The semiconductor lasers operating with self-sustained pulsation are under developing to be lasers which are less disturbed by the optical feedback from a surface of optical disk. Structures setting saturable absorbing regions utilizing the multi-layer configuration become popularly used for giving stronger pulsation. However, the quantum (intensity) noise in these lasers tends to be enhanced. The ridge stripe structure, of which almost self-sustained pulsation lasers consist, seems to give a leak current flowing along plane of the cladding region. Such leak current also increases the quantum noise. In this paper, theoretical calculations of operating characteristics, such as the self-sustained pulsation, the optical output, the quantum noise as well as the transverse filed profile, are theoretically analyzed by including the above mentioned several phenomena.

A current-to-frequency converter using switched-current (SI) circuits is proposed. The SI integrator with a hold-and-reset switch can control integration by the output signals. In the proposed circuit the oscillation frequency can be controlled by the input current, and the circuit is operated in the current domain. This is verified by HSPICE simulations.

We consider statistical multiplexing for various types of input data with different statistics in an integrated multimedia system such as ATM networks. The system is assumed to have a constant service rate and a finite buffer. The bit-rate of each data input is variable and is modeled by a fractional Brownian motion process. Under a criterion of quality of service, we obtain an acceptable region of statistical multiplexing. We introduce a new method of investigating the acceptable region of a statistical multiplexer. The results show that transmitting multitype input processes will increase the multiplexing gain.

This letter proposes a Perfect-Reconstruction (PR) encryption scheme based on a PR QMF bank. Using the proposed scheme, signals can be encrypted and reconstructed perfectly by using two Periodically Time-Varying (PTV) digital filters respectively. Also we find that the proposed scheme has a "good" encryption effect and compares favorably with frequency scramble in the aspects of computation complexity, PR property, and degree of security.

The address-based queues are widely used in shared buffer ATM switches to guarantee the order of the cell delivery. In this paper, we propose an address-based queue mechanism to achieve an efficient use of the shared memory under a multicast service. In the switch, both cells and the address queues share the common memory. Each queue length changes flexibly according to the number of the stored cells. Our approach significantly reduces the cell loss probability as compared with the previously proposed approaches.

We analyze M,MMPP/G/1 finite queues with queue-length-threshold (QLT) scheduling policy and Bernoulli schedule where the arrival of type-1 customers (nonreal-time traffic) is Poisson and the arrival of type-2 customers (real-time traffic) is a Markov-modulated Poisson process (MMPP). The next customer to be served is determined by the queue length in the buffer of type-1 customers. We obtain the joint queue length distribution for customers of both types at departure epochs by using the embedded Markov chain method, and then obtain the queue length distribution at an arbitrary time by using the supplementary variable method. From these results, we obtain the loss probabilities and the mean waiting times for customers of each type. The numerical examples show the effects of the QLT scheduling policy on performance measures of the nonreal-time traffic and the bursty real-time traffic in ATM networks.

This paper proposes a new method for estimating route outage probability in non-regenerative repeater digital microwave radio systems. In this method, the route outage probability is estimated by various means, including path correlation of fading occurrence and C/N degradation corresponding to the number of non-regenerative repeater stations with and without demodulator devices. In the conventional method, the path correlation is treated as 0 and the C/N degradation is taken as a constant value on each path. To confirm the proposed method's effectiveness, a field test is carried out in which 16QAM signals pass through two non-regenerative repeater stations. The results obtained are in good agreement with the estimated outage probability.

In order to investigate the nonlinearity and color responses of visual evoked potentials (VEPs), which have been useful in objectively detecting human color vision characteristics, a nonlinear system identification method was applied to VEPs elicited by isoluminant color stimuli, and the relationship between color stimuli and VEPs was examined. VEPs of normal subjects elicited by chromatically modulated stimuli were measured, and their binary kernels were estimated. Results showed that a system with chromatically modulated stimuli and VEP responses can be expressed by binary kernels up to the second order and that first- and second-order binary kernels depended on the color of the stimulus. The characteristics of second-order kernels reflected the difference between two chromatic channels. Opponent-color responses were included in first-order binary kernels, suggesting that they could be used as an index to test human color vision.

In this paper, a design concept that offers ATM-VP connections with different protection levels is presented. The users have the choice to select the protection level they wish, the network transport service they need, and the worst cell loss they can tolerate at call set up time, and pay accordingly. Besides, an advanced adaptive traffic control scheme that simplifies call and cell processing is also presented. Many important functions such as call admission, VC-bandwidth reservation, cell-level congestion control, etc. are efficiently performed at the boundary of the backbone network. In this way is given a suitable answer to the important question: "How can future telecommunication networks based on ATM provide services with customized availability ?" A platform that outlines the potential interaction between restoration methods and congestion avoidance schemes is also obtained.

