This paper considers a probabilistic model for a database recovery action with checkpoint generations when system failures occur according to a renewal process whose renewal density depends on the cumulative operation period since the last checkpoint. Necessary and sufficient conditions on the existence of the optimal checkpoint interval which maximizes the ergodic availability are analytically derived, and solvable examples are given for the well-known failure time distributions. Further, several methods to be needed for numerical calculations are proposed when the information on system failures is not sufficient. We use four analytical/tractable approximation methods to calculate the optimal checkpoint schedule. Finally, it is shown through numerical comparisons that the gamma approximation method is the best to seek the approximate solution precisely.

It is shown that a three-fluid model, which was successfully introduced to explain microwave characteristics of high-Tc superconductors phenomenologically, is suit also to explain those of low-Tc superconductors. In this model, the two contributions of a residual normal electron, in addition to a super and a normal electron in the two-fluid model, and of the temperature (T) dependence of momentum relaxation time τ for the two normal electrons are taken into account. Measured results of the T dependence of surface resistance Rs for a Nb film with critical temperature Tc9.2K agree very well with an Rs curve calculated using the present model, where a residual surface resistance at T0K, Rso, and the T dependence of τ were determined using the surface reactance at 0K Xso37.6mΩ calculated using the BCS theory to fit a calculated Rs curve with the measured values as a function of T. Furthermore, microwave characteristics predicted from the BCS theory cannot be explained phenomenologically using the conventional two-fluid model. This difficulty can be solved by using an improved two-fluid model, called the two-fluid (τ) model, where the T dependence of τ is taken into account. Finally the frequency dependence of Rs calculated for the Nb film is f1.9 for the BCS theory and f2.0 for the three-fluid (τ) model on the assumption of the frequency independence of τ.

A CAD-based faulty portion diagnosis technique for CMOS-LSI with single fault using abnormal Iddq has been developed to indicate the presence of physical damage in a circuit. This method of progressively reducing the faulty portion, works by extracting the inner logic state of each block from logic simulation, and by deriving test vector numbers with abnomal Iddq. To easily perform fault diagnosis, the hierarchical circuit structure is divided into primitive blocks including simple logic gates. The diagnosis technique employs the comparative operation of each primitive block to determine whether one and the same inner logic state with abnormal Iddq exists in the inner logic state with normal Iddq or not. The former block is regarded as normal block and the latter block is regarded as faulty block. Faulty portion of the faulty block can be localized easily by using input logic state simulation. Experimental results on real faulty LSI with 100k gates demonstrated rapid diagnosis times of within ten hours and reliable extraction of the faulty portion.

To implement the PGPS packet scheduling algorithm in high speed networks is more difficult since it is based on real time simulation of an equivalent fluid-model system leading to a higher implementation time complexity. A modified approach to PGPS is the SCFQ scheme. This scheme is easy to implement, but has an increasing end-to-end delay bound. The VC packet scheduling algorithm provides the same end-to-end delay bound as PGPS does, but has the disadvantage of unfairness. As SCFQ, SFQ is much easier to implement than PGPS and achieves the same fairness, but has a higher end-to-end delay bound than PGPS. We propose a new packet scheduling algorithm, called Minimum Starting-tag Fair Queueing (MSFQ), which assigns the virtual time to be the minimum starting tag over all backlogged connections. MSFQ is much easier to implement than PGPS and provides the same end-to-end delay bound for each connection and fairness as PGPS. In this paper, we will show the end-to-end delay bound and fairness of MSFQ and compare 5 rate-based packet scheduling algorithms including PGPS, VC, SCFQ, SFQ, and MSFQ focusing on end-to-end delay bound, fairness, and implementation time complexity.

