一种适用于SF-OFDM系统的波束形成技术

在正交频分复用（OFDM）系统中使用空频传输分集是未来宽带无线通信中的重要技术。由于在各个终端采用多天线进行收发，导致使用空频-OFDM（SF-OFDM）传输分集的系统受到增强的共信道干扰（CCI）。本文提出了一种适用于SF-OFDM系统的波束形成方案，该方案能有效的抑制共信道干扰。在该方案中，基于盲转向的波束形成被应用于SF-OFDM系统中。分析和仿真结果表明，该方案具有良好的共信道干扰抑制能力。此外，该方案能够利用不同波达角（DOA）信号间的相对时延来增强系统性能。     

OFDM系统的自适应符号同步算法

本文提出了一种在OFDM系统中基于导频符号的自适应符号同步新算法,它利用FFT的特性,采用频域同步方法,对符号定时进行估计。该算法计算量小,插入的导频数少,并且同步捕获速度、精度高低,可以灵活调节。仿真结果表明,该算法能简单而有效地获取符号同步,自适应性强。     

一种优化的OFDM符号定时与频偏估计算法及其FPGA实现

符号定时与频偏估计是OFDM系统中的关键技术之一.本文分析了符号定时偏差与载波频偏对OFDM系统性能的影响,提出了一种优化的最大似然同步算法,并给出了在FPGA中的硬件实现方案,得到其仿真结果.传统的循环前缀符号同步算法,仅仅利用一个OFDM符号的循环前缀及其相应部分的相关性,其相关峰值不明显,同步效果不理想.本文提出一种充分利用连续多个OFDM符号同时进行相关功率运算,在同样信噪比的情况下,相对于单个OFDM符号进行同步估计的系统,符号定时与频偏估计的精度更高,误差更小.     

一种新型的短波39音OFDM时频同步方法

针对短波39音OFDM系统,提出了一种新型的符号同步和载波频偏估计方法。与传统方法相比,该方法能够保证更加精确的符号和载波同步。最后通过系统仿真验证了这一结果。     

一种符号快速定时同步方法的研究

符号定时同步是数字解调中一个重要的关键环节，实现快速符号定时同步后可减少信息帧报头的长度，提高帧的传输效率。本文基于报头的“10”码推导了一种快速定时同步方法，适合于工程中的数字化实现。     

OFDM系统符号粗同步技术

OFDM作为一种无线信道环境下高速传输技术近来受到越来越广泛的关注。而符号同步是OFDM系统优良性能的基础,本文提出了正交频分多径(OFDM)的符号粗同步的三种算法。通过Matlab仿真确定其三种算法的优劣,并选择最好算法设计相应的符号同步估计器。     

基于IEEE 802.11n无线局域网系统的符号同步

IEEE 802.11n无线局域网标准为了避免不必要的波束成型采用了循环移位机制,该机制对符号同步造成障碍,使得符号同步产生所谓的假多径问题。针对这个问题,本文提出了一种采用移位叠加的本地训练序列互相关的同步方法。通过对IEEE 802.11n无线局域网系统进行建模仿真,对新提出的方法和前人所提出的方法进行比较。最终验证该同步方法具有实用性,能够大幅度的提升同步的精度,使得符号同步的定位误差控制在2个采样点之内。     

基于四维混沌系统的OFDM同步算法

针对传统同步算法计算复杂度高,符号同步和载波同步精度低,保密性差等缺点,提出一种基于四维混沌系统的OFDM同步算法.首先通过分析该四维系统的动力学特性、对初始值的敏感性和计算Lyapunov指数等方式,证明该系统是一个新混沌系统,并分析生成的混沌序列相关性质.然后将混沌序列用于构造一个L等分的同步训练序列,基于该同步训练序列提出一种新的OFDM系统符号同步和载波同步方法.理论分析和仿真结果表明新算法计算复杂度低,符号同步和载波同步精度高,增强了系统保密性.     