Various techniques of single-electron circuit simulation are presented. The subjects include visualization of state probabilities, accurate yet reasonably fast steady-state analysis and SPICE-based high-speed simulation for circuits composed of Single-Electron Transistors (SETs). The visualized state probabilities allow one to grasp the dynamics of a single-electron circuit intuitively. The new algorithm for steady-state analysis uses the master equation and Monte Carlo method in combination. We suppose this is the best way to perform steady-state analysis. The SPICE-based simulator significantly outperforms the conventional reference simulator in speed. It is, to the best of our knowledge, the only simulator that can simulate SET circuits for real applications. It also facilitates the study of the integration of SETs and MOSFETs.

We propose a novel opto-electronic memory device using a single quantum dot (QD) and a logic device using coupled QDs (CQD) which performs (N)AND and (N)OR operations simultaneously. In both devices, occupation/unoccupation by a single electron in a QD is viewed as a bit 1/0 and data input/output (I/O) is performed by irradiation/absorption of photons. The (N)AND/(N)OR operations are performed by the relaxation of the electronic system to the Fock ground state which depends on the number of electrons in the CQD. When the device is constructed of semiconductor nanostructures, the main relaxation process is LA-phonon emission from an electron. Theoretical analysis of the device shows that (i) the error probability in the final state converges with the probability with which the system takes excited states at thermal equilibrium, i. e. , depends only on the dissipation energy and becomes smaller as the dissipation energy becomes larger, and (ii) the speed of operation depends on both the dissipation energy and dissipative interactions and becomes slower as the dissipation energy becomes larger if LA-phonon emission is taken into account. If the QDs are InAs cubes with sides of 10 nm and they are separated by the AlSb barrier with a width of 10 nm, the speed of operation and the error probability are estimated to be about 1 ns and about 0. 2 at 77 K, respectively. The basic idea of the device is applicable to two-dimensional (2D) pattern processing if the devices are arranged in a 2D array.

Since an orthogonal multi-carrier signal has large peak power, intermodulation distortion occurs due to the non-linearity of the power amplifier. This distortion severely deteriorates the performance of the multi-carrier system. Especially when carriers are modulated by information bits which produce the same phase shift or the alternative phase shift, the modulated signal has maximum peak power at the input of the amplifier. In order to avoid these phase shifts (code sequences), we propose a code reversal technique which suppresses the maximum peak power of multi-carrier signals for intermodulation compensation. This method utilizes the reversal codes which are added to the original information bits. We also show the effectiveness of the code reversal technique combined with error correction coding and examine the optimum operating point of the amplifier.

This paper analyzes a finite buffer M/G/1 queue with two classes of customers who are served by a combination of head-of-the-line priority and push-out schemes. This combination gives each class of customers two different types of priorities with respect to both delay and loss. There are two models considered. The first one is that one class of customers has a higher priority over the other class with respect to both delay and loss; the second one is that one class has a higher priority with respect to loss and the other has high-priority with respect to delay. For both of these models, the joint probability distribution of the number of customers of both classes in the buffer is derived by a supplementary variable method. Using this probability distribution, we can easily calculate the loss probabilities of both classes, the mean waiting time for high-priority customers with respect to loss and the upper bound for mean waiting time for low-priority customers with respect to loss. Numerical examples demonstrate an effect of the combination of different types of priorities.

This paper focuses on competitive learning algorithms for WTA (winner-take-all) networks which perform rotation invariant pattern classification. Although WTA networks may theoretically be possible to achieve rotation invariant pattern classification with infinite memory capacities, actual networks cannot memorize all input data. To effectively memorize input patterns or the vectors to be classified, we present two algorithms for learning vectors in classes (LVC1 and LVC2), where the cells in the network memorize not only weight vectors but also their firing numbers as statistical values of the vectors. The LVC1 algorithm uses simple and ordinary competitive learning functions, but it incorporates the firing number into a coefficient of the weight change equation. In addition to all the functions of the LVC1, the LVC2 algorithm has a function to utilize under-utilized weight vectors. From theoretical analysis, the LVC2 algorithm works to minimize the energy of all weight vectors to form an effective memory. From computer simulation with two-dimensional rotated patterns, the LVC2 is shown to be better than the LVC1 in learning and generalization abilities, and both are better than the conventional Kohonen self-organizing feature map (SOFM) and the learning vector quantization (LVQ1). Furthermore, the incorporation of the firing number into the weight change equation is shown to be efficient for both the LVC1 and the LVC2 to achieve higher learning and generalization abilities. The theoretical analysis given here is not only for rotation invariant pattern classification, but it is also applicable to other WTA networks for learning vector quantization.

