Adaptive antenna array using real symmetric array covariance matrix

A novel scheme using a real symmetric array covariance matrix for an adaptive antenna array in DS/CDMA is proposed. A real symmetric array covariance matrix is estimated from a complex array covariance matrix using a unitary transformation and Toeplitz matrix approximation methods. The Hermitian Toeplitzation method not only estimates a persymmetric matrix form for a real symmetric array covariance matrix but also enhances the performance of the received signal by removing the undesired effect obtained from a complex array covariance matrix. Simulation results demonstrate the effectiveness of the proposed scheme     

基于混沌寻优的DOA估计

提出用混沌优化的方法来实现阵列信号波达方向(DOA)的极大似然估计。基于混沌运动的遍历性、内在的随机性、规律性等特点的混沌优化算法是一种有效的全局优化算法,其计算复杂度较低。仿真结果表明该文提出的方法在获得与AP算法相当测向精度和测向分辨率的情况下有更低的计算量;在相干信号的情况下,其性能比AP算法有较大的提高;同时其基于轨道搜索的结构易于并行实现,以进一步满足实时性的要求。     

用禁忌搜索实现DOA估计

为解决DOA参数估计搜索算法中局部极值和实时性等问题,从现代优化理论的角度出发,选用比遗传算法、模拟退火法更易利用问题特殊信息的禁忌搜索算法来求解DOA的极大似然估计.理论分析和仿真结果表明:该方法不仅能获得全局最优解;而且在获得与AP算法相当测向精度和测向分辨率的情况下,有更低的计算量;对相干信号,其性能比AP算法有较大的提高.     

一种基于窄带信号多普勒频率测量的运动目标直接定位方法

相比于常规的两步定位方法,目标直接定位方法具有更高的定位精度,但现有的直接定位方法主要是针对静止目标所提出的,并具有较大的运算量.本文提出了一种针对匀速运动目标的多普勒频率直接定位方法.文中首先基于最大似然准则推导了直接估计目标初始位置和运动速度的优化模型,针对该优化模型是以矩阵特征值的形式给出而难以数值求解的问题,提出了一种基于矩阵特征值扰动定理的Newton型迭代算法,该算法可以避免多维参数网格搜索所导致的庞大运算量.此外,文中还推导了关于目标初始位置、运动速度以及运动航迹估计的克拉美罗界的闭式表达式.数值实验表明新方法的目标位置估计方差可以达到克拉美罗界,并且具有较少的运算量.     

利用多普勒的运动单站直接定位算法

针对利用运动单站接收辐射源信号进行目标定位过程中,传统两步定位算法测量参数时会产生信息损失,从而导致估计精度不够理想的问题,提出了一种联合多普勒的运动单站直接定位算法。该算法通过构造代价函数,得到包含辐射源位置信息的共轭矩阵,然后分别针对未知信号和已知信号通过特征值分解求取共轭矩阵的最大特征值,最后进行二维格网型空间索引得到辐射源的位置估计。同时,本文还推导了相应的克拉美罗下界(CRLB),并分析了多普勒测量存在误差下算法的定位性能以及算法的运算量。通过理论分析和仿真实验可以表明,所提出的运动单站直接定位算法对目标位置估计误差能够逼近CRLB,且与两步定位算法相比,具有更好的定位精度。      

部分均匀环境下适用于空间对称线阵的修正广义似然比检测方法

针对部分均匀高斯干扰环境下的点目标检测问题,该文基于广义似然比准则(GLRT)提出一种适用于空间对称线阵的修正GLRT检测方法.考虑到采样时存在的目标能量泄漏,在接收信号建模时采用目标能量泄漏采样模型弥补泄漏损失,并基于干扰协方差矩阵的斜对称结构降低对辅助数据的需求,最终联合待检测数据和辅助数据实现未知参数的估计,得到...     

相干源二维波达方向估计

本文分析了平面阵接收信号的协方差矩阵，发现它可分解为一个广义对称矩阵与一个非广义对称矩阵之和，利用信号协方差矩阵的这一结构特征，重点研究了相干源二维波达方向（DOA）估计．该方法通过构造一个差矩阵，求出其本特征值对应的任一特征向量，利用谱函数估计相干源二维DOA．简要分析了二维DOA估计的分维处理。     

Properties of the Eigenvectors of Persymmetric Matrices with Applications to Communication Theory

The matrices which are symmetric about both diagonals (persymmetric matrices) occur often in communication and information theory problems. There have been a number of problems whose solution involves the eigenvectors of persymmetric matrices. This paper summarizes a number of properties of the eigenvectors of persymmetric matrices and demonstrates how they can be applied to characterize and simplify the solution to a number of communication problems.     

