Laser clipping distortion in analog and digital channels

The exact carrier-to-nonlinear distortion (C/NLD) ratio, resulting from laser clipping, is computed for the low, center, and high channels of the analog and digital bands of a hybrid fiber/coax system. The computed results indicate that high capacity digital channels can be added to present analog systems without affecting the high performance analog channels     

A new approach for nonlinear distortion correction in endoscopicimages based on least squares estimation

Images captured with a typical endoscope show spatial distortion, which necessitates distortion correction for subsequent analysis. In this paper, a new methodology based on least squares estimation is proposed to correct the nonlinear distortion in the endoscopic images. A mathematical model based on polynomial mapping is used to map the images from distorted image space onto the corrected image space. The model parameters include the polynomial coefficients, distortion center, and corrected center. The proposed method utilizes a line search approach of global convergence for the iterative procedure to obtain the optimum expansion coefficients. A new technique to find the distortion center of the image based on curvature criterion is presented. A dual-step approach comprising token matching and integrated neighborhood search is also proposed for accurate extraction of the centers of the dots contained in a rectangular grid, used for the model parameter estimation. The model parameters were verified with different grid patterns. The distortion-correction model is applied to several gastrointestinal images and the results are presented. The proposed technique provides high-speed response and forms a key step toward online camera calibration, which is required for accurate quantitative analysis of the images.     

Techniques for evaluating harmonic distortion in class-AB output stages: A tutorial

In this paper, we discuss and provide a detailed tutorial of four different methods for analytically evaluating the harmonic distortion in class-AB stages. All the methods are suitable for pencil-and-paper analysis and are based on modeling the stage with a specific non-linear function. We analyze them in details and extend some of them for predicting harmonic distortion behavior in a wide range of input signal amplitude. Comparisons made by means of simulations, reveal that some methods are more precise than others but require more computational effort. On the contrary, some of them are simple to use but are less precise. Moreover, some are more appropriate for predicting HD₂ and others for HD₃, only. Results of the present paper may be used by designers to choose the more efficient method for analyzing distortion in class-AB stages. Gianluca Giustolisi was born in Catania, Italy, in 1971. He received the Laurea degree (cum laude) in electronic engineering and the Ph.D. degree in electrical engineering from University of Catania, Catania, Italy, in 1995 and 1999, respectively. Currently he is associate professor at Dipartimento di Ingegneria Elettrica Elettronica e dei Sistemi (DIEES), University of Catania. His research interests include analysis, modelling and design of analog integrated circuits and systems with particular emphasis on non-linear and low-voltage applications. Gianluca Giustolisi is IEEE Member. Gaetano Palumbo was born in Catania, Italy, in 1964. He received the laurea degree in Electrical Engineering in 1988 and a Ph.D. degree from the University of Catania in 1993. Since 1993 he conducts courses on Electronic Devices, Electronics for Digital Systems and basic Electronics. In 1994 he joined the DEES (Dipartimento Elettrico Elettronico e Sistemistico), now DIEES (Dipartimento di Ingegneria Elettrica Elettronica e dei Sistemi), at the University of Catania as a researcher, subsequently becoming associate professor in 1998. Since 2000 he is a full professor in the same department. His primary research interest has been analog circuits with particular emphasis on feedback circuits, compensation techniques, current-mode approach, low-voltage circuits. Then, his research has also embraced digital circuits with emphasis on bipolar and MOS current-mode digital circuits, adiabatic circuits, and high-performance building blocks focused on achieving optimum speed within the constraint of low power operation. In all these fields he is developing some the research activities in collaboration with STMicroelectronics of Catania. He was the co-author of three books “CMOS Current Amplifiers” and ”Feedback Amplifiers: theory and design” and “Model and Design of Bipolar and MOS Current-Mode Logic (CML, ECL and SCL Digital Circuits)” all by Kluwer Academic Publishers, in 1999, 2001 and 2004, respectively. He is a contributor to the Wiley Encyclopedia of Electrical and Electronics Engineering. He is the author of more than 250 scientific papers on referred international journals (over 100) and in conferences. Moreover he is co-author of several patents. In 1999/2001 and 2004/2005 he served as Associated Editor of the IEEE Transactions on Circuits and Systems part I for the topic “Analog Circuits and Filters” and “Digital Circuits and Systems”, respectively. In 2005 he was one of the 12 panelists in the scientific-disciplinare area 09 - industrial and information engineering of the CIVR (Committee for Evaluation of Italian Research), which has the aim to evaluate the Italian research in the above area for the period 2001–2003. In 2003 he received the Darlington award. Since 2006 he is serving as Associated Editor of the IEEE Transactions on Circuits and Systems part I. Prof. Palumbo is an IEEE Senior Member.     

