In this paper, we propose an approach to solve the power control issue in a DS-CDMA cellular system using genetic algorithms (GAs). The transmitter power control developed in this paper has been proven to be efficient to control co-channel interference, to increase bandwidth utilization and to balance the comprehensive services that are sharing among all the mobiles with attaining a common signal-to-interference ratio(SIR). Most of the previous studies have assumed that the transmitter power level is controlled in a constant domain under the assumption of uniform distribution of users in the coverage area or in a continuous domain. In this paper, the optimal centralized power control (CPC) vector is characterized and its optimal solution for CPC is presented using GAs in a large-scale DS-CDMA cellular system under the realistic context that means random allocation of active users in the entire coverage area. Emphasis is put on the balance of services and convergence rate by using GAs.

Recently, Kasahara and Murakami proposed new product-sum public-key cryptosystems using the Chinese remainder theorem as the trapdoor. We proposed 'Yaezakura' as the high-density product-sum PKC applying the method using the reduced bases. In this paper, we propose another high-density scheme with the Chinese remainder theorem trapdoor using the message extension. We also show that the proposed scheme is invulnerable to the low-density attack. In the proposed scheme, the sender can freely select the positions of the dummy messages.

Over recent years, "Internet-able" applications and architectures have been used to support domains where there are multiple interconnected systems that are both decentralized and autonomous. In enterprise-level data management domains, both the schema of the data repository and the individual query needs of the users evolve over time. To handle this evolution, the resulting architecture must enforce the autonomy in systems that support the client needs and constraints, in addition to maintaining the autonomy in systems that support the actual data schema and extraction mechanisms. At the MITRE Corporation, this domain has been identified in the development of a composite data repository for the Center for Advanced Aviation System Development (CAASD). In the development of such a repository, the supporting architecture includes specialized mechanisms to disseminate the data to a diverse evolving set of researchers. This paper presents the motivation and design of such an architecture to support these autonomous data extraction environments. This run-time configurable architecture is implemented using web-based technologies such as the Extensible Markup Language (XML), Java Servlets, Extensible Stylesheets (XSL), and a relational database management system (RDBMS).

The imprecise computation is one of the promising schemes in the real time systems to adapt quality of computations to change of load with keeping the deadlines of tasks in the systems. When overload occurs in the systems, the minimum requirements on the deadline are assured by decreasing quality of the computation. This paper describes how to apply the concept of the imprecise computation to automobile control in the expressway assuming the intelligent transportation system (shortly, ITS). The deadline violation of tasks for automobile control in the expressway induces collision of automobiles. Regardless of whether the expressway is congested or not, collision of automobiles must be avoided. To satisfy such requirement, the concept of the imprecise computation is effective. This paper proposes an adaptive scheduling using the imprecise computation to avoid collision of automobiles and increase throughput, and shows results of simulation experiments about an adaptive scheduling for automobiles control.

There is an ever-increasing demand for better performance and scalability in workflow systems. We describe how mobile agents can be used to satisfy such a requirement. For the purpose two important design issues are pointed out in workflow execution and architecture levels. Agent delegation models and a 3-layer architecture are suggested in mobile agent based workflow systems as a solution for each consideration. Workload is statically distributed over task performers based on the proposed method. As a result the performance and the scalability are improved. The effectiveness is shown through stochastic Petri-nets simulation through comparison with client-server based- and another mobile agent-based workflow systems.

System needs of growing systems including heterogeneous functions and operations are increased. High assurance system that achieves high reliability and high availability is very important for such systems. In order to realize high assurance system, we developed the assurance technology based on ADS (Autonomous Decentralized System). When a growing system changes or grows, its reliability may be lowered. In this paper, we clarify the risk factors which lower the reliability and quality of a growing system when the system is modified. We will then examine the technology to eliminate or mitigate those risk factors, and propose adaptive assurance technology that can minimize the risk. We also applied this technology to ATOS for Tokyo Metropolitan Railway Network as an example of really changing and growing system and mention its effectiveness. ATOS; Autonomous Decentralized Transport Operation Control System.

The heterogeneous autonomous decentralized system technology offers a way to integrate different types of context-related autonomous decentralized (sub) systems into a coherent system. The aim of this research is to model and evaluate the communication capacity among the subsystems connected by communication gateways of a heterogeneous autonomous decentralized system. Failures of subsystems and communication gateways in the system are taken into account. We use graphs to represent the topologies of heterogeneous autonomous decentralized systems and use the residual connectedness reliability (RCR) to characterize the communication capacity among its subsystems connected by its gateways. This model enables us to share research results obtained in residual connectedness reliability study in graph theory. Not to our surprise, we learnt soon that computing RCR of general graphs is NP-hard. But to our surprise, there exist no efficient approximation algorithms that can give a good estimation of RCR for an arbitrary graph when both vertices and edges may fail. We proposed in this paper a simulation scheme that gave us good results for small to large graphs but failed for very large graphs. Then we applied a theoretical bounding approach. We obtained expressions for upper and lower bounds of RCR for arbitrary graphs. Both upper and lower bound expressions can be computed in polynomial time. We applied these expressions to several typical graphs and showed that the differences between the upper and lower bounds tend to zero as the sizes of graphs tend to infinite. The contributions of this research are twofold, we find an efficient way to model and evaluate the communication capacity of heterogeneous autonomous decentralized systems; we contribute an efficient algorithm to estimate RCR in general graph theory.

