This paper summarizes power reduction methods applicable for VLSI bus systems in terms of reduction of signal swing, effective capacitance reduction and reduction of signal transition, which have been studied in authors' research group. In each method the basic concept is reviewed quickly along with some examples of its application. A future perspective is also described in conclusion.

It is now known that a seemingly random irregular time series can be deterministic chaos (hereafter, chaos). However, there can be various kind of noise superimposed into signals from real systems. Other factors affecting a signal include sampling intervals and finite length of observation. Perhaps, there may be cases in which a chaotic time series is considered as noise. J. Theiler proposed a method of surrogating data to address these problems. The proposed method is one of a number of approaches for testing a statistical hypothesis. The method can identify the deterministic characteristics of a time series. In this approach, a surrogate data is formed to have stochastic characteristics with the statistic value associated with the original data. When the characteristics of the original data differs from that of a surrogate data, the null hypothesis is no longer valid. In other words, the original data is deterministic. In comparing the characteristics of an original time series data and that of a surrogate data, the maximum Lyapunov exponents, correlation dimensions and prediction accuracy are utilized. These techniques, however, can not calculate the structure in local subspaces on the attractor and the flow of trajectories. In deal with these issues, we propose the trajectory parallel measure (TPM) method to determine whether the null hypothesis should be rejected. In this paper, we apply the TPM method and the method of surrogate data to test a chaotic time series and a random time series. We also examine whether a practical time series has a deterministic property or not. The results demonstrate that the TPM method is useful for judging whether the original and the surrogate data sets are different. For illustration, the TPM method is applied to a practical time series, tap water demand data.

This paper presents a new data hiding scheme via steganographic image transformation, which is different from conventional data hiding techniques. The transformation is achieved in the frequency domain and the concept of Fourier filtering method is used. An input image is transformed into a fractal image, which can be used in Computer Graphic (CG) applications. One of the main advantages of this scheme is the amount of data to be hidden (embedded) is equal to that of the host signal (generated fractal image) while it is in general limited in the conventional data hiding schemes. Also both the opened fractal image and the hidden original one can be properly used depending on the situation. Unauthorized users will not notice the "secret" original image behind the fractal image, but even if they know that there is a hidden image it will be difficult for them to estimate the original image from the transformed image. Only authorized users who know the proper keys can regenerate the original image. The proposed method is applicable not only as a security tool for multimedia contents on web pages but also as a steganographic secret communication method through fractal images.

The design of effective traffic and resource management policies is a key issue in the deployment of ATM-satellite systems. This paper proposes a technique of call admission control and dynamic resource management to support ATM traffic classes in satellite environments. The effectiveness of the strategy is assessed by referring to the EuroSkyWay multimedia satellite platform, based on Ka-band payload and on-board processing. The main advantage is the effective exploitation of the satellite bandwidth by means of the statistical multiplexing of traffic sources and the guarantee of QoS provisioning to both real-time and non real-time, constant and variable bit rate sources.

This paper proposes the iterative quasi-oldest-cell-first (i-QOCF) scheduling algorithm, a new scheduling algorithm for input-queued ATM switches with virtual output queuing (VOQ). In the i-QOCF scheduling algorithm, each input port and each output port maintains its own list. The length of the list can be N, 2 N, ..., B N, where B is the size of the separate queue for an output port at input ports, and N is the number of output ports. The list maintained by an input port contains the identifiers for those output ports to which that input port will send a cell. The list maintained by an output port contains the identifiers for input ports that have a cell destined for that output port. If we use a list whose length is B N, then the identifiers in the list appear in the oldest order, and i-QOCF gives preference to cells that have been waiting for the longest time. If we use a list whose length is less than B N, then the identifiers in the list appear in the quasi-oldest order, and i-QOCF gives preference to cells that have been waiting for the quasi-longest time. We determine the performance of i-QOCF in a comparison with i-OCF in terms of cell delay time. We find that an input-queued ATM switch with i-QOCF and VOQ can achieve 100% throughput for independent arrival processes. Under uniform traffic, 3-QOCF is enough to achieve convergence during one cell time. If we use 3-QOCF, the list length is 3 N, then its cell delay time is almost the same as that of 4-OCF (Oldest-Cell-First).

This paper presents a 7th-order channel-select filter for a spread-spectrum wireless receiver operating with a minimum power supply of 2.5 V. The channel-select filter implements a sharp transition from 2 MHz to 4 MHz and a stopband attenuation of 50 dB. The 7th-order filter is realized by a cascade of a passive RC integrator, a 3rd-order leapfrog filter, an operational amplifier based differentiator, a 2nd-order notch filter, and a 1st-order allpass filter. It is designed in a 0.35 µm single-poly BiCMOS process. Simulation results show feasibility of the proposed filter.