Numerical simulation of clipping induced distortion in externallymodulated lightwave AM-SCM systems

For the first time to our knowledge the results of numerical simulation, and experimental verification, of clipping induced distortion in externally modulated lightwave AM-SCM CATV systems are presented. Comparison of these results with clipping induced distortion in directly modulated systems show a remarkable outcome: under the same modulation conditions the composite triple beat (CTB) distortion component in externally modulated systems is 6 dB higher than in directly modulated systems     

A new approach to authentication of binary images for multimedia communication with distortion reduction and security enhancement

A new approach to binary image authentication in multimedia communication with distortion reduction and security enhancement is proposed. Special codes are embedded into the blocks of given images and verified to accomplish the authentication purpose. Enhancement of security in detecting tampered images is achieved by randomly generating the codes and embedding them into randomly selected locations in the image blocks. The reduction of image distortion coming from pixel value replacement in code embedding is carried out by allowing multiple locations for embedding the codes. Security analysis and experimental results are also included to show the effectiveness of the proposed approach.     

LED clipping distortion compensation in optical wireless communication via multiple transmit LEDs

A method to reduce signal clipping distortion in indoor optical wireless communication systems based on orthogonal frequency division multiplexing (OFDM) modulation is presented in this paper. Compensating the resulting clipping distortion due to LED operational constrains is achieved through the use of iterative signal clipping (ISC) and multiple light emitting diodes (LED) at the transmitter. ISC technique is based on iterative clipping of the time domain OFDM signal and transmission from a multiple LED transmitter. Transmit LEDs are synchronized, located close to each other, and placed to emit light in the same direction. Hence, the channel path gains from each LED to the receiver photo diode are similar. The received signals from the different LEDs add coherently at the receiver. Reported results demonstrate that the effect of distortion due to clipping is eliminated or significantly reduced based on the considered number of LEDs.     

电视节目直播谨防音频消波失真

电视节目直播的音频处理流程与录播不同，加上现场节目音、视频传输的实时性和不可加工性存在非线性失真。通过对音频消波失真产生原因的分析，强调音频电平匹配的重要性，并改善失真的方法。     

Approximate dynamic model for evaluating distortion in a semiconductor laser under overmodulation

Overmodulation of a directly modulated semiconductor laser causes distortion in the optical signal. This distortion can be analyzed, in a first approach, using the model of a static limiter for the laser. In this letter, the dynamic effects in overmodulation of a semiconductor laser are addressed for a sinusoidal modulating current and an improved model is proposed by introducing an hysteresis. A time delay is taken into account for evaluating additional dynamic distortion arising when the optical intensity rises above threshold.     

A new method for distortion correction of electronic endoscope images

A new method to correct the barrel distortion of an electronic endoscope image is presented. A correction model assuming circularly symmetric distortion is introduced with the following model parameters: the center of distortion and the coefficients of polynomials representing the distortion correction in the radial direction. If the imaging system is distortion-free, straight lines in the object space should be imaged as straight lines. Based on this criterion, a distorted image of a standard pattern consisting of a grid of several straight lines is recorded, and the model parameters are then estimated as a basis for straightening distorted lines. This method has the advantage of not needing a careful placement of the standard pattern for calibration. Correction results are presented for the grid pattern chart to verify a sufficient degree of correction. Examples of distortion correction of real intestinal images and physicians' comments are also presented.     

