A new edge element analysis of dispersive waveguiding structures

A new functional is rigorously selected for the edge element method to solve the 2-D¹/₂ guided wave problems. The variational formulation is derived from the vector wave equation without any assumption or simplifications, and therefore the formulation is the full-wave analysis. Moderate to heavy ohmic loss and dielectric loss are taken into account in a natural and consistent manner. As a result, finite cross-section of arbitrary shape and finite conductivity can be handled without imposing the impedance boundary condition (IBC). The DEC may no longer be held for high-speed microelectronics applications, where the cross-section dimension may have been in the same order of the skin depths of some frequency components. The propagation modes are obtained by solving the large scale generalized eigenvalue and eigenvector equations employing the subspace iteration method. The spurious modes are totally suppressed in the whole frequency range of interest. Numerical examples of dielectric waveguides and microstrip transmission lines with finite conductivity are conducted     

Hierarchical vector finite elements for analyzing waveguiding structures

In this paper, we extend the finite-element method into hierarchical higher order bases and the inexact Helmholtz decomposition. With the help of hierarchical basis functions, the approach can adopt well into the p version adaptive process. On the other hand, the inexact Helmholtz decomposition enhances the stability of the finite-element procedure when the operating frequency is low or the element size is very small compared to the wavelength. This approach can also enhance the h version adaptive mesh refinement process since the process may cause very small elements near a singular region. To accomplish the inexact Helmholtz decomposition for the edge elements, the lowest order curl conforming basis functions, the tree-cotree splitting, is utilized, and the general procedure is presented. As a result, a combination of hierarchical higher order basis functions with the inexact Helmholtz decomposition can improve the efficiency and the stability of the hp adaptive mesh refinement process. The accuracy and stability of the proposed approach are also discussed through numerical examples.     

Spatial error concealment with sequence-aligned texture modeling and adaptive directional recovery

A spatial error concealment technique based on the sequence-aligned texture modeling and the adaptive directional recovery is proposed in this work. The sequence alignment technique captures the local variation and the global trend of image textures with surrounding uncorrupted pixels, and provides the best texture model under a given cost function. With the derived texture model, geometric interpolation is used to recover lost pixels adaptively based on pixel locations. There are four candidate modes of pixel sequences to recover lost pixels, and one of them is selected for the concealment purpose. The selection criterion is based on the texture pattern modes of surrounding uncorrupted blocks. The pixel sequences used for error concealment can be obtained from the computation of the decoder or the side information from the encoder. Extensive experimental results are given to demonstrate that our error concealment technique outperforms several benchmark methods in both objective and subjective tests.     

A three-dimensional time-domain finite-element formulation for periodic structures

A formulation is presented for a three-dimensional time-domain finite-element method that can be used to analyze the scattering of a plane wave obliquely incident on a (doubly) infinite periodic structure using one unit cell. A broadband frequency response can be obtained in a single execution. The specifics of the method are shown for scattering problems, but it should be straightforward to extend it to radiation problems. The method solves for a transformed field variable (instead of solving directly for the electric field) in order to easily enable periodic boundary conditions in the time domain. The accuracy and stability of the method is demonstrated by a series of examples where the new formulation is compared with reference solutions. Accurate results are obtained when the excitation (frequency range) and the geometry are such that no higher order propagating Floquet modes are present. The accuracy is degraded in the presence of higher order propagating modes due to the rather simple absorbing boundary condition that is used with the present formulation. The method is found to be stable even for angles of incidence close to grazing.     

