This paper considers Quasi-Reduced ordered Multi-valued Decision Diagrams with k bits (QRMDD(k)s) to represent binary logic functions. Experimental results show relations between the values of k and the numbers of nodes, the memory sizes, the numbers of memory accesses, and area-time complexity for QRMDD(k). For many benchmark functions, the numbers of nodes and memory accesses for QRMDD(k)s are nearly equal to of the corresponding Quasi-Reduced ordered Binary Decision Diagrams (QRBDDs), and the memory sizes and the area-time complexities for QRMDD(k)s are minimum when k = 2 and k = 3-6, respectively.

A random number generator composed of single electron devices is presented. Due to stochastic behavior of electron tunneling process, single electron devices have intrinsic randomness. Using its randomness, a true random number generator can be implemented. Although fluctuation of device parameters degrades the performance of the proposed circuit, we show that the adjustment of the bias voltages can compensate the fluctuation.

We developed a compact, 16-channel integrated optical subscriber module for one-fiber bi-directional optical access systems. They can support more subscribers in a limited mounting space. For ultimate compactness, we created 8-channel integrated super-compact optical modules, 4-channel integrated limiting amplifiers, and 4-channel integrated LD drivers for Fast Ethernet. We introduce a new simulation method to analyze the electrical crosstalk that degrades sensitivity of the optical module. A new IC architecture is applied to reduce electrical crosstalk. We manufactured the optical subscriber module with these optical modules and ICs. Experiments confirm that the module offers a sensitivity of -27.3 dBm under 16-channel 125 Mbit/s simultaneous operation.

This paper proposes an inter-symbol interference (ISI) suppression scheme using only the even-numbered sub-carriers for the fixed-rate OFDM systems with the 2-dimensional modulation. The proposed scheme is based on the principle that the first half of the waveform in the time domain is the same as the second half when an OFDM symbol is composed of only the even-numbered sub-carriers. The feature of the proposed scheme is that, in the case of the maximum multipath delay beyond the duration of the guard interval, the OFDM symbol with only the even-numbered sub-carriers is transmitted in order to generate the extended virtual guard interval and that the high-level modulation with the sub-carrier power enhancement is applied to achieve the constant data rate. In addition, at the receiver, only the second half of the OFDM symbol is used for the FFT processing to avoid the ISI. Moreover, the condition of the maximum multipath delay is notified to the transmitter by using the feedback channel. Numerical results given by computer simulation showed that the proposed scheme provides far better bit error rate (BER) performance than the traditional OFDM transmission using all sub-carriers under the multipath delay beyond the duration of the guard interval.

In this paper, first, we consider how to illustrate the effect of background noise to the measurement of room acoustics under a background noise of arbitrary distribution type. Two kinds of estimation methods are proposed to evaluate a proper reverberation time of a room by observing real unrefined decay curves, which can not realize smoothly a sufficient decay of 60 dB in a low frequency region, especially under a contamination of background noise. In the first method, an observation equation is derived from a stochastic model by means of well-known Sabine's differential equation, which is approximately rewritten in a matched form of difference equation especially to preserve its original physical meaning and functional linearity on the reverberation parameter. The effect of background noise is eliminated by employing a generalized state estimation algorithm based on Bayes' theorem. In the second one, after reflecting the effect of background noise in an observation equation of measuring model, a well-known mutual information criterion is introduced to estimate a reverberation time especially based on the basic property of statistical independency between signal and background noise. Finally, the effectiveness of the proposed methods are experimentally confirmed too by applying it to the actual measurement of a reverberation time in the actual living situation of room contaminated by a background noise. The proposed methods are, however, some technique using actively the higher order correlation beyond a linear one, and so they are methodology-trials which should coexist with other techniques.

