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.

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.

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.

Video services such as video-on-demand are expected to be a motivation for deploying multimedia services in residential areas. These services should increase customer demand for video channels as customer demands become more sophisticated and diverse in the future. Therefore, it is important to determine how network configurations (i.e. network transition scenarios) should evolve in response to changes in access network demand. This paper proposes economical deployment of access networks based on transition scenarios. We conclude that transition scenarios offer more economical deployment than single-network configurations. Two transition scenarios, from passive double-star to fiber single-star, and from hybrid fiber-coax to fiber single-star, are evaluated as examples. These transition scenarios are economical even when customer demand changes. The transition starting time affects the present worth of annual charges (PWAC) of access networks more than the transition period does.

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.

A hybrid network architecture using subcarrier multiplexed optical fiber (SCMOL) and coaxial cable is proposed in this paper for the access link of future personal communication systems (PCS) between tiny passive radio base stations in microcells and remote central base stations. Results indicate that the required number of laser diodes, photodetectors and amount of fiber could be reduced by more than 4 times with the proposed hybrid access link compared to the point-to-point SCMOL link and the network cost would decrease proportionally.

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.

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.

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.

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.

This paper describes communication traffic characteristics in cellular systems employing the concept of reuse partitioning and Dynamic Channel Assignment. Such systems hava a problem of the spatial unbalance of blocking probability. The objective of this paper is overcoming this problem. To accomplish this objective, we use a method for analyzing communication traffic characteristics. We also show results on traffic characteristics in the systems.

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.

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 simple algorithm is proposed for representing nonseparable functions by equivalent separable functions. In this algorithm, functions are first represented by computational graphs, which are directed graphs representing the computational process of the functions. Then, the vertices of the computational graphs are searched in preorder or postorder, and the transformation to separable forms is performed at the places where it is necessary. By this repetition of the transformation, nonseparable functions are represented by separable functions automatically. The proposed algorithm will be useful in various fields of science and engineering because funcutions of one variable are easy to deal with.

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.

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.

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.

Exploring enormous state graphs represented implicitly by ordered binary decision diagrams (OBDDs) is one of the most successful applications of OBDDs. However, our worst-case analysis of implicit graph representations by OBDDs shows that there are cases where OBDD representations are not optimal and require more space than adjacency lists. As an improvement, we propose a new type of BDDs, called Patricia BDDs, which are capable of implicit representation of graphs while their worst-case sizes are kept equal or less than adjacency lists and OBDDs.

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.

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.