高速移动环境下OFDM系统载波同步的混合结构算法

在分析载波频偏OFDM系统信号模型基础上，提出了基于前导符号循环前缀相关和前导符号相关的混合结构载波同步的算法，将基于循环前缀相关的方法和前导符号相关的方法融合，从链路级研究了易于实现的载波同步算法，在高速无线多径Rayleigh信道下，车速120km／h时，比较了两种不同的载波同步算法仿真结果。     

一种适用于宽带短波通信OFDM系统符号定时同步的新方法

针对宽带短波通信正交频分复用（OFDM）系统,提出了一种不需要数据辅助的高效符号定时同步方法。该方法利用OFDM符号中的空载波不传输任何数据这一特性,通过最小化空载波上的数据能量来将符号定时点锁定在安全区域内,从而完成符号定时同步。该方法可以有效对抗多径效应,适用于短波通信系统。最后将该方法与Al-Dweik同步方案在宽带短波信道条件下进行了仿真对比,结果表明该方法有着更精确的符号定时同步性能,并且适用于各种星座图调制。     

平板缝隙天线的计算机辅助设计

基于边值积分方程方法的小型平面缝隙阵的机助设计方法。这种计算方法是严格的。但即使对于小型阵，计算量也相当大。对小型阵提出缝列与耦合分支分别设计的方法，并给出模型实验结果。实验结果表明，对于一般指标的方阵，这种方法是可行的。对于低分瓣和超低旁瓣阵，尤其大型阵，还需以严格计算代替大量实验，去寻求简化计算的经验方法，建立一种半经验的机助设计方法。     

含逻辑门的武器系统效能评估方法研究

在模糊综合评判和灰色聚类评价法中,各个指标间总是采用单一的线性加权的方法.为了充分体现各个指标间复杂的聚合关系,排除“一票否决”式指标对总体效能的影响,借鉴逻辑门思想,加入了“与”、“或”逻辑关系.通过实例验证,证明了方法的可行性,解决了“一票否决”式指标对评估方法的影响;同时也为现有评估方法的改进提供了有益的参考.     

The application of the conjugate gradient method for the solution of electromagnetic scattering from arbitrarily oriented wire antennas

The method of conjugate gradients is applied to the analysis of radiation from thin-wire antennas. With this iterative technique, it is possible to solve electrically large arbitrarily oriented wire structures without storing any matrices as is conventionally done in the method of moments. The basic difference between the proposed method and Galerkin's method, for the same expansion functions, is that for the iterative technique we are solving a least squares problem. Hence, as the order of the approximation is increased, the proposed technique guarantees a monotonic decrease of the least squared error (parallel AI - Yparallel^{2}), whereas Galerkin's method does not. Even though the method converges for any initial guess, a good one may significantly reduce the time of computation. Also, explicit error formulas are given for the rate of convergence of this method. Hence, any problem can be solved to a prespecified degree of accuracy. It is shown that the method has the advantage of a direct solution as the final solution is obtained in a finite number of steps. The method is also suitable for solving singular operator equations in which case the method monotonically converges to the least squares solution with minimum norm. Numerical results are presented for the thin-wire antennas and are compared with the solution obtained by the method of moments.     

Model-Based Satellite Image Fusion

A method is proposed for pixel-level satellite image fusion derived directly from a model of the imaging sensor. By design, the proposed method is spectrally consistent. It is argued that the proposed method needs regularization, as is the case for any method for this problem. A framework for pixel neighborhood regularization is presented. This framework enables the formulation of the regularization in a way that corresponds well with our prior assumptions of the image data. The proposed method is validated and compared with other approaches on several data sets. Lastly, the intensity-hue-saturation method is revisited in order to gain additional insight of what implications the spectral consistency has for an image fusion method.     

