This letter points out that while a class of conditions presented in Matsuoka K. [1] are truly sufficient for absolute stability of neural networks, the proof of the sufficiency given in [1] is not sound. As a remark, a mathematically rigorous proof of the sufficiency of the class of conditions for absolute stability of neural networks is provided.

The paper deals with the evaluation of performance of current cellular systems which are required to accommodate in an already operating system a wide range of new services, with different quality requirements (on delays, retransmission rates, etc.), and often characterised by a high burstiness (i. e. with relatively short traffic bursts, interleaved by comparatively long silence periods). To this end, an extension of packet communications is appealing for its inherent flexibility; standardisation of packet protocols for data transmission over idle GSM channels is in progress, and a similar service exploiting AMPS radio and network resources is already specified as Cellular Digital Packet Data. In both cases voice traffic retains a higher priority. The paper focuses on the evaluation of the effect of this additional traffic on existing voice traffic in a GSM Phase 2+ system. Although voice calls experience the same channel availability, their performance are worsened by the higher co-channel interference due to the higher average channel occupancy. This impairment cannot be tackled, as a matter of course, by increasing the re-use distance as this would affect the overall system capacity. The paper suggests the use of smart planning strategies capable to ease control of interference levels with a negligible impact on system complexity and signalling load.

A new multi-functional card with a display, sounder and input keys, and related communication equipment, including a microwave base station and a contactless surface reader/writer, have been developed to perform the functions of positioning, paging, returning a message and identity certification. We confirmed that a prototype subsystem was capable of providing a simple and automatic call forwarding service. The multi-functional card as an ID card and a personal data terminal, and its subsystem can provide new personal services for a multimedia office.

This paper is a brief survey of mobile applications of meteor burst communications (MBC). Though the capacity of MBC systems is generally not large, this unique long distance communication method has at least two selling points when applied to mobiles. First of all, it is cheap. Secondly, it can easily offer nationwide seamless service. Thus, since the late 1980s, mobile MBC systems have been attracting interests of the industry. Although MBC is today a well established communication technique, there are some difficulties to be overcome before it is widely applied to mobile systems. Two most serious problems are the rather large antenna size and high transmitter power inherent to this beyond line of sight communication which relies on weak reflections of low VHF (typically 35 to 50 MHz) radio waves from ionized meteor trails. Some reduced sized antennas which can be mounted on the roofs of trucks have been tested. The problem of large peak power (a few hundred watts for mobile remotes) is much alleviated by the very low duty cycle (usually less than 1%) of remote transmitters due to their bursty transmissions responding to the probe signals from the master station via infrequent meteor reflections. In this paper, some land and maritime mobile MBC systems are brieflyintroduced.

In future mobile radio, high-speed transmission and efficient spectrum utilization will be important. However, multipath propagation with large delay difference and cochannel interference are obstacles to the advanced mobile communication system. An adaptive antenna can suppress multipath signals and cochannel interference signals. This paper reviews basic performance of multipath fading reduction and cochannel interference suppression using the adaptive antenna. After a brief explanation of adaptive antenna concepts, we show simulation and experimental results of the fading reduction. It is pointed out that the adaptive antenna cancels multipath signals with large delay difference strongly. This feature is very important for high-speed TDMA systems. Moreover, it is shown from simulation results that the adaptive antenna improves the spectrum efficiency by suppressing the cochannel interference signals.

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.

String grammars (languages) have been extensively studied from 60's. On the other hand, the transformational grammar, proposed by N. Chomsky, contains the transformation from the set of derivation trees of context-free language to the surface set. And the grammar regarded a tree as an input sentence to some transducer. After that from latter half of 60's, the studies of acceptors, transducers, and so on, whose input is a tree, have been studied extensively. And recently some pushdown tree automata were introduced, and their fundamental properties and some other various properties were investigated [11]-[17]. Furthermore, a top-down pushdown tree transducer (t-PDTT for short), which is an extension of a top-down pushdown automaton (t-PDTA for short), was introduced and its fundamental properties were investigated [19]. In this paper, we define the various subclasses of context-free tree grammar (CFTG for short) by the combination of variables contained in the rules. Furthermore, we consider a monadic case of CFTG which is a special case of CFTG. Based on these definitions, we classify the subclasses of CFTG, and we investigate some inclusion properties of subclasses of CFTL (where CFTL indicates the class of context-free tree languages).

The performance of direct-detection optical synchronous code-division multiple-access (CDMA) systems using pulse position modulation (PPM) signaling (PPM/CDMA) with interference canceller is analyzed. In optical CDMA systems, it is known that the maximum number of simultaneous users in CDMA systems is limited by the maximum tolerable interference among users. If the receiver is able to estimate this interference and cancel or reduce its effect, the capacity of CDMA systems can be increased and the system performance can be improved. There are some ways to increase the system performance, that is, using PPM and interference canceller. However, the system using both PPM and interference canceller has not been analyzed. In this paper, the upper bound on the bit error probability of optical synchronous PPM/CDMA systems with interference canceller is derived, and the bit error probability of optical synchronous PPM/CDMA systems is evaluated under the assumption of number-state light field where the background noise is negligible. We compare the bit error probability of the optical synchronous PPM/CDMA systems with interference canceller to that of the optical synchronous PPM/CDMA systems without interference canceller and to those of optical synchronous OOK/CDMA systems with and without interference canceller. We show that optical synchronous PPM/CDMA systems with interference canceller have better bit error probability performance.

