Efficient query processing in multi-dimensional indexing structures is an important issue for multimedia data applications. In this paper, we propose incremental k-nearest neighbor query (k-NNQ) and range query algorithms for R-tree based structures. The novel aspect of these algorithms is that they make use of the notion of VP filtering, a concept borrowed from the MVP-tree. The filtering notion allows for delaying of computational overhead until absolutely necessary. By so doing, we attain considerable performance benefits while paying insignificant overhead during the construction of the index structure. We implemented our algorithms and carried out experiments to demonstrate the capability and usefulness of our method. Results show that improvements range from 8% to 23% in response time for the experimental environment that we considered.

This paper focuses on the comparison of OFDM system channel estimation using time domain techniques and using frequency domain techniques. The channel model is based on the Taiwan DTV field-testing results, with static and dynamic multipath distortion. The simulation results prove that the channel estimation performance of the OFDM system in the time domain is better than in the frequency domain.

Magnetic random access memory (MRAM) possesses the attractive properties of non-volatility, radiation hardness, nondestructive readout, low voltage, high access speed, unlimited read and write endurance and high density. MRAM technology is described for the devices using giant magnetoresistance (GMR) and tunneling magnetoresistance (TMR) materials in this paper. The TMR type MRAM architectures using ferromagnetic tunneling junctions (MTJ) are more attractive for mainstream RAM applications than the GMR type, because the signal of the TMR type is larger than that of the GMR type. A MRAM device with an MTJ plus MOS transistor switch architecture, which can provide large signal-to noise ratio, is detailed. A design of the MTJ element is discussed and the requirements for the junction resistance and the TMR needed for the memory device are demonstrated based on the simple signal voltage calculations. The TMR significantly decreases with increasing bias voltage, which leads to the reduction of the signal voltage for the actual MRAM. A ferromagnetic double tunneling junction is proposed for the high density MRAM application demanding large signal voltage, because of the smaller degradation of the TMR for the bias voltage, compared with that of the conventional single junctions. Recent trials of MRAM fabrication are introduced, which demonstrates high-speed access time. Finally, challenges for the higher bit density MRAM above Gb are discussed, and it is noticed that higher signal voltage, lower power consumption for writing and novel cell designs are needed for the achievement.

We propose a novel optical add/drop multiplexer (OADM) utilizing free spectral range (FSR) periodicity of an arrayed-waveguide multiplexer (AWG). In this OADM, wavelength-division multiplex (WDM) signal is multiplexed and/or de-multiplexed in two steps. Power penalty due to coherent crosstalk is drastically reduced compared with that of conventional OADM where AWG multiplexers are opposite to each other. The calculated power penalty due to the coherent crosstalk is about 0.7 dB after the 16 OADMs in the case of 128 wavelengths. It was confirmed through a computer simulation that more than one hundred channels at 10 Gbps data rate could be accommodated in an OADM network with 16 nodes. These results show that the OADM network with over 1 Tbps capacity and 16 nodes could be constructed.

We demonstrate, through numerical simulations, the possibility of trans-oceanic single channel transmission at 160 Gbit/s with no active control. This was achieved using short period dispersion management, which supports short pulse propagation at practical map strengths. We demonstrate that through careful selection and optimisation of the system parameters the performance of this system can be extended. We also define the tolerable limits of the system to the residual dispersion slope and polarisation mode dispersion.

We investigated the characteristics of optical duobinary signals in achieving high fiber input power transmission focusing on the idea of optimum residual dispersion equalization. We confirm through calculations and experiments that setting the total link dispersion at a non-zero value allows high fiber launched power (+18 dBm) and large dispersion tolerance (350 ps/nm) at 10 Gbit/s. We demonstrate repeaterless 250-km single mode fiber (SMF) transmission with a 10-Gbit/s optical duobinary signal. We also demonstrate high-speed complete optical duobinary coding and transmit synchronous digital hierarchy (SDH) frames over optical duobinary signals for the first time.

The effectiveness and possible applications of all-optical signal processing using highly-nonlinear dispersion-shifted fibers (HNL-DSFs) are described. Transparent and simultaneous processings of multi-channels WDM signal are key features of optical fiber processors. Simultaneous wavelength conversion of 3210 Gb/s WDM signal by four-wave mixing, all-optical 3R regeneration of 220 Gb/s WDM signal using nonlinear loop mirrors, and simultaneous recovery of 2020 GHz WDM optical clocks by supercontinuum were successfully demonstrated using HNL-DSFs, and possible applications of ultra-fast and multi-channel processing in future photonic networks are discussed.

