分布式MIMO数字阵列雷达阵元优化配置

为了合理分配相参增益和空间分集增益在分布式多输入多输出(MIMO)数字阵列雷达系统中的比重,研究了其阵元的优化配置问题。首先,根据MIMO雷达信号模型将阵元配置问题转化为目标散射系数矩阵的分块划分问题;然后,依据子块内信号相参处理,子块间信号非相参处理的方式推导了似然比检测器;最后,分别从检测概率最大、探测距离最远和总的阵元数最少三个方面给出了阵元优化配置的表达式并进行了仿真分析。研究结果表明:应首先利用相参增益将回波信噪比提高到一定值后才能利用空间分集增益;分置接收天线比分置发射天线牺牲的相参增益少;当检测概率大于0.8时,分置两个收发共用的相控阵天线可使系统阵元总数最少,否则无需天线分置。     

阵列天线多载波DS-CDMA系统基于子空间的信道估计

阵列天线多载波DS-CDMA系统在未来移动通信中具有重要的应用前景。本文研究了阵列天线多载波DS-CD MA系统基于子空间的信道盲估计方法。通过在阵列天线多载波DS-CDMA系统下构造统一的信号模型,实现了基于子空间的信道盲估计。仿真结果表明所提出的方法可有效地对阵列天线多载波DS-CDMA系统的信道参数进行估计,并可抵抗适度的远近效应。     

应用子空间方法实现米波雷达超角分辨实验研究

应用阵列信号的子空间方法实现天线转动时的多目标超分辨处理，给出计算机模拟结果，并介绍了实现阵列信号子空间法的实验系统。实验方法及实验结果均表明该方法的有效性。     

用于测向测速的二维谱估计方法

雷达应用领域中的一个重要问题是测向测速,精确地测定多普勒频率和方位角能够实现对目标回波信号的高分辨率处理,从而进行目标跟踪。本文提出一种超分辨的二维谱估计方法,它利用的是阵列处理技术,对天线接收数据进行本征分析,将信号数据张成一个空间并对其进行分解,根据正交原理分割成信号子空间和噪声子空间,构造出噪声本征矢量,利用信号子空间与噪声子空间的正交性,在空间谱上形成极值点,从而达到对方向和速度的二维高分辨率估计。该方法应用于相控阵雷达信号检测,可以精确地测定多普勒频率和方位角度,提取多个空间运动目标的二维信息。文章的最后给出了计算机模拟成像结果,验证了算法的有效性。     

用于测向测速的二维谱估计方法

雷达应用领域中的一个重要问题是测速，精确地测定多谱勒频率和方位角能够实现对目标回波信号的离分辨率处理，从而进行目标跟踪，本文提出一种超分辨的二维谱估计方法，它利用的是阵列处理技术，对天线接收数据进行本征分析，将信号数据张成一个空间并对其进行分解，根据正交原理分割成信号子空间和噪声子空间，构造出噪声本征矢量，利用信号子空间与噪声子空间的正交性，在空间谱上形成极值点，从而达到对方向和速度的二维高分辨率     

多信号极化与到达角估计算法

论述了一种基于子空间方法的多信号极化与到达角估计问题的算法，该方法采用了有子天线均匀线阵，利用子阵列输出信号数据矩阵中包含的信号空间的不变结构用矩阵束方法解出信号极化与到达角的估计值并自动进行参数的配对，避免了参数的多维搜索配对过程。数值仿真的结果证实了该方法的有效性。     

基于随动天线的雷达主瓣干扰抑制

针对雷达系统主瓣干扰问题,本文提出了一种基于随动天线的干扰抑制算法。假设雷达站配置了一个主天线和一个随动天线,其中随动天线仅配备了接收机。主瓣干扰抑制算法是分两步进行的,第一步是基于特征值分解和特征子空间,完成初步干扰对消;第二步是将预处理后的随动天线的信号作为参考信号完成二次对消。通过仿真实验比较了本文提出的算法和已有算法的性能,结果显示本文提出的基于随动天线的算法可有效地对抗多个主瓣干扰源。     

基于累积量的极化敏感阵列信号DOA和 极化参数的同时估计

本文研究极化敏感阵列非高斯窄带信号二维波达方向(DOA)和极化参数的同时估计问题.所考虑的极化敏感阵列包含一个特定子阵,该子阵由空间稀疏伸展三极子天线和两个导引阵元组成.分析了3维极化-角度域相干结构的平凡模糊问题,对利用并行累积量ESPRIT分别恢复出的信号3维极化-角度域相干结构和空域相干结构信息进行联合完成了非线性极化信号二维DOA和极化参数的同时估计.给出了一种相位缠绕解决方案并讨论了空间伸展三极子天线的可选择结构.     

