In estimating the performances of Distributed control Dynamic Channel Assignment (DDCA) strategies in sector cell layout systems, we find that sector cell layout systems with DDCA achieved a large system capacity. Moreover, we also indicate the problem, which is the increase of occurrences of cochannel interference, raised by using DDCA in sector cell layout systems. The new channel assignment algorithm, which is called Channel Searching on Direction of Sector (CSDS), is proposed to cope with the problem. CSDS assigns nominal channels to each sector according to their direction so that the same frequency channel tends to be used in sectors having the same direction. We show, by simulations, that CSDS is an adequate algorithm for sector cell layout systems because it significantly improves performance on co-channel interference while only slightly decreasing system capacity.

A hierarchical relaxation method is presented for detecting local features in moving images. The relaxation processes are performed on the temporal-spatial pyramid, which is a multi-resolution data structure for the moving images. The accurate and high speed edge detection can be obtained by using infomation in the neighboring frames as well as the processed results in the higher layers of the pyramid.

A new current-mode analog BiCMOS multiplier/divider circuit based on the translinear principle is presented. This circuit can be implemented by a standard 0.8µm BiCMOS process. The simulation results showed that the circuit realizes the high-speed and high-precision operation with a 3V supply.

This paper proposes Channel Reservation for Ahead Cells (CRAC)" scheme for street micro-cellular systems. The scheme enables mobiles to reserve the same channel over several cells at once. This paper analyzes both CRAC and FCA (Fixed Channel Assignment) in a ring-shaped service area where high speed mobiles and low speed mobiles move. In the analysis, the priority control which prioritizes hand-off calls and reservation calls over new calls over new calls is also taken into account. Obtained results include the blocking rate, the forced call termination rate, the average number of channel changings and the system utilization. From numerical results, CRAC is found to perform better than FCA with regard to the average number of channel changings and the forced call termination rate.

During the last decade the decrease in the size of computing machinery, coupled with the increase in their computing power has lend to the development of the concept of mobile computing. Effects of this new vision is currently evident in the flourishing numbers of mobile telephones and portable computing units. In this paper we briefly investigate some issues concerning the security of mobile computing systems, within the framework of the categories of mobility, disconnection, data access modes and scale of operation (Imielinski & Badrinath, 1993). In contrast to previous works which concentrate on security in wireless communications, we focus on the security of interactions which are built upon the underlying wireless communications medium. Some conclusions are presented on the future directoins for security research in mobile computing sysytems.

As the rise of the Internet greatly affects the construction of networks in the coming era of multimedia, we try to find the factors of development and problems of the Internet. Furthermore, we give light to the requirements on networks based on multimedia applications tailored to each homes. As a result of those two analyses, we point out that the Asynchronous Transfer Mode (ATM) type Internet utilizing ATM technology, which makes up for the drawbacks of information management function of the Internet, is promising. Furthermore, we point out that intelligence, which provides the network with the information management and information search functions, is necessary to be introduced into networks. So we propose a network function model, which will realize such functions.

A self-organizing neural network model of spatio-temporal visual receptive fields is proposed. It consists of a one-layer linear learning network with multiple temporal input channels, and each temporal channel has different impulse response. Every weight of the learning network is modified according to a Hebb-type learning algorithm proposed by Sanger. It is shown by simulation studies that various types of spatio-temporal receptive fields are self-organized by the network with random noise inputs. Some of them have similar response characteristics to X- and Y-type cells found in mammalian retina. The properties of receptive fields obtained by the network are analyzed theoretically. It is shown that only circularly symmetric receptive fields change their spatio-temporal characteristics depending on the bias of inputs. In particular, when the inputs are non-zero mean, the temporal properties of center-surround type receptive fields become heterogeneous and alter depending on the positions in the receptive fields.

In this paper, we present an exact analysis and an efficient matrix-analytic procedure to numerically evaluate the performance of cellular mobile networks with hand-off. In high-capacity micro-cell cellular radio communication networks, a cell boundary crossed by moving users can generate many hand-off attempts. This paper considers such a priority scheme that some channels and buffers are reserved for hand-off calls to reduce the forced termination of calls in progress. Performance characteristics we obtained include blocking probability, channel utilization, average queue length and average waiting time for hand-off calls. Using the matrix-analytic solution for the stationary state probability distribution, we also derive the probability distribution of the waiting time of a hand-off call. Numerical results show how priority can be provided to hand-off calls according to the number of reserved channels and buffer size. They also clarify the effect of the hand-off priority scheme on the standard deviation of waiting time of a hand-off call.

