Design of Smearing Filters for Data Transmission Systems

In this paper, we introduce a new approach to design smearing and desmearing filters for data transmission systems to suppress pulse-like disturbances inserted in the communication channel. Our method is based on time domain considerations. It consists of the optimization of two merit factors defined for the impulse response functions of the filters. The first one is a measure of the smearing efficiency, and the second one is a measure of the amount of intersymbol interference caused by the insertion of the two filters in the transmission system. Our method will be applied to smearing and desmearing filters for baseband signals as well as for passband signals. In particular, we show that our method leads to filters having a better smearing efficiency and a simpler implementation than the filters obtained by the classical frequency domain approach.     

Time-invariant and time-varying multirate filter banks : application to image coding

This paper reviews various concepts and solutions of time-invariant and time-varying multirate filter banks. It discusses their performance for image and video coding at low bit rates, and their applicability in the mpeg-4 framework. Time-invariant multirate filter banks, and methods of design with different criteria appropriate for signal compression are first presented. Several procedures of quantization, namely scalar and lattice vector quantization, with bit allocation optimized in the rate-distortion sense, are used for the encoding of the subband signals. A technique of rate-constrained lattice vector quantization (rc-lvq), combined with a three components entropy coding, allow, together with distortion psychovi-sual weighting mechanisms to obtain significant visual improvements versus scalar quantization or the zerotree technique. However, time-invariant multirate filter banks, although efficient in terms of compression, are not well suited for content-based functionalities. Content-based features may require the ability to manipulate and thus encode a given region in the scene independently of the neighbouring regions, hence the use of transformations that can be adapted to arbitrary size bounded supports. Also, to increase the compression efficiency, one may want to adapt the transformation to the region characteristics, and thus use transform switching mechanisms, with soft or hard transitions. Three main classes of transformations can address these problems: shape-adaptive block transforms, transforms relying on signal extensions and transforms relying on time-varying multirate filter banks. These various solutions, with their methods of design, are reviewed. Emphasis is put on an extension of the SDF (symmetric delay factorization) technique which opens new perspectives in the design of time-bounded and time-varying filter banks. A region-adapted rate-distortion quantization algorithm has been used in the evaluation of the transformations compression efficiency. The coding results illustrate the interest of these techniques for compression but also for features such as quality scalability applied to selected regions of the image.     

Invariancies in punctured convolutional codes-their effect onViterbi synchronization

This paper studies the invariance of a given punctured convolutional code to an affine class of symbol transformations known to commonly occur in digital transceiver systems. A set of conditions to test the invariance of a code to these transformations has been derived, followed by two proposed methods to compensate for an invariant transformation. The viability of these methods has been examined by doing an invariant factor decomposition on the equivalent code generator matrix (obtained from the original code generator matrix and the given transform). The knowledge of the transformation and the nature of its occurrence greatly determines which method of compensation could be used. This study has much use in not only enabling a code designer to evaluate the invariance of an affine transformation to a given code, but also on the other hand to make the appropriate choice of code generators, puncturing schemes, and bit-to-constellation symbol mapping; so as to allow a channel coding scheme to be either sensitive or invariant to a given transformation, depending upon design objectives     

Hybrid Coding of Pictorial Data

Two hybrid coding systems utilizing a cascade of a unitary transformation and differential pulse code modulators (DPCM) systems are proposed. Both systems encode the transformed data by a bank of DPCM systems. The first system uses a one-dimensional transform of the data where the second one employs two-dimensional transformations. Theoretical results for Markov data and experimental results for a typical picture are presented for Hadamard, Fourier, cosine, slant, and the KarhunenLoeve transformations. The visual effects of channel error and also the impact of noisy channel on the performance of the hybrid system, measured in terms of the signal-to-noise ratio of the encoder, is examined and the performance of this system is compared to the performances of the two-dimensional DPCM and the standard two-dimensional transform encoders.     