Current computation on complex structures by finite-element method

The finite-element method is applied to compute the skin current and radar cross-sections of perfectly conducting square surfaces. The predictions are compared with those given other methods. The efficiency, economy, accuracy and applications     

New error recovery strategy for 64 kbit/s video codecs

A new error recovery strategy for 64 kbit/s video codecs is described. Unlike existing strategies of error recovery in which a new frame is transmitted on the detection of a channel error, the new strategy uses previous frames which are known to be correct. Computer simulations of the technique are performed and subjective and quantitative results are obtained     

Transient analysis of adaptive filters with error nonlinearities

The paper develops a unified approach to the transient analysis of adaptive filters with error nonlinearities. In addition to deriving earlier results in a unified manner, the approach also leads to new performance results without restricting the regression data to being Gaussian or white. The framework is based on energy-conservation arguments and avoids the need for explicit recursions for the covariance matrix of the weight-error vector.     

New structures for adaptive filtering in subbands with critical sampling

Some properties of an adaptive filtering structure that employs an analysis filterbank to decompose the input signal and sparse adaptive filters in the subbands are investigated in this paper. The necessary conditions on the filterbank and on the structure parameters for exact modeling of an arbitrary linear system with finite impulse response (FIR) are derived. Then, based on the results obtained for the sparse subfilter structure, a new family of adaptive structures with critical sampling of the subband signals, which can also yield exact modeling, is obtained. Two adaptation algorithms based on the normalized LMS algorithm are derived for the new subband structures with critical sampling. A convergence analysis, as well as a computational complexity analysis, of the proposed adaptive structures are presented. The convergence behavior of the proposed adaptive structures is verified by computer simulations and compared with the behavior of previously proposed algorithms.     

Electrodynamic analysis of interaction of electromagnetic waves with nonlinear gyromagnetic inclusions in waveguiding structures

A numerical method is developed for solution of 3D nonlinear boundary value problems of electromagnetics. The method proposed is applied for the numerical investigation of propagation, diffraction, and distributed interaction of electromagnetic waves in a strip-slot waveguiding structure containing a ferrite inclusion.     

Nonlinear prism coupling in waveguiding structures deposited on to semiconductor-doped glass

The fabrication procedure and properties of an optical nonlinear guided-wave structure are reported. The structure consists of a thin film of Corning 7059 glass deposited by RF planar magnetron sputtering on a surface of CdSxSe1?x doped glass. The limiting action in power-dependent prism coupling into the structure is described.     

Hybrid finite-element analysis of electromagnetic plane wavescattering from axially periodic cylindrical structures

In many antenna systems the primary feed or the subreflector will most often be supported by struts which obstruct the aperture and therefore cause a reduction in the directivity and an increase in sidelobe levels. So as to be able to design new structures which avoid these drawbacks, the problem of plane wave scattering from an infinite axially periodic cylinder of arbitrary geometric and material parameters is analyzed by a hybrid finite element/boundary element method. Covariant-projection edge elements are employed in the inhomogeneous region of the unit cell and the scattered field is expanded in terms of cylindrical Floquet harmonics. The resulting practical numerical procedure has been tested to ensure that power conservation rules are obeyed and checked satisfactorily against both analytical results and measurements on periodically loaded struts     

A left-handed composite medium based on waveguiding structures with a bianisotropic filling

A new composite medium based on waveguiding structures loaded with bianisotropic gratings of planar double split rings (PDSRs) and planar helices is considered. The microwave transmission spectra of this medium are studied experimentally. The effective parameters of the medium are determined theoretically, and its passbands are investigated. The characteristics of the medium are compared to those of infinite homogeneous bianisotropic media. A relationship between the spectral transmission characteristics and the type of resonance excitation is established. The transparency bands and overforbidden bands of the composite medium are revealed. The combinations of the medium’s effective parameters that correspond to these bands are determined. It is shown that the transparency bands where the medium is characterized simultaneously by negative permittivity and negative permeability can be identified.     

