Electronics and Communications in Japan (Part III: Fundamental Electronic Science)最新文献

This paper proposes a method for detecting a signal embedded in nonstationary noise. In most past studies of the signal detection problem, random noise is considered as a stationary stochastic process, since it is mathematically easy to handle. However, the noise observed in practice contains many nonstationary elements with time-varying (evolutionary) statistical properties. In this study, observational noise is modeled as a probability density function with slowly evolving parameters. Then, based on the evolving spectral representation, the nonstationary observation data are transformed to a stationary process. A new method is proposed as follows. It is assumed that nonstationarity remains in the stationarized observation data in the interval containing the signal, due to the effect of the signal. Then the signal is detected by testing for stationarity. In the proposed method, Priestley's evolutionary spectrum is used in the spectral representation of the nonstationary stochastic process, and the method of Okabe and colleagues based on the KM₂O-Langevin equation is used for the stationarity test. The effectiveness of the proposed method is verified by a simulation experiment. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 3, 90(8): 29–38, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjc.20302

The impressive generalization capacity of AdaBoost has been explained using the concept of a margin introduced in the context of support vector machines. However, this ability to generalize is limited to cases where the data does not include misclassification errors or significant amounts of noise. In addition, the research of Schapire and colleagues has served to provide theoretical support for these results from the perspective of improving margins. In this paper we propose a set of new algorithms, AdaBoost_Reg,ν-Arc, and ν-Boost, that attempt to avoid the overfitting that can occur with AdaBoost by introducing a normalization term into the objective function minimized by AdaBoost. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 3, 90(9): 69– 78, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjc.20344

This paper proposes a real-valued orthogonal periodic sequence of a period N=2^ν derived from a real-valued shift-orthogonal finite-length sequence of length M=2^ν+1. This paper also explains the principle of a fast correlation algorithm that efficiently executes periodic correlation processing for this real-valued orthogonal periodic sequence. The sidelobe of an aperiodic autocorrelation function for a real-valued shift-orthogonal finite-length sequence (length of M) is 0 except for the right and left ends of the shift. If the subsequent sequence of first values repeatedly overlap the final values of this sequence, a real-valued orthogonal periodic sequence of a period N=M−1 can be obtained. A real-valued orthogonal periodic sequence of a period N=2^ν generated from real-valued shift-orthogonal finite-length sequence of length M=2^ν+1 is obtained by convoluting partial sequences and based on that controls the number of multiplications and the number of additions to increment on the order of Nlog₂N without using fast Fourier transformation. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 3, 90(10): 18–28, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjc.20294

Real-valued shift-orthogonal finite-length sequences are sequences in which the side lobes of the aperiodic autocorrelation function become 0, except for the endpoints of the shift to both sides, and can be applied in pulse compression radar and spread spectrum communications. In this paper, a fast correlation algorithm for efficiently calculating the periodic correlation function is discussed for real-valued shift-orthogonal finite-length sequences with length M=2^ν+1. For input data, including a real-valued shift-orthogonal finite-length sequence over a certain range, the value of the aperiodic correlation function is found in a certain shift range. Based on the synthesis of this sequence by the convolution of ν+1 partial sequences, the correlation processing is broken down into correlation processing of the ν+1 stages of partial sequences. As a result, the number of multiplications and the number of additions can be suppressed on the order Mlog₂M. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 3, 90(9): 18– 30, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjc.20301

Coordinated checkpointing techniques ensure that a consistent global state is maintained by means of coordination between processes. The approach requires that application messages temporarily cease to be exchanged but the rollback procedure when recovering from a fault is consequently simplified and the recovery costs are small. With current reductions in communications costs, the importance of coordinated techniques may be seen to be growing. However, in large-scale systems there is a possibility that performance will be seriously impaired due to the frequent halting of the exchange of messages. In this paper we propose a method whereby coordination is performed at only a subset of the checkpoint generation points that are periodically visited while at the remaining points each process independently generates an incremental snapshot. This method aims to both alleviate the performance degradation incurred from coordination and to realize relatively high-speed recovery. In evaluating the effectiveness of this method we estimate the checkpointing overheads and recovery costs using a probabilistic model and simulations and compare it with existing coordination methods. The results show that the proposed method is more effective than existing coordination methods from the perspective of both performance and reliability in environments with a relatively low frequency of messages. In addition, we perform comparisons of two different delta schemes for representing the incremental snapshots and discuss which environments they are each respectively suited to. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 3, 90(8): 39– 53, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjc.20296

Microbubbles exposed to ultrasound exhibit extremely nonlinear conspicuous behaviors. Medical imaging makes wide use of the pulse inversion method, in which only this nonlinear component is extracted by adding the received signals obtained by sending the phase inverted ultrasonic pulses twice. Further, there have been research efforts to use this nonlinear behavior for sonochemical healing of tumors by the efficient generation of acoustic cavitation by illumination with the second harmonic superimposed on the fundamental wave. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 3, 90(8): 63–69, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjc.20259

Face detection from images is a complex and nonlinear problem due to the various kinds of face images. This problem is solved by conversion of the original feature vectors extracted from images into high-dimension feature vectors using nonlinear mapping, and then finding face/nonface discriminant functions in the mapping space. If such discriminant functions are based on the inner products of high-dimension vectors, such inner products can be easily obtained by substitute calculations of kernel functions in the original feature space. However, in conventional recognition algorithms using kernel functions, numerous features are required to improve recognition accuracy. This paper proposes a new face detection method that uses generation and selection of features on the basis of Kullback-Leibler divergence (KLD). KLD refers to a distance between the distributions of face and nonface data for certain features. Features with large KLD are used for face detection. Moreover, by evaluating the features based on their KLDs, we can generate new features, and deal with different kinds of features concurrently. In experiments, a classifier designed by the proposed method achieved high recognition performance, while using few features. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 3, 90(10): 29– 39, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjc.20347

In 1996 Rosenthal and York proposed (time-invariant) BCH convolutional codes [4] in which the parity check matrix of a BCH code is used in the construction of the convolutional code. The lower bound on the minimum free distance of a BCH convolutional code is guaranteed by the BCH limit. In this paper we propose a periodically time-variant convolutional code that can be constructed not only using the BCH parity check matrix but using the check matrix of any binary linear block code and show that the lower bound on the minimum free distance is guaranteed by the minimum free distance of the binary linear block code. In addition, taking 12 binary linear block codes as examples, we perform comparisons of the proposed codes with BCH convolutional codes using three evaluation criteria (minimum free distance, number of delay elements, coding rate) and show that there exist proposed codes that are superior to existing ones. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 3, 90(9): 31– 40, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjc.20271

The distribution of secret information so that no one knows which information is being passed to whom, such as in a poker game or the like, is an important issue for security. Secret information distribution is expected to have applications in key distribution, electronic voting, and so on. A secret information distribution method must maintain the secrecy and untraceability of the distributed content, without requiring any effort on the part of the recipient. In this paper, the authors propose a distribution method, using third-party organizations, in which the recipient can easily receive the distribution without having to engage in any of the distribution work itself; the distribution work can be divided among any number of third-party organizations in order to diffuse the danger, and thus untraceability and secrecy are maintained so long as there is no collusion or fraud among all the organizations. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 3, 90(8): 9– 17, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjc.20308