New THz radiation devices made of high-Tc superconductors are fabricated and their characteristics are studied in detail. Ultrashort electromagnetic pulses with 0.5 ps width have been radiated into free space from current biased devices made of superconducting YBa2Cu3O7 (YBCO) films by exciting with femtosecond laser pulses. The Fourier spectrum of them extends up to 3 THz. The radiation mechanism is ascribed to the ultrafast supercurrent modulation by the optical pulses. The THz waveform is analyzed using rate equations describing the relaxation of photoexcited quasiparticles. By the improvement of the device structure and the collecting optics, the radiation power can be increased up to 0.5 µW. A new type THz radiation from YBCO films under an external magnetic field without a transport current is also reported.

We present a novel replication technique for parallel applications where instances of the replicated application are active on different group of processors called replicas. The replication technique is based on the FTAG (Fault Tolerant Attribute Grammar) computation model. FTAG is a functional and attribute based model. The developed replication technique implements "active parallel replication," that is, all replicas are active and compute concurrently a different piece of the application parallel code. In our model replicas cooperate not only to detect and mask failures but also to perform parallel computation. The replication mechanisms are supported by FTAG run time system and are fully application-transparent. Different novel mechanisms for checkpointing and recovery are developed. In our model during rollback recovery only that part of the computation that was detected faulty is discarded. The replication technique takes full advantage of parallel computing to reduce overall computation time.

The construction of fault-tolerant processor arrays with interconnections of cube-connected cycles (CCCs) by using an advanced spare-connection scheme for k-out-of-n redundancies called "generalized additional bypass linking" is described. The connection scheme uses bypass links with wired OR connections to spare processing elements (PEs) without external switches, and can reconfigure complete arrays by tolerating faulty portions in these PEs and links. The spare connections are designed as a node-coloring problem of a CCC graph with a minimum distance of 3: the chromatic numbers corresponding to the number of spare PE connections were evaluated theoretically. The proposed scheme can be used for constructing various k-out-of-n configurations capable of quick broadcasting by using spare circuits, and is superior to conventional schemes in terms of extra PE connections and reconfiguration control. In particular, it allows construction of optimal r-fault-tolerant configurations that provide r spare PEs and r extra connections per PE for CCCs with 4x PEs (x: integer) in each cycle.

The authors previously proposed a reconfigurable architecture called the "XL-scheme" in order to cope with processor element (PE) faults as well as link faults. However, they described an algorithm for compensating only for link faults. They determined the potential ability to tolerate faults of the XL-scheme for simultaneous faults of links and PEs, and left a reconstruction algorithm for simultaneous PE and link faults to be studied in the future. This paper briefly explains the XL-scheme and gives a reconstruction algorithm for simultaneous PE and link faults. The algorithm first replaces faulty PEs with healthy ones and then replaces faulty links with healthy ones. We then compute the reliabilities of the mesh-arrays with simultaneous PE and link faults by simulation. We compare the reliability of the XL-scheme with that of the one-and-half track switch model. It is seen that the former is much larger than the latter. Furthermore, we show the result for processing time.

A new scheme based on hierarchical information organization and situation awareness to support network manager in failure localization is proposed. This paper integrates the situation theory for the needs of fault management to model the states and events. As the result, the proposed information model includes four fault management viewpoints to support situational, functional, logical and physical analysis within the respective networks. Object-oriented analysis is applied to construct the information. The correlation of network situation is derived by description logic. The proposed classification algorithm is applied to solve the situation awareness problem. By using this proposal the correlation performance is enhanced to logarithmic order.

In this paper, we propose a new switching network architecture with output queueing, The proposed switch, FBSF (FAB Banyan Switching Fabrics) can deliver up to 2r packets simultaneously destined for the same outlet in a single time slot. The switch fabrics consist of Batcher sorter, a radix-r double shuffle network r-packet distributors, two FAB networks, and output buffer modules. The performance of the switch fabric is evaluated by measures of throughput, average queue length, average waiting time, and packet loss rate. Numerical and simulation results indicate that the switch exhibits very good delay-throughput performance over a wide range of input traffic.

