Single and stacked circular microstrip patch antennas backed by acircular cavity

In this communication, a full wave moment method solution for a probe-fed circular microstrip patch antenna, backed by a circular cavity both in single and in stacked configurations, is used to analyze the effect of a parasitic patch on antenna bandwidth. In addition, the effect of recessing a single patch into the antenna cavity is studied. In both cases, theoretical results for the scattering and radiation characteristics of the antenna are presented     

Independent Component Analysis-Based Background Subtraction for Indoor Surveillance

In video surveillance, detection of moving objects from an image sequence is very important for target tracking, activity recognition, and behavior understanding. Background subtraction is a very popular approach for foreground segmentation in a still scene image. In order to compensate for illumination changes, a background model updating process is generally adopted, and leads to extra computation time. In this paper, we propose a fast background subtraction scheme using independent component analysis (ICA) and, particularly, aims at indoor surveillance for possible applications in home-care and health-care monitoring, where moving and motionless persons must be reliably detected. The proposed method is as computationally fast as the simple image difference method, and yet is highly tolerable to changes in room lighting. The proposed background subtraction scheme involves two stages, one for training and the other for detection. In the training stage, an ICA model that directly measures the statistical independency based on the estimations of joint and marginal probability density functions from relative frequency distributions is first proposed. The proposed ICA model can well separate two highly-correlated images. In the detection stage, the trained de-mixing vector is used to separate the foreground in a scene image with respect to the reference background image. Two sets of indoor examples that involve switching on/off room lights and opening/closing a door are demonstrated in the experiments. The performance of the proposed ICA model for background subtraction is also compared with that of the well-known FastICA algorithm.      

基于插值圓阵的宽带信号二维空间谱估计

在阵列信号处理中,确定信号的波达方向(DOA)需要估计信号的二维(2-D)空间谱。C。Usha Padmini等人(1994)已证明,圆阵用于估计宽带信号的DOA时具有许多好的特性。尤其是在基于圆阵的宽带信号子空间一维DOA估计中,即使不用延迟抽头也不会出现频率-方向模糊。在估计宽带信号的2-D空间谱时,我们发现用不带延迟抽头的圆阵会出现频率-仰角模糊。本文提出了一种用插值圆阵估计宽带信号2-D空间谱的新方法。在估计中,采用大孔径的圆阵(rmin/2)能获得更好的分辨性能和估计稳健性。     

A fast valley-based segmentation for detection of slowly moving objects

Moving object detection in a video sequence is the first and most important step in many computer vision applications. However, it is challenging for a machine to match with the human visual perception level. Motion information of slowly moving object is highly erroneous in comparison with fast moving object. Therefore, in real time, accurate segmentation of slowly moving objects is more challenging. In this paper, a fast and efficient segmentation algorithm is proposed for the detection of slowly moving object in a video sequence. The proposed method has three steps to extract the slowly moving object in a video. In the first step, an averaging frame difference method is proposed to extract the motion information. In the second step, a valley-based thresholding is proposed to segment all the frames of a video. In the final step, the motion information and spatial homogeneous region information are merged to extract the slowly moving object.     

Dynamic Fractional Frequency Reuse (DFFR) with AMC and Random Access in WiMAX System

In this paper; dynamical resource allocation scheme is proposed to improve throughput and fairness in the modern broadband wireless systems such as IEEE 802.16 Worldwide Interoperability for Microwave Access. To assign the subcarriers to users, dynamic fractional frequency reuse is used. In dynamic fractional frequency reuse, each cell is partitioned into two regions, one called super region and another called regular region. Regular region is divided into 3 parts which correspond to the three sectors. In this method, a utility function is firstly used for the subcarrier allocation to the geographical regions and then opportunistic scheduling is applied for the assignment subcarriers to users in each cell. In order to increase the throughput of the system, adaptive modulation and coding techniques are used. Using dynamic fractional frequency reuse reduces fairness among users of a cell. Therefore a random access sub-band is applied to improve the fairness of the system.     

基于多级描述模型的渐进式图像内容理解

针对目前基于内容的图像检索技术中低级特征无法准确全面地描述高级语义的问题,本文提出了一种基于多级图像描述模型的渐进式图像内容理解.该图像描述模型在不同层次上对图像内容进行分析和提取,实现了图像内容的全方位描述,从底层向高层的过渡是渐进式的图像理解过程.特别是从视觉感知层到目标层,体现了图像低级特征与高级语义之间的过渡.本文给出了一种基于先验知识的上下文驱动的目标理解算法,实现了图像语义的提取.作为一个应用实例,本文给出了以上方法在基于内容的图像检索技术中的具体应用.     

