Cutoff rate of m-ary PPM is derived for an avalanche photodiode (APD) based receiver. The cutoff rate is compared among m=8-256 under the condition of the same total signal energy in 256 slots, where the effects of the timing jitter and atmospheric turbulence are included. Numerical results are shown for the illustrative examples of the cutoff rate.

Many algorithms have been introduced to obtain giga-bit routing performance by reducing searching time. As most of them, however, have not considered the importance of update time and memory requirement seriously, they couldn't work well in real networks. We propose a flexible and fast IP lookup algorithm, named FFILA, considering these factors and compare the performance of our scheme with that of the conventional scheme of Patricia trie.

Ag(40 wt%)-Pd(60 wt%) alloy has been widely applied to contact materials installed in various electromechanical devices. However, in application to the down sized relays, failure due to contact resistance is caused easily by both growth of oxide film on the contact surface and low contact force. To solve the increase in contact resistance, an overlay of thin Au or thin Au-Ag (8-10 wt%) has been used on the alloy. Despite this, cleanliness and low hardness of these overlays cause adhesion, or sticking, at contact interface. Increase in contact resistance and sticking are contrary to each other. In order to eliminate these contrary properties, the author studied improving the Ag-Pd alloy with a dopant. Low level of contact resistance for both static and dynamic contacts of Ag-Pd with Mg doping was found even if the contact surface was covered with an oxide contaminant film. This paper presents the excellent contact resistance and adhesion behaviors of Ag-Pd-Mg alloy and their mechanisms, and also presents in the later part, surface contamination behaviors for organic gases.

Grid computing can help to promote high-performance computing at a low overall cost by encouraging research centers to share their resources. However, research staff usually finds it quite hard to use Grids effectively, due to the need of installing and managing new Grid software. Thus, Grid portals are created, making it easier to take advantage of the full capability of the Grid, favoring in this way its use. The goal of this paper is to describe the process of design and implementation of a Grid Portal with the aim of both supporting distributed high-performance resources and make its use by researchers as transparent as possible. This portal uses standard Grid and Web technologies. We have designed the portal so that it can be adapted to different existing Grid infrastructures, based on the Globus Toolkit, and new functionalities can be easily added. The first prototype of the portal has been tested on an experimental Grid platform, and we present encouraging experiences carried out there.

In General Packet Radio Service (GPRS), combined mobility management is defined to efficiently perform both GSM and GPRS mobility management in a combined manner. In this letter, an enhanced scheme for combined mobility management based on a new mobile station (MS) state model is proposed. The steady state probabilities of the proposed MS state model are derived and the performance of the proposed scheme is analyzed. The results show that the proposed scheme outperforms the conventional scheme, especially for low mobility MSs.

We had previously proposed a fuzzy logic-based buffer management scheme (BMS) called fuzzy early detection (FED), which was designed to improve transmission control protocol (TCP) performance over the unspecified bit rate (UBR) service of asynchronous transfer mode (ATM) networks. Since a weakness in FED was discovered later, we present a refined version of it named FED+ here. Maintaining the design architecture and the algorithm of FED, FED+ further adopts a specific per virtual connection accounting algorithm to achieve its design goals. The effects of TCP implementation, TCP maximum segment size, switch buffer size and network propagation delay on FED+ performance are studied through simulation. Its performance is then compared with those of pure early packet discard (EPD), P-random early detection (P-RED) and FED. Our evaluations show that FED+ is superior to the others if the issues of efficiency, fairness, robustness, buffer requirement and the ease of tuning control parameters of a BMS are considered collectively.

We presented a wall charge controlled ac PDP driving method which has advantages of less number of sub-fields and no dynamic false contours compared to the conventional driving method. In this method, a sub-field exhibited different light intensity according to the initial wall charge quantity set during the address period. Even though one can set 10 different wall charge states by changing the data pulse widths, we decided to define three states, 'on,' 'half-on,' and 'off.' By adding one state, the number of sub-field required to achieve 243 gray levels was reduced from 8 to 5. Furthermore, one can realize seven sub-fields, 255 gray level, complete stretched-out coding with which one can eliminate the dynamic false contours. Since this method can reduce number of sub-fields, it is suitable for higher resolution PDP's with more scan lines.

