OSCA-CFAR在K分布杂波背景下的性能分析

本文证明了形状因子已知条件下有序统计平均（OSCA）恒虚警检测器在K分布杂波背景下具有恒虚警性能，分析了均匀K分布杂波背景和多目标情况下该检测器的性能，并与OS和OSGO-CFAR进行了比较，仿真结果表明OSCA在两种环境下均具有最好的检测性能。     

基于自动删除算法的最大选择恒虚警检测器

基于自动删除单元平均(ACCA)恒虚警算法,提出一种新的恒虚警检测器(ACCAGO-CFAR)以提高CFAR检测的性能。它的前沿和后沿滑窗均采用ACCA算法来产生2个局部估计,取其中最大值作为总的背景功率水平估计,从而设置自适应检测门限。在SwerlingⅡ型目标假设下,推导出ACCAGO-CFAR在均匀背景下虚警概率P_(fa)的解析表达式。通过与其他现有方案进行比较,结果表明ACCAGO在均匀背景及多目标和杂波边缘引起的非均匀背景中,均具有较好的检测性能,尤其是在杂波边缘环境中,它的虚警尖峰比ACCA小近2个数量级,并且处理时间也比ACCA大为缩短。     

基于异常单元删除的改进CFAR检测器

雷达在大入射余角海杂波下进行检测时易受到功率突然增大的杂波异常单元影响,虚警率及误检率较高。为解决此问题,提出具有杂波抑制模块与恒虚警模块的二级检测器。杂波抑制模块通过参考单元的协方差矩阵构造正定矩阵,求解其矩阵范数用以估计杂波功率水平,根据功率水平设置一个动态门限,剔除异常单元后的杂波作为待检测信号输入恒虚警模块,恒虚警模块使用基于有序数据可变性的自动删除平均（ACCA-ODV-）CFAR检测器来改进传统变化指数恒虚警（VI-CFAR）检测器。仿真结果表明,新检测器在均匀杂波环境中检测性能与单元平均恒虚警(CA-CFAR)检测器几乎相同,在多目标环境中检测性能远远优于最大选择恒虚警(GO-CFAR)检测器、最小选择恒虚警(SO-CFAR)检测器、CA-CFAR检测器及VI-CFAR检测器,在杂波边缘环境中虚警控制能力仅次于VI-CFAR检测器与GO-CFAR检测器。综合考虑实测数据中各个检测器的检测结果,改进后的检测器在高分辨率大入射余角情况下具有最优的检测性能。     

K—分布杂波的顺序统计恒虚警性能分析

研究 Ｋ—分布杂波背景下的顺序统计恒虚警检测器的性能,分析检测器在均匀统计独立杂波背景下的性能,给出了理论门限系数值及其仿真的门限系数值,并讨论相关杂波的恒虚警性能。分析了检测器在杂波的边缘和存在多目标及干扰时的目标检测性能。从仿真结果分析得出, Ｏ Ｓ— Ｃ Ｆ Ａ Ｒ 检测器在杂波边缘及多目标情况下具有比单元平均恒虚警（ Ｃ Ａ— Ｃ Ｆ Ａ Ｒ）好得多的性能,特别是在参考单元比较少的情况下。     

基于UMVE算法的恒虚警检测器

基于无偏最小方差估计（UMVE）算法，提出了一种新的恒虚警检测器（UMVEM-CFAR）。它的前沿和后沿滑窗均采用UMVE算法来产生局部估计，再对两者求和得到背景功率水平估计。在SwerlingⅡ型目标假设下，推导出UMVEM-CFAR在均匀背景下虚警概率Pfa和检测概率Pd及多目标环境下检测概率只的解析表达式，与OS—CFAR相比，UMVEM在均匀背景和多目标环境下均具有最好的检测性能，并且它的处理时间只有OS的一半。     

