A phase shifter configuration based on a bandpass filter that can change the phase continuously is discussed. In this configuration, the phase change due to resonance is used by making variable the center frequency of a filter with a broad passband. The configuration consisting of varactor diodes loaded on a microstrip line filter with short-circuited stubs to decrease the insertion loss is studied in detail by analysis and experiment. The possibility of application to a phase shifter is verified. (c) 2007 Wiley Periodicals, Inc.
Self-assembled InAs quantum dots are expected to be applied as active layers for long-wavelength emitting devices used in fiber-optic communications. A problem with these is the deterioration of emission efficiency accompanying the accumulation of strain from increasing wavelengths to beyond the 1.3-µm range on GaAs substrates. However, with the application of a GaInAsSb covering layer containing a small quantity of antimony (Sb), as proposed in this research, it will become possible to improve the emission efficiency and to have long-wavelength emission in the 1.5-µm band. Meanwhile, in order to use such quantum dots as surface-emitting devices, the in-plane polarization characteristics must be clarified. However, the polarization characteristics of quantum dots containing Sb have not been reported before now. In this paper, we focus on the influence on the emission characteristics of the transformation of the dot shape due to the addition of Sb. The polarization characteristics of photoluminescence due to the addition of Sb and of In to the cover layer are measured, the dependency of the polarization degree on the dot structure is evaluated, and guidelines for surface-emitting-type device applications are given. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 90(10): 1–8, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.20352
In recent years technology has been in practical use which performs PET image reconstruction using a Maximum Likelihood (ML) estimation or a Maximum A Posteriori (MAP) estimation to improve the quality of the reconstructed images. Generally speaking, these methods require minimization of a convex cost function based on an iterative method and are accompanied by many problems related to the computational complexity. In this paper we propose a new Row-Action type image reconstruction method that uses duality of nonlinear programming to rapidly converge with a small computational complexity per iteration. The proposed method has various advantages compared to the conventional methods. Examples of the advantages include: (1) avoids limit cycles and rapidly converges to true solutions, (2) can easily handle nonnegative constraint, (3) sufficient reconstructed images are obtained in one iteration, (4) easy to implement with a small number of empirically set parameters. The effectiveness of the proposed method is presented through simulated experiments and results of applications to clinical PET data are also presented. (C) 2007 Wiley Periodicals, Inc.
A ring resonator filter with a stub (ring filter) has a band-stop filter characteristic. The attenuation frequencies are at two symmetric locations with respect to the center frequency of the passband. If the range between these two attenuation frequencies is considered as the passband, the loss is low and the group delay is constant in the passband region. In the present paper, the condition of the ripple generation in the passband is derived for the ring filter. Further, the ripple frequencies under the ripple generation conditions are numerically obtained and compared with the measured results. Next, the passband group delay is analytically derived and compared with the measured value. Further, a method of cascading the ring filters is studied. It is found that the transfer function of the cascaded ring filter is expressed in terms of a rational function of the Richard variable Omega = jtan theta. It is shown that a set of the characteristic impedances realizing the desired rational function can be inversely calculated. (C) 2007 Wiley Periodicals, Inc.
This paper proposes a blind identification algorithm of a multivariate autoregressive moving average model based on independence of source signals. In such a model, it is difficult to perform blind identification due to nonlinear regression problems. This difficulty is overcome by introducing a feedback structure into the independent component analysis. By using a polynomial matrix fraction, coefficients matrices are exactly identified whereas a conventional method gives mere approximate results. The effectiveness of the proposed method has been confirmed through numerical simulations. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 90(11): 17–25, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/ecjb.20418
Much research has been performed regarding attempts to solve NP hard or NP complete problems using neural networks, because high-speed solutions then become possible through parallel processing. However, there is still the local minima problem. The Inverse Function Delayed (ID) model used in this paper is shown to be a powerful avoidance algorithm for the local mininia problem, because the dynamics of the model can cause negative resistance and the local minima can be destabilized by this negative resistance. In this paper, the differences with the conventional Hopfield model and the hysteresis neuron model, due to the parameters of the ID model, are discussed successively. Moreover, from a general energy function E of the optimization problem, when a static output state is the solution representation, it is shown that the global minima and the local minima can be separated using the ID model in a problem where E = 0 in the global minimum state. Afterwards, the parameter dependence of the success rate is discussed. As a result, a numerical experiment confirmed that a wide optimal parameter range showing a 100% success rate is obtained, though there is a slight special oscillating state (limit cycle). (C) 2007 Wiley Periodicals, Inc.