In this paper we describe a new framework of feature compensation for robust speech recognition, which is suitable especially for small devices. We introduce Delta-cepstrum Normalization (DCN) that normalizes not only cepstral coefficients, but also their time-derivatives. Cepstral Mean Normalization (CMN) and Mean and Variance Normalization (MVN) are fast and efficient algorithms of environmental adaptation, and have been used widely. In those algorithms, normalization was applied to cepstral coefficients to reduce the irrelevant information from them, but such a normalization was not applied to time-derivative parameters because the reduction of the irrelevant information was not enough. However, Histogram Equalization (HEQ) provides better compensation and can be applied even to the delta and delta-delta cepstra. We investigate various implementation of DCN, and show that we can achieve the best performance when the normalization of the cepstra and the delta cepstra can be mutually interdependent. We evaluate the performance of DCN using speech data recorded by a PDA. DCN provides significant improvements compared to HEQ. It is shown that DCN gives 15% relative word error rate reduction from HEQ. We also examine the possibility of combining Vector Taylor Series (VTS) and DCN. Even though some combinations do not improve the performance of VTS, it is shown that the best combination gives the better performance than VTS alone. Finally, the advantage of DCN in terms of the computation speed is also discussed.

Among several methods of storing XML documents, a straightforward yet efficient method is to store a string representation of the XML document. An XML node is usually represented by a region coordinate, which is a pair of integers expressing the start and end positions of the substring corresponding to the node. This approach, however, has the drawback that a change of a node's region coordinate causes change of the region coordinates of many other elements. This recomputation normally degrades the performance of XML applications, especially when content is updated frequently. In this paper, we propose the Relative Region Coordinate (RRC) technique to effectively reduce the cost of recomputation. The main idea is to express the coordinate of an XML element in the region of its parent element. We present a method to integrate the RRC information into XML systems and provide experimental results that demonstrate the effectiveness of the RRC in the content update.

The exciting goals of ubiquitous computing and communication services can only be achieved if we can increase the efficiency with which the location of mobile terminals can be managed; current mobile infrastructures are not efficient since they treat all mobile terminals uniformly despite that fact that many mobiles often move together (i.e. passengers on the same train or a group of cars on a road). This paper presents a hierarchical location management scheme that handles such grouped mobiles collectively and so reduces the overhead costs of location management. In our scheme, mobiles that move together for long enough form a mobile network and make a hierarchy in the wireless access network. The scheme also adjusts the number of mobile networks to keep communication overhead low. We apply the scheme to Mobile IPv6 and evaluate the resulting performance improvement. Simulation results confirm that our hierarchical approach can greatly reduce the overhead costs of location management, and that it is very practical since it can flexibly develop suitable mobile networks.

In this letter, we propose an enhanced time-based registration method and analyze the performance numerically. In the analysis, we assume Poisson call arrival distribution and exponential cell resident time. The performance of the enhanced time-based registration method is compared with the performance of the original time-based registration method. In the comparisons, we see that in a certain range of parameters, the enhanced time-based registration method has better performance.

Generating the identifiers of XML nodes is a crucial task in XML applications. On the other hand, the structural information of XML data is essential to evaluate the XML queries. Several numbering schemes have been proposed so far to express the structural information using the identifiers of XML nodes. In this paper, we introduce a new numbering scheme called recursive UID (rUID) that has been designed to be robust in structural update and applicable to arbitrarily large XML documents. We investigate the applications of rUID to XML query processing in a system called SKEYRUS, which enables the integrated structure-keyword searches on XML data. Experimental results of the performance of SKEYRUS are also reported.

In order to stabilize a convey-crane with only cart position measurement, this paper designs an additional dynamics with which the parallel-connected system is feedback passive. Since the crane system can be stabilized with a proportional-derivative (PD) law, the additional system is constructed by using the PD gains, and the closed-loop system exhibits almost same performances with the PD law. With the proposed control law, the transfer function of the additional system has the form of sH(s) with a strictly positive real (SPR) H(s).

A series of micromagnetic models including simulations of the 3D thin film write head field, the GMR read head, the thin film media and channel codes are utilized to study the recording performance in longitudinal hard disk drives (HDD) at extremely high densities. The (0, 4/4) encoder is utilized to translate the user data into (0, 4/4) constrained codes, before the write process is performed. The write current is achieved from the constrained code in the NRZ format. The read back voltage is reshaped to the PR-IV signal and the Viterbi detector is utilized to recover the data. In a medium of 10 nm grains, the recording linear density limits with the PRML method are about 1000 kfci, which is 1.5 times of those with the PD channel.

