This paper presents fully digital high speed (17.6Mb/s) burst modem for Offset Quadrature Phase Shift Keying (OQPSK), which employs novel digital modem VLSICs. The modulator VLSIC directly generates modulated intermediate frequency (IF) signals in a fully digitalized manner. A newly proposed digital reverse-modulation and pre-filtered carrier filter-limiter scheme realizes low power consumption and stable operation in a low Eb/No condition. The demodulator VLSIC also achieves fast bit-timing acquisition in burst mode. Moreover, it supports stable initial burst acquisition by a novel automatic frequency control (AFC) acquisition detector and a digital burst detector. A digital burst automatic gain control (AGC) compensates burst-to-burst level differences without analog circutits. Performance evaluation results show that the new modem achieves satisfactory bit-error-rate performance in severe environments. The developed modem has been employed in a commercial portable earth station for ISDN services and reduces the hardware size to one third that of the conventional one.

The fault tolerant computer (FTC) is applied as a communication or database server in the information service and computer aided process control fields. User requires of the FTC are to provide the current level of performance and software transparency needing no additional dedicated program for fault tolerance. To meet these requirements, we propose quadprocessor redundancy (QPR) architecture that combines dualRISC based duplicated CPUs integrating main memories, and duplicated I/O subsystems by using some additional hardware. Duplicated CPUs run under the instruction level synchronization (lock step operation) , and the duplicated I/O subsystems are managed by an operating system. When a fault is detected, the faulty CPU is isolated by hardware. User program is continuously executed by the remaining CPU. We applied the QPR to our UNIX servers, and achieved satisfactory levels of performance.

In this paper, we present a first step for developing a method of verifying both safety and correctness of object-oriented design specification. At first, we analyze the discrepancies, which can occur between requirements specification and design specification, to make clear target faults. Then, we propose a new design review method which aims at detecting faults in the design specification by using three kinds of information tables. Here, we assume that component library, standards for safety and design specification obtained from the Booch's object-oriented design method are given. At the beginning, the designers construct a design table based on a design specification, and the verifiers construct a correctness table and a safety table from component library and standards for safety. Then, by comparing the items on three tables, the verifiers review a given design specification and detect faults in it. Finally, using a small example of object-oriented design specification, we show that faults concerning safety or correctness can be detected by the new design review method.

In this paper, we show an entropy-based approach to the privacy of multi-party protocols. First, we formulate the amount of leaked information by using mutual information for a two-party case. This is a better measure for some situations than the combinatorial measure known so far. Next, we apply multi-terminal information theoty to more than two parties and give the first formulation of the leaked information for more than two parties.

Narrow-beam and low threshold current characteristics have been realized for a 1.3 µm FS-BH (Facet Selective growth Buried Heterostructure) laser diode monolithically integrated with a tapered waveguide lens by a selective area epitaxial growth technique. The beam divergences in the perpendicular and horizontal directions have been reduced down to about 12. By the introduction of the strained quantum well structure and the optimized cavity structure, the threshold current has been kept as low as 6 mA which is comparable to the conventional Fabry-Perot laser diodes. Even at high temperature as high as 85, the threshold current and the operation current (P=10 mW) have been suppressed to as low as 23 mA and 63 mA, respectively. Furthermore error-floor-free characteristics for 622 Mbps-50 km transmission have been confirmed under severe optical feedback condition.

We studied three types of lasers emitting narrow beam divergence of output light: 1) a spot-size converter integrated laser diodes (SS-LDs) with a vertically tapered waveguide, 2) one with a laterally tapered waveguide, and 3) one consisting of a small cross section of active region. We compared them with regard to their performance in coupling efficiency to a cleaved single mode fiber, threshold current, output power, and reliability. Both the spot-size converted integrated lasers with vertically and laterally tapered waveguide repeatedly provided low threshold currents of as low as 6 mA and low coupling loss to the fiber of 1.2 to 2.5 dB in two inch wafer processes. As a result of the aging test, the SS-lasers were predicted to have the same degradation rate as a conventional buried heterostructure laser. The laser having a small cross section of active layer also has low coupling loss and high efficiency up to 85.