A new distortion measure for motion estimation in motion-compensated hybrid video coding

In the video coding standards MPEG-x and H.26x, a motion-compensated prediction technique is used for enhancing the coding performance of bitrate reduction or peak signal to noise ratio (PSNR) improvement. This technique takes advantage of the correlation between consecutive frames in the time domain, which is relatively higher than that between adjacent blocks in the spatial domain. In order to utilize the correlation between consecutive frames, the conventional video coding standards have used the motion estimation (ME) and compensation technique, where the Sum of the Absolute Differences (SAD) is usually used as the distortion measure. The ME estimates the reference block that could minimize the residual signal between the current and reference blocks. However, the SAD is not appropriate to the specific sequences that have global or local illumination changes. In addition, the high-resolution video sequences have higher spatial correlation than the low-resolution video sequences in general. Therefore, a new distortion measure that can consider spatial and temporal correlation simultaneously may be helpful to enhance the coding performance. The proposed distortion measure searches for a reference block that minimizes the motion-compensated residual signal when the DC-component is predicted. In our proposed algorithm, the maximum BD-rate improvement is up to 13.6% for illumination-changed video sequences, and the average BD-rate improvement is 6.6% for various high-resolution video sequences in the baseline profile.     

A practical approach to evaluating test results

The author describes the procedure used at NCR Corporation to evaluate the data collected during usability tests. He points out that it can be overwhelming to face a mass of data to be compiled, categorized, analyzed, and evaluated at the end of a test, with limited time available for producing a report. This situation is avoided by defining, before a test, the tools that will be used to collect the test data and the process by which the results will be evaluated, and then performing the preliminary evaluation of data in a process parallel with the test itself. At the end of the test, an evaluation meeting is held at which the cumulative results are reviewed and solutions to the problems that have been identified are defined     

A new approach for evaluating the performance of a symbol timingrecovery system employing a general type of nonlinearity

A new technique is presented for evaluating the jitter performance of a symbol timing recovery (STR) subsystem for digital data transmission systems. The STR system consists of any even-symmetric zero-memory nonlinear device followed by a narrowband filter tuned to the pulse repetition frequency. Exact analytical expressions are derived for the mean and the mean-square values of the timing wave, based on iterative computations of high-order moments of the input signal. Then, the root mean-square (RMS) jitter performance is determined as a function of various system parameters such as the power series expansion of the zero-memory nonlinear device, the rolloff factor of the input pulse shape, and the postfiltering. Finally, the numerical results obtained from some specific examples serve to illustrate several aspects of the timing recovery problem     

降低可见光OFDM系统限幅失真的部分线性压扩变换研究

针对可见光正交频分复用（OFDM）系统发光二极管（LED）限幅失真严重的问题,提出一种部分线性压扩变换方法。输出光功率约束较大或较小时,在发射端对直流光正交频分复用（DCO-OFDM）双极性信号中的正信号或负信号进行线性压缩变换,在接收端对压扩信号进行扩展变换可以有效地减小限幅噪声。输入信号功率一定时,在有效信噪比最大原则下对部分线性压扩变换系数和直流偏置进行优化,系统能够获得最佳性能。仿真实验表明,随着约束光功率增大,系统性能越差,且压缩系数的最优值也越小。随着QAM调制阶数的增加,部分线性压扩变换获得的性能增益越小。      

A discretizing approach for evaluating reliability of complexsystems under stress-strength model

This paper introduces a new discretizing approach for evaluating reliability of any complex system where analytic methods fail to offer a closed-form solution. Numerical analyses on 4 important engineering items have been used to examine the closeness between the proposed reliability estimators and the simulated values. A comparative study between the discretizing approach of English et al. (1996) and ours indicates that our approach is in no way less efficient. It can also retain TFR, DFR, IFRA properties of the original distribution     