Recent progress on photonic crystal fibers is reviewed aiming at their application to high performance networks. A photonic crystal fiber has an array of air holes surrounding the silica core region. Light is confined to the core by the refractive index difference between the core and the array of air holes. Photonic crystal fibers have special characteristics compared with conventional single mode fibers. One is that the dispersion characteristics can be designed. Another characteristic, that strong birefringence can be established by sizing and/or arranging the air holes, is expected to realize a polarization maintaining fiber with high birefringence of the order of 110-3. This paper will describe the characteristics of dispersion controlled PCFs and polarization maintaining PCFs that include supercontinuum generation and absolute single polarization characteristics for various types of optical devices in high performance network systems.

A number-conserving cellular automaton (NCCA) is a cellular automaton (CA) such that all states of cells are represented by integers and the sum of the cell states is conserved throughout its computing process. It can be thought of as a kind of modelization of the physical conservation law of mass or energy. It is known that the local function of a two-dimensional 45-degree reflection-symmetric von Neumann neighbor NCCA can be represented by linear combinations of a binary function. In spite of the number-conserving constraints, it is possible to design an NCCA with complex rules by employing this representation. In this paper, we study the case in which the binary function depends only on the difference of two cell states, i.e., the case in which the function can be regarded as a unary one and its circuit for applying rules to a cell only need adders and a single value table look up module. Even under this constraint, it is possible to construct a logically universal NCCA.

In this paper a new adaptive multi-input multi-output (MIMO) channel estimation and multiuser detection algorithm based kernel space iterative inversion is proposed. The functions of output signals are mapped from a low dimensional space to a high dimensional reproducing kernel Hilbert space. The function of the output signals is represented as a linear combination of a set of basis functions, and a Mercer kernel function is constructed by the distribution function. In order to avoid finding the function f(.) and g(.), the correlation among the output signals is calculated in the low dimension space by the kernel. Moreover, considering the practical application, the algorithm is extended to online iteration of mixture system. The computer simulation results illustrated that the new algorithm increase the performance of channel estimation, the global convergence, and the system stability.

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.

We present a learning algorithm of the Hopfield neural network for minimizing edge crossings in linear drawings of nonplanar graphs. The proposed algorithm uses the Hopfield neural network to get a local optimal number of edge crossings, and adjusts the balance between terms of the energy function to make the network escape from the local optimal number of edge crossings. The proposed algorithm is tested on a variety of graphs including some "real word" instances of interconnection networks. The proposed learning algorithm is compared with some existing algorithms. The experimental results indicate that the proposed algorithm yields optimal or near-optimal solutions and outperforms the compared algorithms.

In this paper, we propose a new content delivery platform on the ITS (Intelligent Transport Systems) road-vehicle communication system on the basis of ROF (Radio over Fiber). The platform is strongly motivated by the ROF communication system capabilities of (1) broadband access, (2) integrated multiple service transmission interface, and (3) simultaneous use of a single and downsized vehicle terminal shared among multiple services based on a multi-mode software radio system. Content is delivered on per reservation basis, as is carefully envisaged as a primary service which is subjected to immaturity of early ITS road-vehicle communication systems, and is provided in limited service areas such as parking on main highways. After the reservation, requested content is stored in a cache connected to a ROF local station via optical fiber. At the designated time, the content is delivered from the cache to a target terminal by way of the ROF local station at high-speed. It can also be done by moving the content from the cache to another cache depending on the target terminal location in a flexible and reliable manner, even if the target terminal could not reach the place at the time designated in the reservation. Such flexibility and reliability are required for consequent practical application, and are provided using information given in the reservations. We implement a preliminary system to evaluate the proposed platform from the viewpoints of (1) processing time from logging into the system for a reservation to delivering content to the target terminal and (2) amount of control traffic required for the delivery. The results show that the proposed platform in which content is delivered from a cache connected with a ROF local station distributed geographically is effective. We also evaluate content delivery throughput using the system connected with an actual ROF local station, and show that the effective throughput is 40 Mbps and the proposed platform is a promising ITS service platform. The paper concludes by discussing future study toward realizing a more promising and practical system.

An optical fiber biosensor using adsorption LB films has been investigated for the application to the glucose detection in blood. The adsorption LB film containing glucose oxidase (GOD: the enzyme in human body) was deposited on the core portion of optical fiber and the variation of absorption spectra due to the reactions of GOD, glucose, and hemoglobin was measured. The relatively high response time of 60 s and glucose sensitivity as low as 20 mg/dl were obtained. The results demonstrate that the optical fiber bio-sensor using adsorption LB film can be used as a glucose sensor.