Bilinear signal synthesis in array processing

Multiple source signals impinging on an antenna array can be separated by time-frequency synthesis techniques. Averaging of the time-frequency distributions (TFDs) of the data across the array permits the spatial signatures of sources to play a fundamental role in improving the synthesis performance. Array averaging introduces a weighting function in the time-frequency domain that decreases the noise levels, reduces the interactions of the source signals, and mitigates the crossterms. This is achieved independent of the temporal characteristics of the source signals and without causing any smearing of the signal terms. The weighting function may take noninteger values, which are determined by the communication channel, the source positions, and their angular separations. Unlike the recently devised blind source separation methods using spatial TFDs, the proposed method does not require whitening or retrieval of the source directional matrix. The paper evaluates the proposed method in terms of performance and computations relative to the existing source separation techniques based on quadratic TFDs.     

An Analysis of Error Behavior in the Implementation of 2-D Orthogonal Transformations

The paper analyzes the effect of finite-length arithmetic in the calculation of 2-D linear transformations employed in some picture coding algorithms. Since the condition of zero-error in general direct and reverse transformations leads to results of little practical importance, an analysis is carried out on the statistical properties of error in 2-D linear transformation with given length of arithmetics. Then the important case of discrete cosine transform (DCT) applied to real images is considered in detail. The results of the paper allow a circuit designer to determine the representation accuracy of the one- and two-dimensional coefficients required to satisfy a preassigned reconstruction error on the image.     

基于星点质心运动轨迹模糊星图退化参数估计

当运动角速度超过允许的最大角速度时,星敏感器工作在动态环境下,星点的灰度特征将不再呈高斯分布,这将影响质心计算的精度。给出了在角速度的影响下星点质心运动轨迹的解析解,并结合曝光时间短的特点,对轨迹的参数方程进行简化并通过仿真分析验证了其精确性。分析了退化星点灰度分布特征,并结合星点质心运动轨迹方程提出基于质心运动轨迹对星图的退化参数进行估计的方法。通过仿真实验,完成了对退化长度及退化方向的估计,对退化长度的估计误差不超过0.8 个像素,对退化方向的估计误差不超过2,并证实了该方法能有效提高质心计算精度。     

利用空时分组编码技术提高数据传输速率的研究

未来的通信对移动通信业务的要求越来越高，随着从单纯语音业务到多媒体业务的转变，通信中数据传输速率成为抑制日后发展的因素之一。因此人们努力研究各种高效的编码、调制以及传输的技术，用以提高数据的传输速率。空时编码是近年提出的重要技术之一，这种技术已经在第三代移动通信(3G)方案中广泛应用。本文在介绍简单的空时分组编码原理的基础上，着重研究了对共道信号产生的干扰进行抵消抑制的技术。采用具有干扰抵消技术的空时分组编码系统进行并行数据传输可以充分利用干扰信号之间的相关性进行有效的抵消处理，在原有的信道上能够极大的提高数据的传输速率。文中提出了一种利用多种调制方式抗干扰性能的不同，对共道信号进行分步解码来削弱共道干扰的影响的空时分组编码并行传输策略。这种方法能够进一步提高信号传输的性能，为提高通信系统的数据传输速率做出了保证。     

Analytical calculation of the RFOC method in single-phase induction motor

This study discusses the different techniques for speed control of single-phase induction motor with two asymmetrical main and auxiliary windings based on Rotor Field-Oriented Control (RFOC) method. In the presented methods, transformation matrices are introduced and applied to the equations of single-phase induction motor. It is shown by applying these rotational transformations to the unbalanced equations of single-phase induction motor, equations of single-phase induction motor are transformed into symmetrical equations. These rotational transformations are achieved based from the steady-state equivalent circuit of single-phase induction motor. Finally, a method for RFOC of single-phase induction motor is proposed. Results show the good performance of the proposed method.     

