To provide the processor arrays with adequate fault-tolerant capabilities, a number of spare or redundant processors are prepared within the arrays. For such processor arrays, reconfiguration should be executed to bypass faulty processors. Concerning reconfiguration of processor arrays, Melhem presented a minimization problem (called the SPA problem). The SPA problem is to find an assignment of spare processors to faulty processors that minimizes the number of dangerous processors. Here, the dangerous processors are processors, for which there remains no longer any spare processor to be assigned when one more faults occur. In this paper, we present a more rigorous definition of the SPA problem, in which input parameters are n² ordinary processors, 2n spare processors and m (mn²) faulty processors, and the output is an optimal assignment of spare processors to faulty processors, in the sense that the number of dangerous processors is minimum. Then, we develop an efficient algorithm based on the necessary and sufficient conditions, which allows highly efficient computation of spare processor assignment. The worstcase time complexity of the proposed algorithm is O(n²).

A computing system, which plays an important role in our society, should be operated with high reliability and performance. A multisystem is one of the typical fault-tolerant computing systems, and is widely used in our society because of its high reliability and performance. In this paper we discuss a multisystem composed of two processors and buffer(s), and evaluate the system taking account of the reliability, performance and computational demands simultaneously. We propose two models for the system from the viewpoint of job assignment. Applying Markov renewal and queuing theories, we obtain the reliability/performance measures for each model. Using the numerical results of our models, we compare two models and show the impact of job assignment on the evaluation measures based on our numerical examples.

Software development managers and users have been interested in software availability for the software operational phase. It is of great importance to assess software reliability and performance during the operation phase. Therefore, we discuss software availability measurement based on software reliability growth models which describe behavior of software errors detected during the testing and operation phase. These models are formulated by nonhomogeneous Poisson processes (NHPP). The software availability index is defined as the possible system utilization factor which means the percentage of time that the software system will be available for operation. We show numerical examples on software availability measurement for actual software error data.

In traditional system-level fault diagnosis in the presence of intermittent faults, intermittent faults can escape detection by fault free units. This paper focuses on a system under hybrid fault situations where all the intermittent faults either pass or fail all the tests of the fault free units which test them. A new diagnosable system is introduced where no syndrome from a hybrid fault situation is identical to one from a special class of hybrid fault situations whenever for every pair of allowable fault sets, there is some difference between two sets of permanent faults as their subsets. Although the faults whose the intermittent nature is rather restrictive than the previous one are considered in this paper, the new diagnosability is shown to be equivalent to the previously known t/γ/τ-diagnosability. This indicates that there is a distinct tradeoff between the intermittent nature of the faults and the unique diagnosability of permanent faults in a hybrid fault situation.

This paper proposes a new masking method for asymmetric line faults in LSIs using semi-distance codes, a class of non-linear codes. Faults caused by open or short circuit defects in line areas of LSIs can be made asymmetric by controlling the bus drive and the bus terminal gates. The conditions required for codes to mask these faults are clarified and the codes satisfying these conditions for random faults and adjacent faults, caused by line bridging defects, are constructed by using a new concept of semi-distance. This masking technique has the advantage that no additional circuits, such as error decoders, are needed. The codes have been applied to the bus lines in the address decoders of the 4-Mbit ROMs to improve fabrication yield of the LSIs.

There have been many studies on fault-tolerance for making highly reliable systems. As the demand for high-speed computers grows, the design of their clock systems becomes a major research subject not only in achieving high performance, but also in reducing assembly and maintenance costs. In this paper, two different kinds of highly reliable clock generators are proposed. Their hardware construction is very simple, because they have only several clock oscillators synchronized with each other using a coupling device. On the other hand, their usages are different. One is used as a crystal coupled clock generator to have a fault-tolerancy, and the other is used as a quick start clock generator for those systems which requires a rapid start necessarily. At first, clock synchronization of the multiple oscillators synchronized with each other using a coupling device, is discussed. This clock synchronization becomes the basic technique for the two clock generators which will be proposed in this paper. By connecting each oscillators using a coupling device, those oscillators easily synchronize with each other. Furthermore, by choosing coupling devices adequately, the proposed clock generator can have a fault tolerant property. Second, the crystal coupled fault-tolerant clock generator suitable for non stop operation even if one of the generators halts by some faults is proposed. To satisfy a fault tolerant property, the crystal resonator was found to have a good characteristic as a coupling device. This is because crystal shows a rapid transformation in the reactance value according to the small deviation of the oscillator's frequency. Finally, another clock generator with a quick start is also described. This quick start clock generator also consists of the coupled oscillator and it uses the same technique of the fault-tolerant clock generator. An oscillator having high Q ordinarily needs a longer set up time compared with those oscillators having a low Q. An oscillator coupled with a vibrating oscillator can start its oscillation quickly with a start of power supply.