This paper addresses output regulation for nonlinear systems driven by a time varying parameter. The derivative information of the time varying parameter is necessary for the improved regulation performance but it is not readily available in general. In this paper, we propose a velocity estimation of the time varying parameter for use in the control law without amplifying noise signals.

A hierarchical structure of the statistical models involving the parametric, state space, generalized state space, and self-organizing state space models is explained. It is shown that by considering higher level modeling, it is possible to develop models quite freely and then to extract essential information from data which has been difficult to obtain due to the use of restricted models. It is also shown that by rising the level of the model, the model selection procedure which has been realized with human expertise can be performed automatically and thus the automatic processing of huge time series data becomes realistic. In other words, the hierarchical statistical modeling facilitates both automatic processing of massive time series data and a new method for knowledge discovery.

Super-anomalous elliptic curves over a ring Z/nZ ;(n=Πi=1k piei) are defined by extending anomalous elliptic curves over a prime filed Fp. They have n points over a ring Z/nZ and pi points over Fpi for all pi. We generalize Satoh-Araki-Smart algorithm and Ruck algorithm, which solve a discrete logarithm problem over anomalous elliptic curves. We prove that a "discrete logarithm problem over super-anomalous elliptic curves" can be solved in deterministic polynomial time without knowing prime factors of n.

In future multimedia mobile communication systems, heterogeneous users will require very different and time-varying transmission rates. Thus, they should be supported with a novel approach that can accommodate the fluctuating data rates in wireless channels. In this paper, a simple method that is used to admit the rates successfully is proposed. The method is also distributed in a sense that it can be implemented at each mobile without any interaction with other mobiles. The method consists of power control with a higher SIR (signal to interference ratio) target and periodic adjustment of the data rate. We prove a good rate admission property of the proposed method and verify its performance with numerical investigation.

In this paper, a token-controlled network with exhaustive service strategy is analyzed. The mean and variance of service time of a station, and the mean token rotation time on the network are derived under the condition that the buffer capacity of each station is individually finite. For analysis, an extended stochastic Petri-net model of a station is presented. Then, by analyzing the model, the mean service time of a station and the mean token rotation time are derived, as functions of the given network parameters such as the total number of stations on the network, the arrival rate of frames, the transmission rate of frames, and the buffer capacity. The variance of service time of a station is also derived. By examining derived results, it is shown that they exactly describe the actual operations of the network. In addition, computer simulations with sufficient confidence intervals help to validate the results.

Multi-path propagation structure in the urban mobile communication environment of 25 GHz band has been measured by means of newly developed "multi-path propagation parameter measurement equipment," which is capable of estimating coupled DOA (Direction Of Arrival), TOA (Time Of Arrival) and relative field strength by super resolution techniques. Before measurement, basic performance of the equipment has been evaluated in the anechoic chamber in order to ascertain limitation on measurement. For practice and verification of outdoor propagation characteristics, basic data have been collected in a works where accurate buildings and road layout is known. Sub-sequently, data have been collected in the urban mobile communication environment and following characteristics have been confirmed. 1) DOA and TOA of wave reflected by the side of building almost follow the ray-trace. 2) Street trees make 25 GHz band wave attenuate. 3) There are such unusual cases that it is possible to communicate in spite of out of line-of-sight by multi-path propagation. 4) Narrow streets have very complicated propagation structures. Finally, technologies that should be developed for the high-speed digital mobile communication are proposed based on the measurement results.

We have two goals in this paper. One is the comparison of Spread Spectrum (SS) CDMA and Spread Time (ST) CDMA. The other is to propose a new SS-ST CDMA system, which is an adaptive CDMA with both merits of SS and ST CDMA. SS and ST CDMA are compared from the view point of two dimensional space "frequency (B Hz)-time (T Sec)" together with their communication capacity. A primary modulation is assumed to be PPM in ST CDMA, and FSK in SS CDMA which is regarded as PPM in frequency axis. Both SS and ST CDMA are combined to give the proposed SS-ST CDMA, where transmitted signals are spread both in time and frequency domain. In order to realize the proposed system, a transmitter model is presented, and two receiver structures are discussed. The discrete Fourier transform (DFT) is employed for the system flexibility. Although SS, ST and SS-ST CDMA are shown to have the same capacity of 0.7213, the combined SS-ST CDMA has a merit of adaptability to adjust spreading gain of ST and SS according to property of channels, an impulsive noise dominated or a CW interference dominated channel. Numerical results of DFT are also shown to illustrate the waveform and spectrum of the proposed SS-ST CDMA system. Finally the symbol error probability performance of ST PPM, SS FSK and combined SS-ST systems in CW and impulsive environment is presented.

