviets viewed these organizations with suspicion, hesitating to engage in political dialogue with them. However, in the 1970s, political and military events in the region, as well as modifications in the Kremlin's Cold War strategies, led to a general shift towards the Middle East in Soviet foreign policy. Soviet leaders showed increased willingness to provide certain Palestinian organizations with arms with which to conduct terrorist activities against Israeli, pro-Israeli, Jewish and Western targets. The article explores the complex relations between Palestinian organizations and the USSR in the field of international terror. The study also exposes and analyzes the nature and content of Soviet–Palestinian arms dialogues and transactions. It provides clear evidence that Soviet policymakers and other luminaries were fully informed of, and sometimes directly involved in, these transactions and dialogues at the highest levels.     

A1 Qaeda and the radical Islamic challenge to western strategy

The September 11 global crisis prompted by the attacks on the World Trade Center and the Pentagon raises major questions concerning the nature and trajectory of terrorism in the post-Cold War global order. Hitherto, terrorism has been largely debated by analysts at the level of nation states. Terrorist and insurgent movements have also been largely anchored in nationalist and ethnic power bases even when they have sought to mobilise a transnational ideological appeal on religious or class grounds. There have been a few exceptions to this pattern such as the alliance between the German Baader-Meinhof group and the Japanese Red Army Faction, but even such international alliances as this did not, until at least the 1980s, presage anything like a global terrorist network necessitating a global strategic response. This study examines terrorism and global strategic responses.     

Reviews

Douglas S. Derrer, We Are All the Target: A Handbook of Terrorism Avoidance and Hostage Survival. Annapolis, MD: US Naval Institute Press, 1992. Pp. x+135, notes, index. $14.95. ISBN 01–55750–150–5

Ian Knight, Zulu: Isandlwana and Rorke's Drift, 22–23 January 1879. London: Windrow & Greene, 1992. Pp.136, 150 illus., incl 8 colour plates, maps, biblio. £35. ISBN 1–872004–23–7

Ian Knight, By the Orders of the Great White Queen: Campaigning in Zululand through the Eyes of the British Soldiers, 1879. London: Greenhill Books and Novato: Presidio Press, 1992. Pp. 272, 17 illus., 1 map. £18.95. ISBN 1–85367–122–3

Manfried Rauchensteiner and Erwin A. Schmidl (eds.), Formen des Krieges: vom Mittelalter zum ‘Low‐intensity’ Conflict’. Graz : Verlag Styria, 1991. Pp.208. DM35. ISBN 3–22–12139–7

Harold J. Kearsley, Maritime Power and the Twenty‐First Century. Dartmouth: Dartmouth Publishing Company, Limited, 1992. Pp.xv + 203, 13 diagrams, index. £32.50. ISBN 1–85521–288–9     

Helping hands: external support for the KNU insurgency in Burma

This article analyses to what extent the Burmese KNU insurgency made use of external support from states, refugees, and diasporas. Based on extensive fieldwork it is concluded that support from neighbouring states and refugees has for years kept the Karen rebellion alive. Western countries perceived forms of resistance to the illegitimate Burmese regime as just and have therefore played a crucial role in the continuation of conflict in Karen State. It is important that policymakers and donors as well as executing organizations continue to reflect critically on the way they exercise their work.     

基于GTST-DMLD-ESD的装备RMS建模仿真

装备的RMS是装备的重要设计参数,是影响战备完好和保障能力的关键因素.引入GTST-DMLD作为主要建模工具,建立起装备系统的RMS描述模型,以ESD为补充和扩展,对维修过程进行建模.并以GTST-DMLD-ESD模型作为装备RMS仿真的核心,对装备RMS仿真模型的总体框架进行了研究,并对各模块进行了较为详细的探讨.     

Panjwai: a tale of two COINs in Afghanistan

The US Army has two approaches to counterinsurgency operations in Afghanistan. One is hard, or combat-focused, and the other is soft, or development-focused. This study examines two US Army task forces deployed to Panjwai District, Afghanistan from 2012 to 2013. CTF 4-9 and 1-38 offer a meaningful comparison because they pursued these contrasting approaches among the same population and against the same enemy at the same time and place. The study compares each unit’s approach and finds that neither approach was successful absent the other. The article concludes by recommending further research into combining the approaches at the operational level.