This paper investigates the accepting powers of multi-inkdot two-way alternating pushdown automata (Turing machines) with sublogarithmic space and constant leaf-size. For each k1, and each m0, let weak-ASPACEm [L(n),k] denote the class of languages accepted by simultaneously weakly L(n) space-bounded and k leaf-bounded m-inkdot two-way alternating Turing machines, and let strong-2APDAm[L(n),k] denote the class of languages accepted by simultaneously strongly L(n) space-bounded and k leaf-bounded m-inkdot two-way alternating pushdown automata. We show that(1) strong-2APDAm [log log n,k+1]weak-ASPACEm[o(log n),k]φfor each k1 and each m1, and(2) strong-2APDA(m+1) [log log n,k]weak-ASPACEm[o(log n),k]φfor each k1 and each m0.

A fault in multi-processing system arbitration circuits result in incorrect arbitration or abnormal operation of the system. A highly reliable system requires dependable arbitration in order to operate properly. Previously, we proposed alternate competing arbitration suitable for highly reliable systems. In this paper, we propose a method for improvement of fault detection and location using additional checkers. This method is effective to maintain reliability of the system.

This paper proposes a new approach for distributing millimeter wave signals from a central location to micro-base-stations using optical fiber links. The links utilize two Mach-Zehnder external optical modulators (EOMs) to perform all optical down-conversion, eliminating the need for a local oscillator or laser diode in the micro-base-station. A simple model of the EOMs is developed to illustrate the principle of dual-EOM mixing. The characteristics of conversion loss and intermodulation are examined for two cases: where the EOMs are operated in the linear mode and where the local oscillator's EOM is biased as a frequency doubling modulator. Additionally, we examined the use of an optical amplifier to reduce conversion loss for these two cases. The measured conversion loss of the link was 82 dB, and we estimated this could be reduced to about 48 dB by employing an optical amplifier and a more efficient EOM for RF reception.

The storage utilizations of existing similar key search files based on B+-tree and extensible hashing were under 70% and should be improved. A similar key search file based on extensible hashing with partial expansion and that on linear hashing with partial expansion are proposed. Computer simulations on about 230 thousand English words show that the storage utilizations of the files with 32 expansive steps are about 97%.

This paper describes the technological issues in achieving a low-cost hybrid WDM module for access network systems. The problems which should be resolved in developing a low-cost module are clarified from the viewpoint of the module assembly in mass production. A design concept for a low-cost module suitable for mass production is indicated, which simplifies the alignment between a laser diode and a waveguide, and reduces the number of the components such as lenses and mirrors. The low-cost module is achieved by employing a flip-chip bonding method with passive alignment using a spot-size converter integrated laser diode (SS-LD) and p-i-n waveguide photodiodes (WGPDs) on a planar lightwave circuit (PLC) platform. We confirm that the SS-LD and the WGPD provide high coupling efficiency with a large tolerance for passive alignment. To achieve a high-sensitivity receiver, the module is designed to employ an asymmetric PLC Y-splitter that prefers a PD responsivity to an LD output power because of the high-coupling efficiency of the LD, and to employ a bare preamplifier mounting to reduce the parasitic capacitance into a preamplifier. We also demonstrate the dynamic performance for a 50-Mb/s burst signal, such as a high sensitivity, an instantaneous AGC response, and a small APC deviation of the transceiver.

In this paper, we evaluate the throughput performance of CDMA Slotted ALOHA systems. To improve the throughput performance, we employ the Quasi-synchronous sequences and the Modified Channel Load Sensing Protocol as an access control procedure. As a result, we found a good throughput by the QS-sequences. By employing MCLSP, we can keep the maximum throughput even in high offered load and in the presence of a long access timing delay, which is one of the issue in satellite packet communication systems.

In this paper, two new signature schemes whose security is based on both discrete logarithms and factorization are proposed to enhance the security of the OSS signature scheme. The major benefit of these new signature schemes is that the signer dose not need to know how to factor p-1, thus it is possible for every user to employ the same modulus p, where p is the modulus commonly used in the system. Furthermore, two identification schemes based on this advantage are also developed in this paper.

