We have achieved the room temperature cw lasing operation of GaInAsP/InP surface emitting lasers for the first time. By employing a buried heterostructure with 1.3 µm range active region and a MgO/Si heat sink mirror, cw operation was obtained up to 14 with the threshold current of 22 mA.

A coherent communication system using squeezed light is one of candidates for a realization of super-reliable systems. In order to design such a system, it is essential to understand and to analyze modulators mathematically. However, quantum noise of squeezed light has a colored spectrum which changes with respect to phase of a local laser. Therefore the optimization of the relationship between signal and quantum noise spectrums is required at a modulator to obtain the ultimate performance of the communication system. In this paper, some ideas of modulators for squeezed light are proposed and their spectrum transformations are given. After the brief summary of squeezed quantum noise, a new concept which originates from the restriction of the local laser phase is applied to it. This concept makes a problem originated from a colored quantum noise spectrum more serious. It results in the optimization problem for the relationship between the quantum noise spectrum and signal power spectrum. The solution of this problem is also given under the restriction of local laser phase. As a result, a general design theory for coherent communication system using the squeezed light is given.

Since the time required for testing logic circuits is proportional to the number of test vectors, the size of test sets as well as test generation time is one of the most important factors to be considered in test generation. The size of test sets becomes an essential issue, especially for scan designed circuits, because of the need to shift a test vector serially into the scan path. In this paper, we propose new methods of generating compact test sets to detect al the irredundant single stuck-at faults in combinational circuits. The proposed algorithms calculate a test function for each fault which corresponds to the set of all test vectors for the fault and generate a compact test set by analyzing the test functions. The analysis is based on finding a test vector which detects the largest number of remaining faults. Since our methods select a test vector among all the test vectors, represented by a test function, for a target fault, smaller test sets can be generated, in general, than that by conventional test set compaction methods. The experimental results show that the size of test sets generated by our method is about one-third as large as that without compaction.

Fiber-optic passive double star (PDS) network is described as an access network for microcellular radio communication systems. The intrinsic characteristics of the PDS network, reduction in the optical fiber count and flexible access capability, are examined. A unit cell structure is introduced which enables the PDS network to be effectively incorporated into the access portion of microcellular radio communication systems. The reduced total fiber length in the unit cell structure based on the PDS network is discussed in comparison with the conventional architecture. Calculations show that there is an optimum splitting ratio that minimizes the total fiber length. When the microcell radius and service area radius are 100m and 10km, respectively, the total fiber length of the PDS network is reduced to only about 9% of that of the conventional single star (SS) network for a splitting ratio of 34. Resource sharing and handover between microcells in a unit cell are performed by using the dynamic channel allocation function of the PDS system. Substantial performance improvement for loaded traffic can be obtained by resource sharing. When the splitting ratio is 32, the available traffic of a base station (BS) increases from 0.9 [erl/BS] to 3.4 [erl/BS] by adopting dynamic channel allocation for the lost call probability of 0.01.

Acceleration techniques have been incorporated into the generalized method of characteristics (GMC) to perform transient analysis of uniform transmission lines, for the special case when the transmission lines are driven by digital signals. These techinques have been proved to improve the simulation speed to a great extent when the analysis is carried out using iterative waveform relaxation method. It has been identified that the load impedance connected to the transmission line has a bearing on the efficiency of one of these acceleration techniques. Examples of an RLCG line terminated with linear loads as well as nonlinear loads are given to illustrate the advantage of incorporating these acceleration techniques.

A quantum interconnection scheme by controlling the Coulomb interaction between ballistic electrons is proposed in which 2DEG (2 dimensional electron gas) plays the role of an interconnection medium. This concept brings up new possibilities for the interconnection approach in various fields such as parallel processing, telecommunications switching, and quantum functional devices. Cross-over interconnection, address collision, and address selection in a quantum information network system were analyzed as the first step. The obtained results have shown that the interconnection probability can be controlled by the velocity and timing of the ballistic electron emission from the emitter electrode. The proposed interconnection scheme is expected to open up a new field of quantum effect integrated circuits in the 21st century.