Reduction of the complexity of the NLMS algorithm has recceived attention in the area of adaptive filtering. A processing cost reduction method, in which the component of the weight vector is updated when the absolute value of the sample is greater than or equal to an arbitrary threshold level, has been proposed. The convergence analysis of the processing cost reduction method with white Gaussian data has been derived. However, a convergence analysis of this method with correlated Gaussian data, which is important for an actual application, is not studied. In this paper, we derive the convergence cheracteristics of the processing cost reduction method with correlated Gaussian data. From the analytical results, it is shown that the range of the gain constant to insure convergence is independent of the correlation of input samples. Also, it is shown that the misadjustment is independent of the correlation of input samples. Moreover, it is shown that the convergence rate is a function of the threshold level and the eigenvalues of the covariance matrix of input samples as well as the gain constant.

In this paper, a feasible optical code-division multiple-access (CDMA) technique is proposed for high-speed computer networks using prime codes and optical signal processing to guarantee real-time data communications. All-optical architectures for fastly tunable CDMA encoders and decoders are presented, which can be feasibly implemented in the optical domain by using electrooptic switches and optical delay lines. This can support an ultrahigh throughput and a very fast reconfiguration time. Furthermore, we present a self-synchronized sample technique to ensure the correct phase synchronization between optical clock stream and asynchronous electronic data at each electrooptic modulator of an optical CDMA transmitter.

Precise direct mounting of laser diode (LD) and photodiode (PD) chips on silica planar lightwave circuits (PLCs) has been investigated for application to transceiver modules. To achieve submicron optical alignment, self-aligned index marks on the PLCs and LDs were directly detected by transmission infrared light. The repeatability of the positioning was measured to be within 0.125 µm. The output power of the resultant module was 0.2 mW at 80 mA. A waveguide-type PD was also mounted in the same way, and module sensitivity of 0.25 A/W was demonstrated.

A main result in this paper is that for a Hopfield-type neural circuit with a symmetric connection matrix T, the negative semidenfiniteness of T is a necessary and sufficient condition for absolute exponential stability. While this result extends one of absolute stability in Forti, et al. [1], its proof given in this paper is simpler, which is completed by an approach different from one used in Forti et al. [1]. The most significant consequence is that the class of neural networks with negative semidefinite matrices T is the largest class of symmetric networks that can be employed for embedding and solving optimization problem with global exponential rate of convergence to the optimal solution and without the risk of spurious responses.

This paper describes the concept of the regional community network system. The system provides PC connectionless communication services to residential customers and a platform on which customers can construct closed user groups. The proposed system is superior to conventional dial-up PC communications from the viewpoint of quick response and communication charge. A new mechanism of group management using the MAC addresses of the interface cards embedded in the ONU and PC terminals is proposed. Conventional telecommunication services, multi-channel video distribution services, and connectionless computer communication services can be provided simultaneously by utilizing the fiber-optic access system. The regional community network system is promising for the construction of a regional information platform and would be one of the forces driving FTTH.

A deterministic pushdown automaton (dpda) having just one stack symbol is called a deterministic restricted one-counter automaton (droca). A deterministic one-counter automaton (doca) is a dpda having only one stack symbol, with the exception of a bottom-of-stack market. The class of languages accepted by droca's is a proper subclass of the class of languages accepted by doca's. Valiant has shown that the regularity problem for doca's is decidable in a single exponential worst-case time complexity. In this paper, we prove that the class of languages accepted by droca's which accept by final state is incomparable with the class of languages accepted by droca's which accept by empty stack (strict droca's), and that the intersection of them is equal to the class of strict regular languages. In addition, we present a new direct branching algorithm for checking the regularity for not only a strict droca but also a real-time droca which accepts by final state. Then we show that the worst-case time complexity of our algorithm is polynomial in the size of each droca.

RCS fluctuation of targets such as ships can be reduced by the high-resolution radar. The high-resolution radar resolves the total radar echo into several parts which do not interfere each other. The reduction of interference gives stable target RCS. A simple model of the RCS fluctuation reduction is presented. Typical data for ships taken by an experimental radar which has range resolution about 0.75 m, are also shown. The analysis results show that the RCS fluctuation reduction agree with the simple model well.