This paper proposes a receding horizon control scheme for a set of uncertain discrete-time linear systems with randomly jumping parameters described by a finite-state Markov process whose jumping transition probabilities are assumed to belong to some convex sets. The control scheme for the underlying systems is based on the minimization of an upper bound on the worst-case infinite horizon cost function at each time instant. It is shown that the mean square stability of the proposed control system is guaranteed under some matrix inequality conditions on the terminal weighting matrices. The proposed controller is obtained using semidefinite programming.

A self-similar behavior characterizes the traffic in many real-world communication networks. This traffic is traditionally modeled as an ON/OFF discrete-time second-order self-similar random process. The self-similar processes are identified by means of a polynomially decaying trend of the autocovariance function. In this work we concentrate on two criteria to build a chaotic system able to generate self-similar trajectories. The first criterion relates self-similarity with the polynomially decaying trend of the autocovariance function. The second one relates self-similarity with the heavy-tailedness of the distributions of the sojourn times in the ON and/or OFF states. A family of discrete-time chaotic systems is then devised among the countable piecewise affine Pseudo-Markov maps. These maps can be constructed so that the quantization of their trajectories emulates traffic processes with different Hurst parameters and average load. Some simulations are reported showing how, according to the theory, the map design is able to fit those specifications.

This short paper is a written version of one part of the plenary address given at the November 1999 NOLTA symposium held at the Hilton Waikoloa Village in Hawaii. I was invited by Professor Shin'ichi Oishi, a general vice-chairman of the symposium, to give a survey of some of my own research. I was happy to do that--in the context of a description of what Bell Labs.' research environment was like in its math center in the 1960's, and why I feel that today's young researchers are often too constrained in that they are typically not encouraged to try to do really interesting work. Here the emphasis is on only the origins of input-output stability theory.

In this paper, we shall construct mathematical theory based on the concept of set-valued mappings, suitable for available operation of network systems extraordinarily complicated and diversified on large scales. Fundamental conditions for availability of system behaviors of such network systems are clarified in a form of fixed point theorem for system of set-valued mappings.

We study a class of nonlinear dynamical systems to develop efficient algorithms. As an efficient algorithm, interior point method based on Newton's method is well-known for solving convex programming problems which include linear, quadratic, semidefinite and lp-programming problems. On the other hand, the geodesic of information geometry is represented by a continuous Newton's method for minimizing a convex function called divergence. Thus, we discuss a relation between information geometry and convex programming in a related family of continuous Newton's method. In particular, we consider the α-projection problem from a given data onto an information geometric submanifold spanned with power-functions. In general, an information geometric structure can be induced from a standard convex programming problem. In contrast, the correspondence from information geometry to convex programming is slightly complicated. We first present there exists a same structure between the α-projection and semidefinite programming problems. The structure is based on the linearities or autoparallelisms in the function space and the space of matrices, respectively. However, the α-projection problem is not a form of convex programming. Thus, we reformulate it to a lp-programming and the related ones. For the reformulated problems, we derive self-concordant barrier functions according to the values of α. The existence of a polynomial time algorithm is theoretically confirmed for the problem. Furthermore, we present the coincidence with the gradient vectors for the divergence and a modified barrier function. These results connect a part of nonlinear and algorithm theories by the discreteness of variables.

Software defined radio (SDR) is receiving much attention as the key technology to realize the next generation wireless communication system. This paper proposes the concept of system diversity on SDR and investigates the effectiveness of system diversity by using a concrete simulation model. System diversity allows the wireless communication system being used to be dynamically changed in addition to the signal processing algorithm or modulation/coding scheme being used. To clarify the validity of system diversity, we examine a system simulation model consisting of three wireless communication systems; algorithms are introduced to show how system diversity can be controlled using the QoS parameters of received signal level, data transmission rate, and channel capacity. The process by which system diversity switching is triggered is elucidated, and a practical example is introduced. Simulation results confirm that system diversity offers higher performance in terms of data throughput and system channel capacity than existing wireless communication systems. Finally, a comprehensive algorithm is described that protects existing single-mode traffic from being degraded by SDR switching.