The finite reconfigurability and local reconfigurability of graphs were proposed by Sha and Steiglitz [1], [2] in connection with a problem of on-line reconfiguraion of WSI networks for run-time faults. It is shown in [2] that a t-locally-reconfigurable graph for a 2-dimensional N-vertex array AN can be constructed from AN by adding O(N) vertices and edges. We show that Ω(N) vertices must be added to an N-vertex graph GN in order to construct a t-locally-reconfigurable graph for GN, which means that the number of added vertices for the above mentioned t-locally-reconfigurable graph for AN is optimal to within a constant factor. We also show that a t-finitely-reconfigurable graph for an N-vertex graph GN can be constructed from GN by adding t vertices and tN + t (t+1)/2 edges.

This paper introduces a new recursive factorization of the polynomial, 1-zN, over the real numbers when N is an even composite integer. The recursive factorization is applied for efficient computation of the discrete Fourier transform (DFT) and the cyclic convolution of real sequences with highly composite even length.

Given the tremendous growth in the cellular phone system and the Personal Hadny-phone System (PHS), it is to be expected that demands for mobile computing using those wireless infrastructures, that is mobile computer access, will dramatically increase. This paper describes high-quality and high-speed data transmission technology for PHS mobile computing and current PHS data transmission standardization activities. Furthermore, wireless agent communication and a service example are presented together with the concept of background communication for the coming wireless multimedia services.

This paper describes the performance of a video communication system over mobile radio channels. Mobile channel quality changes rapidly due to various factors. When compressed video data is transmitted through these channels, it is indispensable to employ an error control scheme because reconstructed video quality is seriously degraded by channel error. To control this error, an automatic repeat request (ARQ) scheme is often employed, however, this incurs a cost. The benefit of a non-degraded reconstructed video sequence is offset by the transmission delay due to ARQ retransmission. We apply to a video communication system a selective-repeat ARQ which is combined with the coding control scheme to reduce the transmission delay. We evaluate the quality of the reconstructed video sequence and transmission delay using computer simulations and make clear its applicability over Rayleigh and Nakagami-Rican fading channels and intersymbol interference.

This paper proposes a novel FEC (forward error correction) scheme for high-speed wireless systems aiming at mobile computing applications. The proposed scheme combines inner nonredundant error correction with outer parallel encoding random FEC for differentially detected QPSK (quadrature phase shift keying) signals. This paper, first, examines error patterns after the differential detection with nonredundant error correction and reveals that particular double symbol errors occur with relatively high probability. To improve the outer FEC performance degradation due to the double symbol errors, the proposed scheme uses I and Q channel serial to parallel conversion in the transmission side and parallel to serial conversion in the receiving side. As a result, it enables to use simple FEC for the outer parallel encoding random FEC without interleaving. Computer simulation results show the proposed scheme employing one bit correction BCH coding obtains a required Eb/No improvement of 1.2 dB at a Pe of 10-5 compared to that with the same memory size interleaving in an AWGN environment. Moreover, in a Rician fading environment where directional beam antennas are assumed to be used to improve the degradation due to severe multipath signals, an overall Eb/No improvement at Pe of 10-5 of 3.0 dB is achieved compared to simple differential detection when the condition of delay spread of 5 nsec, carrier to multipath signal power ratio of 20 dB and Doppler frequency at 20 GHz band of 150 Hz.

A noise reduction filter composed of a sandglass-type neural network (Sandglass-type Neural network Noise Reduction Filter: SNNRF) was proposed in the present paper. Sandglass-type neural network (SNN) has symmetrical layer construction, and consists of the same number of units in input and output layers and less number of units in a hidden layer. It is known that SNN has the property of processing signals which is equivalent to KL expansion after learning. We applied the recursive least square (RLS) method to learning of SNNRF, so that the SNNRF became able to process on-line noise reduction. This paper showed theoretically that SNNRF behaves most optimally when the number of units in the hidden layer is equal to the rank of covariance matrix of signal component included in input signal. Computer experiments confirmed that SNNRF acquired appropriate characteristics for noise reduction from input signals, and remarkably improved the SN ratio of the signals.