基于轮廓曲线和局部特征点的自动人耳识别

针对人耳识别问题,提出了一种由粗到细的两步识别方法.首先采用边界跟踪算法从侧脸图像上提取外耳及其轮廓曲线,然后利用基于改进Hausdorff距离的轮廓曲线对齐方法对图像库进行筛选得出候选的人耳图像,最后通过使用广义外耳局部特征点匹配方法从候选图像中精确匹配出与待测人耳相同的图像.采用轮廓曲线和局部特征点作为识别特征向量,利用改进Hausdorff 距离作为匹配量度方法,实现了基于2-D灰度侧脸图像的完全自动人耳识别,较有效地克服了光照和旋转角度变化对外耳识别的影响.实验结果表明,该方法计算量小、适应性强、鲁棒性好,极具实用价值.     

Efficient and simple analytical expression for slot antennaproblems

When a narrow slot is used to radiate energy into free space and the moment method is used to analyse its characteristics, a quadruple singular integral with a partial differential operator is encountered. A new rigorous and simple method is presented for performing the integration. The time cost using the method presented is much shorter than that using the earlier method. This method is especially suitable for CAD     

An efficient heuristic for standard-cell placement

A new method is presented for optimization of the one and two-dimensional quadratic assignment problem. The method is suitable for placement problems as they appear in sea-of-gates and standard-cell layout styles for VLSI design. The method is based on recursive partitioning and is a generalization of the method introduced by Kuh et al. It is more flexible than Kuh's method because it does not require a special distribution of the external connections on the boundary of the chip. The time complexity of the algorithm is O(_n Iog²_n). A numerical evaluation of the method is presented, which shows its efficiency for generating near optimal solutions for the quadratic assignment problem as well as for practical standard-cell placement problems.     

Asymptotical orthonormalization of subspace matrices without square root

Subspace computation is fundamental for many signal processing applications. A well-known tool for computing the principal subspace of a data matrix is the power method. During the iterations of the power method, a proper normalization is essential to avoid numerical overflow or underflow. Normalization is also needed to achieve desirable properties such as orthonormalized subspace matrices. A number of normalization techniques for the power method is reviewed, which include the conventional as well as nonconventional ones. In particular, a new method of normalization is introduced to achieve asymptotical orthonormalization of subspace matrices without the use of square root. This method is among a class of normalization methods that allow a simple adaptive implementation of the power method for subspace tracking.     

Voltage Induction Method for Microwave Susceptibility Measurements

A voltage induction method of microwave susceptibility measurement has been proposed. A signal from a one-turn coil wrapped directly on a magnetic sample is phase sensitively detected, and the real and imaginary parts of susceptibility as a function of magnetic field are directly indicated on an oscilloscope. Analysis shows this method to have a much higher sensitivity for small samples than the conventional cavity perturbation method. Also, this method is characterized by a higher stability, since the measurement is not for the perturbation of the resonant curve of high Q cavity, but for RF magnetic flux in a sample which is relatively stable for a frequency fluctuation of the signal source, independent of the sample volume. This method has been checked with good agreement against a perturbation method for a sample where both methods could be used. A YIG film, which is too small (4 mm by 4 mm by 0.3/spl mu/) to obtain any detectable perturbation of cavity parameters, was successfully measured by this method. The new method allows very rapid measurement combined with a very simple procedure for the relative measurement of susceptibility.     

Rank‐based dynamic frequency hopping without strict coordination in IEEE 802.22 WRAN system

In IEEE 802.22 wireless regional area networks (WRAN), it is indispensable to prevent the in‐use channel from interfering with incumbent services such as digital TV. To achieve this end, in this paper, we propose a dynamic frequency hopping based on rank accounting. In this method, a base station utilizes a ranking database where a rank of a channel which is used frequently is high. Each base station uses an idle channel whose rank is the highest based on the database, and hence this can reduce the number of channels which are used for the data transmission. Moreover, the proposed method performs interference avoidance processes. The proposed method does not require a strict coordination for base stations. We evaluate the performance of the proposed method with simulation. Numerical examples show that the failure probability of the channel switching for the proposed method is smaller than that for the conventional random method. It is also shown that the number of channels that are used for the data transmission can be reduced by using the proposed method. Finally, we investigate the performance of the proposed method in some situations. Copyright © 2011 John Wiley & Sons, Ltd.