Let W be a real symmetric matrix associated with a weighted 2-connected planar graph. It is important to study a fast algorithm to solve the linear system Wx = c, since the system has many various applicaions, for example to solve partial defferencial equations numerically. In this paper, a new algorithm for the solution of a linear system of equations by Δ-Y transformations is proposed, and a sufficient condition for using this algorithm is proved. We show that this algorithm solves in O (n3/2) time a linear system associated with a planar graph which is embedded a cylinder graph with n vertices.

We have devised a polynomial time algorithm to decide the security of cryptographic protocols formally under certain conditions, and implemented the algorithm on a computer as a supporting system for deciding the security. In this paper, a useful approach is presented to decide security problems which do not satisfy some of the above-mentioned conditions by using the system. For its application, we consider a basic security problem of Kerberos protocol, whether or not an enemy can obtain the session key between a client and a server by using any information not protected in communication channels and using any operation not prohibited in the system. It is shown that Kerberos is secure for this problem.

SOI DRAM's are candidates for giga-bit scale DRAM's due to the inherent features of SOI structure, and are also desired to be used as low-voltage memories which will be used in portable systems in the forthcoming multimedia era. However, some drawbacks are also anticipated owing to floating substrate effects. In this report, the advantages and problems concerning SOI DRAM's were reconsidered by evaluation of our test devices and also by analysis with device and circuit simulators for their future prospects. The following advantages of SOI DRAM's were verified. Low-voltage operation, active current reduction and speed gain were obtained by the reduced junction capacitance and the back-gate-bias effect. Static refresh characteristics were improved due to the reduced junction area. Soft error immunity was improved greatly by the complete isolation of the active region when the body potential is fixed. The problems that need to be resolved are closely related to the floating substrate effect. The soft error immunity in a floating body condition and the dynamic refresh characteristics were degraded by the instability of the floating body potential. Process and device approaches such as the field-shield-body-fixing method as well as circuit approaches like the BSG scheme are required to eliminate the floating substrate effects. From these investigations it can be said that a low-voltage DRAM with a current design rule would be possible if we pay close attention to the floating-substrate-related issues by optimizing various process/device and circuit techniques. With further development of the technology to suppress the floating substrate effects, it will be possible to develop simple and low-cost giga-bit level SOI DRAM's which use the SOI's inherent features to the full.

In this paper, we describe the design and implementation of a hypermedia system that has the following characteristics. First, being designed according to the Dexter hypertext reference model, it has a layered architecture and thus maintains commonality with other hypermedia systems based on the Dextermodel. Second, being designed based on the MHEG standard, it has data structures that are inherently suitable for data interchange and synchronization. Third, adopting the MIME protocol, it provides multimedia mail services. Finally, being built on top of an object-oriented DBMS, it makes it easy to represent Dexter and MHEG models and also provides efficient storage and search capabilities. The contribution of this paper is combining these characteristics to build an integrated hypermedia system reflecting reference architectures and international standard efforts.

There have been semantics for logic programs as sets of definite clauses over sequence domains in [2],[6]. The sequence of substitutions caused by resolutions for logic programs can be captured by a fixpoint of a functional [3],[16]. In [15], a functional is regarded as a behaviour of a dataflow network, the semantics over sequence domains induces dataflow computing for logic programs. Also it may provide a transformation of logic programs to functional programs[16]. Motivated by dataflow computing constructions for logic programming, this paper deals with fixpoint semantics over sequence domains for logic programs with equations and negations. A transformation, representing deductions caused by resolutions and narrowings, is associated with a logic program with equations, modified from the operator in [18], so that it may be represented by a continuous functional over a sequence domain, and its least fixpoint is well-defined. An explicit construction of such a continuous functional of sequence variables is necessary for dataflow computing, and we should prove that the functional of sequence variables can exactly represent the transformation concerned with sets. For a general logic program, a functional is constructed over a sequence domain so that it may reflect a consistency-preserving renewal function for the pair of atom sets on the basis of the 3-valued logic approach as in [7], and [11]. It is a problem to construct the domain for the functional representing a generation of atom sets interpreted as true and negation as failure in the generation, for general logic programs. The functional is monotonic over a complete partial order and its least fixpoint is well-defined, although the least fixpoint is not always obtained by the limit of finite computing, because of the functional being not necessarily continuous.