We present a multichannel speech enhancement method based on MAP speech spectral magnitude estimation using a generalized gamma model of speech prior distribution, where the model parameters are adapted from actual noisy speech in a frame-by-frame manner. The utilization of a more general prior distribution with its online adaptive estimation is shown to be effective for speech spectral estimation in noisy environments. Furthermore, the multi-channel information in terms of cross-channel statistics are shown to be useful to better adapt the prior distribution parameters to the actual observation, resulting in better performance of speech enhancement algorithm. We tested the proposed algorithm in an in-car speech database and obtained significant improvements of the speech recognition performance, particularly under non-stationary noise conditions such as music, air-conditioner and open window.

In this paper, I propose dynamic gamma control (DGC) as a new contrast enhancement technology for liquid crystal displays. Unlike conventional technologies involving the manipulation of digital image data, DGC modifies analog gamma reference voltages in accordance with the image data distribution. A digital gamma buffer (DGB) and a new system architecture were developed for DGC implementation. Experimental results show that DGC can increase the contrast ratio of 5 images twofold on average.

Distributed denial-of-service attacks on public servers have recently become more serious. More are SYN Flood attacks, since the malicious attackers can easily exploit the TCP specification to generate traffic making public servers unavailable. To assure that network services will not be interrupted, we need faster and more accurate defense mechanisms against malicious traffic, especially SYN Floods. One of the problems in detecting SYN Flood traffic is that server nodes or firewalls cannot distinguish the SYN packets of normal TCP connections from those of SYN Flood attack. Moreover, since the rate of normal network traffic may vary, we cannot use an explicit threshold of SYN arrival rates to detect SYN Flood traffic. In this paper we introduce a mechanism for detecting SYN Flood traffic more accurately by taking into consideration the time variation of arrival traffic. We first investigate the statistics of the arrival rates of both normal TCP SYN packets and SYN Flood attack packets. We then describe our new detection mechanism based on the statistics of SYN arrival rates. Our analytical results show that the arrival rate of normal TCP SYN packets can be modeled by a normal distribution and that our proposed mechanism can detect SYN Flood traffic quickly and accurately regardless of time variance of the traffic.

We investigated physical conditions for optimum display systems on various TV viewing conditions, and found that visual brightness function could be derived from relationships between Steven's power law and Bartleson-Breneman's brightness function, and that the optimum physical contrast ratio and compensated gamma for display system with adaptation luminance level could be obtained from the proposed brightness function.

Color reproductions in most LCD are quite different from those of standard CRT (cathode ray tube) monitor display because of the nonlinear characteristic in subtractive color reproduction. Moreover, gray scale CCT (correlated color temperature) reproductions in a typical mobile phone LCD depend on the input RGB levels. A simple LUT (Look-up table) method for constant gray scale CCT and gamma characteristic of mobile phone LCD is presented in this paper. We investigate the mobile phone LCD's characteristic of compensation of CCT with using the LUT. LCD's CCT is maintaining about 7500 K, which is the target CCT of mobile phone LCD in this paper. Also LCD's gamma is similar to target gamma.

This study shows the effectiveness of using gamma distribution in the speech power domain as a more general prior distribution for the model-based speech enhancement approaches. This model is a super-set of the conventional Gaussian model of the complex spectrum and provides more accurate prior modeling when the optimal parameters are estimated. We develop a method to adapt the modeled distribution parameters from each actual noisy speech in a frame-by-frame manner. Next, we derive and investigate the minimum mean square error (MMSE) and maximum a posterior probability (MAP) estimations in different domains of speech spectral magnitude, generalized power and its logarithm, using the proposed gamma modeling. Finally, a comparative evaluation of the MAP and MMSE filters is conducted. As the MMSE estimations tend to more complicated using more general prior distributions, the MAP estimations are given in closed-form extractions and therefore are suitable in the implementation. The adaptive estimation of the modeled distribution parameters provides more accurate prior modeling and this is the principal merit of the proposed method and the reason for the better performance. From the experiments, the MAP estimation is recommended due to its high efficiency and low complexity. Among the MAP based systems, the estimation in log-magnitude domain is shown to be the best for the speech recognition as the estimation in power domain is superior for the noise reduction.