Characterizations of GaN films grown with indium surfactant by RF-plasma assisted molecular beam epitaxy

A small indium flux was used as a surfactant during the growth of gallium nitride by rf-plasma assisted molecular beam epitaxy. The effects of the In surfactant on the optical and structural properties of undoped GaN were studied by photoluminescence (PL), X-ray diffraction, atomic force microscopy (AFM), and Rutherford backscattering spectrometry (RBS). PL studies show that the use of In surfactant is beneficial to the reduction of deep-level defects. The X-ray rocking curves demonstrate a 20% decrease in the full width at half maximum value for the films grown with In surfactant. AFM studies show that the root mean squared surface roughness for films grown with and without In surfactant are 5.86 and 6.99 nm respectively indicating significant improvement in surface morphology. The improved surface morphology is attributed to the enhanced 2-dimensional growth promoted by the application of In surfactant. RBS studies show that the χ_min values along [0 0 0 1] direction are 2.06% and 2.16% for the samples grown with and without In surfactant respectively. Off-normal ion channeling studies were performed to further investigate the effects of In surfactant on the crystallinity. It is found that the number density of stacking faults is smaller for the sample grown with In surfactant compared to the one grown without In surfactant. However, defect analysis shows that dislocations are found in the sample grown with In surfactant in contrary to the one grown without In surfactant. We speculate that there is a thickness limit of GaN grown with In surfactant and the thickness of our samples exceed this limit, leading to the presence of dislocation.     

Building kernels from binary strings for image matching.

In the statistical learning framework, the use of appropriate kernels may be the key for substantial improvement in solving a given problem. In essence, a kernel is a similarity measure between input points satisfying some mathematical requirements and possibly capturing the domain knowledge. In this paper, we focus on kernels for images: we represent the image information content with binary strings and discuss various bitwise manipulations obtained using logical operators and convolution with nonbinary stencils. In the theoretical contribution of our work, we show that histogram intersection is a Mercer's kernel and we determine the modifications under which a similarity measure based on the notion of Hausdorff distance is also a Mercer's kernel. In both cases, we determine explicitly the mapping from input to feature space. The presented experimental results support the relevance of our analysis for developing effective trainable systems.     

Cluster-Based and Distributed IPv6 Address Configuration Scheme for a MANET

In a Mobile Ad hoc Network (MANET), after a mobile node is configured with a unique IP address it can perform the unicast communications. In order to reduce the address configuration cost and shorten the latency, this paper proposes an IPv6 address configuration scheme for a MANET. In the scheme, the cluster-based architecture is proposed. In the architecture, the clustering mechanism is combined with the address configuration process in order to achieve the low-cost and low-latency address configuration for all nodes in a MANET. Based on the architecture, the distributed address configuration algorithm is proposed. In the algorithm, a cluster member acquires an address from a cluster head within one-hop scope, so the address configuration task is distributed around cluster heads. In this way, the address configuration in different clusters can be performed in parallel, so the address configuration delay is shortened and the network scalability is improved. The address reclamation/maintenance algorithm is also proposed so that the address resources released by failed nodes can be rapidly recovered for reuse. Finally, the merging/splitting algorithm is proposed in order to ensure that no address collision happens in a MANET. This paper analyzes the performance parameters of the proposed scheme, and the data results show that the proposed scheme effectively reduces the address configuration cost and shortens the delay.     

Algorithms for Dynamic Routing in All-Optical Networks

In this paper, we have studied a number of algorithms for routing in all-optical wavelength routed networks. We have considered situations where a lightpath is dynamically created in response to a request for communication and the WDM channels constituting the lightpath are reclaimed when the communication is over. We have looked at two schemes for dynamic wavelength allocation. In the first scheme we have assumed the existence of a central agent to maintain a database of existing lightpaths where the central agent attempts to generate a new lightpath in response to a request for communication. In the second scheme, we attempt to generate a new lightpath using a distributed algorithm. In the first scheme we have exploited the existence of multiple paths between any pair of nodes in a network in order to reduce the blocking probability. For the second scheme, we have proposed three distributed strategies to determine, if possible, a lightpath when there is a request for communication. Each of these strategies have their advantages and disadvantages in terms of the expected blocking probability and the set-up time. We have studied the performances of both the schemes using Monte Carlo simulation.     

