We propose a method of reducing laser-clipping-induced distortion in a subcarrier multiplexed (SCM) optical-cable TV system. This scheme reduces amplitude peaks of the SCM signal by controlling the phases of video carriers to prevent the clipping which occurs when these peaks fall below the threshold of a laser-diode. It is experimentally shown that using this method reduces the bit error rate in an AM-VSB / QAM hybrid optical-transmission system.

The small planar packaging (SPP) system described here can be combined with card-on-board (COB) packaging in high-speed asynchronous transfer mode (ATM) switching systems with throughput of over 40-Gb/s. The SPP system provides high I/O pin count density, high packaging density and high cooling capability. Prototype SPP system with air flow control structure for switching MCMs is constructed. Each MCM contained a 35 array of low thermal resistance butt-lead pin-grid-array on a glass ceramic substrate measuring 100170 mm with a plate fin heat-sink. This allows a power dissipation of more than 125 W per MCM, and 300 W per printed circuit board (PCB). Obtained board level heat flux density of the SPP system is 0. 37 W/cm2, which is six times that of conventional COB packaging. The SPP system combined with the COB packaging provides a small system foot-print and compact hardware for high-speed, large capacity ATM switching systems. This high-performance air cooling technology will be especially useful for future broadband ISDN high-speed switching systems.

We investigate the basic properties of focused electron beam (FEB)-damaged Josephson junctions on silicon (Si) substrates for high-frequency device applications. YBa2Cu3O7-y (YBCO) Josephson junction arrays were also fabricated by FEB irradiation to confirm the junction uniformity and to investigate their applicability. The junctions exhibit resistively shunted junction (RSJ)-like current-voltage (I-V) curves and the microwave-induced Shapiro steps for all operation temperatures. Two-junction arrays show single-junction-like behavior with the Shapiro steps in an array up to 2 mV. Microwave-induced Shapiro steps correspond to the double voltages Vn=2nVJ, where VJ=f0h/2e in two-junction arrays. The microwave power dependence of I-V curves shows the steps corresponding to the RSJ model.

This paper addresses the problem of determining the 3-D pose of a curved rigid object from a single 2-D image. The surface of the object are assumed to be modeled with several patches, each of which be expressed by an implicit polynomial. Moreover, the sensed data are assumed to be the coordinates of those points that are on the image contours. Based on the idea of contour matching, the algorithm proposed computes the parameters defining the pose of the object, and achieves the segmentation of the sensed data and the recognition of the object.

In order to lessen overflow or underflow problem in numerical computation, several new floating-point arithmetics have been proposed. The significant advantage of these new arithmetics is that a number can be represented in a wider range since the fields of exponent and mantissa are changed depending on the magnitude of number. The main issues of these arithmetics are how to find the boundary between exponent and mantissa as well as to convert the formats between new floating-point arithmetic and fixed-point arithmetic quickly. In this paper, a CAM-based array converter based on the Universal Representation of Real number (URR) floating-point arithmetic is described. Using match retrieval device CAM, the detection of the boundary can be accomplished faster than conventional circuits. Arranging the basic cells into iterative array structure, the fast separation/connection operation is achieved. The speed, area and power consumption of the converter is estimated.

A new broadband buffer circuit technique and its analytical design method are proposed for a high-speed decision circuit featuring both a higher input sensitivity and a larger phase margin. The buffer circuit characteristics are significantly improved by employing a series peaking source follower (SPSF), where a peaking inductor is inserted between the first and second source follower stages. Optimization of the peaking inductance successfully enhances the 3-dB bandwidth of the data-input buffer and the clock buffer by 7 GHz for both, over conventional double-stage source follower SCFL buffers. The proposed circuit technique and design method are applied to a 10-Gbit/s decision circuit by the use of production-level 0. 5 µm GaAs MESFETs. The fabricated decision circuit achieves a data input sensitivity of 43 mVp-p and a phase margin of 240 both at 10-Gbit/s: a 230 mVp-p smaller input sensitivity and a 35 larger phase margin than those of conventional non-peaking inductor types.

A correction of the physical optics approximation by accounting for the presence of specific currents concentrated near shadow boundaries on the surface of a convex non-metallic scatterer is analysed by considering a canonical problem of diffraction of a plane electromagnetic wave incident normally to the axis of an infinite circular cylinder with impedance boundary conditions. The analysis focuses on the development of Fock-type asymptotic representations for magnetic field tangent components on the surface of the scatterer. The Fock-type representation of the surface field is uniformly valid within the penumbra region, providing a continuous transition from the geometrical optics formulas on the lit portion of the surface to the creeping waves approximation in the deep shadow region. A new numerical procedure for evaluating Fock-type integrals is proposed that extracts rapidly varying factors and approximates the rest, slowly varying coefficients via interpolation. This allows us to obtain accurate and simple representations for the shadow boundary currents that can be directly inserted into the radiation integral and effectively integrated. We show that accounting for the shadow boundary currents considerably improves the traditional PO analysis of the high-frequency electromagnetic fields scattered from smooth and convex non-metallic obstacles, particularly near the forward scattering direction.