基于杂波分布特性的恒虚警率检测器设计

针对单元平均恒虚警率(CA-CFAR)检测器在非平稳环境下检测性能下降的问题,提出了一种基于杂波分布特性的自适应恒虚警率检测器设计方法。主要思路为：在已知背景杂波类别的前提下,选择相匹配的恒虚警率检测器来提高目标的检测性能。基于实测数据,通过在不同杂波类别的区域人工加运动目标的方式,经过与CA-CFAR检测结果的仿真实验对比,验证了所提恒虚警率检测器的有效性。     

基于改进型恒虚警的毫米波雷达检测算法

为了提高毫米波雷达在多目标环境下的检测性能,在变化指数恒虚警（Variability Index CFAR,VI-CFAR）的基础上提出了一种改进算法,即当背景环境为多目标环境时,采用KL散度单元筛选恒虚警（Kullback–Leibler Trimmed Mean CFAR,KLTM-CFAR）替换单元平均恒虚警（Cell Averaging CFAR,CA-CFAR）与最小选择恒虚警（Smallest of CFAR,SO-CFAR）进行策略选择,有效避免了毫米波雷达在多目标环境下的目标遮蔽问题,提升了检测性能。对改进后的检测算法进行了仿真分析,结果表明,多目标环境下,在其他几种检测器基本丧失检测能力的情况下,该检测器仍保持着90%以上的检测概率,并且在均匀环境和杂波边缘环境下,也有较为良好的表现。     

一种基于检测统计量的SOSGO-CFAR 检测算法

提出了一种新的恒虚警检测算法SOSGO-CFAR.该算法应用检测单元采样作为选择参考单元的依据,使用了基于转换恒虚警(S-CFAR)和排序选大恒虚警(OSGO-CFAR)的复合算法.文章给出了该算法在均匀背景中的数学分析.并在均匀背景、杂波边缘和多目标情况下,用MonteCarlo方法进行了仿真分析.结果表明,该检测器既具有均匀背景下和CA-CFAR相近的良好性能,在杂波边缘环境中,具有接近OSGO-CFAR的性能,且在多目标环境中,其性能明显好于S-CFAR.     

高分辨SAR图像自动区域筛选目标检测算法

在G0分布背景杂波假设下,基于VI-CFAR算法该文提出一种自动区域筛选的恒虚警目标检测算法,以解决高分辨SAR图像复杂环境背景下的目标检测问题。该算法首先利用变化指数(VI)统计量对局部参考窗内的均匀区域进行筛选,以剔除参考窗内具有目标干扰点的非均匀区域;然后利用均值比(MR)统计量对参考窗内同质的均匀区域进行区域合并,以解决杂波边界处的背景杂波筛选问题;最后利用筛选到的同质均匀区域内的像素集合进行背景杂波参数估计,对待检测区域实现二值检测。通过实测SAR图像车辆目标检测实验表明,在多目标和杂波边界复杂环境背景下,该算法具有较稳定的检测性能和虚警抑制能力。     

基于Grubbs法则的改进CAG-CFAR检测器

针对传统恒虚警检测器在多目标情况下出现性能下降的问题，提出了一种基于格拉布斯（Grubbs）法则的改进CAG-CFAR检测器，即CAGp-CFAR检测器。该方法利用Grubbs法则实现对参考窗中奇异值、干扰目标的有效剔除，极大地降低了多目标环境中均值类恒虚警检测器的“遮盖效应”，在多目标环境下具备良好的应用潜力。考虑到CAG-CFAR检测器进行野值剔除时对样本概率密度函数存在一定限制，本文算法进一步对CAG-CFAR检测器的复杂结构进行了合理简化，具备更强的工程应用价值。仿真结果表明该方法在各类典型杂波背景中都具备良好的检测性能。     

An Adaptive Multitaper-SVD Spectrum Sensing Method for OFDM-Based Cognitive Radio Systems