In the circumstances we want to deal with, transmission channel is limited and global motion can happen by camera movement, and also there exists a region-of-interest (ROI) which is more important than background. So very low bit rate coding algorithm is required and processing of global motion must be considered. Also ROI must be reconstructed with required quality after decoding because of its importance. But the existing methods such as H. 261, H. 263 are not suitable for such situations because they do not compensate global motion, which needs large amount of transmission bits in motion information and degrades image quality. And also they can not reconstruct ROI's with high quality because they do not consider the fact that ROI's are more important than background. So a new coding scheme is proposed that describes a method for encoding image sequences distinguishing bits between ROI and background. Simulations show that the suggested algorithm performs well especially in the circumstances where background changes and the area of ROI is small enough compared with that of background.

This paper proposes a novel synchronous acquisition method with an adaptive filter in asynchronous direct sequence/code division multiple access (DS/CDMA) communication systems. An adaptive filter is used in a single-user receiver, in complete synchronization of desired user's signal, the tap coefficients of the filter are controlled to orthogonalize to all other user's spreading sequences without knowledge of the sequences, amplitude and time delays of the signals. While, in the proposed system for synchronous acquisition, the tap coefficients are controlled to orthogonalize to all user's sequences including desired user's signal. The synchronous acquisition can be achieved by using the difference of cross-correlation function value between desired user's sequence of inphase and the tap coefficients for each phase. The principle and performance evaluation for the proposed method are shown. As a result, compared to an acquisition method of conventional sliding correlator, considerable improvement of the average acquisition time can be achieved in large power multiple access interference environment.

A single-stage dual-frequency matching network that can simultaneously transform a transistor reflection coefficient to zero at two separate frequencies (a lower frequency fL and a higher frequency fH) is proposed. The network is made by adding a shorted stub, the length of which is a quarter-wavelength at fH, to a conventional L-section matching network composed of a series transmission line and an open stub. The concept of dual-frequency matching is based on the fact that the synthesized shunt admittance of the open and shorted stubs changes from capacitive at fH to inductive at fL. By means of the single-stage matching network, broad-band amplifier performance, the bandwidth of which is given as (fH-fL), can be easily obtained with almost the same design procedures and circuit area used for conventional narrow-band amplifiers. In this paper, the function of the dual-frequency matching network is analyzed in detail and an application of the matching technique to a two-stage amplifier is described. A broad-band performance of |S21|>7.4 dB at 27.0-62.5 GHz has been achieved with a GaAs P-HEMT two-stage MMIC amplifier.

It is well known that M-ary/spread spectrum (M-ary/SS) system is superior to direct-sequence spread spectrum system under AWGN, and can achieve high spectral efficiency. On the other hand, however, the main drawback of this system is that the synchronization acquisition is difficult. In this paper, we propose a new synchronization acquisition method of M-ary/SS system. This method acquires the code synchronization by introducing a symmetrical property in spreading sequences, and detecting this property with the differential decoding technique. As spreading sequences, a set of orthogonal sequences and a set of non-orthogonal sequences are considered. The strong features of proposed systems are that the systems can acquire the code synchronization in carrier band and can reduce the complexity of calculation greatly. Among the comparison results of the systems with newly proposed orthogonal and some specific non-orthogonal spreading sequences, it is especially noted that the latter can reduce the mean acquisition time and calculation complexity much greater than the former.

This paper is concerned with CDMA applied to personal and mobile communications on a global basis using multiple low earth orbital satellites (LEOS). We focus our attention on some unique aspects of LEOS systems and discuss their influences on the CDMA system performance as well as the techniques for coping with these aspects. We deal with three kinds of important items that are unique to LEOS systems; Doppler frequency shift due to satellite movement, propagation delay affecting packetized data transmission and geographical nonunifomity in traffic.

In this paper, we study and analyze the overall acquisition performance of the combined acquisition-tracking synchronization loop for direct-sequence spread-spectrum (DS-SS) signals in the presence of Doppler shift. We consider both the change of effective search rate and the impact on the detection probability due to Doppler for the acquisition loop. We also determine the acquisition behavior of the digital delay lock loop (DDLL) in the presence of code Doppler. As a result, the influence of the DDLL's acquiring capability on the complete acquisition process is investigated and some numerical results are presented to demonstrate the acquisition performances of this combined loop which are quite different from the previous reports.