基于空时频协方差矩阵重构的高效跳频信号DOA估计

为了充分利用跳频信号的空域信息来进行信号的DOA估计,在信号空时频分析的基础上,本文提出了一种基于协方差矩阵重构的高效跳频信号DOA估计方法。首先将接收信号的均匀线阵（uniform linear array, ULA）平均划分成2个子阵,分别对每个子阵接收到的信号进行时频分析,在时频域选择有效跳,构造每跳的空时频矩阵（spatial time-frequency distribution, STFD）,然后求得2个子阵的互协方差矩阵。将2个子阵的互协方差矩阵进行重构运算得到等效的信号子空间,最后构造空间谱多项式求根估计出信号的DOA。仿真结果表明该方法相比于以往改进类子空间算法能够有效提高估计精度和降低算法复杂度。      

一种基于导向矢量变换的DOA估计预处理方法

针对大多数空间谱估计算法在目标数量大于阵列自由度时失效这一问题,该文基于内插阵列变换思想,提出一种基于导向矢量变换的空域滤波方法。利用目标分布的先验信息,将观测空间划分为若干子空间,保证每一子空间内的目标数量小于阵列自由度;使用内插阵列变换方法,将整个观测空间的导向矢量变换为子空间的导向矢量,抑制子空间外的目标,从而将观测空间内大量目标的DOA估计问题转化为若干子空间内的常规DOA估计问题。计算机仿真结果验证了方法的有效性。     

基于非均匀采样的空间谱估计

文中引入非均匀采样对阵列通道进行建模,提出一种基于阵列非均匀采样的DOA估计方法.该方法利用非均匀采样的时间间隔随机性,每一次快拍都等效于随机改变空间阵元的间隔,相当于基于虚拟阵列变换得到一个时变的自适应的虚拟非均匀阵列结构.基于阵列非均匀采样的空间谱估计能突破空域采样定理的限制,使用较大的阵元间距检测出来波方向,克服了均匀采样条件下阵元间距增大引起的角度模糊现象,而且增大的阵元间距也提高了空间谱估计的分辨率和精度.进一步的实验表明该方法的有效性并改善了小信噪比条件I)OA估计精度.     

基于空间谱估计的多干扰源分辨技术研究

为实现反辐射导弹分辨多个干扰源,根据空间谱估计原理,提出采用均匀圆形阵列天线结构对目标进行测向定位,并运用MUSIC算法估计其到达角,实现空域分辨。建立了基于均匀圆阵的二维DOA估计模型,讨论了角分辨算法在导引头中的具体应用。仿真结果证明了采用该方法能够有效分辨多个干扰源。     

一种空-频联合最优滤波的被动宽带检测方法

常规宽带能量检测在多目标、强干扰环境下输出信噪比(SNR)降低,检测性能大幅度下降.针对此问题,该文提出一种将子阵导向最小方差(STMV)宽带空域自适应波束形成与频域Eckart滤波结合的空-频联合最优滤波宽带检测方法.该方法首先通过子阵导向最小方差波束形成进行空间自适应处理,利用自适应波束形成的干扰抑制能力在空域实现最优滤波;然后通过最大似然估计实时估计信号和噪声的功率谱,构造Eckart滤波对自适应波束形成的输出分配不同权重进行加权滤波,从而实现频域信噪比最大化.所提方法通过空-频联合最优滤波,降低空域旁瓣干扰和频带内噪声的影响,使得输出信噪比最大,从而有效地改善目标宽带检测能力,提高被动声呐的宽带检测性能.仿真和试验数据处理结果验证了该方法的有效性.     

极化分集下的共形阵列波达方向估计

提出了一种基于双馈源共形阵列的极化分集信号盲极化波达方向(Direction of Arrival,DOA)估计方法.通过投影和旋转变换,分析并给出了双馈源共形阵列下正交极化分集信号的等效导向矢量,将信号空间划分为两个正交极化信号子空间,实现了正交极化信号的盲极化分离.在此基础上给出了基于多重信号分类(Multiple Signal Classification,MUSIC)的极化信号的DOA估计算法.该算法无需估计极化参数,能够实现任意共形阵列对正交极化分集信号的DOA估计,最大估计信号数目能够超过阵元个数.仿真实验验证了该算法具有很好的估计性能.     