Redundancy is introduced by sampling a bandlimited signal at a higher rate than the Nyquist rate. In the cases of erasures due to fading or jamming, the samples are discarded. Therefore, what we get at the output of the receiver is a set if nonuniform samples obtained from a uniform sampling process with missing samples. As long as the rate of nonuniform samples is higher than the Nyquist rate, the original signal can be recovered with no errors. The sampling theorem can be shown to be equivalent to the fundamental theorem of information theory. This oversampling technique is also equivalent to a convolutional code of infinite constraint length is the Field of real numbers. A DSP implementation of this technique is through the use of a Discrete Fourier Transform (DFT), which happens to be equivalent to block codes in the field of real numbers. An iterative decoder has been proposed for erasure and impulsive noise, which also works with moderate amount of additive random noise. The iterative method is very simple and efficient consisting of modules of Fast Fourier Transforms (FFT) and Inverse FFT's. We also suggest a non-linear iterative method which converges faster than the successive approximation. This iterative decoder can be implemented in a feedback configuration. Besides FFT, other discrete transforms such as Discrete Cosine Transform, Discrete Sine Transform, Discrete Hartley Transform, and Discrete Wavelet Transform are used. The results are comparable to FFT with the advantage of working in the field of real numbers.

We propose a decoding algorithm for the t-EC/AUED code proposed by Böinck and Tiborg. The proposed algorithm also reveals some remarkable properties of the code.

Let U denote a set comprising elements called "keys." The goal of the nearest point problem is to search quickly for a key among some keys x1 , xn that is the nearest to a reference key x under a partial order relation defined as (x, y) (x, z) for x, y, zU if d(x, y)d(x, z) given a wide-sense distance measure d. This article proposes a method of rearranging x1 , xn into a binary perfectly-balanced tree for solving quickly the nearest point problems. Further, computational performances of the proposed method are evaluated experimentally.

Gamma(γ)-ray irradiation effects have been investigated on three types of low-noise HEMTs, AlGaAs/GaAs conventional HEMT (conv. HEMT), AlGaAs/InGaAs pseudomorphic HEMT (P-HEMT) and InAlAs/InGaAs/InP HEMT (InP-based HEMT). The dose of irradiated γ-rays ranges from 1105 to 1108 rad. DC and RF characteristics of each type of HEMT are measured before and after irradiation and the parameter changes are investigated. For conv. HEMT and P-HEMT, no degradation of DC parameter is observed up to 108 rad, while noise figure (NF) at 12 GHz remains constant up to 107 rad and degrades by 0.1 dB at 108 rad. The InP-based HEMT shows IDSS and gm increase by about 10% at a dose of 108 rad and its NF at 18 GHz lowers gradually with the radiation dose. It has been found that the radiation hardness is greater than 107 rad for all types of HEMTs and over a hundred years of life can be expected against γ-ray irradiation in the space environment.

This paper summarizes basic system design for an optical fiber feeder for microcellular mobile communication systems. The optical feeder enables compact and low cost base stations, easy radio channel control and flexible mobile communication systems. Basic transmission characteristics are investigated through optical transmission experiments. By using these results, feeder performance is estimated and optimal system parameters are designed.

We discuss delay times derived from the current gain cutoff frequency of a heterostructure field effect transistor and describe three types of novel channel structures for millimeter-wave InP-based HFETs. The first structure discussed is a lattice-matched InGaAs HEMT with high state-of-the art performance. The second structure is an InAs-inserted InGaAs HEMT which harnesses the superior transport properties of InAs. Fabricated devices show high electron mobility of 12,800 cm2/Vs and high transconductance over 1.4 S/mm for a 0.6-µm-gate length. The effective saturation velocity in the device derived from the current gain cutoff frequency in 3.0107 cm/s. The third one is an InGaAs/InP double-channel HFET that utilizes the superior transport properties of InP at a high electric field. Fabricated double-channel devices show kink-free characteristics, high carrier density of 4.51012 cm-2 and high transconductance of 1.3 S/mm for a 0.6-µm-gate length. The estimated effective saturation velocity in these devices is 4.2107 cm/s. Also included is a discussion of the current gain cutoff frequency of ultra-short channel devices.

A model for a large network with an unidirectional linear respone (ULR) is proposed in this letter. This deterministic system has powerful computing properties in very close correspondence with earlier stochastic model based on McCulloch-Pitts neurons and graded neuron model based on sigmoid input-output relation. The exclusive OR problems and other digital computation properties of the earlier models also are present in the ULR model. Furthermore, many analog and continuous signal processing can also be performed using the simple ULR neural network. Several examples of the ULR neural networks for analog and continuous signal processing are presented and show extemely promising results in terms of performance, density and potential for analog and continuous signal processing. An algorithm for the ULR neural network is also developed and used to train the ULR network for many digital and analog as well as continuous problems successfully.