In this paper, the evaluation of a hybrid acquisition performance has been considered for the pilot signal in direct sequence code division multiple access (DS/CDMA) forward link. The hybrid acquisition is introduced by the combination of two schemes, parallel and serial acquisitions. The mean acquisition time of the hybrid acquisition scheme is derived to consider both case 1 (the correct code-phase offsets ae included in one subset) and case 2 (the correct code-phase offsets exist at the boundary of two subsets), which are caused by the distribution of the correct code-phase offsets between two subsets. Detection, false alarm, and miss probabilities are derived for the cases of multiple correct code-phase offsets and multipath Rayleigh fading channel. Results are provided for the acquisition performance with respect to system design parameters such as postdetection integration length in the search and verification modes, subset size, and number of I/Q noncoherent correlators. Also, comparision between hybrid acquisition and parallel acquisition under the same hardware complexity is provided in terms of the minimum mean acquisition time.

When moving images are displayed on color PDPs, motional artifacts such as disturbances of gray scales and colors are often observed. Reduction of the disturbances is essential in achieving PDPs with acceptable picture quality for TV use. The moving picture quality has been improved by using a modified-binary-coded light-emission-period scheme and a 3dimensional (2D in space and 1D in time) scattering technique. In the 10-sub-field modified-binary-code scheme for 256 gray level expression, sub-field B (of period equivalent to 64) and C (128) of conventional 8-sub-field binary-coded scheme are added and then re-distributed into four sub-fields D (48). The modifiedbinary-coded scheme therefore has the light-emitting-period ratio 1:2:4:8:16:32:48:48:48:48. The maximum period, 128 of the conventional, is reduced to 48. By using the modified-binary-coded scheme, the motional artifacts are reduced significantly, but still perceptible because they appear in forms of continuous lines. In order to make the disturbance less conspicuous, a 3D scattering technique is introduced. The technique has been made possible because of the redundancies of the modified-binary-coded scheme: namely, (1) the position of sub-field-block A (63) can be placed at one of the five positions among four sub-fields D (48), (2) there are various choices when newly assigning one of the four sub-fields D, (3) one can arbitrarily choose whether or not to assign a new sub-field D between the gray levels 48-63, 96-111, 144-160, and 192-207. By randomly selecting one of these emission patterns, the disturbances change their forms from continuous lines to scattered dots. The randomization can be performed at each horizontal line of the display, at each vertical line, at each pixel, of at each TV field. An appreciable improvement of moving picture quality has been realized without influencing the still image.

Maximal-ratio combining (MRC), which maximizes the carrier to noise ratio (CNR) of the combined signal, generally requires envelope detection and multiplication having linear characteristic over a wide dynamic range to generate a weighting factor for each branch. In this paper, we propose a simplified two-branch diversity combining scheme without linear envelope detection. The proposed scheme, called "level comparison weighted combining (LCWC),"is simplified in a manner that its weighting factor for each branch is generated from hard-decision results of comparing signal envelopes between two branches. Performance of LCWC is evaluated by computer simulation and laboratory experiment, which shows that its diversity gain is almost identical to that of MRC in a Rayleigh fading channel.

In this paper, a new method for measuring three-dimensional (3D) moving facial shapes is introduced. This method uses two light sources and a slit pattern projector. First, the normal vectors at points on a face are computed by the photometric stereo method with two light sources and a conventional video camera. Next, multiple light stripes are projected onto the face with a slit pattern projector. The 3D coordinates of the points on the stripes are measured using the stereo vision algorithm. The normal vectors are then integrated within 2D finite intervals around the measured points on the stripes. The 3D curved segment within each finite interval is computed by the integration. Finally, all the curved segments are blended into the complete facial shape using a family of exponential functions. By switching the light rays at high speed, the time required for sampling data can be reduced, and the 3D shape of a moving human face at each instant can be measured.