Robust test has been proposed to overcome the potential invalidation of the two-patten test due to hazards. However, it is difficult to generate robust test patterns and they may not exist for some stuck-open faults. In this paper, to overcome this difficulty, we propose a new testable design method with the robustness. Since a faulty gate is regarded as a tri-state element, the gate output node can be set to arbitrary logic value from the outside of a circuit. In the proposed method, on the basis of this idea, each output of the gate can be set to any logic value by an extra driver. Then, it is checked what value the output gives. Any stuck-open fault can be detected by one test pattern by this method which can be implemented relatively easily. To reduce the number of observalbe points, we also consider a method for selecting internal observable points without losing the property of the robustness. As a result, output nodes of reconvergent gates are used as internal observable points. Experimental results of the pattern generation for some benchmark circuits are given.

This paper considers a test set for a multibit shifter which can execute arbitrary bit length shifting/rotating operations. The multibit shifter consists of several stages of sub-shifters, each of which can shift/rotate its inputs by an arbitrary number of bits less than or equal to a predetermined constant. Outputs of one sub-shifter are shifted/rotated in the next sub-shifted. All of the sub-shifters have the same structure, and are constructed with multiplexers. Every sub-shirter is separately tested. All of the multiplexers in each sub-shifter are tested in parallel and exhaustively. A minimum test set for every sub-shifter can be obtained by the use of an algorithm which generates a Boolean 2^pq matrix M such that any 2^pp submatrix of M includes all bit patterns of length p, where p and q (pq) are the numbers of input lines in a multiplexer and those in a sub-shifter, respectively. A complete test set for the multibit shifter can be easily obtained as the union of minimum test sets for all sub-shifters.

This letter proposes a concurrent fault detection scheme for a butterfly unit in an FFT processor. A fault in a butterfly unit is detected by recomuting. Input data to the butterfly unit is coded by a bit rotation and used for recomputing. The recomputed outputs are decoded and compared with the output for the first computation. The hardware overhead for the scheme is O(N) and the time overhead is O(log (N)) where N is the number of input data.

It is important that efficient squaring algorithm is improved since inversion and exponentiation in GF(2^m) can be generally decomposed into squaring and multiplying algorithm. In this letter we give a bit-serial squarer in GF(2^m) when using polynomial basis representation for the elements.

A bit-error-free optical signal switching method from one to another fiber has been proposed for high-bit-rate optical transmission lines. The intensity modulated signal powers of 1.8 Gbit/s, which had been divided by an acousto-optic deflector and propagated through the 2 fibers, were recombined without bit-errors. Optical signals were switched successfully between 25 km long fibers without degradation of bit-error-rate performance.

A numerical design of a matching spiral is proposed for the use as termination in a single-layered redial line slot antenna. The boundary element method is adopted for the analysis of unbounded radiation problems. Satisfactory performance of reflection less than 15 dB is predicted and is verified by experiments.

In this letter, the formulation of dispersive characteristics associated with an orientation polarization is discussed. The formulation is appropriate for use in the finite-difference time-domain (FD-TD) method and is based on the equation of polarization. The validity of the formulation is verified by comparing the calculated complex dielectric constant with analytical values.

The longitudinal chromatic dispersion in single-mode fibers is investigated theoretically and experimentally. With a fabricated tapered fiber evaluation of longitudinal chromatic dispersion is clarified by using simple equation.

The reflectivity spectrum of VPE-Al_xGa_1xSb has been measured over the photon energy range from 1.8 eV to 5 eV. Three peaks which correspond to the -point transition, the spin orbit splitting at the -point, and the X-point transition have been observed in the measured spectrum. The optical constants have been derived by means of the Kramers-Kroig analysis of the reflectivity spectrum.

Transport rate of GaSb in a closed tube vapor phase growth system with iodine as a transport agent was calculated thermodynamically. The calculated maximum transport rate was obtained at iodine density of 0.01-0.02 mg/cm³ in the growth temperature range of 550-600. The calculation was compared with the experimental result of GaSb. The calculated iodine density at which the maximum transport rate was obtained showed a good agreement with the experiment.

A modified SNR for image evaluation for still pictures is presented. This is made by considering a characteristic of a subjective visual response to the image. Two different kinds of impairments which are most typical are considered here. One is a blurring and the other is a random noise.

The basic definition of moment is extended to define the blockwise partial moments. It has been shown that for a class of ideal bandlimited signals, the blockwise partial moments remain invariant. But in case of the actual bandlimited signals, the values of these partial moments are not identical. The deviation from the ideal values is applied to make an evaluation of the actual signals. Two concrete application examples are described. The first example describes a method for evaluating the performance of digital interpolation filter. The usual performance measure, SNR, and the newly proposed measure, m, based on moment deviation method are found to be closely related. Moreover, the new method uses only the actual interpolation output compared to the SNR method where apriori knowledge of ideal output is a must. The second example concerns with the recovery of missing samples in a given bandlimited signal sequence. The recovery based on moment method leads to a simple linear equation structure and hence is easy to apply in practice. It is shown that excellent recovery is possible even for the nonideal bandlimited signals.