The impact of the outer wells on tunneling characteristics is theoretically studied in a new structure with outer wells consisting of wells on both sides of an asymmetrical triple barrier structure. First, the theoretical equation for the transmission coefficient is derived and the resonance conditions are studied. It is found that resonance is not related to the existence of the outer wells and is governed by the two resonance conditions independently existing in the two wells between the barriers. Second, the dwell time of electrons at the two resonant energy values is analyzed. The dwell time in the triple barrier structure with outer wells is compressed to about 14% at the maximum in comparison with the dwell time in the triple barrier structure without outer wells. Even if the dwell time is compared with that in the structure with a prewell, which is a conventional way of reducing the dwell time, a reduction to about 60% is realized. Also, with regard to the current density versus voltage characteristics for the structure with outer wells, it is found that a large current flows at a lower voltage than in the structure without outer wells. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 90(1): 20–31, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/ecjb.20275
In the study of composite reality, in which virtual objects are synthesized and displayed in a real environment, intensive research is under way on virtual reality in order to achieve the virtual representation of real objects with a greater resemblance to reality. The estimation of the surface reflection characteristics of the object is especially important in order to eliminate inconsistencies of shadow between the real environment and the virtual object. To deal with this problem, we are continuing the study of dense estimation of the reflection characteristics of objects from distant images and surface texture images. For objects of complex shape, we have proposed a method of taking account of the effect of mutual reflection due to the secondary reflections on the object surface. However, there remains the problem that the effect of mutual reflection by specular-reflection components cannot be eliminated. Consequently, a method is proposed in this paper which estimates the reflectance with allowance for the effect of mutual reflection, including the specular reflection component on the object surface. Specifically, the method is as follows. First, the illumination conditions with regard to the direction of illumination are determined from the object shape in order to observe the reflection component at a large number of points on the object surface. Based on the determined multiple illumination conditions and the measured data, photon mapping is applied, using the photon distribution on the object surface to estimate the surface reflectance at each point on the surface. In experiments, the estimated reflectance is compared to the results obtained by conventional methods, and it is shown that the proposed method can represent objects faithfully under various illumination conditions in the virtual environment. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 90(1): 50–60, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.20324
Low-power design is important for extending the life of batteries and chips and simplifying cooling systems. In this paper, a low-power design method for FPGA using extra flip-flops is presented. Each of the extra flip-flops is driven by a phase-shifted clock, which makes the application of this method easier. We tested our method on an AES circuit, a DES circuit, an 8-bit multiplier, and a 16-bit multiplier. Power consumption reductions of up to 70.67, 15.69, 4.43, and 28.54%, respectively, were achieved. (c) 2007 Wiley Periodicals, Inc.
This paper proposes a new type of indoor human detection system using UHF-band TV receiving waves (below referred to as "UHF-TV waves"). Due to the use of TV broadcasting waves as radio transmission sources, the proposed systems need no transmitter; the systems are composed only of receiving systems, including a receiving antenna and a receiver. The proposed systems can detect the presence or absence of humans in a room, based on the principle that the received levels fluctuate due to multipath fading or shadowing with human presence. It is noteworthy that the proposed systems utilize the indoor multipath radio propagations of broadcasting waves to detect the human presence. In order to investigate the capabilities of human detection systems using UHF-TV waves, we measured the received levels of UHF-TV waves in a room with or without human presence. Our proposed systems were able to detect a human presence by using an appropriate threshold of the received level fluctuation. The monitoring time of only 7 seconds allows 100% detection probability in the proposed detection system. (c) 2007 Wiley Periodicals, Inc.