Cognitive radio (CR) has been proposed and widely investigated as an approach for increasing the spectrum efficiency. CR devices exploit so called white spaces in the spectrum allocated to the primary users (PU) by a process commonly referred to as the spectrum sensing. In this work, we use the singular value decomposition (SVD) for spectrum sensing in orthogonal frequency division multiplexing-based (OFDM) CR systems. A single input multiple output channel is assumed between the PU and the secondary user equipped with multiple antennas. At the CR side, the multitaper method (MTM) is used for the spectrum sensing in each antenna. As a first contribution, we aim at reducing the time necessary to perform spectrum sensing. To this end, we propose an adaptive MTM–SVD spectrum sensing method that decreases the sensing time. As a second contribution, we formulate a three dimensional SVD (referred to as 3-D SVD) scheme that efficiently processes signals and quantities related to multiple antenna traffic, OFDM multiple blocks and different tapers, simultaneously. Simulation results indicate that the proposed adaptive MTM–SVD decreases the sensing time by about 61–69 % for various proposed adaptive algorithms, compared to the conventional MTM–SVD method. Besides, performance improvement in probability of detection is achieved from 2–13 % for a predefined probability of false alarm by using adaptive MTM–SVD. In addition to further reduction of the sensing time, the proposed 3D-MTM–SVD outperforms conventional methods for the low probability of the false alarm.     

方差均值平方比恒虚警检测器

为了提高雷达恒虚警(Constant False Alarm Rate,CFAR)检测器在多目标背景下的鲁棒性,更好地检测目标,提出了一种新的基于方差均值平方比(VMSR)的恒虚警检测器,并建立了相应的检测器模型,得出了标称化因子T值和置信区间(a,b)。在均匀背景和多目标背景下,对VMSR检测器进行了仿真分析。在均匀背景下,VMSR检测性能优于OS,相比CA仅有很小的检测损失;在多目标背景下,VMSR检测性能相比OS得到了提升,特别是在干扰目标个数r>N-k时,OS不能有效检测出目标,而VMSR仍能保持较好的检测性能。结果表明,VMSR在多目标背景下检测性能优于OS,其在多目标背景下具有较强的鲁棒性。     

Robust video multicast with joint network coding and video interleaving

In this work, we propose a cross-layer solution to robust video multicast in erasure networks based on random linear network coding (RLNC) in the network layer and video interleaving (VI) in the application layer, and call it the joint RLNC-VI scheme. In the RLNC implementation, we partition one video coding unit (VCU) into several priority levels using scalable properties of H.264/SVC video. Packets from the same priority level of several VCUs form one RLNC generation, and unequal protection is applied to different generations. RLNC provides redundancy for video packets in the network layer and has proved to be useful in a multicast environment. Then, we propose a new packet-level interleaving scheme, called the RLNC-facilitated interleaving scheme, where each received packet corresponds to a new constraint on source packets. As a result, it can facilitate the RLNC decoding at the destination node. Furthermore, we study the problem of optimal interleaving design, which selects the optimal interleaving degree and the optimal redundancy of each generation. The tradeoff between delay and received video quality due to the choice of different VCUs is also examined. It is shown by simulation results that the proposed RLNC-VI scheme outperforms the pure RLNC method for robust video multicast in erasure networks. This can be explained by two reasons. First, the VI scheme distributes the impact of the loss (or erasure) of one VCU into partial data loss over multiple neighboring VCUs. Second, the original video content can be easily recovered with spatial/temporal error concealment (EC) in the joint RLNC-VI scheme.     

Exact analysis of OS modified versions with noncoherent integration

This paper deals with the exact detection analysis of the Ordered-Statistic(OS) processor along with OS Greatest Of(OSGO) and OS Smallest Of(OSSO) modified versions, for Mpostdetection integrated pulses when the operating environment is nonhomogeneous. Analytical results are presented in multiple-target case as well as in regions of clutter power‘transitions. The primary and the secondary interfering targets are assumed to be fluctuating in accordance with the SWII target fluctuation model. As the number of noncoherently integrated pulses increases,lower threshold values and consequently better detection performances are obtained in both homogeneous and multiple target background models. However, the false alarm rate performance of OSSO-CFAR(Constant False Alarm Rate) scheme at clutter edges is worsen with increasing the postdetection integrated pulses. As predicted, the OSGO-CFAR detector accommodates the presence of spurious targets in the reference window, given that their number is within its allowable range in each local window, and controls the rate of false alarm when the contents of the reference cells have clutter boundaries.     