一种微型飞行器时空调制OFDM通信与跟踪系统

为了解决微型飞行器在特殊环境下的通信跟踪和多模导航定位问题,该文提出了一种新型的微型飞行器通信跟踪与辅助导航定位综合方案,其核心思想是在发射端发射一种载有空间方位信息的OFDM时空调制信号,以解决通信与二维测向跟踪问题。系统发射端采用八天线阵列,两天线一组发射OFDM信号,每个OFDM信号子载波中包含数字通信信息和空间方位信息,微型飞行器通过简单的单天线接收信号和多值分辨算法,解算出二维空间信息,实现高精度测向定位。文中给出了天线阵的结构,时空调制OFDM信号的设计,仰角方位角粗测和精测算法。并仿真了高斯信道下的二维空间信息的测向性能。     

多径信道中基于盲波束成形的CDMA多用户检测和伪码估计

在分析阵列天线接收的多径CDMA信号的基础上,发掘阵列信号子空间与扩频用户伪码序列的关系,对传统的子空间波束成形器结构做了改进,提出一种新的基于盲波束成形的伪随机码序列盲估计算法。算法采用复独立分量分析法迭代,得到盲波束成形器系数,能在波达方向未知的情况下,估计各个用户的扩频序列。本文同时提出一种基于盲波束形成的异步多径CDMA信号多用户检测算法,可以在未知各个用户扩频码和波达方向的先验知识条件下,完成多径异步CDMA信号的多用户检测。算法由于同时利用了扩频增益和阵列天线分集增益,相比于单天线多用户检测算法性能有所提高。理论分析和仿真结果验证了算法的可行性。      

Subspace Smoothing for Direction of Arrival Estimation in DS-CDMA Systems

In this paper a subspace processing method is introduced that can be used for direction of arrival estimation of coherent signals in an asynchronous DS-CDMA system. Conventional methods of direction of arrival estimation are not directly applicable to the case of multiple coherent signals that impinge on an antenna array from different directions. Some preprocessing is essential prior to estimation in this case. The proposed method exploits the spreading code and the path delays of the desired user to eliminate the contribution of undesired paths in the signal subspace. To this end, the signal subspace is mapped to a new subspace which contains the spatial-temporal signature of the desired signal. Once the desired subspace is created, conventional methods such as MUSIC and ESPRIT can be employed to estimate the desired directions of arrival. It is proved that the obtained direction of arrival estimator, based on the proposed method, is consistent. Also, the estimation performance is evaluated by comparing the proposed method with conventional estimation methods.     

Adaptive blind estimation algorithm for OFDM-MIMO radio systems over multipath channels

This paper investigates the blind algorithm for channel estimation of Orthogonal Frequency Division Multiplexing-Multiple Input Multiple Output (OFDM-MIMO) wireless communication system using the subspace decomposition of the channel received complex baseband signals and proposes a new two-stage blind algorithm. Exploited the second-order cyclostationarity inherent in OFDM with cyclic prefix and the characteristics of the phased antenna, the practical HIPERLAN/2 standard based OFDM-MIMO simulator is established with the sufficient consideration of statistical correlations between the multiple antenna channels under wireless wideband multipath fading environment, and a new two-stage blind algorithm is formulated using rank reduced subspace channel matrix approximation and adaptive Constant Modulus (CM) criterion. Simulation results confirm the theoretical analysis and illustrate that the proposed algorithm is capable of tracking matrix channel variations with fast convergence rate and improving acceptable overall system performance over various common wireless and mobile communication links.     

Joint angle and delay estimation (JADE) for multipath signalsarriving at an antenna array

In wireless communications, mobiles emit signals that arrive at a base station via multiple paths. Estimating each path's angle-of-arrival (AOA) and propagation delay is necessary for several applications, such as mobile localization for emergency services. We propose a novel subspace approach to estimate the AOA and delays of multipath signals from digitally modulated sources arriving at an antenna array. Our method uses a collection of estimates of a space-time vector channel. The Cramer-Rao bound (CRB) and simulations are provided     

Spatial polarimetric time-frequency distributions for direction-of-arrival estimations