The gamma correction for the CMOS image sensors are implemented by the method of piecewise linear approximation through a look-up table. In this paper, we propose a quantitative criterion to select the piece linear segment with the same output interval for the reduction of the error between the value of piece linear approximation and gamma correction. After the gamma correction is implemented, the average error occurred by implementing color interpolation in each segment is a basis for the optimum selecting of the piece linear segment of the gamma correction for the CMOS image sensors.

Multilayered filters with a dielectric distribution along their thickness forming a one-dimensional quasi-fractal structure are theoretically analyzed, focusing on exposing their resonant properties in order to understand a dielectric Menger's sponge resonator [4],[5]. "Quasi-fractal" refers to the triadic Cantor set with finite generation. First, a novel calculation method that has the ability to deal with filters with fine fractal structures is derived. This method takes advantage of Clifford algebra based on the theory of thin-film optics. The method is then applied to classify resonant modes and, especially, to investigate quality factors for them in terms of the following design parameters: a dielectric constant, a loss tangent, and a stage number. The latter determines fractal structure. Finally, behavior of the filters with perfect fractal structure is considered. A crucial finding is that the high quality factor of the modes is not due to the complete self-similarity, but rather to the breaking of such a fractal symmetry.

This letter presents two methods of modeling phoneme durations. One is the context-independent phoneme duration modeling in which duration parameters are stored in each phoneme. The other is the context-dependent duration modeling in which duration parameters are stored in each state shared by context-dependent phonemes. The phoneme duration model is compared with a without-duration model and a state duration model. Experiments are performed on a database collected over the telephone network. Experimental results show that duration information rejects out-of-task (OOT) words well and that the context-dependent duration model yields the best performance among the tested models.

It is an important problem to estimate component reliabilities. For a series system due to cost and time constraints associated with failure analysis, all components cannot be investigated and the cause of failure is narrowed to a subset of components in some cases. When such a case occurs, we say that the cause of failure is masked. It is also necessary in some cases to take account of the influence of an environmental stress on all components. In this paper, we consider 2 and 3-component series systems when the component lifelengths are exponentially distributed and an environmental stress follows either a gamma or an inverse Gaussian distribution. We show that the lifelength of the system and the cause of failure are independent of each other. By comparison between the hazard functions in both models, we see that quite short and long lifelengths are more likely to occur in a gamma model than in an inverse Gaussian one. Assuming that the masking probabilities do not depend on which component actually fails, we show that the likelihood function can be factorized into three parts by a reparametrization. For some special cases, some estimators are given in closed-form. We use the computer failure data to see that our model is useful to analyze the real masked data. As compared with the Kaplan-Meier estimator, our models fit this computer data better than no environmental stress model. Further, we determine a suitable model using AIC. We see that the gamma model is fitted to the data better than the inverse Gaussian one. From a limited simulation study for a 3-component series system, we see that the relative errors of some estimators are inversely proportional to the square root of the expected number of systems whose cause of failure is identified.

A new multi-luminance-level subfield method is proposed to reduce the low gray-level contour of an alternate current plasma display panel (AC-PDP). The minimum or maximum luminance level per sustain-cycle can be altered by simultaneously applying the proper auxiliary short pulses. As a result, the multi-luminance levels per one or two sustain pulse pairs can be expressed by properly adjusting the auxiliary short pulses for the one or two sustain-cycle subfields, thereby suppressing a low gray-level contour of AC-PDP.