LDPC编码系统符号同步技术

根据低密度校验码(LDPC)译码算法的统计特性,分析了接收端符号同步误差对译码性能的影响。针对 LDPC 编码系统的特点提出了一种新的符号同步误差校正算法,该算法通过 4 倍过采样技术判断同步误差的大小,并通过插值方式对精确同步采样点的信号进行估计。对于信噪比极低的通信系统,当存在较大符号同步误差时,该算法可以保证 LDPC 编码系统的性能接近精确同步情况下的性能。     

用2.5维的边缘元法分析屏蔽导波结构中含非匀质基片的微带线

微波单片集成电路（MMIC）的优化设计已受到工业界的关注，而MMIC元件广为采用含非匀质基片的微带线。用2．5维的边缘元法研究了这类屏蔽导波结构的色散特征，所导出的公式适用于各种复杂形状的导波结构。对某些简单结构，该结果与用其它解析和数值方法得出的数据相符；对某些复杂结构，提供的新结果预示了扩展应用的可能性。     

Lower error bound for oversampled subband adaptive filters

The authors evaluate error performance limitations in oversampled subband adaptive filter applications based on an analysis of aliasing in the subband signals. The power spectral density of the minimum error signal is given by the aliased signal components. The presented analysis closely agrees with simulation results     

Three-dimensional edge-based finite-element analysis for discretebodies of revolution

An extension to three-dimensional (3-D) edge-based finite-element analysis for modeling electrically large fan-like bodies as discrete bodies of revolution is given. By exploiting the overlapping symmetries between a fan-like body and a modal expansion of the electromagnetic fields, only one lobe of the problem need be solved by the finite-element method without introducing approximations. This computational scaling makes possible the solution of electrically large structures much more efficiently. However, a periodic phase-boundary condition (PBC) must be applied to the faces of the mesh describing a single slice of the body and this condition must be enforced on both the electric and magnetic fields for a robust solution. Details on the implementation of the PBCs are given along with results which validate the overall technique     

New adaptive partial distortion search using clustered pixel matching error characteristic.

In order to reduce the computation load, many conventional fast block-matching algorithms have been developed to reduce the set of possible searching points in the search window. All of these algorithms produce some quality degradation of a predicted image. Alternatively, another kind of fast block-matching algorithms which do not introduce any prediction error as compared with the full-search algorithm is to reduce the number of necessary matching evaluations for every searching point in the search window. The partial distortion search (PDS) is a well-known technique of the second kind of algorithms. In the literature, many researches tried to improve both lossy and lossless block-matching algorithms by making use of an assumption that pixels with larger gradient magnitudes have larger matching errors on average. Based on a simple analysis, it is found that, on average, pixel matching errors with similar magnitudes tend to appear in clusters for natural video sequences. By using this clustering characteristic, we propose an adaptive PDS algorithm which significantly improves the computation efficiency of the original PDS. This approach is much better than other algorithms which make use of the pixel gradients. Furthermore, the proposed algorithm is most suitable for motion estimation of both opaque and boundary macroblocks of an arbitrary-shaped object in MPEG-4 coding.     

Method for error recovery of line spectral frequencies

The authors have exploited the ideas used in vector quantisation for error recovery of scalar quantised LSFs. The good performance of this method has provided high resistance of the LSFs to channel errors, outperforming other schemes by, possibly, a considerable margin. Better objective and subjective performances were obtained with this new method which obviates the need for more powerful FEC schemes for transmission over noisy channels.<>     

A floating-point arithmetic error analysis of direct and indirectcoefficient updating techniques for adaptive lattice filters

The ways in which finite precision arithmetic effects can deleteriously manifest themselves in both the stochastic gradient and the recursive least squares adaptive lattice filters are discussed. closed form expressions are derived for the steady-state variance of the accumulated arithmetic error in a single adaptive lattice coefficient using a floating-point stochastic arithmetic error analysis. The analytical results show that the performance of adaptive lattice filters using a direct updating computational form is less sensitive to finite precision effects than that of adaptive lattice filters using an indirect updating computational form. In addition, a method for reducing the self-generated noise is presented. Experimental results obtained on a 32-b floating-point hardware implementation of the adaptive lattice filters and with computer simulations are included to verify the analytical results describing the effects of finite precision on adaptive lattice filters