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.

The uncertainty involved in the gradient constraint for optical flow detection is often modeled as constant Gaussian noise added to the time-derivative of the image intensity. In this paper, we examine this modeling closely and investigate the error behavior by experiments. Our result indicates that the error depends on both the spatial derivatives and the image motion. We propose alternative uncertainty models based on our experiments. It is shown that the optical flow computation algorithms based on them can detect more accurate optical flow than the conventional least-squares method.

A method based on clustering is presented for restoring and segmenting gray scale images. An optimum clustering obtained by a gradient method gives an image with gray scale values which vary smoothly in each segmented region. The method is also applied to restoration from sparsely sampled data.

In this paper, we propose a timing constrained database system which accesses a database at a host computer via a mobile support server with a wireless portable computer running in mobile computing environments, so that we can provide seamless database access between a communication cell and the host computer even if the user of the portable computer moves from one communication cell to another. Then, we also provide some new kind of database cache algorihm, such as all-cell-cache, neighbour-cell-cache, 1-cell-skip-cache, 2-cell-skip-cache and 3-cell-skip-cache methods, each of which manages the data downloading and uploading among the host database and some cell databases at the mobile support servers so as to minimize the database access fault probability when the user moves from one communication cell to another. And, we show the averaged database access time and the averaged database cache hit ratio which are computed by simulating each of the above database cache algorithms with random variables generation method. Finally, we conclude that each above cache alogorithm is advantageous to the database in mobile computineg einvironments.

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.

To improve the efficiency for the threshold schemes, the major problem is that the secret shadows cannot be reused after renewing or recovering the shared secret. However, if the secret shadows cannot be reused, the established threshold scheme is limited to be used only once. It is inefficient to reconstruct the whole secret sharing system. Therefore, we introduce an efficient dynamic threshold scheme. In the new scheme, the shadowholders can reuse the secret shadows no matter that the shared secret is renewed or recovered. In addition, the new scheme provides a way by which the dealer can renew the shared secret or reconstruct the secret sharing system, efficiently. Therefore, this scheme is good for maintaining the important secrets.

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.

In the usual optical flow detection, the gradient constraint, which expresses the relationship between the gradient of the image intensity and its motion, is combined with the least-squares criterion. This criterion means assuming that only the time derivative of the image intensity contains noise. In this paper, we assume that all image derivatives contain noise and derive a new optical flow detection technique. Since this method requires the knowledge about the covariance matrix of the noise, we also discuss a method for its estimation. Our experiments show that the proposed method can compute optical flow more accurately than the conventional method.

Either GMW sequence or m-sequence possesses a 2-valued auto-correlation function which helps to improve the performance of a RAKE receiver. However, their cross-correlation functions are less well controlled. Before they can be applied to a CDMA system, it is necessary to construct their sub-families (taking advantage of their large family size) which offer satisfactory cross-correlation functions. This paper studies several algorithms for constructing those quasi-optimum sub-families in terms of minimized bit error rate under co-channel interference. The study shows that the performance of resultant sub-families is sensitive to sub-family sizes and algorithms. A new criterion based on combined (even and odd) maximum cross-correlation for code selection is introduced, and highest-peak-deleting and most-peak-deleting algorithms are suggested for constructing quasi-optimum sub-families of GMW and m-sequences.

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.

We present a volume rendering algorithm which renders images at approximately two to seven times the speed of a conventional ray caster with almost no visible loss of image quality. This algorithm traverses the volume data in object order and renders the image by performing ray casting for the pixels within the footprint of the voxel (i.e., rectangular prism) being processed. The proposed algorithm supports the rendering of both single and multiple isosurfaces with arbitrary opacity values. While the projection approach to volume rendering is not new, we present an algorithm specifically designed for the perspective projection, evaluate its rendering speed for both single and multiple isosurfaces with arbitrary opacity values, and examine how efficiently it uses cache memory.

In this paper, we propose an analytic model using a semi-markov process for parallel computers which provides hardware support for a cache coherence mechanism. The model proposed here, the Semi-markov Memory and Cache coherence Interference model, can be used for the performance prediction of cache coherence based parallel computers since it can be easily applied to descriptions of the waiting states due to network contention or memory interference of both normal data accesses and cache coherence requests. Conventional analytic models using stochastic processes to describe parallel computers have the problem of numerical explosion in the number of states necessary as the system size increases even for simple parallel computers without cache coherence mechanisms. The number of states required by constructing our proposing analytic model, however, does not depend on the system size but only on the kind of cache coherence protocol. For example, the number of states for the Synapse cache coherence protocol is only 20, as is described in this paper. Using the proposed analytic model, we investigate several comparative experiments with widely known simulation results. We found that there is only a 7.08% difference between the simulation and our analytic model, while our analytic model can predict the performance of a 1,024 processor system in the order of microseconds.