Adaptive Gabor transformation for image processing

An algorithm that computes the Gabor coefficients of an image is presented. An adaptive filter that uses the complex least mean-square algorithm for their computation is proposed, and its numerical characteristics are discussed. It is shown that the filter is stable under certain conditions. Because the Gabor transformation seems to be an excellent tool for image compression, the efficiency of information coding using the Gabor coefficients is investigated and compared with coding that uses the coefficients of the discrete cosine transformation (DCT). Properties of both transformations are discussed.     

Use of Error Correcting Codes on Memory Words for Improved Reliability

Application of error correcting coding is often employed to improve system operation and reliability. By means of suitable reliability models and simple analysis, the effect of error correcting coding of memory words on the overall reliability of the system is discussed. Introduction of error correcting facilities will generally have three significant effects on the system: 1) increased hardware, which is also subject to failures and hence tends to lower reliability; 2) the system's ability to function in the presence of a certain class of failures; and 3) quicker detection of errors, which also means an improved repair rate. To illustrate the extent to which the above three factors govern the reliability improvement due to coding, three types of systems are considered. These systems use the same basic processor and memory units but differ in their structure and complexity. Other factors besides the three above which control the reliability improvement due to coding are the system structure and the relative sizes of processor and memory hardware.     

Oblique generalizations of the Walsh basis

An approach to building generalized oblique discrete Walsh basis is suggested. Methods that allow forming transformation matrices based on oblique discrete Walsh functions are developed. Some properties of the suggested oblique discrete Walsh transformations and their applications to synthesizing algorithms of parametric estimation of polynomial trend models of digital signals are considered.     

Performance of asymmetric digital subscriber lines in an impulse noise environment

The paper presents a numerical study of the impact of impulse noise on asymmetric digital subscriber lines (ADSL). Methods for simulating the effect of impulse disturbances on a discrete multitone system are first presented, and actual measured noise bursts are then used for the simulations as if they were deterministic signals, in order to characterize their effects on ADSL systems. It is shown that, while a combination of coding, interleaving, and 6-dB margin is adequate in protecting ADSL systems from isolated impulses, an impulse train with long duration can cause a significant number of error bits in the system. In this case, a tradeoff among the number of error seconds, the maximum reach, and the coding delay must be made.     

Fractal image coding: a review

An approach to image coding based on a fractal theory of iterated contractive transformations defined piecewise is described. The main characteristics of this approach are that it relies on the assumption that image redundancy can be efficiently captured and exploited through piecewise self-transformability on a block-wise basis, and it approximates an original image by a fractal image, obtained from a finite number of iterations of an image transformation called a fractal code. This approach is referred to as fractal block coding. The general coding-decoding system is based on the construction, for an image to be encoded, of a fractal code-a contractive image transformation for which the original image is an approximate fixed point-which, when applied iteratively on any initial image of the decoder, produces a sequence of images which converges to a fractal approximation of the original. The design of a system for the encoding of monochrome digital images at rates below 1 b/pixel is described. Ideas and extensions from the work of other researchers are presented     

离散Walsh-Haar变换的快速算法

Walsh-Haar函数系是一种具有良好的全局/局部性质的函数系,与其对应的离散变换是一种正交变换,有着广阔的应用前景。该文给出了离散Walsh-Haar变换及其逆变换的定义,并运用二分技术得到了离散Walsh-Haar变换的快速算法。文中的设计思想和方法可用于研究其它序的离散Walsh-Haar变换和其它的正交变换的快速算法。     

Hybrid Digital-Analog Coding with Bandwidth Compression for Gaussian Source-Channel Pairs