利用S-B自适应采样方法加速基于空间映射技术的神经网络建模

将空间映射技术用于辅助神经网络的建模可以帮助降低神经网络的复杂程度，从而达到降低训练成本的目的。但是，不论是空间映射技术还是神经网络的训练，需要大量的采样是这一技术中一个关键问题。本文将一种灵活高效的自适应采样技术运用在基于空间映射技术的神经网络建模过程中，大大减少了建模需要的采样时间，提高了最终得到模型的精度。     

Electromagnetic Potentials and Field Expansions for Plasma Radiation in Waveguides

In order to calculate the raditaion from plasmas placed in waveguides it is necessary to know the field produced by arbitrarily moving charged particles in a waveguide. In this paper modal expansions for the vector and scalar potentials due to arbitrarily moving charged particles in a waveguide are derived and provide the extension of the Lienard-Wiechert potentials to a waveguide environment. In addition, for a plasma filled waveguide, a modal expansion is given of the electric field directly in terms of mode coupling with the charge motion. Expressions for the spectral distribution of the radiation are given, both in general and for cyclotron radiation. Some specific results for the H/sub 10/ mode excited in a rectangular guide by cyclotron motion are also presented.     

Designing the focused and wide beam pattern in linear and planar phased‐MIMO radar considering the antennas' overlap

Phased‐array multiple‐input multiple‐output (MIMO) radar is a new method for collocated MIMO radar, benefiting from its advantages without losing the coherent processing gain considered the main feature of phased‐array radars. In this method, the whole array is divided into several overlapping subarrays; then a waveform is allocated to the antennas of each subarray, which are orthogonal to other subarray's waveforms. In order to obtain a desired beam pattern, appropriate weighting coefficients for each subarray should be designed. This study aimed to design the phased‐MIMO radar's weighting coefficient matrix in two modes: In the first mode, the aim is to design a beam pattern, which has the maximum value in direction of the desired targets. In the second mode, a desired beam pattern is defined, and the coefficients should calculated in such a way that the obtained pattern be as much as possible compatible with the desired patter. In the two modes, the design, at first, is accomplished for linear array and then is extended to the planar array. Moreover, the impact of subarrays' overlap and the power constraints is investigated. The proposed methods, in special cases, are applicable in MIMO and phased‐array radars, too.     

Propagation constant and radiation resistance of linear non-resonant antenna in weakly ionized plasma†

In a series of studies of linear antennas immersed in weakly ionized plasma, the authors have investigated radiation properties of resonant and non-resonant antennas. In parts I and II of the series, propagation constant on antenna wire was considered the same as in free space and the effect of collision frequency was taken into account wherever effective. In part HI a general propagation constant for the resonant finite-sized dipole was assumed but the effect of collision frequency was neglected. In the present work called part IV of the series, a thin non-resonant end-fed antenna is employed as a source and radiation in the first Fraunhofer zone under similar conditions is considered. General expressions for radiation resistance for both the electromagnetic and electro-acoustic modes have been obtained. As a particular case, radiation resistance of each mode for optimized linear non-resonant end-fed antenna is calculated and the results are then compared with those of resonant dipole treated earlier in part III.     

3D model retrieval by sample based alignment

In 3D model retrieval, preprocessing of 3D models is needed, in which alignment is a key factor that significantly affects retrieval performance. In particular, the anti-rotation image feature can obtain the alignment effect of 3D model views. In practice, the focus of many users of 3D models is not just on retrieval performance, but the use of aligned models for different purposes. In this paper, we propose a method, namely Sample Based Alignment (SBA) for better 3D model alignment and retrieval. In SBA, given a class, a sample model is used as the target for alignment, after which each 3D model in this class is then aligned one by one, i.e., the 3D model is actually rotated. Our experimental results, based on two 3D model datasets and performance comparisons with other methods, demonstrate the superiority of the SBA method over state-of-the-art methods in terms of 3D model retrieval and classification.     