Thermal stability of anisotropic and isotropic Co alloy thin-film media is investigated. The orientation ratio of CoCrTa(Pt)/Cr media was controlled by the mechanical texture of the NiP/Al substrates. Bulk magnetic properties, delta M curves and time decay of magnetization in the circumferential and radial directions were measured. The maximum magnetic viscosity coefficient calculated from the time decay of magnetization in the circumferential direction was higher than that in the radial direction for a mechanically textured sample, while it was similar in both directions for a non-textured sample. The magnetic viscosity coefficient in the circumferential direction is smaller than that in the radial direction when the reverse field is in the range of the demagnetization field for thin-film recording media. This implies that an anisotropic sample (namely, a sample with a high orientation ratio) will be more thermally stable when it is not exposed to a large external magnetic field.

In this paper, system capacity of the reverse link of a wireless multimedia CDMA system with transmission power control is analysed for receivers with and without CCI cancellers. For N classes of users, system capacity is represented by a point in an N-dimensional space. It is shown that system capacity is improved considerably with CCI cancellers, that system capacity region is non-convex in general, and that its boundary is well approximated with a unique hyper plane when CCI cancellers are fully employed.

We propose precise write-time compensation for nonlinear transition shift in magnetic tape recording using d=1 runlength-limited (RLL) code as a channel modulation. In this write-time compensation approach, the write current transitions having a transition within 3 bits earlier are shifted so as to minimize the transition shift of the readback signal. First, we precisely measured the nonlinear transition shift using a VCR. Next, based on this measurement, we simulated the effects of the write-time compensation, verifying them in recording experiments with a VCR. The results show that when the optimum read equalization is applied to the readback signal, this write-time compensation approach increases the eye height and eye width while improving the byte error rate by about two orders.

Traffic management schemes such as Connection Admission Control (CAC), policing, and traffic shaping are important to provide multimedia communications with better Quality of Service (QoS). In the conventional model, admission control and policing are done at intermediate nodes, and traffic shaping is done at the edge of a network. However, QoS of communications should be defined between tasks or threads rather than between hosts. Therefore traffic management inside a host is as important as that in networks. We propose software-based traffic management architecture over a real-time microkernel. The architecture focuses on the interface between a network driver and user threads calling the driver. We categorized services of communication threads into three classes: Real-Time at Guaranteed Rate (RT-GR), Real-Time at Available Rate (RT-AR), and Best-Effort (BE). Our architecture is designed for an environment containing a mixture of these services. In the architecture, a sender periodic thread of RT-GR or RT-AR is executed such that the sending rate matches a user-specified rate. The network driver monitors the per-flow rate of injected data and discards the data if the injected rate exceeds the user-specified rate. To avoid the continuous discarding of data, the sending thread can adjust its sending rate by periodically looking at logged data concerning the rate. RT-AR service can achieve more than the specified rate when bandwidth is available. The scheme of software traffic management is effective in attaining higher throughput not only for full-duplex Ethernet but also for ATM because the difference of rate between hardware and software is reduced. In this paper, we describe the design and implementation of the software-based traffic management architecture on Real-Time Mach. The results of performance evaluations demonstrate that our traffic management scheme performs well for full-duplex Ethernet.

In this paper, we will present a study of the time-dependence effect in alumite perpendicular media at different thicknesses. Important parameters of the time-dependence effect such as magnetic viscosity and activation volume are investigated. Viscosity as a function of applied field (viscosity curve) exhibits a short plateau at a low field and then decreases monotonously with increasing field. After correcting for the demagnetizing field, the shape of the intrinsic viscosity curves changes to the well-known shape of the viscosity curve of in-plane media, i. e. , they have a peak near Hc. The intrinsic viscosity curves obtained from the experiments were fitted to an analytical model by Chantrell et al., from which, we found that the effective switching volumes obtained by fitting are much smaller than the column volumes, indicating that the reversal mechanism is incoherent.

Given a Petri net N=(P, T, E), a siphon is a set S of places such that the set of input transitions to S is included in the set of output transitions from S. Concerning extraction of one or more minimal siphons containing a given specified set Q of places, the paper shows several results on polynomial time solvability and NP-completeness, mainly for the case |Q| 1.

Internet communication is increasingly becoming an important element in daily life. Keeping this network safe from malicious elements is an urgent task for network management. To maintain the security level networks are generally, monitored for indications of usage with ill-intentions. Such indications are events which need to be collated, correlated and analyzed in real-time to be effective. However, on an average medium to large size network the number of such events are very large. This makes it practically impossible to analyze the information in real-time and provide the necessary security measures. In this paper, we propose a mechanism that keeps the number of events, to be analyzed, low thereby making it possible to provide ample security measures. We discuss a real-time Intrusion Detection System (IDS) for detecting network attacks. The system looks out for TCP ACK/RST packets, which are generally caused by network scans. The system can extract the tendency of network flows in real-time, based on the newly developed time-based clustering and Dynamic Access Tree creation techniques. The algorithm, implemented and deployed on a medium size backbone network using RMON (Remote MONitoring) technology, successfully detected 195 intrusion attempts during a one month period. The results of the pilot deployment are discussed. In this paper, the proposal, implementation and evaluation will be described.