We describe the first highly nonlinear dispersion-flattened polarization-maintaining photonic crystal fiber designed for nonlinear optics applications in the 1.55 µm region. The nonlinear coefficient of the fiber is 19 (W-1km-1), which is ten times that of dispersion shifted fiber. The chromatic dispersion and dispersion slope of the fiber at 1.55 µm are -0.23 ps/km/nm and 0.01 ps/km/nm2, respectively. We demonstrate the generation of a supercontinuum using the photonic crystal fiber. A symmetrical supercontinuum over 40 nm is obtained by injecting 1562 nm, 2.2 ps, and 40 GHz optical pulses into the 200 m-long photonic crystal fiber.

We propose a simple method for the chromatic dispersion measurement of optical fibers by using bi-directional modulation of a Mach-Zehnder electro-optical modulator embodied in a fiber loop mirror. The detected output of the bi-directionally modulated light, with time difference, creates fading in the RF domain. Dispersion is found by measuring the period of fading at different wavelengths.

A negative thermal expansion ceramic substrate and an athermal fiber Bragg grating component with the substrate were subjected to reliability tests. We confirmed that the component has adequate durability for use as optical filters in the WDM system, under test conditions of damp heat, low temperature, mechanical shock and vibration. (50 words)

The auction is a popular way of trading. Despite of the popularity of the auction, only a small number of papers have addressed the protocol which realize the double auction. In this paper, we propose a new method of double auction which improves the algorithm of the existing double auction protocol. Our new method is based on the idea of number comparison which is realized by homomorphic encryption. The new method solves the problem of the privacy of losing bids found in the existing algorithm. The buyers and the sellers can embed a random number in their bidding information by the use of the homomorphic encryption. The players in an auction cannot get anyone else's bidding information. The new method is more efficient than the existing ones. Our new method satisfies the criteria for the auction protocol.

We propose a method of IP traffic management where the TCP performance at a bottleneck link is estimated from monitored data about the behavior of the number of active flows versus link utilization, which are both easy to measure. This method is based on our findings that (i) TCP performance remains constant as long as the link utilization is below some threshold value, but becomes degraded when it exceeds this value and (ii) the number of active flows increases linearly with link utilization up to the same value, and the increase becomes nonlinear above it. Though this threshold may vary depending on traffic/network conditions, our method requires neither predetermination of a threshold on the basis of assumed traffic conditions nor direct measurement of TCP performance.

This letter proposes a novel technique for evaluating the longitudinal distribution of the Raman gain characteristics in optical fibers connected to a reference optical fiber with a known Raman gain efficiency. This technique can evaluate the Raman gain efficiency in test fibers using a simplified experimental setup. We performed experiments on various test fibers and confirmed that their Raman gain efficiency can be obtained easily and accurately by employing a reference fiber.

Finding a nonnegative integer solution x for Ax = b (A Zmn, b Zm1) in Petri nets is NP-complete. Being NP-complete, even algorithms with theoretically bad worst case and with average complexity can be useful for a special class of problems, hence deserve investigation. Then a Grobner basis approach to integer programming problems was proposed in 1991 and some symbolic computation systems became to have useful tools for ideals, varieties, and algorithms for algebraic geometry. In this letter, Grobner basis approach is applied to three typical problems with respect to state equation in P/T Petri nets. In other words, after Grobner bases are derived by the tool Maple 7, we consider how to derive the T-invariants and particular solutions of the Petri nets by using them in this letter.

An approach to minimum mean-squared error (MMSE) decoding for vector quantization over channels with memory is presented. The decoder is based on the Gilbert channel model that allows the exploitation of both intra- and inter-block correlation of bit error sequences. We also develop a recursive algorithm for computing the a posteriori probability of a transmitted index sequence, and illustrate its performance in quantization of Gauss-Markov sources under noisy channel conditions.