Blind downlink channel estimation for TDD‐based multiuser massive MIMO in the presence of nonlinear HPA

In time division duplex (TDD)‐based multiuser massive multiple input multiple output (MIMO) systems, the uplink channel is estimated and the results are used in downlink for signal detection. Owing to noisy uplink channel estimation, the downlink channel should also be estimated for accurate signal detection. Therefore, recently, a blind method was developed, which assumes the use of a linear high‐power amplifier (HPA) in the base station (BS). In this study, we extend this method to a scenario with a nonlinear HPA in the BS, where the Bussgang decomposition is used for HPA modeling. In the proposed method, the average power of the received signal for each user is a function of channel gain, large‐scale fading, and nonlinear distortion variance. Therefore, the channel gain is estimated, which is required for signal detection. The performance of the proposed method is analyzed theoretically. The simulation results show superior performance of the proposed method compared to that of the other methods in the literature.     

Spectrum-energy-efficient sensing with novel frame structure in cognitive radio networks

Cooperative spectrum sensing (CSS) is a promising technology in spectrum sensing with an admirable performance. In this paper, we define a utility function which jointly considers the spectrum-efficiency and the energy-efficiency. In a single-user sensing scenario, by maximizing the utility function, a rigorous analytical expression for the optimal threshold of the energy detector is derived. In CSS, the general frame structure is inefficient since the time consumed by reporting contributes little to the sensing performance. In this paper, we propose a novel CSS frame structure, in which one secondary user's (SU's) reporting time is also used for other SUs’ sensing. For time varying channels, collecting the sensing results at different time points is expected to achieve a time diversity gain for a SU, then the novel multi-minislot CSS scheme is proposed. In CSS, the optimal randomized rule and the optimal final decision threshold are derived. Simulation results show a significant improvement of the utility by using the proposed multi-minislot CSS scheme. It is also shown that there exists an optimal number of cooperating SUs that maximizes the utility, and the optimal number decreases as the price of the sensing energy increases.     

Performance analysis of closed-loop transmit diversity in thepresence of feedback delay

In this paper, a bit-error-rate (BER) analysis for closed-loop transmit diversity in a time-selective Rayleigh fading channel containing feedback delay is presented. In the absence of feedback delay, closed-loop transmit diversity always outperforms open-loop transmit for a given transmitted signal energy. This is no longer true in the presence of feedback delay. We derive closed-form expressions of the average BER for this case assuming QPSK and BPSK signaling. The results of the analysis are instrumental for comparing closed-loop with open-loop schemes under given operating conditions. In particular, we demonstrate that, for a given transmitted energy and number of transmit antennas, open-loop outperforms closed-loop at sufficiently fast channel fading. We also show that, for a given transmitted signal energy and fading rate, closed-loop outperforms open-loop for sufficiently large numbers of transmit antennas while the total average transmitted signal energy is kept constant. For some special cases, closed-form expressions for the fading rate at which the performance of open-loop is equal to closed-loop are obtained     

Design methodology of a reduced-scale test bench for fault detection and diagnosis

Condition monitoring is a crucial task for electromechanical system reliability and quality enhancement, which leads to early electrical and mechanical faults detection. In this paper, the design of a scaled test bench including its main subsystem components at initial stage is presented for the assessment of new methods dedicated to electrical and mechanical faults detection and diagnosis in electromechanical systems. In this paper a design methodology is proposed for developing a reduced-scale test bench dedicated to condition monitoring. Dimensional analysis is applied for ensuring the similarity between the scaled test bench and the full-size systems to be emulated. In addition, the scaled test bench includes the required instrumentation as well as an acquisition platform for development of condition monitoring strategy to batch condition monitoring of full-size systems. Finally, the similarity is evaluated by comparing both the simulation and the experimental results.     

Linear precoding via conic optimization for fixed MIMO receivers

In this paper, the problem of designing linear precoders for fixed multiple-input-multiple-output (MIMO) receivers is considered. Two different design criteria are considered. In the first, the transmitted power is minimized subject to signal-to-interference-plus-noise-ratio (SINR) constraints. In the second, the worst case SINR is maximized subject to a power constraint. It is shown that both problems can be solved using standard conic optimization packages. In addition, conditions are developed for the optimal precoder for both of these problems, and two simple fixed-point iterations are proposed to find the solutions that satisfy these conditions. The relation to the well-known uplink-downlink duality in the context of joint transmit beamforming and power control is also explored. The proposed precoder design is general, and as a special case, it solves the transmit rank-one beamforming problem. Simulation results in a multiuser system show that the resulting precoders can significantly outperform existing linear precoders.