We developed compact high-power photonic millimeter-wave emitter (PME) modules for 60-GHz fiber radio links. The PME chip is a monolithic integration of a uni-traveling-carrier photodiode (UTC-PD) and an antenna. One module was fabricated by attaching the chip and a plastic housing to a metal substrate, and the equivalent-isotropic radiated power (EIRP) of over 8 dBm was obtained with weak directivity of the radiated pattern. This module is suitable for point-to-multi-point communication. It is very compact, 29 24 6 mm. A module whose antenna gain was increased by attaching a dielectric lens to it was also fabricated, and the estimated EIRP of 18 dBm was obtained. This type of module is suitable for point-to-point communication and it too is compact, 29 24 17.5 mm. We achieved high-speed error-free data transmission of 1.25- and 2.5-Gbit/s phase-shift keyed (PSK) signal. The maximum distances of free-space propagation were estimated to be 18.2 and 8.9 m at bit rates of 1.25 and 2.5 Gbit/s, respectively.

A new fuzzy logic-based buffer management scheme (BMS) called fuzzy early detection (FED) is presented to improve transmission control protocol (TCP) performance over the unspecified bit rate (UBR) service of asynchronous transfer mode (ATM) networks. FED uses early congestion detection and selective packet discard (ECD/SPD) strategies to achieve its design goals, and adopts early packet discard (EPD) to prevent frequent buffer overflows. Two variants of FED are constructed for comparison purposes. FED performance is then evaluated against those of its variants, pure EPD and P-random early detection (P-RED) through various simulations. The effects of TCP implementation, TCP maximum segment size (MSS), network's propagation delay (PD) and switch buffer size (SBS) on their performances are studied. The overall result shows that FED is superior to the other BMSs when the criteria of efficiency, fairness, scalability and switch buffer requirement are considered collectively.

In this paper, we describe an adaptive integration method for an audio-visual speech recognition system that uses not only the speaker's audio speech signal but visual speech signals like lip images. Human beings communicate with each other by integrating multiple types of sensory information such as hearing and vision. Such integration can be applied to automatic speech recognition, too. In the integration of audio and visual speech features for speech recognition, there are two important issues, i.e., (1) a model that represents the synchronous and asynchronous characteristics between audio and visual features, and makes the best use of a whole database that includes uni-modal, audio only, or visual only data as well as audio-visual data, and (2) the adaptive estimation of reliability weights for the audio and visual information. This paper mainly investigates two issues and proposes a novel method to effectively integrate audio and visual information in an audio-visual Automatic Speech Recognition (ASR) system. First, as the model that integrates audio-visual speech information, we apply a product of hidden Markov models (product HMM), the product of an audio HMM and a visual HMM. We newly propose a method that re-estimates the product HMM using audio-visual synchronous speech data so as to train the synchronicity of the audio-visual information, while the original product HMM assumes independence from audio-visual features. Second, for the optimal audio-visual information reliability weight estimation, we propose a Gaussian mixture model (GMM) based-MCE-GPD (minimum classification error and generalized probabilistic descent) algorithm, which enables reductions in the amount of adaptation data and amount of computations required for the GMM estimation. Evaluation experiments show that the proposed audio-visual speech recognition system improves the recognition accuracy over conventional ones even if the audio signals are clean.

An improved movement-based registration scheme reduces location update cost on conventional movement-based location update scheme but increases uncertainty of the position of a mobile terminal (MT). The effect of this uncertainty of the MT position on the paging cost of the improved movement-based registration scheme is analyzed. We show that the paging cost of the improved movement-based registration scheme in [2] is underestimated, especially for large values of movement threshold. The result shows that the underestimation cannot be ignored.

Two types of p-i-n diode devices, namely an amplitude shift keying switch and a phase shift keying switch, were developed by using an NRD guide at 77 GHz. In order to apply these devices to radar systems, an SPDT switch with a low insertion loss of less than 2.5 dB and a high isolation of more than 25 dB was fabricated by using the former switch. Moreover, a BPSK modulator, composed of the latter switch together with a circulator and a ceramic resonator loaded band-pass filter, was designed and evaluated for use in spread spectrum radar systems in this frequency range.

An analytic approximation of the information reduction factor is presented in an efficient manner for the case of two-dimensional measurement vector and a four-sigma validation gate. This analytic approximation allows us to efficiently evaluate performance prediction for the probabilistic data association (PDA) filter using the hybrid conditional average (HYCA) algorithm.