This paper describes a simple polarization-independent wavelength conversion method using degenerated four-wave mixing (FWM) in single-mode fibers pumped with cross-polarized high frequency, saw-tooth pulses from a single pump source. Successful polarization-independent wavelength conversion is experimentally confirmed with less than 12% and 5.6% variation using a gain-switched LD pumping and a mode-locked fiber laser pumping, respectively. We clarify that the interference effect between two orthogonal pump pulses must be taken into account to achieve a good polarization-insensitive operation, since even the small pulse edges bring about the large polarization fluctuations when they are interfered. Furthermore, it is reveal that the shorter pump pulse broadens its own spectrum due to the self-phase modulation in fibers, resulting in poor FWM efficiency. Finally, possibility of high-speed operation is discussed taking into account the pump pulse conditions.

We fabricated a 1.55-µm polarization insensitive Michelson interferometric wavelength converter (MI-WC). The MI-WC consists of a two-channel spot-size converter integrated semiconductor optical amplifier (SS-SOA) on a planar lightwave circuit (PLC) platform. Clear eye opening and no power penalty in the back-to-back condition were obtained at 10 Gb/s modulation. We also confirmed the polarization insensitive operation on the input signal. Moreover, for an application of the MI-WC to DWDM networks, we demonstrated the selective wavelength conversion of 2.5 G/s optical packets from Fabry-Perot laser diode (FP-LD) light to four ITU-T grid wavelengths. We confirmed the good feasibility of this technique for use in DWDM networks. The wavelength conversion we describe here is indispensable for future all-optical networks, in which optical signal sources without wavelength control will be used at user-end terminals.

We have developed a new planar lightwave circuit (PLC) platform eliminating Si terraces for hybrid integrated optical modules. This PLC platform has the advantage of a lower fabrication cost than the conventional PLC platform with an Si terrace, because it does not require fabrication processes such as Si terrace forming and mechanical polishing. Using our new PLC platform structure, we fabricated a transceiver for optical access networks and an 8-channel multi-channel photoreceiver for wavelength division multiplexing (WDM) interconnection systems.

We have developed a new planar lightwave circuit (PLC) platform eliminating Si terraces for hybrid integrated optical modules. This PLC platform has the advantage of a lower fabrication cost than the conventional PLC platform with an Si terrace, because it does not require fabrication processes such as Si terrace forming and mechanical polishing. Using our new PLC platform structure, we fabricated a transceiver for optical access networks and an 8-channel multi-channel photoreceiver for wavelength division multiplexing (WDM) interconnection systems.

In the circuit-switching literature, the Least Loaded Path Routing (LLR) concept has been shown to be very simple and efficient. However, it seems that there is no unique definition for the "least busy" path, i.e., how to measure the degree of "busy" of a path. In this paper, we examine six ways of defining the least busy path and a random policy. The performance of these policies is evaluated via both simulation and analysis. Our numerical results show that all policies, include the random policy, have almost the same performance under most of the network configurations. Only under extremely low traffic load conditions, the difference between the policies becomes significant. However, the magnitude of the difference is still very small (about 0.001). Therefore, we conclude that how to select the alternate path does not affect the performance of LLR-based routing algorithms significantly when the call blocking probability is not too small. Instead, we found that the trunk reservation level affects the performance of LLR-based routing algorithms significantly.

We propose a new intelligent blind source separation algorithm for the mixture of sub-Gaussian and super-Gaussian sources. The algorithm consists of an update equation of the separating matrix and an adjustment equation of nonlinear functions. To verify the validity of the proposed algorithm, we compare the proposed algorithm with extant methods.