Enhancement of service to closed spaces (independent spaces) via a repeater with several transmission lines is attracting attention as a means of expanding the service area of information transmission by MIMO. The propagation path in such environments becomes a multi-keyhole environment in the equivalent sense. The existence of a keyhole causes a reduction of communication capacity. However, in a multi-keyhole environment, the impact is reduced because multi-stream transmission becomes possible. In this paper, we propose a MIMO repeater system and a multi-keyhole model that realize repeater functions to a closed space while high-speed and high-reliability communication characteristic to MIMO are maintained. The eigenvalue distribution, average communication capacity, and average BER characteristics of the MIMO repeater channel are ascertained by computer simulations. The number of repeater antennas needed for relaying with the MIMO function maintained is determined. (c) 2007 Wiley Periodicals, Inc.
This paper describes a learning method of color transformation considering local illumination changes in a scene for interactive object recognition. We deal with refrigerator scenes with external and internal light. The external illumination changes are expressed in terms of locations in the refrigerator and the parameters are learned. Because the intensity of the internal illumination depends not only on the location but also on the transmissivity of target objects and existence of shading objects, we try recognizing objects by changing the intensity and determine one at which the object is successfully recognized. Experiments of object detection show the effectiveness of our method. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 90(12): 99–110, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.20426
A 60-GHz frequency-stabilized small oscillator consisting of a Gunn diode, a circulator, and a matched termination is fabricated by using NRD guides. The emphasis in this paper is adaptability to a rectangular waveguide circuit. To this end, an NRD guide-waveguide transition is designed. In the 60-GHz NRD Gunn diode oscillators to date, Gunn diodes sealed in a package dedicated to the NRD guide have been placed on special order. With a view to cost reduction, a Gunn diode mount is conceived in which a general-purpose-type Gunn diode can be used. The oscillation output of the fabricated oscillator is 13 dBm and the phase noise at 300 kHz offset is -113 dBc/Hz. Further, the frequency variation due to ambient temperature change is -1.3 ppm/degrees C so that the fabricated millimeter-wave oscillator is highly stable, with medium power output and low noise. (C) 2007 Wiley Periodicals, Inc.
In this paper, NRD-guide and waveguide H-plane transitions are proposed to propagate a millimeter wave from the dielectric strip to the upper surface of the conductor plate through a waveguide made by excavating the conductor plate. As a result, they have a bandwidth of about 4 GHz with |S11|≤−15 dB and a low transition loss of 0.2 dB in the 60-GHz band. An NRD-guide upper side dielectric lens antenna was designed and fabricated as an application of the proposed transition. It had a wide bandwidth of about 6 GHz with |S11|≤−15 dB, high efficiency of about 78%, and a low sidelobe strength of less than −27 dB. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 90(5): 39–48, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.20294
The new digital terrestrial television transmission signals use the OFDM system. This system has the fundamental problem that the peak power to average power ratio (PAPR) of the signal is significant. In this paper, a satellite communication system is proposed as a supplemental network for digital terrestrial broadcasting. It is shown that effective use of the satellite power becomes possible at a large PAPR by using the FM system with a constant signal envelope as the secondary modulation, so that the problem can be resolved. It is shown analytically that a larger FM gain can be obtained by limiting the peak voltage of the OFDM signal by clipping. The degradation of the BER caused by clipping is derived by simulation and the system is optimized with regard to the degree of clipping. Taking the size and operational cost of the receiving station into account, channel design is performed assuming a real satellite channel. The overall transmission characteristics such as the transmission capacity of the satellite repeater and the channel quality are discussed. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 90(11): 74–84, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/ecjb.20385