共形阵列非圆信号波达方向估计算法

受共形载体变曲率结构的影响,各天线单元指向不尽相同,使得共形天线阵列呈现极化多样性。因此,共形天线阵列的建模过程中需考虑不同阵元的极化响应特性。基于柱面共形天线阵列的快拍数据模型,利用非圆信号的特性对阵列输出进行扩展,基于秩亏理论和子空间原理实现信号波达方向（DOA）估计,所提方法估计精度高,不需要参数配对。存在相干信源时,提出对扩展后的虚拟阵列进行划分,对划分出的子阵进行虚拟的空间平滑,实现解相干的预处理操作。仿真结果表明该方法能有效应用于柱面共形阵列非圆信号DOA估计,并提高了空间分辨率。      

宽带信号源的波达方向估计新方法

针对信号源数多于天线阵元数的情况,提出了一种新的宽带信号波达方向(DOA)的估计方法.与传统方法一样,首先把宽带信号分解为互不重叠的窄带部分,通过将信号频率的不同等效为阵元间距的不同而得到多个阵列,合理组合这些阵列可以获得一个多阵元的虚拟阵列,对此虚拟阵列的输出运用传统的窄带信号子空间方法即可进行高分辨DOA估计.不需要对阵列输出进行"聚焦"变换及角度预估计,并且利用两个阵元即可对多个宽带信号进行空间谱估计.仿真结果证明了该方法在信号源数多于阵元数情况下的有效性.     

基于均分阵元的空域平滑技术研究

空间谱估计是现代信号处理研究的重要课题,对于非相干信号的DOA估计,采用MUSIC就能取得好的分辨效果,对此算法进行了简要介绍.对于广泛存在的相干信号,直接采用MUSIC则存在很大的模糊性甚至失效,为了准确地进行DOA估计,必须经过预处理解相干.针对传统的空域平滑处理,提出了均分阵元的空间平滑技术,经仿真验证,新方法可行、有效,最后分析了该方法的优势和弊端.     

宽带双圈圆阵二维DOA系统中通道复增益估计方法

本文研究了基于双圈圆阵的二维DOA估计系统中通道复增益的估计问题.通过将阵列分割成子阵的办法,将问题转化为线阵系统中信号方向角和通道增益的联合估计问题.运用信号子空间对信号DOA和通道增益的约束关系,在无校准源时,可以得到通道增益的估计.     

一种新的去相关算法—随机空间增益法

本文提出了一种以空间增益随机变化的方法来去掉相关信源之间的相关性,以获得对相关信源的DOA的估计.该算法隔裂了天线阵元的损失数与相关信源数的直接关系,减少了天线阵元的开支,并且具有算法简单,运算量小的特点.理论分析与计算机仿真表明该算法切实可行、有效并且易于实现.     

Spatial Modulation

Spatial modulation (SM) is a recently developed transmission technique that uses multiple antennas. The basic idea is to map a block of information bits to two information carrying units: 1) a symbol that was chosen from a constellation diagram and 2) a unique transmit antenna number that was chosen from a set of transmit antennas. The use of the transmit antenna number as an information-bearing unit increases the overall spectral efficiency by the base-two logarithm of the number of transmit antennas. At the receiver, a maximum receive ratio combining algorithm is used to retrieve the transmitted block of information bits. Here, we apply SM to orthogonal frequency division multiplexing (OFDM) transmission. We develop an analytical approach for symbol error ratio (SER) analysis of the SM algorithm in independent identically distributed (i.i.d.) Rayleigh channels. The analytical and simulation results closely match. The performance and the receiver complexity of the SM-OFDM technique are compared to those of the vertical Bell Labs layered space-time (V-BLAST-OFDM) and Alamouti-OFDM algorithms. V-BLAST uses minimum mean square error (MMSE) detection with ordered successive interference cancellation. The combined effect of spatial correlation, mutual antenna coupling, and Rician fading on both coded and uncoded systems are presented. It is shown that, for the same spectral efficiency, SM results in a reduction of around 90% in receiver complexity as compared to V-BLAST and nearly the same receiver complexity as Alamouti. In addition, we show that SM achieves better performance in all studied channel conditions, as compared with other techniques. It is also shown to efficiently work for any configuration of transmit and receive antennas, even for the case of fewer receive antennas than transmit antennas.     