一种解决蓝牙码间串扰的新方法

针对现有蓝牙技术规程中实际存在的一些问题进行了研究,并依照蓝牙规程,对其在高斯白噪声以及多径信道下的传输进行了仿真和分析,发现蓝牙技术中所采用的慢跳频技术并不能很好地抵抗多径干扰;在此基础上提出,若在蓝牙技术中加入一种网格维特比译码算法能有效地降低误码率,从而可以提高蓝牙的传输距离。     

A moment-based approach to registration of images with affinegeometric distortion

A new method is described for automatic control point selection and matching. First, reference and sensed images are segmented and closed-boundary regions are extracted. Each region is represented by a set of affine-invariant moment-based features. Correspondence between the regions is then established by a two-stage matching algorithm that works both in the feature space and in the image space. Centers of gravity of corresponding regions are used as control points. A practical use of the proposed method is demonstrated by registration of SPOT and Landsat TM images. It is shown that the authors' method can produce subpixel registration accuracy     

A new approach for VoIP traffic characterization

The letter proposes a new frame generation model for those audio codecs which handle SID frames and deduces an analytical expression for the mean bit rate at the input of the IP network as a function of the number of frames per packet. The new model is experimentally validated for the G.729B, G.723.1, and GSM AMR codecs. Results show that the error of the estimation of the mean bit rate can be reduced significantly compared to the traditional on-off model.     

A new computational approach for cortical imaging

Estimation of current or potential distribution on the cortex is used to obtain information about neural sources from the scalp recorded electroencephalogram. If the active sources in the brain are superficial, the estimated field distribution on the cortex also yields information about the active source configuration. In these cases, these methods can be used as source localization methods. In this study, we concentrate on finite-element-based cortex potential estimation. Usually these methods require surface interpolation of the recorded voltages at the electrodes onto the entire scalp surface. We propose a new computational approach which does not require the use of surface interpolation but does it implicitly and uses only the recorded data at the electrodes. We refer to this method as the systematic approach (SA). We compare the SA with the surface interpolation approach (IA) and show that the SA is able to produce somewhat better accuracy than the IA. However, the main asset is that the sensitivity of the cortical potential maps to the regularization parameter is significantly lower than with the IA.     

A new approach for TU complex characterization

In this paper, we present a new TU complex detection and characterization algorithm that consists of two stages; the first is a mathematical modeling of the electrocardiographic segment after QRS complex; the second uses classic threshold comparison techniques, over the signal and its first and second derivatives, to determine the significant points of each wave. Later, both T and U waves are morphologically classified. Amongst the principal innovations of this algorithm is the inclusion of U-wave characterization and a mathematical modeling stage, that avoids many of the problems of classic techniques when there is a low signal-to-noise ratio or when wave morphology is atypical. The results of the algorithm validation with the recently appeared QT database are also shown. For T waves these results are better when compared to other existing algorithms. U-wave results cannot be contrasted with other algorithms as, to our knowledge, none are available. Examples showing the causes of principal discrepancies between our algorithm and the QT database annotations are also given, and some ways of attempting to improve and benefit from the proposed algorithm are suggested.     

A novel approach for evaluating the performance of SPC productcodes under erasure decoding

Product codes are powerful codes that can be used to correct errors or recover erasures. The simplest form of a product code is that where every row and every column is terminated by a single parity bit, referred to as single parity check (SPC) product code. This code has a minimum distance of four and is thus guaranteed to recover all single, double, and triple erasure patterns. Judging the code performance based on its minimum distance is very pessimistic because the code is actually capable of recovering many higher erasure patterns. This paper develops a novel approach for deriving an upper bound on the post-decoding erasure rate for the SPC product code with iterative decoding. Simulation shows that the derived bound is very tight