Mobile computing networks make it possible to offer information access to mobile users. In order to transfer data over mobile networks efficiently, appropriate data transmission control methods for mobile terminals must be established. This paper focuses on spot communication systems to transmit data at high speeds between base stations and mobile terminals. It proposes a flexible and efficient data transmission method that is suitable for spot communication systems. The proposed method transfers subsets of the data to the base stations that are best sited relative to the mobile terminal. This helps to reduce the traffic load of the network significantly. Simulation results confirm the validity of the proposed method. Furthermore, the data receiving time of the mobile terminal, which is an important measure in evaluating the Quality of Service (QoS) for data transmission is analyzed. The result shows that the traffic load in the network is reduced significantly while the QoS is well maintained.

We consider the problem of placing resources in a distributed computing system so that certain performance requirements may be met while minimizing the number of resource copies needed. Resources include special I/O processors, expensive peripheral devices, or such software modules as compilers, library routines, and data files. Due to the delay in accessing each of these resources, system performance degrades as the distance between each processor and its nearest resource copy increases. Thus, every processor must be within a given distance k1 of at least one resource copy, which is called the k-bounded placement problem. The structure of a distributed computing system is represented by a graph. The k-bounded placement problem is first transformed into the problem of finding smallest k-dominating sets in a graph. Searching for smallest k-dominating sets is formulated as a state-space search problem. We derive heuristic information to speed up the search, which is then used to solve the problem with the well-known A* algorithm. An illustrative example and some experimental results are presented to demonstrate the effectiveness of the heuristic search.

Mobile radio and Internet communications services are penetrating our society at an exponential rate of growth. The Internet is the most important driving force towards establishing a multimedia society. Mobile communication systems add an important capability to our communications society, i. e. , mobility. The third generation mobile communications system called IMT-2000 is expected to play an important role in this soon-to- arrive multimedia society. Wideband mobile services based on IMT-2000 will soon become a reality (early 2001). First, we look at the trends of wireless access technologies, centering on IMT-2000. Wideband direct sequence code division multiple access (W-CDMA) will be a major component of a global IMT-2000 standard. Then, we address advanced wireless techniques, i. e. , interference cancellation and employing an adaptive antenna array, which can enhance W-CDMA at a later date. Finally, requirements are discussed for future wireless techniques that will support a fully mobile multimedia communications society.

The differential 4-quadrature (D4Q) coherent optical system which does not need absolute phase information is proposed. The input information is encoded in the relative position of the present symbol with respect to the reference frame constructed by the previous 3 symbols. The general theory of the system operation including encoding and decoding is presented. This system does not need to track the fluctuation of the states of polarizations which is essential for most other polarization modulation systems. As an example, the 4-symbol D4Q system is described. And the saddle point approximation is applied to estimate the bit error rate performance. The analytic approximation agrees with the simulation results very well.

A new type of Meteor Burst Communication (MBC) network is developed. Each unit of the network is based on a DSP board running a modem software. All the fundamental blocks and functions of a modem are implemented in software. Unlike hardware modems, this software modem has flexibility of system configuration and operation. The system implements adaptability in terms of modulation type (number of phases in MPSK) using a unique dynamic channel estimation scheme appropriate for MBC channel. An MBC network protocol is implemented within the modem software. Some preliminary experiments were carried out for differential BPSK and differential QPSK modulations over a practical meteor burst link, and the results are presented.

Software radio base and personal station prototypes are proposed and implemented. The prototypes are composed of RF/IF, A/D and D/A, pre- and post-processors, CPU, and DSP parts. System software is partitioned into CPU program and DSP program to use processor resources effectively. They support various air interfaces, some of which are equivalent to the 384 kbit/s transmission rate PHS (personal handy phone system) and a 96 kbit/s transmission rate system. The base station can also be used as a communication bridge between two systems. In order to ease IF filter requirements, the zero-stuff method is employed. Basic transmission and receiving performances are evaluated in an experiment and their results agree well with those expected.

1.5 µm-band LiNbO3 quasiphase matched (QPM) wavelength converters consisting of a periodical domain inverted structure and a proton exchanged waveguide, have been studied in detail both theoretically and experimentally. Optimum device fabrication conditions are investigated with respected to waveguide propagation loss, coupling loss to a single-mode fiber and wavelength conversion efficiency. A normalized conversion efficiency as high as 200 %/W (by a SHG measurement) and a fiber-to-fiber insertion loss of less than 3.5 dB (@1.55 µm) is obtained for a wavelength converter module with a device length of 40 mm. It is shown that a highly uniform periodical domain inverted structure and a uniform proton exchange waveguide are key to obtaining efficient wavelength conversion. The tolerance of the waveguide width fluctuation is found to be very critical and is less than 20 nm for a 40 mm-long device. Future optimization of LiNbO3 QPM wavelength converters and the possible device applications in future optical communication systems are also presented.