The present paper discusses several promising application areas for optical data links based on high-performance vertical-cavity surface-emitting laser diodes (VCSELs). Both 850 and 980 nm emission wavelength devices realized in the GaAs-AlGaAs or InGaAs-AlGaAs material systems are considered. We show data transmission results of 10 Gb/s signals at 830 nm wavelength over a new high-bandwidth multimode silica fiber of up to 1.6 km length. The same fiber type is employed to demonstrate the first 40 Gb/s transport over 300 m distance by means of a 4-channel coarse wavelength-division multiplexing approach. A first 1 10 linear VCSEL array capable of 10 Gb/s per channel operation is presented for use in next generation parallel optical modules. To improve the singlemode emission characteristics for output power in the 5 mW range we introduce a new device concept incorporating a long monolithic cavity. For low-cost short-distance data links we investigate graded-index polymer optical fibers and report on up to 9 Gb/s transmission over a length of 100 m. Polymer waveguides are also used in an optical layer of a hybrid electrical-optical printed circuit board. Transmitted 10 Gb/s optical data over a prototype board show the potential of this new technology. Finally we present two-dimensional VCSEL arrays for highly parallel data transport on a CMOS chip level. Both 980 and 850 nm bottom emitting devices with modulation capabilities up to 12.5 Gb/s are discussed.

Adaptation of software components to the requirements is one of the key concerns in Component Based Software Development (CBSD). In this paper, we propose a formal approach to compose component based systems which are adaptable to the requirements. We focus on the functional aspects of software components and requirements, which are expressed in S-sorted functions. Those S-sorted functions are transformed into Colored Petri Nets (CPN) models in order to evaluate connectivity between the components, and to evaluate adaptability of composed systems to the requirements. The connectivity is measured based on colors or data types in CPN, while the adaptability is measured based on functional equivalency. We introduce simple glue codes to connect the components each other. The paper focuses on business applications, however the proposed approach can be applied to any other domains as far as the functional adaptability is concerned.

In this paper, we consider the net assignment problem in the logic emulation system. This problem is also known as the board-level-routing problem. There are field programmable logic arrays (FPGAs) and crossbars on an emulator board. Each FPGA is connected to each crossbar. Connection requests between FPGAs are called nets, and FPGAs are interconnected through crossbars. We are required to assign each net to the suitable crossbar. This problem is known to be NP-complete in general. A polynomial time algorithm is known for a certain restricted case, in which we treat only 2-terminal nets. In this paper we propose a new polynomial time algorithm for this case.

Recent progress in ultrahigh bit rate optical transmission using time-division multiplexing and wavelength-division multiplexing is described. Latest over 1 Tbit/s transmission experiments are shown and the possibility of higher bit rate transmission is discussed.

Method invocation mechanism is one of the essential features in object-oriented programming languages. This mechanism contributes to data encapsulation and code reuse, but there is a risk of runtime type errors. In the case of object-oriented databases (OODBs), a runtime error causes rollback. Therefore, it is desirable to ensure that a given OODB schema is consistent, i.e., no runtime error occurs during the execution of queries under any database instance of the OODB schema. This paper discusses the computational complexity of the type-consistency problem. As a model of OODB schemas, we adopt update schemas introduced by Hull et al., which have all of the basic features of OODBs such as class hierarchy, inheritance, complex objects, and so on. The type-consistency problem for update schemas is known to be undecidable. We introduce a subclass of update schemas, called acyclic schemas, and show that the type-consistency problem for acyclic schemas is in coNEXPTIME. Furthermore, we show that the problem for recursion-free acyclic schemas is coNEXPTIME-hard and the problem for retrieval acyclic schemas is PSPACE-complete.

In the filed of cognitive psychology, simple recurrent networks are used for modeling the natural language processing in the human brain. For example, Elman experimentally showed that the simple recurrent networks can predict the right-most word in sentential forms of a particular grammar which can generate compound sentences with high probability. Concerning these results, it is natural to ask whether the computational capability of the simple recurrent networks is sufficient to recognize natural languages. In this paper, we assume that the range of a function computed at each gate of a simple recurrent network is a finite set. This is a quite realistic assumption, because we cannot physically implement a gate whose range is an infinite set. Then, we define equivalence relations between simple recurrent networks and Mealy machines or Moore machines, which are finite automata with output. Then, under our assumption, we show (1) a construction of a Mealy machine which simulates a given simple recurrent network, and (2) a construction of a simple recurrent network which simulates a given Moore machine. From these two constructions, we can conclude that the computational capability of the simple recurrent networks is equal to that of finite automata with output under our assumption.

The demonstrated capacity of 40-Gb/s WDM systems is now exceeding 3-Tb/s. We will discuss some of the enabling technologies for these high capacities and some of the technologies that may push the aggregate capacity of WDM systems towards 10-Tb/s.