In this paper, we evaluate the performance of a new join algorithm, called hybrid join, which improves both the sort-merge and the hash-partitioned join algorithms. The hybrid join consists of completely sorting only the smaller relation and partitioning the other one into ranged buckets according to the order statistics of the sorted relation. The final joining is performed on the sorted relation and the ranged buckets. By analytical comparisons, we show that the hybrid join always outperforms the sort-merge join and guarantees better performance than that of the hash-partitioned join in practical situations. The analyses of the performances for the various methods are validated by simulation experiments.

A digital image processing system, which consists of a monochromator, a CCD camera, a video cassette recorder, a digital image memory, and a personal computer, is assembled for the measurement of the spatial distribution of the intensity of the spectrum line emitted by plasma. The system is applied to observe a spectrum of the light from the plasma being in contact with neutral gas. The spatial distribution of the spectrum line explains mixing mechanism of plasma and gas.

It is known that multiple trellis coded PSK (MTC-PSK) can achieve larger performance gain, and trellis coded continuous phase modulation (CPM) combined with Multi-h scheme can also achieve good power bandwidth tradeoffs. In this paper, we propose multiple trellis coded CPFSK (MTC-CPFSK), combined with Multi-h scheme to achieve further coding gain over MTC-PSK. We find that MTC-CPFSK with Multi-h scheme achieves lager squared minimum Euclidean distance and diminishes the number of merge events up to 10T_s depth in the state trellis. We also find that the number of merge events whose squared Euclidean distance is near to squared minimum Euclidean distance may be increased by employing MTC-CPFSK, compared to TC-CPFSK.

A Circularly-Polarized Radial Line Slot Antenna (CP-RLSA) is a high gain planar antenna for DBS reception. From the practical point of view, it is necessary to overlook the performance of RLSA as a function of various design parameters. This paper presents the general design of CP-RLSA with uniform slot density and predicts the bandwidth and the gain of RLSA by array antenna analysis. In the calculation, the slot coupling is evaluated by full wave analysis and the effects of all the design parameters are taken into account. The long line effect reduces the bandwidth of RLSA monotonously with the antenna diameter. The bandwidth is limited by slot resonance as well and the overall bandwidth is less dependent of the diameter. 3dB bandwidth of 650 MHz is predicted for antenna diameter of 600 mm, for example. Among various design parameters, permittivity of slow wave structure affects the bandwidth and gain considerably; ε_γ1.41.8 is preferable. On the other hand, the height of waveguide and the slot pair angular spacing have little influence, though lower waveguide and smaller spacing are advantageous for a stable rotational symmetry of inner field.

The basic properties of 1.55µm GaInAsP/InP distributed reflector (DR) laser were analyzed from the view points of active region structure and π/2 phase shift position. By introducing SCH structure with thin active layer, differential quantum efficiency could be improved up to 60-70% without sacrificing threshold current density. Optimum π/2 phase shift position for high power operation was found to be located inside the active region at a distance of 0.3 times of active region length from the joint portion between active and passive regions.

Current leakage along longitudinal direction, from active region to connected external waveguide or neighboring opto-electronic (O-E) functional region, commonly occurs in integrated type semiconductor lasers. This current leakage degrades not only lasing characteristics but also interrupts operation of neighboring functional devices. In this paper, the longitudinal current leakage is analytically given for an integrated laser by introducing an effective length of leakage current along the longitudinal direction. The minimum lengths of active region and isolation region to minimize the influence of longitudinal current leakage were clarified. As the results, shortening of current injection region with respect to the active region length as well as increasing sheet resistance were found to be effective for reduction of leakage current.

A rigorous analysis of magnetostatic forward volume wave resonators with circular metal edge is presented. The problem is cast into dual integral equations using Hankel transform. To solve the dual integral equations, along with an unknown function in the space domain, the kernel of the Hankel transform is also expanded in terms of the Jacobi polynomials. Thus the dual integral equations are systematically reduced to a set of algebraic equations. Theoretical results are compared with experimental ones to show an good agreement between them.

Miniaturized sealed contacts can be made highly reliable by controlling the atmosphere. This paper studies the effects of oxygen concentration on adhesion and contact resistance characteristics as well as those of oxygen dissipation for silver-palladium alloy and gold-palladium alloy contact. There is a permissible oxygen concentration range where adhesion is prevented and contact resistance is also stable. This range depends on the corrosive resistance of the contact materials. Oxygen concentration varies not only due to air leakage, but also due to oxygen dissipation caused by the oxidation of contact metals in sealed contact enclosures. If the most suitable contact materials and oxygen concentration are selected, the oxygen concentration range can be wide enough to allow changes in oxygen concentration within the enclosures. Switches where silver-palladium alloy mating with gold-palladium alloy contacts are sealed in a nitrogen atmosphere containing about 5% oxygen are confirmed to have characteristics that satisfy the conditions required for practical speech path equipment. This confirms that atmosphere control is a practical way to produce highly reliable sealed contacts.