Time-frequency distributions (TFDs) are traditionally applied to a single antenna receiver with a single polarization. Recently, spatial time-frequency distributions (STFDs) have been developed for receivers with multiple single-polarized antennas and successfully applied for direction-of-arrival (DOA) estimation of nonstationary signals. In this paper, we consider dual-polarized antenna arrays and extend the STFD to utilize the source polarization properties. The spatial polarimetric time-frequency distributions (SPTFDs) are introduced as a platform for processing polarized nonstationary signals, which are received by an array of dual-polarized double-feed antennas. This paper deals with narrow-band far-field point sources that lie in the plane of the receiver array. The source signals are decomposed into two orthogonal polarization components, such as vertical and horizontal. The ability to incorporate signal polarization empowers the STFDs with an additional degree of freedom, leading to improved signal and noise subspace estimates for direction finding. The polarimetric time-frequency MUSIC (PTF-MUSIC) method for DOA estimation based on the SPTFD platform is developed and shown to outperform the time-frequency, polarimetric, and conventional MUSIC techniques, when applied separately.     

Array processing for nonstationary interference suppression inDS/SS communications using subspace projection techniques

Combined spatial and time-frequency signatures of signal arrivals at a multisensor array are used for nonstationary interference suppression in direct-sequence spread-spectrum (DS/SS) communications. With random PN spreading code and deterministic nonstationary interferers, the use of antenna arrays offers increased DS/SS signal dimensionality relative to the interferers. Interference mitigation through a spatio-temporal subspace projection technique leads to reduced DS/SS signal distortion and improved performance over the case of a single antenna receiver. The angular separation between the interference and desired signals is shown to play a fundamental role in trading off the contribution of the spatial and time-frequency signatures to the interference mitigation process. The expressions of the receiver signal-to-interference-noise ratio (SINR) implementing subspace projections are derived, and numerical results are provided     

基于子空间方法的阵列天线方向向量自适应盲估计

利用传统子空间法估计方向向量要求阵元数必须大于信号源数,要求在无线通信系统中是不现实的,因为移动用户数是很大的,为突破这一限制,本文提出了一种基于子空间法的阵列天线方向向量自适应盲估计算法.通过各阵元接收信号相加,得到叠加的期望数据源特征波形;通过子空间方法,将叠加信号用信号子空间的基表示,由于叠加信号中包含方向向量,从而得到期望数据源的方向向量估计,该算法不要求阵元数大于数据源数.仿真结果表明算法是有效的.     

天线组阵中基于SUMPLE的联合信号检测

针对低信噪比下天线组阵信号的检测问题,本文提出了一种基于SUMPLE合成的联合检测算法。传统信号检测算法在低信噪比下的检测效率很低,并且难以直接应用于多天线组阵系统。本算法综合利用SUMPLE合成时权值收敛特性以及各路信号之间强相关性,对信号存在性进行检测。理论分析和仿真结果表明,该算法具有适用于多天线组阵系统以及检测概率高的优势。并且在接收信号信噪比低至-12dB时,算法仍然有80%以上的检测概率,提高了传统多天线组阵信号检测的性能。      

Blind space-time multiuser channel estimation in time-varying DS-CDMA systems

A multistep linear prediction (MSLP) approach is presented for blind channel estimation for short-code direct sequence code division multiple access signals in time-varying multipath channels using a receiver antenna array. The time-varying channel is assumed to be described by a complex exponential basis expansion model. First, a recently proposed MSLP approach to blind channel estimation for time-varying single-input multiple-output (SIMO) systems is extended to time-varying multiple-input multiple-output (MIMO) systems to define a "signal" subspace. Second, the knowledge of the spreading code of a desired user is exploited in conjunction with the signal subspace to estimate the time-varying channel of the desired user up to an unknown time-invariant scale factor. Equalization/detection for the desired user can be then carried out if the information sequence is differentially encoded/decoded. Sufficient conditions for channel identifiability are investigated. Three illustrative simulation examples are provided.     

Correlation and channel capacity of MIMO systems employing multimode antennas

A novel way of exploiting higher modes of antennas as diversity branches in multiple-input-multiple-output (MIMO) systems is introduced. Essentially, antennas employing multiple modes offer characteristics similar to an antenna array, through multiple modes and using only a single element. The physical mechanism that yields different received signals is the fact that each mode has a different radiation pattern. Analytical expressions for the correlation between signals received by different modes are presented for a biconical and a circular microstrip antenna that employs higher order modes. It is found that the correlation is low enough to yield a significant diversity gain. Furthermore, the channel capacity of a MIMO system using a multimode antenna, i.e., an antenna employing multiple modes, is found to be comparable to the capacity of an array. Since only one element is needed, the multimode antenna offers several advantages over traditional arrays, and is an interesting antenna solution for future high capacity MIMO systems.