Cascade Control of PM DC Drives Via Second-Order Sliding-Mode Technique

This paper presents a novel scheme for the speed/position control of permanent-magnet (PM) dc motor drives. A cascade-control scheme, based on multiple instances of a second-order sliding-mode-control (2-SMC) algorithm, is suggested, which provides accurate tracking performance under large uncertainty about the motor and load parameters. The overall control scheme is composed of three main blocks: 1) a 2-SMC-based velocity observer which uses only position measurements; 2) a 2-SMC-based velocity control loop that provides a reference command current; and 3) a 2-SMC-based current control loop generating the reference voltage. The proposed scheme has been implemented and tested experimentally on a commercial PM dc motor drive. The experimental results confirm the precise and robust performance and the ease of tuning and implementation, featured by the proposed scheme.      

APES算法在MIMO雷达参数估计中的稳健性研究

 多输入多输出(MIMO,Multiple-Input Multiple-Output)雷达用多个发射天线同时发射多个独立信号照射目标,并使用多个接收天线接收目标回波信号.本文研究了MIMO雷达中参数估计的稳健性问题.本文应用幅度相位估计(APES,Amplitude and Phase EStimation)技术,利用目标的方位角最大似然估计值,得到了衰落向量的APES估计算法.考虑到方位角估计的不准确性,借鉴稳健的Capon波束形成器的设计思想,本文推导了衰落向量的稳健的APES估计算法.仿真实验表明,衰落向量的APES算法与稳健的APES算法性能十分接近.因此,衰落向量的APES估计算法是稳健的.     

双层新型左手超介质覆层在WLAN天线中的应用

研究加载左手超介质覆层对天线性能改进为目的,基于传统的开口谐振环和金属杆的变形组合,设计出一种等效介电常数和磁导率均小于0的多左手频带超介质覆层。将此覆层加载在工作频段为5.15-5.35GHz,5.725-5.825GHz的WLAN微带天线上,天线工作频率降低且辐射方向图得到了良好的改善。HFSS和MATLAB仿真结果表明,设计的左手超介质覆层在2-3.5GHz, 3.8-7.3GHz和7.5-12GHz三个频段具有左手特性,WLAN双频天线在加载双层左手超介质覆层后,工作频率分别降低了0.04GHz和0.09GHz,其最大增益分别提高了1dB和1.4dB,从而验证了设计的正确性。同时为设计性能更为优良的左手超介质覆层天线提供了新思路。     

Robust multiple signal classification algorithm based on the myriad covariation matrix

A robust version of the multiple signal classification (MUSIC) bearing estimation algorithm based on robust statistics is developed for a direct sequence-code division multiple access impulsive noise channel. The proposed subspace algorithm is computed by using the antenna array covariance matrix, which is derived from the robust maximum likelihood estimator of location. Each element of the robust covariance matrix is computed as the sample myriad of a window of the received observations. The MUSIC antenna array scheme is jointly used to mitigate the effects of multipath and impulsive noise. Simulation results demonstrate that the proposed scheme significantly outperforms the other linear and nonlinear schemes     

Novel Planar Metamaterial with a Negative Refractive Index

A new planar metamaterial (MTM) with simultaneous negative values of permittivity (ε) and permeability (μ) is proposed. Our MTM is composed of two identical copper patterns etched on both sides of dielectric laminate, which is very thin and easy to fabricate. Unlike conventional MTMs, the proposed structure shows a negative refractive index (NRI) behavior with respect to a normally incident wave. To explain the underlying principle of the NRI characteristics, an equivalent resonant circuit model based on surface current density distribution is investigated. An eigenmode analysis and a three‐dimensional wave simulation for the stacked MTM prism are also performed to verify the existence of negative refraction. The experimental results from the transmission and reflection measurement ensure the validity of our design approach and show good agreement with the theoretically predicted effective medium parameters.