二维多源测向的实时处理算法及实现

研究用二维MUSIC算法，解决阵列处理二维多源测向的快速实现问题。利用阵列流形具有的对称性，减少阵列流形和空间谱的计算量。在判定出信号源个数后，有选择地使用信号子空间或噪声子空间去计算空间谱，进一步减少计算量。采用2片ADI公司的高性能DSP芯片（ADSP21160），用并行处理方法实现了二维多源测向的实时处理。     

Client‐Side Deduplication to Enhance Security and Reduce Communication Costs

Message‐locked encryption (MLE) is a widespread cryptographic primitive that enables the deduplication of encrypted data stored within the cloud. Practical client‐side contributions of MLE, however, are vulnerable to a poison attack, and server‐side MLE schemes require large bandwidth consumption. In this paper, we propose a new client‐side secure deduplication method that prevents a poison attack, reduces the amount of traffic to be transmitted over a network, and requires fewer cryptographic operations to execute the protocol. The proposed primitive was analyzed in terms of security, communication costs, and computational requirements. We also compared our proposal with existing MLE schemes.     

基于重要性抽样的最大似然方位估计方法

最大似然估计是公认的最佳估计器,但是计算量很大.为了解决它的计算量大的问题,本文把蒙特卡罗方法与最大似然方位估计相结合,提出一种基于重要性抽样的最大似然方位估计新方法(Maximum Likelihood DOA Estimator Based on Importance Sampling,简称ISMLE).研究结果表明,ISMLE方法不但保持了原最大似然方位估计方法的优良性能,而且大大减小了计算量,把原方法的计算复杂度从O(L^K)减少到O(K×H).     

New adaptive beamforming algorithm employing forward/backwardaveraging and signal enhancement schemes

We introduce the new adaptive beamforming algorithm which improves the performance of an adaptive antenna array system through a forward/backward averaging scheme of the post-correlation signal vector and a signal enhancement scheme using Hermitian Toeplitzation of an array covariance matrix in DS/CDMA. A forward/backward averaging scheme decorrelates the received correlated signal after despreading in a matched filter and the Hermitian Toeplitzation scheme enhances the performance of the received signal by removing the undesired effect obtained from an array covariance matrix estimation. It is shown through simulation results that the performance of the proposed algorithm is very superior to that of the conventional Wiener maximal ratio combining (MRC) algorithm     

Maximum-likelihood bearing estimation with partly calibrated arraysin spatially correlated noise fields

The problem of using a partly calibrated array for maximum likelihood (ML) bearing estimation of possibly coherent signals buried in unknown correlated noise fields is shown to admit a neat solution under fairly general conditions. More exactly, this paper assumes that the array contains some calibrated sensors, whose number is only required to be larger than the number of signals impinging on the array, and also that the noise in the calibrated sensors is uncorrelated with the noise in the other sensors. These two noise vectors, however, may have arbitrary spatial autocovariance matrices. Under these assumptions the many nuisance parameters (viz., the elements of the signal and noise covariance matrices and the transfer and location characteristics of the uncalibrated sensors) can be eliminated from the likelihood function, leaving a significantly simplified concentrated likelihood whose maximum yields the ML bearing estimates. The ML estimator introduced in this paper, and referred to as MLE, is shown to be asymptotically equivalent to a recently proposed subspace-based bearing estimator called UNCLE and rederived herein by a much simpler approach than in the original work. A statistical analysis derives the asymptotic distribution of the MLE and UNCLE estimates, and proves that they are asymptotically equivalent and statistically efficient. In a simulation study, the MLE and UNCLE methods are found to possess very similar finite-sample properties as well. As UNCLE is computationally more efficient, it may be the preferred technique in a given application     

Estimation of direction-of-arrivals based on the array manifold space

In this paper, a high resolution technique for estimating DOAs of spatially close source signals is presented. It is observed that the array manifold over a sector of interest is rank deficient and the dimension of the array manifold space, which is the range space of the array manifold, is less than the number of sensors in the array. The true signal subspace is a subspace in the array manifold space. A novel technique is provided that searches for the signal subspace in this array manifold space. The resulting estimated signal subspace has minimum principal angles with the data signal subspace generated by eigen-decomposing the covariance matrix of the array data vector. It is proved that the proposed estimator is asymptotically consistent and the estimated signal subspace is closer to the true signal subspace than the data signal subspace formed by MUSIC. The proposed novel technique has better performance than the MUSIC algorithm. Its performance is comparable to MLE and MD-MUSIC yet it requires only one-dimensional searches and is computationally much less intense. Simulation results are presented to show the effectiveness of the proposed technique, and comparisons with MUSIC, MLE, and MD-MUSIC algorithms are also included.This research was supported by TRIO and NSERC.     