Checkers, self-testers, and self-correctors for a function f are powerful tools in designing programs that compute f. However, the relationships among them have not been known well. In this paper, we first show that (1) if oneway permutations exist, then there exists a language L that has a checker but does not have a self-corrector. We then introduce a novel notion of "self-improvers" that trans form a faulty program into a less faulty program, and show that (2) if a function f has a self-tester/corrector pair, then f has a self-improver. As the applications of self-improvers, we finally show that (3) if a function f has a self-tester/corrector pair, then f has a flexible self-tester and (4) if a function f has a self-tester/corrector pair, then f has self-improver that transforms a faulty program into an alomost correct program.

For designing the underwater transmission system using directly projected audible sound by underwater loudspeaker to prevent a diving accident and/or to give a working instrucion, it is important to estimate the transmission loss for a wall not onl for pure tones but also for wideband signal such as voice and noise. In this paper, two practical methods of evaluating the underwater insulation effect for a single wall are discussed. One is a reconfirmation that the mass law which is frequently used in air still explains the transmission loss in water. Because parameters such as surface density and sound velocity in the mass law are widely changeable depending on the depth in water, much complexity is involved in preparing a theoretical curve for every parameter. So to avoid such complexity, a unified parameter Φ(=ωm cos θ/2ρc) is introduced to describe the mass law. This newly presented curve as a function of Φ is in good agreement with all rearranged experimental data for every kind of plates. The other is a proposition of new evaluating method of insulation effect of a wall for a wideband signal, using an idea of (100-α) percentage point of the noise level probability destribution, Lα. Firstly proposed method is confirmed experimentally and secondly proposed method is confirmed by a simulation experiment.

In this paper, new wavelet bases are presented. We address problems associated with the proposed matched filter in multirate systems, using an optimum receiver that maximises the SNR at the sampling instant. To satisfy the Nyquist (ISI-free transmission) and matched filter (maximum SNR at the sampling instant) criteria, the overall system filtering strategy requires to split the narrowest filter equally between transmitter and receiver. In data transmission systems a raised-cosine filter is therefore often used to bandlimit signals from which wavelet bases are derived. Sampling in multiresolution subspaces is also discussed.

This paper is concened with the design and implementation of a 2-channel, 2-dimensional filter bank using rectangular (analog/digital) and quincunx (digital/digital) sampling. The associated analog low-pass filters are separable where as the digital low-pass filters are non-separable for a minimum sampling density requirement. The digital low-pass filters are Butterworth type filters, N = 9, realized as LWDFs. They, when itterated, approximate a valid scaling function (raised-consine scaling function). The obtained system can be used to compute a discrete wavelet transform.

The present paper examines a two-dimensional (2-D) joint-process lattice estimator and its implementation for image restoration. The gradient adaptive lattice (GAL) algorithm is used to update the filter coefficients. The proposed adaptive lattice estimator can represent a wider class of 2-D FIR systems than the conventional 2-D lattice models. Furthermore, its structure possesses orthogonality between the backward prediction errors. These results in superior convergence and tracking properties versus the transversal and other 2-D adaptive lattice estimators. The validity of the proposed model for image restoration is evaluated through computer simulations. In the examples, the implementation of the proposed lattice estimator as 2-D adaptive noise cancellator (ANC) and 2-D adaptive line enhancer (ALE) is considered.

Roundoff error due to iterative computation with finite wordlength degrades the quality of decoded images in fractal image coding that employs a deterministic iterated function system. This paper presents a state-space approach to roundoff error analysis of fractal image coding for grey-scale images. The output noise variance matrix and the noise matrix are derived for the measures of error and the output noise variance is newly defined as the pixel mean of diagonal elements of the output noise matrix. A quantitative comparison of experimental roundoff error with analytical result is made for the output noise variance. The result shows that our analysis method is valid for the fractal image coding. Our analysis method is useful to design a real-time and low-cost decoding hardware with finite wordlength for fractal image coding.

For finite Volterra series systems, this paper investigates the stability of the exact model matching (EMM) control we have already presented. First, in order to analyze the stability of the EMM system, we present modified small gain theorems depending on the magnitude of the external input (s) in the cases of one input and two inputs. Next, with the help of the theorem for feedback systems with two inputs, we clarify the condition under which the control system is stable for the reference input magnitude within a certain range, and is also robust for small disturbances. The modified small gain theorems are effective for the stability analysis of the nonlinear feedback control systems which do not have affine finite gain.