We propose a new active vision system that mimics a saccadic movement of human eye. It is implemented based on a new computational model using neural networks. In this model, the visual pathway was divided in order to categorize a saccadic eye movement into three parts, each of which was then individually modeled using different neural networks to reflect a principal functionality of brain structures related with the saccadic eye movement in our brain. Initially, the visual cortex for saccadic eye movements was modeled using a self-organizing feature map, then a modified learning vector quantization network was applied to imitate the activity of the superior colliculus relative to a visual stimulus. In addition, a multilayer recurrent neural network, which is learned by an evolutionary computation algorithm, was used to model the visual pathway from the superior colliculus to the oculomotor neurons. Results from a computer simulation show that the proposed computational model is effective in mimicking the human eye movements during a saccade. Based on the proposed model, an active vision system using a CCD type camera and motor system was developed and demonstrated with experimental results.

For FA (factory automation) and ATE (automatic test equipment) in the industrial area, the standard bus is required to increase the system performance of multiprocessor environment. VME (versa module european package format) bus is appropriated to the standard bus but has the features that is the small of package and the low density of board. Beside, the density of board and semiconductor have grown to become a significant issues that affect the development time, project cost and field diagnostics. To fit this trend, in this paper, the author composed Revision C. 1 (IEEE Std. P1014-1987) of the integrated environment for the main function such as arbitration, interrupt and interface between VMEbus and several control modules. Also the designed VME system controller is implemented on FPGA that can be located even into Slot 1. The control and function modules are coded with VHDL mid-fixed description method and then those operations are verified by simulation. As a result of experiment, the author confirmed that the most important about the operation of Bus timer that Bus error signal should occur within 56 µs, and both control and function modules have the reciprocal operation correctly. Thus, the constructed VHDL library will be able to apply the system based VMEbus and ASIC design.

File system buffers provide memory space for data being transferred to and from disk and act as caches for the recently used blocks, and the buffer manager usually reads ahead data blocks to minimize the number of disk accesses. However, if several multimedia files with different consumption rates are accessed simultaneously from the file system in which LRU buffer replacement strategy is used, the read-ahead blocks of the low rate file are unloaded from memory to be used for loading a data block of a high data rate file, therefore they should be reloaded again into memory from disk when these blocks are actually referenced. This paper proposes and implements a new buffer cache management scheme for a multimedia file system and analyzes the performance of the proposed scheme by modifying the file system kernel of FreeBSD. In this proposed scheme, initially, some buffers are allocated to each opened multimedia file, privately, then these buffers are reused for other data blocks of that file when they are loaded from the disk. Moreover, the number of private buffers allocated for the file is dynamically adjusted according to its data rate. An admission control scheme is also proposed to prevent opening of a new file which may cause overloads in the file system. Experimental results comparing proposed scheme with the original FreeBSD and a simple CTL-based model show that the proposed buffer management scheme could support the realtime play back of several multimedia files with various data rates concurrently without helps of a realtime CPU and disk scheduling.

When a failure or upset occurring in a controller computer induces a task failure durable for a substantial period, system dynamics apparently deviates from its desirable sample paths, and loses its stability in an extreme case for the period to exceed the hard deadline in a real-time control system. In the paper, we propose an algorithm to combine the deadlines of all elementary tasks (derived formerly by our work) executed in several operation modes with multi-sampling periods. This results in computing the hard deadline of the entire system through modifying task-state equations to capture the effects of task failures and inter-correlations among tasks.

It has been proposed that the collaborative working environments have been created by the computing assistance for human behaviors with the instructions of related information and items. The purpose of this study is to propose the collaboration mechanism and the environments constrained by the roles. The basic principle at issue in this studies is that all members should behave autonomously, and behave collaboratively with understanding the surrounding environments. We have already presented the Distributed Collaborative Computing architecture called Noah that has the concept of field with tupple space. On this mechanism, we designed the role-based cooperative work environments on the collaboration and coordination mechanism. We applied this mechanism to the typical models in the industrial system's domain.

A generalized class of consecutive-k-out-of-n:G systems, referred to as Con/k*/n:G systems, is studied. A Con/k*/n:G system has n ordered components and is good if and only if ki good consecutive components that originate at component i are all good, where ki is a function of i. Theorem 1 gives an O(n) time equation to compute the reliability of a linear system and Theorem 2 gives an O(n2) time equation for a circular system. A distributed computing system with a linear (ring) topology is an example of such system. This application is very important, since for other classes of topologies, such as general graphs, planar graphs, series-parallel graphs, tree graphs, and star graphs, this problem has been proven to be NP-hard.