A GeSi avalanche photodetector grown on a silicon-on-insulator (SOI) passive waveguide is demonstrated. The absorption layer of the detector consisits of alternating layers of 66 Ge0. 44Si0. 56 and 480 Si on SOI substrate. The thick SOI waveguide couples the light from an optical fiber into the GeSi/Si strain-limited thin absorption region. The detector exhibits low dark current, sharp breakdown and an external responsivity of 0. 2 A/W at 1. 3 µm wavelength.

A multicarrier modulation called orthogonal frequency division multiplex (OFDM) is attracting attention as a transmission scheme which is robust against multipath propagation. A major disadvantage of OFDM is that it is sensitive to nonlinear distortion due to its wide transmission amplitude range. The scope of this study is to cope with the nonlinear problem. We propose a nonlinear distortion compensation scheme using an iterative method which has been applied to an image signal restoration.

This paper proposes a high-speed connection admission control scheme, named PERB CAC (CAC based on Prior Estimation for Residual Bandwidth). This scheme estimates the residual bandwidth in advance by generating a series of virtual requests for connection. When an actual connection request occurs, PERB CAC can instantaneously judge if the required bandwidth is larger than the estimated residual bandwidth, so the connection set-up time can be greatly reduced. Therefore, PERB CAC can realize high-speed connection set-up.

This study shows the effectiveness of the simulation probability density function (p. d. f. ) based on the Bhattacharyya bound from the point of view of the twisted distribution. As a result, the simulation p. d. f. related to the Bhattacharyya bound is asymptotically optimal for the trellis coded modulation scheme under some practical conditions. And the optimality is also confirmed by a numerical example.

This paper describes subband-crosscorrelation analysis (SBXCOR) using two input channel signals. SBXCOR is an extended signal processing technique of subband-autocorrelation analysis (SBCOR) that extracts periodicities associated with the inverse of center frequencies present in speech signals. In addition, to extract more periodicity information associated with the inverse of center frequencies, the multi-delay weighting (MDW) processing is applied to SBXCOR. In experiments, the noise robustness of SBXCOR is evaluated using a DTW word recognizer under (1) a simulated acoustic condition with white noise and (2) a real acoustic condition in a sound proof room with human speech-like noise. As the results, under the simulated acoustic condition, it is shown that SBXCOR is more robust than the conventional one-channel SBCOR, but less robust than SBCOR extracted from the two-channel-summed signal. Furthermore, by applying MDW processing, the performance of SBXCOR improved about 2% at SNR 0 dB. The resultant performance of SBXCOR with MDW processing was much better than those of smoothed group delay spectrum (SGDS) and mel-filterbank cepstral coefficient (MFCC) below SNR 10 dB. The results under the real acoustic condition were almost the same as the simulated acoustic condition.

A turbo TCM system is applied to a channel with overall noise which is equal to the additive combination of impulsive Gaussian noise and Additive White Gaussian Noise (AWGN). By taking the distribution of the previously mentioned overall noise into account, a decoding algorithm for Poisson occurrence impulsive noise is derived as an extension of that for AWGN. A simulation result shows that Eb/N0 difference from Shannon limit to realize BER=10-4 is 0. 493 dB. To investigate the effect of burst noise, we discuss the case of additive impulsive noise with Markovian occurrence which is represented by Hidden Markov Model. A decoding algorithm for Markovian noise is proposed. In the iterative decoding for the Markovian channel, the decoding algorithms for Markovian and Poisson noise are applied separately to the two component decoders. The decoding algorithm for Markovian noise is used in the component decoder wherein received signal is directly fed, while the decoding algorithm for Poisson noise is used in the component decoder wherein received signal is fed after passing an interleaver. This paper also shows simulation results that include the effects of varying the noise parameters in the decoding. In the Markovian case, when smaller value of variance of impulsive noise is used, the observed flattening of BER performance is more serious compared to the effect in the Poisson noise channel. No flattening is observed when large value is used.