Oracle Spatial的空间查询分析功能浅析

Oracle Spatial为全关系型GIS的发展起到不可估量的作用，但是使用时大多只涉及空间数据的存储，对于Oracle Spatial强大的空间查询分析功能涉足不多。基于此本文分析了Oracle Spatial最常见的空间分析查询功能，并结合实例阐述了各自的特点和适用范围。     

Computationally Efficient Spatial Interpolators Based on Spartan Spatial Random Fields

This paper addresses the spatial interpolation of scattered data in $d$ dimensions. The problem is approached using the theory of Spartan spatial random fields (SSRFs), focusing on a specific Gaussian SSRF, i.e., the fluctuation-gradient-curvature (FGC) model. A family of spatial interpolators (predictors) is formulated by maximizing the FGC-SSRF probability density function at each prediction point, conditioned by the data. An analytical expression for the general uniform bandwidth Spartan (GUBS) predictor is derived. The linear weights of this predictor involve weighted summations of kernel functions over the sample and prediction points. Approximations for the sums are obtained at the asymptotic limit of a dense sampling network, leading to simplified explicit expressions of the weights. An asymptotic locally adaptive Spartan (ALAS) predictor is defined by means of a kernel family that involves a tunable local parameter. The relevant equations are fully developed in $d=2$. Using simulated data in two dimensions, we show that the ALAS prediction accuracy is comparable to that of ordinary kriging (OK), which is an optimal spatial linear predictor (SOLP). The numerical complexity of the ALAS predictor increases linearly with the sample size, in contrast with the cubic dependence of OK. For large data sets, the ALAS predictor is shown to be orders of magnitude faster than OK at the cost of a slightly higher prediction dispersion. The performance of the ALAS predictor and OK are compared on a data set of rainfall measurements using cross validation measures.      

Spatial light modulators

Near real-time reusable spatial light modulators for coherent optical data processing are reviewed. The PROM, liquid crystal, and electron beam addressed DKDP and oil film light valves appear to be the most promising devices for coherent optical data processing.     

Spatial optical CDMA

A method for optical signaling is investigated that allows multiple transmitters to simultaneously use the same noncoherent receiving aperture. The signaling is based on the properties of laser speckle interference patterns. Capacity for an interference limited system is explored for a correlation receiver based on random coding. A synchronization scheme is presented that allows a practical implementation of the proposed optical multiple access system     

光折变空间光孤子

回顾了光折变孤子的相关研究及最新进展,描述了光折变孤子的形成及特性,分析了光折变孤子形成的理论机理,展示了光折变孤子的相互作用,说明了光折变孤子的应用价值及缺陷.     

虚拟空间平滑算法

根据MASK、BPSK和AM等信号的实值特性,利用阵列接收数据及其共轭信息,构造了虚拟子阵,提出了虚拟空间平滑算法,较好地解决了信号高度相关问题.虚拟子阵具有M个阵元,避免了阵列孔径的损失,使该算法最大可分辨的相干信号数目为M-1.仿真实验证明,与前后空间平滑算法相比,该算法提高了空间分辨率,适应小样本,在一定程度上可以降低了计算量.     

异构定性空间推理

 现有定性空间推理研究主要解决单类对象、单种空间关系的定性约束满足问题.提出了异构定性空间推理概念,它包括不同种类空间关系结合(异构关系)、不同种类空间对象结合(异构对象)和定性定量对象融合三种情况下的空间关系约束满足问题.提出了三种以上异构关系的结合推理,此前工作以研究二元结合为主;给出了异构对象空间推理算法,此前工作仅研究表示模型;研究了定性定量对象融合的空间推理,该问题也可表达为部分解向全局解的扩展.上述研究结果可应用于环境智能和其他领域.     

Complex Quadrature Spatial Modulation

In this paper, we propose a spatial modulation (SM) scheme referred to as complex quadrature SM (CQSM). In contrast to quadrature SM (QSM), CQSM transmits two complex signal constellation symbols on the real and quadrature spatial dimensions at each channel use, increasing the spectral efficiency. To achieve that, signal symbols transmitted at any given time instant are drawn from two different modulation sets. The first modulation set is any of the conventional QAM/PSK alphabets, while the second is a rotated version of it. The optimal rotation angle is obtained through simulations for several modulation schemes and analytically proven for the case of QPSK, where both results coincide. Simulation results showed that CQSM outperformed QSM and generalized SM by approximately 5 dB and 4.5 dB, respectively, for the same transmission rate. Its performance was similar to that of QSM; however, it achieved higher transmission rates. It was additionally shown numerically and analytically that CQSM outperformed QSM for a relatively large number of transmit antennas.