The coming information society will require images at the high end of the quality range. By using a new method which focuses on the assessment words of the high order sensation, we are investigating the important physical factors for the difficult reproduction of high level, high quality sensation in the electronic capture and display of images. We have found a key assessment word "image depth" that describes appropriately the high order subjective sensation that is indispensable for the display of extra high quality images. Related to the depth of images, we have discovered a new physical factor and the degree of precision required of already known physical factors for the display of extra high quality images. The cross modulation among R, G and B signals is the newly discovered important physical factor affecting the quality of an electronic display. In addition, we have found that very strict control of distortion in the gamma and the step response and the strict suppression of the halation in a CRT display are necessary. We note that aliasing of the displayed images also destroys the sensation of depth. This paper first outlines the overall objective of our work, second considers the important physical factors as important for extra high quality imaging, and then describes the specific effects of cross modulation distortion, gamma, step response, halation and aliasing as they relate to image depth. Finally, the relation of the discussed physical factors with the high order sensation are discussed broadly.

Outage probability evaluation for a new category of wireless access systems is discussed. Wireless access systems dealt with in this paper are links which connect a portable terminal to a base station through a line-of-sight path. It is also assumed that the terminal equipment is operated in a still atate during actual communications. This mobility restriction enables the wireless access to have a capacity as high as the Mbit-order with high quality performance. Multipath fading observed in such a system may have more moderate variations than Rayleigh distribution. This paper tentatively designates the above wireless access as relocatable systems, and attempts to analyze their error performance, approximating the fading characteristics with Gamma-distribution. Also dynamic relations between bit error rate (BER) and signal-to-noise ratio are calculated under Gamma-distribution fading. Based on the analyses prediction methods for outage probability of typical QPSK systems are given, and thus it is established to design the performance aspect of relocatable systems with different features from both fixed and mobile systems.

Gamma(γ)-ray irradiation effects have been investigated on three types of low-noise HEMTs, AlGaAs/GaAs conventional HEMT (conv. HEMT), AlGaAs/InGaAs pseudomorphic HEMT (P-HEMT) and InAlAs/InGaAs/InP HEMT (InP-based HEMT). The dose of irradiated γ-rays ranges from 1105 to 1108 rad. DC and RF characteristics of each type of HEMT are measured before and after irradiation and the parameter changes are investigated. For conv. HEMT and P-HEMT, no degradation of DC parameter is observed up to 108 rad, while noise figure (NF) at 12 GHz remains constant up to 107 rad and degrades by 0.1 dB at 108 rad. The InP-based HEMT shows IDSS and gm increase by about 10% at a dose of 108 rad and its NF at 18 GHz lowers gradually with the radiation dose. It has been found that the radiation hardness is greater than 107 rad for all types of HEMTs and over a hundred years of life can be expected against γ-ray irradiation in the space environment.

A new trial of statistical evaluation for an output response of power linear type acoustic systems with nonstationary random input is proposed. The purpose of this study is to predict the output probability distribution function on the basis of a standard type pre-experiment in a laboratoty. The statistical properties like nonstationarity, non-Gamma distribution property and various type linear and non-linear correlations of input signal are reflected in the form of differential operation with respect to distribution parameters. More concretely, the pre-experiment is carried out for a power linear acoustic system excited only by the Gamma distribution type sandard random input. Considering the non-negative random property for the output response of a power linear system, the well-known statistical Laguerre expansion series type probability expression is first employed as the framework of basic probability distribution expression on the output power fluctuation. Then, the objective output probability distribution for a non-stationary case can be easily derived only by successively employing newly introduced differential operators to this basic probability distribution of statistical Laguerre expansion series type. As an application to the actual noise environment, the proposed method is employed for an evaluation problem on the stochastic response probability distribution for an acoustic sound insulation system excited by a nonstationary input noise.

Multiple-site diversity systems are foreseen for earth to satellite paths operating at frequencies above 10GHz in localities with high rain-induced attenuation. In some severe cases double-site protection can be proved to be inadequate and consequently triple-site diversity becomes indispensable. In the present paper, an approach for the prediction of the triple-site diversity performance based on an appropriate three-dimensional gamma distribution is proposed. The model is oriented for application to earth-space paths located in Japan and other locations with similar climatic conditions. Numerical results are compared with the only available set of experimental data taken from some parts of the United States. Some useful conclusions are deduced.