As a time series prediction model for sequential learning considering memory size limitations, this paper proposes the Adaptive and Sequential Learning Network (ASLN) model. The proposed model sequentially memorizes time sequence information given as the input and then performs prediction based on the memory. While effective use of the memory capacity is attempted for changes in the ambient environment, the model can follow up by varying its own memory. The model memorizes the elements contained in the input time series and the information on their transitions. It identifies the elements with a higher frequency of inputs among the time series and memorizes them as priority items. Information on the transitions of the input elements is represented as a state vector and is memorized by a layered neural network. The state vector maintains information on the past input sequence so that expression of the context is possible. A numerical experiment shows that the proposed model can predict a time series while tracking environmental changes. An experiment on learning of a number sequence was performed, using handwritten number patterns containing fluctuations. The prediction capability was verified with an increasing number of patterns. Guidelines are also provided for setting of parameters, which is important when the model memorizes the transition information of the time series. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 90(12): 129–139, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/ecjb.20406
This paper proposes a method for design of the shape and thickness of a dielectric dome by optimization, aiming at achieving multibeam emission with a uniform high gain for a wide range of angles. The dielectric dome has the features that it does not require a tremendous number of elements, as in the constrained lens, and that excellent multibeam characteristics can be realized over a wider range of angles than in the conventional dielectric lens. These features are demonstrated through an example of the design of a dielectric dome in which a decrease in gain is avoided over a wide range of angles up to 70 ° . The validity of the proposed method is verified by numerical analysis, and also by measurement and evaluation of the radiation pattern of the constructed dielectric dome antenna in the Ka band. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 90(5): 49– 57, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/ecjb.20254
In this paper we present a methodology for formal verification of hardware/software co-designs which are represented in RTL/program codes. Two methodologies are proposed. One is for property checking of the above-mentioned co-designs, and the other is for equivalence checking between design specifications written in program codes and above-mentioned hardware/software co-designs implementing the specifications. The descriptions are translated into FSMD (finite state machine with datapaths) models and described in RTL. Then, descriptions written in different levels are translated into same level descriptions. They can be verified with existing formal verification tools. We also report experimental results. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 90(7): 11–19, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.20371
We propose a statistical regression testing method for evaluating the reliability of software as part of the software maintenance process. Maintenance procedures take up more than half the time of the software development process; in addition, software reliability is an important factor in determining the dependability of a product. Regression tests are performed in order to conserve or improve software reliability as part of the software maintenance process. However, existing systematic testing methods based on regression tests are not necessarily appropriate for evaluating software reliability. The statistical regression testing method is a means for compensating for the flaws of such existing methods. In this method a model of how the user makes use of the software is defined by means of a Markov chain; this is known as the usage model, and then test cases are generated at random according to a probability distribution based on this usage model. In this paper we perform experiments applying the proposed method to a small-scale client server program and demonstrate that the proposed method can be implemented. In addition, we clarify the effects and issues that may be anticipated when applying the method and establish how it may be used in practice. (c) 2007 Wiley Periodicals, Inc.
This paper proposes a system in which a human image with movement is captured by a multiviewpoint camera and is converted in real time to three-dimensional data, which are sent by network transfer so that the image can be displayed at a remote site in three dimensions, using an omnidirectional display device. In the proposed system, the target human image is reconstructed in voxelwise, using parallel volume intersection for multiple images. The reconstructed voxels represent only the presence or absence of the object. Then coloring is required, based on texture information that is obtained by projecting the voxel on each image plane. The judgment as to whether the voxel is visible is important in the coloring process. In this study we attempt to achieve real-time processing from imaging to display. A parallel coloring procedure is developed by using a human image buffer in each camera, so that the visibility of the voxels is judged in real tune. In order to investigate the effectiveness of the system, an experimental system for multiviewpoint image processing was constructed using five cameras and six PCs. A human image with movement was captured and a performance of 2.63 FPS was achieved for reconstruction with a spatial resolution of 96 x 96 x 96 (a voxel size of 10 mm). The reconstructed data were directly transferred to the omnidirectional display device without being stored in memory, and were displayed, demonstrating the effectiveness of the proposed method. (c) 2007 Wiley Periodicals, Inc.