We have designed rapid single-flux-quantum (RSFQ) adder circuits using two different architectures: one is the conventional architecture employing globally synchronous clocking and the other is the data-driven self-timed (DDST) architecture. It has been pointed out that the timing margin of the RSFQ logic is very sensitive to the circuit parameter variations which are induced by the fabrication process and the device parameter uncertainty. Considering the physical timing in the circuits, we have shown that the DDST architecture is advantageous for realizing RSFQ circuits operating at very high frequencies. We have also calculated the theoretical circuit yield of the DDST adders and shown that a four-bit system operating at 10 GHz is feasible with sufficient operating margin, considering the present 1 kA/cm2 Nb Josephson technology.

A new numerical procedure called asymptotic periodic waveform evaluation (APWE) for finding the steady state solution of nonlinear circuits driven by one tone periodic input signal is presented. APWE starts by constructing a virtual system which gives the same periodic steady state waveform as the original system's but with a shorter transient duration. Thus the periodic steady state (PSS) response can be obtained by simply performing transient analysis of the newly derived system for a few periods. An efficient method for solving the nonlinear equations occurred during the transient analysis is presented. To improve the convergence rate of PSS waveform, APWE is combined with extrapolation method. Some simulation results are shown.

We propose a novel soft-decision decoding algorithm for cyclic codes based on energy minimization principle. The well-known soft-decision decoding algorithms for block codes perform algebraic (hard-decision) decoding several times in order to generate candidate codewords using the reliability of received symbols. In contrast, the proposed method defines energy as the Euclidean distance between the received signal and a codeword and alters the values of information symbols so as to decrease the energy in order to seek the codeword of minimum energy, which is the most likely codeword. We let initial positions be the information parts of signals obtained by cyclically shifting a received signal and look for the point, which represents a codeword, of minimum energy by moving each point from several initial positions. This paper presents and investigates reducing complexity of the soft-decision decoding algorithm. We rank initial positions in order of reliability and reduce the number of initial positions in decoding. Computer simulation results show that this method reduces decoding complexity.

A novel cell-level FEC (forward error correction) scheme at SSCS of AAL type 5 for error-free data transmission services in ATM networks is proposed and evaluated. In the proposed cell-level FEC scheme, both the length of user data (e. g. , IP packet) and attached redundant data can be modified based on sender's local decision without any end-to-end parameter re-negotiation procedure. The writing and reading order regarding an interleave matrix for cell-level FEC algorithm are the same, in order to perform pipelining data transmission. The prototype implementation with software processing achieves few Mbps end-to-end throughput. The end-to-end data transmission latency and the amount of retransmission packets due to packet error at the receiver entity are evaluated by computer simulation with correlated cell dropping process. Simulation results show that the benefits of cell-level FEC scheme for the error-free data transmission services, i. e. , by use of cell-level FEC scheme, the amount of retransmitted packets can be reduced, even if the average latency for end-to-end data transmission increases slightly.

The DC component suppressing method, called Guided Scrambling (GS), has been proposed, where a source bit stream within a data block is subjected to several kinds of scrambling and a RLL (Run Length Limited) coding to make the selection set of channel bit streams, then the one having the least DC component is selected. Typically, this technique uses a convolutional operation or GF (Galois field) conversion. A review of their respective symbol error properties has revealed important findings. In the former case, the RS (Reed-Solomon) decoding capability is reduced because error propagation occurs in descrambling. In the latter case, error propagation of a data block length occurs when erroneous conversion data occurs after RS decoding. This paper introduces expressions for determining the decoded symbol error probabilities of the two schemes based on these properties. The paper also discusses the difference in code rates between the two schemes on the basis of the result of calculation using such expressions.

This paper presents the performance of FH/MFSK systems, which exploit silent gaps in speech to accommodate more users, over Rayleigh fading channels. Two kinds of receivers are considered: one uses a threshold on the received signal strength to declare whether the signals were present or not, and the other is assumed to have perfect transmitter-state information obtained from using additional bandwidth. Results show that, if the codeword dropping and codeword error are assumed to be equally costly, the former can achieve slightly better performance than the latter in the decoding error probability. This finding suggests that, for the system to exploit silent gaps in speech, it is advantageous for the receiver to use a threshold to declare whether signals were present or not instead of relying on the transmitter-state information.

In this paper, a virtual-short circuit which consists of only two MOS transistors operated in the weak-inversion region is proposed. It has the advantages of almost zero power consumption, low voltage operation, small chip area, and no needlessness of bias voltages or currents. The second order effects, such as the device mismatch, the Early effect, and the temperature dependency of the circuit are analyzed in detail. Next, current-controlled and voltage-controlled current sources using the proposed virtual-short circuit are presented as applications. The performance of the proposed circuits is estimated using SPICE simulation with MOSIS 1. 2 µm CMOS device parameters. The results are reported on this paper.