Low complexity estimation of carrier and sampling frequency offsets in burst‐mode OFDM systems

We study communications under slowly varying channels, and consider three cases of knowledge of the channel impulse response (CIR): full knowledge, no knowledge, and partial knowledge of the CIR. By partial knowledge, we refer to knowing only either the CIR magnitudes or the CIR phases. It is known that obtaining the exact joint maximum‐likelihood estimate (MLE) of the CFO and the SFO requires a two‐dimensional search. Here, we present a new estimation method which uses the Taylor expansion of the MLE cost function, combined with the best linear unbiased estimator, to obtain a method which does not require such a search. The computational complexity of the new method is evaluated. Numerical simulations demonstrate that the new method approaches the corresponding Cramér‐Rao bound for a wide range of signal‐to‐noise ratios, and has superior performance compared to all other existing methods for approximating the solution for the joint MLE, while maintaining a low computational complexity. Copyright © 2015 John Wiley & Sons, Ltd.     

Maximum-Likelihood Estimator for Coarse Carrier Frequency Offset Estimation in OFDM Systems

Orthogonal frequency division multiplexing (OFDM) systems are more sensitive to carrier frequency offset (CFO) compared to the conventional single carrier systems. CFO destroys the orthogonality among subcarriers, resulting in inter-carrier interference (ICI) and degrading system performance. To mitigate the effect of the CFO, it has to be estimated and compensated before the demodulation. The CFO can be divided into an integer part and a fractional part. In this paper, we investigate a maximum-likelihood estimator (MLE) for estimating the integer part of the CFO in OFDM systems, which requires only one OFDM block as the pilot symbols. To reduce the computational complexity of the MLE and improve the bandwidth efficiency, a suboptimum estimator (Sub MLE) is studied. Based on the hypothesis testing method, a threshold Sub MLE (T-Sub MLE) is proposed to further reduce the computational complexity. The performance analysis of the proposed T-Sub MLE is obtained and the analytical results match the simulation results well. Numerical results show that the proposed estimators are effective and reliable in both additive white Gaussian noise (AWGN) and frequency-selective fading channels in OFDM systems.

基于Jacobi方法的Hermitian矩阵特征分解算法

对一个Hermitian矩阵进行特征分解,通常都是把矩阵转化为实对称矩阵,这样运算量比较大。为了解决运算量的问题,提出基于Jacobi方法的Hermitian矩阵特征分解算法,该算法减少了运算量,能满足实际中的实时性要求。     

一种基于稀布降维处理的高分辨测向方法

针对阵元数一定时大型面阵均匀布阵易产生分辨力与模糊的矛盾问题,提出了一种基于稀布降维的波达方向高分辨估计方法。该方法极大的降低了运算量,同时保持了高分辨的测向精度,较大的改善了角度分嘉串率,计算机仿真证明了该方法的有效性和可行性。     

New applications of the theorem on the extremal properties of the characteristic numbers of a sheaf of Hermitian forms in optimization problems for multifunction antenna arrays

It is shown that optimization problems for multifunction antenna systems can be solved via reduction of new nonclassical functionals to a ratio of Hermitian forms with subsequent application of the theorem on the extremal properties of the characteristic numbers of a sheaf of Hermitian forms. Numerical investigations are performed with an array of rectangular waveguides with vector radiation patterns. The results obtained confirm the high efficiency of the proposed solutions.     

A Biologically Inspired Compound-Eye Detector Array—Part II: Statistical Performance Analysis

This is the second part of our paper. In this paper, we propose, model, and analyze the performance of a detector array for localizing far-field particle-emitting sources, which is inspired by but generalizes the compound eye of insects. The array consists of multiple eyelets, each having a conical module with a lens on its top and an inner subarray containing multiple particle detectors. Using a parametric measurement model introduced for the array in Part I, in this part we analytically and numerically analyze the statistical performance of the array. First, we compute the statistical Cramer-Rao bounds (CRBs) on the errors in estimating the direction of arrival of the incident particles; then we derive a lower bound on the mean-square angular error (MSAE) of source localization for any specific array configuration; thirdly, we consider two source-direction estimators, the maximum likelihood estimator (MLE) and the weighted direction estimator (WDE), and analyze their MSAE performance. In the numerical examples, we quantitatively compare the performance of the proposed array with the biological compound eye; show the array performance as a function of the array configuration variables; optimally design the array configuration; illustrate that the MLE asymptotically attains the performance bound, whereas the WDE is nearly optimal for sufficiently large SNR; and analyze the hardware efficiency by comparing the two MSAE bounds. Potential applications of this work include artificial vision in medicine or robotics, astronomy assisted, security, and particle communications.