Migration transparency is considered in the context of multi-agent systems. A mobile agent architecture is proposed with an Availability service and a Transparency interface. We define mobility as explicit (or proactive) when the agent decides when and where to move and define mobility as implicit (i. e. , transparent or reactive) when it is a consequence of changes in the environment. Implicit mobility of agents is explored in addition to the usual explicit mobility. The search for a target agent (or agency) follows a transparent location and selection. The client agent preferably moves towards the target agent. If not possible, the target agent will move towards the client agent when calling back. If both agents can not move then the execution takes place remotely or is abandoned. Transparency is goal oriented.

The purpose of this note is to carry out study on a 3-out-of-4:G warm standby system with nonidentical components. By using Markov model, the general form solution of stationary availability of the system is obtained. Examples are given to illustrate the solutions of transient and stationary availability of such system.

Packet concentrators are used in many high-speed computer communication systems such as fast packet switches. In these systems, the time available for concentration is very short. It is therefore desirable to realize the packet concentrators as hardware chips for fast concentration. The knockout concentrator was proposed for hardware realization. In this paper, we improve this concentrator to reduce the probability of packet loss, and the improved concentrator is called wraparound knockout concentrator. This concentrator has several wraparound paths within it, and it does not require any additional pin per chip. After contention among the packets in a slot, each winner goes to a distinct output, some losers circulate along the wraparound paths for contention in the subsequent slot, and the remaining losers are discarded. In this manner, some losers are not discarded immediately and they still have the chance to go to the outputs in the subsequent slot, thereby reducing the probability of packet loss. We analyze the number of logic gates required and the probability of packet loss. The numerical results show that if the proposed concentrator has a few wraparound paths, the probability of packet loss can already be reduced by orders of magnitude.

The present paper modifies the algorithm to estimate harmful event frequencies and examines the definition of modes of operation in IEC 61508. As far as the continuous mode concerns, the calculated results coincide with those obtained based on the standard. However, for the intermediate region of medium demand frequencies and/or medium demand durations, the standard gives much higher harmful event frequencies than the real values. In order to avoid this difficulty, a new definition of modes of operation and a shortcut method for allocation of SILs are presented.

We deal here with diagnosis for failures of series/parallel structure system. The conventionals have assumed that the system failure is caused by a single minimal cut set (MCS). The purposes of this paper are to propose a new diagnosis method to identify all MCSs by utilizing the series/parallel structure and repair information without requiring an excessive number of inspections. Moreover, by applying our method to several types of series/parallel structure system, and to system having some kinds of probability distributions, desirable system for our method are persuaded. We evaluate not just the number of inspections but also the cost of diagnosis, and show the condition under which our method is effective.

More than forty thousands computer viruses have appeared so far since the first virus. Six computer viruses on average appear every day. Enormous expansion of the computer network opened a thread of explosive spread of computer viruses. In this paper, we propose a distributed approach against computer virus using the computer network that allows distributed and agent-based approach. Our system is composed of an immunity-based system similar to the biological immune system and recovery system similar to the recovery mechanism by cell division. The immunity-based system recognizes "non-self" (which includes computer viruses) using the "self" information. The immunity-based system uses agents similar to an antibody, a natural killer cell and a helper T-cell. The recover system uses a copy agent which sends an uninfected copy to infected computer on LAN, or receives from uninfected computer on LAN. We implemented a prototype with JAVATM known as a multi-platform language. In experiments, we confirmed that the proposed system works against some of existing computer viruses that can infect programs for MS-DOSTM.

Hash routing is an algorithm for a distributed WWW caching system that achieves a high hit rate by preventing overlaps of objects between caches. However, one of the drawbacks of hash routing is its lack of robustness against failure. Because WWW becomes a vital service on the Internet, the capabilities of fault tolerance of systems that provide the WWW service come to be important. In this paper, we propose a duplicated hash routing algorithm, an extension of hash routing. Our algorithm introduces minimum redundancy to keep system performance when some caching nodes are crashed. In addition, we optionally allow each node to cache objects requested by its local clients (local caching), which may waste cache capacity of the system but it can cut down the network traffic between caching nodes. We evaluate various aspects of the system performance such as hit rates, error rates and network traffic by simulations and compare them with those of other algorithms. The results show that our algorithm achieves both high fault tolerance and high performance with low system overhead.