This paper proposes new recursive fixed-point smoother and filter using covariance information in linear continuous-time stochastic systems. To be able to treat the stochastic signal estimation problem, a performance criterion, extended from the criterion in the H filtering problem by introducing the stochastic expectation, is newly introduced in this paper. The criterion is transformed equivalently into a min-max principle in game theory, and an observation equation in the Krein spaces is obtained as a result. For γ2<, the estimation accuracies of the fixed-point smoother and the filter are superior to the recursive least-squares (RLS) Wiener estimators previously designed in the transient estimation state. Here, γ represents a parameter in the proposed criterion. This paper also presents the fixed-point smoother and the filter using the state-space parameters from the devised estimators using the covariance information.

A general tracking control problem for mobile robots is proposed and solved using the backstepping technique. A global result is given for the kinematic steering system to make the tracking error approaching to zero asymptotically. Based on our efforts, the proposed controller can solve both the tracking problem and the regulation problem of mobile robots. In particular, mobile robots can now globally follow any differentiable with bounded velocities path such as a straight line, a circle and the path approaching to the origin using the proposed controller. Moreover, the problem of back-into-garage parking is also solved by our approach. Some interesting simulation results are given to illustrate the effectiveness of the proposed tracking control laws.

Currently the long memory behavior is associated to stochastic processes. It can be modeled by different models such like the FARIMA processes, the k-factors GARMA processes or the fractal Brownian motion. On the other side, chaotic systems characterized by sensitivity to initial conditions and existence of an attractor are generally assumed to be close in their behavior to random white noise. Here we show why we can adjust a long memory process to well known chaotic systems defined in dimension one or in higher dimension. Using this new approach permits to characterize in another way the invariant measures associated to chaotic systems and to propose a way to make long term predictions: two properties which find applications in a lot of applied fields.

The efficiency-fractional bandwidth product (EB), which is expressed as a ratio of the radiation resistance to the absolute value of the input reactance of an antenna, is used as a performance criterion for small dielectric loaded monopole antennas (DLMAs). The dependence of the EB on the permittivity of the dielectric loading (i.e., the electrical volume) is experimentally and numerically investigated for the first time in antenna research. As a result, it is found that the EBs of the some DLMAs are enhanced over a bare monopole antenna and an EB characteristic curve has a maximum point. This result suggests the presence of the optimum electrical volume for the dielectric loading in order to obtain the best EB performance. A general reason for the existence of the peak value is also explained using a mathematical deduction. Finally the system EB, which is an efficiency-fractional bandwidth product of the DLMA with a practical matching circuit, is defined and its dependence on the relative permittivity is illustrated. Consequently, the existence of the peak value is also confirmed for the system EBs. In addition, it is demonstrated that the enhancement of the system EB is mainly due to the enhancement in the efficiency of the antenna system.

A signal suffers from nonlinear, linear, and additive distortion when transmitted through a channel. Linear equalizers are commonly used in receivers to compensate for linear channel distortion. As an alternative, novel equalizer structures utilizing neural computation have been developed for compensating for nonlinear channel distortion. In this paper, we propose a neural detector based on self-organizing map (SOM) in a 16 QAM system. The proposed scheme uses the SOM algorithm and symbol-by-symbol detector to form a neural detector, and it adapts well to the changing channel conditions, including nonlinear distortions because of the topology-preserving property of the SOM algorithm. According to the theoretical analysis and computer simulation results, the proposed scheme is shown to have better performance than traditional linear equalizer when facing with nonlinear distortion.

Analysis of a novel folded loop antenna for handset is described along with the advanced design concept for handset antennas. The design concept shown in this paper meets the foremost requirement for handset antennas such as (1) small size and yet (2) has capability of mitigating degradation of antenna performance due to the body effect, and (3) of reducing SAR value in the human head at the handset talk position, in addition to the indispensable requirements for handset antennas such as (4) low profile, and (5) light weight. The technology applied is to make this antenna (a) an integrated structure, which is a typical application of the fundamental concept of making antennas small and (b) a balanced structure which has been proved to be very effective to satisfy the requirements (2) and (3). The antenna is essentially a two-wire transmission line, folded at about a quarter-wavelength to form a half-wave folded dipole, and yet appears to be a loop of one-wavelength. It does not have really a balanced structure, as is fed with an unbalanced line; however, the antenna structure itself can eliminate the unbalanced current flow on the feed line as in the balanced antenna system. Both theoretical and experimental analyses have been shown and the usefulness of the antenna is discussed. This paper may suggest the advanced technology and design concept that will be applied to the development of handset antennas toward the future.

The field of mobile communications has continued to spread with astonishing speed in recent years. The expansion of mobile communications and the Internet has not only brought changes to communications services but also exerted huge effects on the economy and daily life. IMT-2000, International Mobile Telecommunications, is the next generation system for mobile communications systems currently being implemented. Standardization and development of IMT-2000 are in much progress under international frameworks to start commercial service by around the year 2001. This paper focuses in particular on radio transmission technology, giving an overall view of IMT-2000 standardization and technological status, as well as future technical directions extending beyond IMT-2000.