Three hybrid digital-analog (HDA) systems, denoted by HDA-I, HDA* and HDA-II, for the coding of a memoryless discrete-time Gaussian source over a discrete-time additive memoryless Gaussian channel under bandwidth compression are studied. The systems employ simple linear coding in their analog component and superimpose their analog and digital signals before channel transmission. Information-theoretic upper bounds on the asymptotically optimal mean squared error distortion of the systems are obtained under both matched and mismatched channel conditions. Allocation schemes for distributing the channel input power between the analog and the digital signals are also examined. It is shown that systems HDA* and HDA-II can asymptotically achieve the optimal Shannon-limit performance under matched channel conditions. Low-complexity and low-delay versions of systems HDA-I and HDA-II are next designed and implemented without the use of error correcting codes. The parameters of these HDA systems, which employ vector quantization in conjunction with binary phase-shift keying modulation in their digital part, are optimized via an iterative algorithm similar to the design algorithm for channel-optimized vector quantizers. Both systems have low complexity and low delay, and guarantee graceful performance improvements for high CSNRs. For memoryless Gaussian sources the designed HDA-II system is shown to be superior to the HDA-I designed system. When applied to a Gauss-Markov source under Karhunen-Loeve processing, the HDA-I system is shown to provide considerably better performance.     

A Method for Extracting the Fundamental-Frequency Positive-Sequence Voltage Vector Based on Simple Mathematical Transformations

In this paper, a novel scheme for obtaining the fundamental-frequency positive-sequence grid voltage is proposed. The method is based on four simple mathematical transformations; two of them are in the stationary reference frame, which are able to eliminate odd harmonics from the original signals. The other two transformations are implemented in a synchronously rotating reference frame in order to eliminate even harmonics. The output of the last transformation block is the input to a synchronous reference-frame phase-locked loop for detecting the frequency and position of the positive-sequence voltage vector. The proposed algorithm was verified through simulations and experiments by applying distorted and unbalanced signals, containing positive and negative-sequence components. The results are in agreement with those theoretically predicted and indicate that the proposed scheme has a great potential for use in grid-connected converter synchronization algorithms.     

Unitary equivalence: a new twist on signal processing

Unitary similarity transformations furnish a powerful vehicle for generating infinite generic classes of signal analysis and processing tools based on concepts different from time, frequency, and scale. Implementation of these new tools involves simply preprocessing the signal by a unitary transformation, performing standard processing on the transformed signal, and then (in some cases) transforming the resulting output. The resulting unitarily equivalent systems can focus on the critical signal characteristics in large classes of signals and, hence, prove useful for representing and processing signals that are not well matched by current techniques. As specific examples of this procedure, we generalize linear time-invariant systems, orthonormal basis and frame decompositions, and joint time-frequency and time-scale distributions. These applications illustrate the utility of the unitary equivalence concept for uniting seemingly disparate approaches proposed in the literature     

An efficient coordinate frame calibration method for 3-D measurement by multiple camera systems

Extrinsic calibration or coordinate frame calibration of multiple cameras is a critical step for conducting three-dimensional measurement effectively from visual images. Based on the concept of relative world coordinate system, an efficient method for calibrating the coordinate frames for multiple cameras has been developed in this paper. Its basic idea is to compute the transformation matrices between cameras from their individual transformation matrices to a relative world coordinate system such that its absolute coordinate information is not required and methods for single camera calibration can be utilized. A solution procedure that separates rotational parameters from translation parameters of transformation matrices has been developed where the rotational parameters are obtained first by solving a set of nonlinear equations involving two Euler angular parameters, while the translational parameters are then calculated analytically. In addition, equations for calculating the depth information and matching lines in general cases have been presented. Finally, a detailed numerical investigation regarding the error and sensitivity analysis of the proposed calibration algorithms has been performed extensively.     

斜坡类信号频谱分析时应注意的一个问题

斜坡类信号属功率无限信号,针对常见于各种复变函数与积分变换类教科书中此类信号的傅里叶变换结果提出了质疑,认为以傅里叶变换所体现的此类信号的频谱特性不具有实际意义或应用背景。通过对傅里叶变换基本定义、运算性质、物理意义以及斜坡信号频谱特性的分析,表明在信号频谱分析过程中,傅里叶变换这一频谱分析工具不一定适用于功率无限信号。