Recently, the small set of nonbinary Kasami sequences was presented and their correlation properties were clarified by Liu and Komo. The family of nonbinary Kasami sequences has the same periodic maximum nontrivial correlation as the family of Kumar-Moreno sequences, but smaller family size. In this paper, first it is shown that each of the nonbinary Kasami sequences is unbalanced. Secondly, a new family of nonbinary sequences obtained from modified Kasami sequences is proposed, and it is shown that the new family has the same maximum nontrivial correlation as the family of nonbinary Kasami sequences and consists of the balanced nonbinary sequences.

A technique for reducing fiber four-wave mixing (FWM) in multichannel transmissions is proposed. Birefringent elements are inserted on the way of transmission lines. Due to the effect of birefringent elements on the polarization states, the effective crosstalk due to FWM is expected to be 3/16 of that in the worst case in conventional systems.

Asymptotic bounds are considered for unidirectional byte error-correcting codes. Upper bounds are developed from the concepts of the Singleton, Plotkin, and Hamming bounds. Lower bounds are also derived from a combination of the generalized concatenated code construction and the Varshamov-Gilbert bound. As the result, we find that there exist codes of low rate better than those on the basis of Hamming distance with respect to unidirectional byte error-correction.

A new Viterbi algorithm with adaptive path reduction method is presented. The proposed system consists of the pre-decoder and reduced path Virerbi decoder. The predecoder separates the mixed channel noise from the received sequence. The number of errors in the pre-decoded error sequence is counted and the path reduction is implemented by the number of errors in pre-decoded error sequence. The path reduction is implemented as a function of channel condition because the errors in the pre-decoded error sequence can be considered as the channel error sequence. Due to the reduction of the path, the number of ACS (add compare select) operations can be reduced, which occupies the dominant part in Viterbi decoding. The ACS reduction ratio for the proposed system achieves up to 30% for the case of (2, 1, 2) Ungerboeck code without degradation of the error performance.

Most of actual environmental systems show a complicated fluctuation pattern of non-Gaussian type, owing to various kinds of factors. In the actual measurement, the fluctuation of random signal is usually contaminated by an external noise. Furthermore, it is very often that the reliable observation value can be obtained only within a definite fluctuating amplitude domain, because many of measuring equipments have their proper dynamic range and original random wave form is unreliable at the end of amplitude fluctuation. It becomes very important to establish a new signal detection method applicable to such an actual situation. This paper newly describes a dynamical state estimation algorithm for a successive observation contaminated by the external noise of an arbitrary distribution type, when the observation value is measured through a finite dynamic range of measurement. On the basis of the Bayes' theorem, this method is derived in the form of a wide sense digital filter, which is applicable to the non-Gaussian properties of the fluctuations, the actual observation in a finite amplitude domain and the existence of external noise. Differing from the well-known Kalman's filter and its improvement, the proposed state estimation method is newly derived especially by paying our attention to the statistical information on the observation value behind the saturation function instead of that on the resultant noisy observation. Finally, the proposed method is experimentally confirmed too by applying it to the actual problem for a reverberation time measurement from saturated noisy observations in room acoustics.

This paper tends to analyze the trends of the research in logic synthesis. The first part is devoted to an expertise of the efficiency of factorization methods developed during the last decade and to the proposal of dedicated methods for complex logic blocks. The second part shows the importance of Binary Decision Diagrams as representation of Boolean functions. Their use in the technology mapping phase of multiplexor-based FPGAs in an industrial tool is taken as illustration.

This paper first proposes a fast fingerprint identification method based on a weighted-mean of binary image, and further investigates optimization of the weights. The proposed method uses less computer memory than the conventional pattern matching method, and takes less computation time than both the feature extraction method and the pattern matching method. It is particularly effective on the fingerprints with a small angle of inclination. In order to improve the identification precision of the proposed basic method, three schemes of modifying the proposed basic method are also proposed. The performance of the proposed basic method and its modified schemes is evaluated by theoretical analysis and computer experiment using the fingerprint images recorded from a fingerprint read-in device. The numerical results showed that the proposed method using the modified schemes can improve both the true acceptance rate and the false rejection rate with less memory and complexity in comparison with the conventional pattern matching method and the feature extraction method.