The term pilot pollution in IS-95 CDMA systems is used to indicate that a large number of equally strong pilot signals is present. Those pilots compete with each other to become the serving one and this causes a very high rotation of pilot leadership at the mobile station. As a consequence, the signaling rate on the traffic channel increases, thus degrading the call quality. We present a method of alleviating the pilot pollution problem by means of repeaters. Simulation studies have been carried out on an actual CDMA network suffering from pilot pollution and the results have been verified by field trials. They indicate that repeaters can effectively improve call quality by altering the spacial distribution of pilot signal strength.

A passive branched optical network unified for broadcasting and communication utilizing a set of Fabry-Perot etalons with different cavity lengths is proposed and its basic operation including thermal stability of broadcasting channel is demonstrated. It is confirmed that a high transmission frequency in common for a pair of fiber Fabry-Perot etalons is always found however environmental temperature changes.

This paper is, in half part, written in review nature, and presents recent theoretical results on linear-filtering and -prediction problems of nonstationary Gaussian processes. First, the basic concepts, signal and noise, are mathematically characterized, and information sources are defined by linear stochastic differential equations. Then, it is shown that the solution to a conventional problem of filtering or prediction of a nonstationary time series is, in principle, reducible to a problem, of which solution is given by Kalman-Bucy's theory, if one can solve a problem of finding the canonical representation of a Gaussian process such that it has the same covariance functions as those of the time series under consideration. However, the problem mentioned above is left open. Further, the problem of time-frequency analysis is discussed, and physical realizability of the evolutionary, i.e., the online, spectral analyzer is shown. Methods for dealing with differential operators are presented and their basic properties are clarified. Finally, some of related open problems are proposed.

A uniquely parsable unification grammar (UPUG) is a formal grammar with the following features: (1) parsing is performed without backtracking, and (2) each nonterminal symbol can have arguments, and derivation and parsing processes accompany unification of terms as in Prolog (or logic programming). We newly introduce a uniquely parallel parsable unification grammar (UPPUG) by extending the framework of a UPUG so that parallel parsing is also possible. We show that, in UPPUG, parsing can be done without backtracking in both cases of parallel and sequential reductions. We give examples of UPPUGs where a given input string can be parsed in sublinear number of steps of the length of the input by parallel reduction.

The head tissue heterogeneity required in the spatial peak specific absorption rate (SAR) assessment for portable telephones was investigated by using the FDTD method in conjunction with an MRI-based human head model. The tissue heterogeneity of the head model was changed from one type of tissue to 17 types of tissue. The results showed that, at 900 MHz and 2 GHz, the homogeneous modeling results in an underestimate about 20% for the λ/2 monopole antenna portable telephones and an overestimate to the same extent for the λ/4 monopole or helical antenna portable telephones. A head model with a simple skin-fat-muscle-bone-brain structure seems to be sufficient to obtain a fairly accurate one-gram or ten-gram averaged spatial peak SAR value in computational dosimetry for portable telephone compliance.

This paper surveys the research topics and results on nonlinear theory and its applications which have been achieved in Japan or by Japanese researchers during the last decade. The paticular emphasis is placed on chaos, neural networks, nonlinear circuit analysis, nonlinear system theory, and numerical methods for solving nonlinear systems.

Fabrication technology for Nb integrated circuits has been developed. In developing fabrication technology, the key process steps are the etching to form fine Nb electrodes and the formation of reliable insulation layers. The standard process has been developed focusing on reproducibility and reliability. In the process, conventional reactive ion etching and RF bias-sputter deposition are used. The number of Nb wiring layers is two, and standard deviation (σ) of critical current is 0.9%, 2.3%, and 4.7% for the junction sizes of 2 µm, 1.4 µm, and 1 µm, respectively. The advanced process has also been developed focusing on capability of increasing the integration scale. Electron-cyclotron-resonance plasma etching and mechanical polishing planarization have been developed as advanced process technology. The number of Nb wiring layers is three, and σ is improved to 0.8%, 0.7%, and 1.7% for the junction sizes of 2 µm, 1.4 µm, and 1 µm, respectively. Integration limits are discussed and it is estimated that the maximum number of junctions is in the order of 105 and 107 for the standard and the advanced process, respectively. A large-scale superconducting circuit such as a several M-bit RAM can be realized in the future by using these fabrication technologies.

A signal processing approach is discussed which has the potential for imaging strongly scattering objects from a series of scattering experiments. The method is based on a linear spectral estimation technique to replace the filtered backpropagation for limited discrete data and a subsequent nonlinear signal processing step to remove the contribution of multiple scattering my means of homomorphic filtering. Details of this approach are discussed and illustrated by applying the imaging algorithm to both simulated and real data.

The finite volume time domain (FVTD) method is applied to electromagnetic wave scattering from random rough dielectric surfaces. In order to gain a better understanding of physics of backscattering of microwave from rough surface, this paper treats both horizontal and vertical polarizations especially at low- grazing angle. The results are compared with those obtained by the Integral equation method and the small perturbation method as well as with the experimental data. We have shown that the present method yields a reasonable solution even at LGA. It should be noted that the number of sampling points per wavelength for a rough surface problem should be increased when more accurate numerical results are required, which fact makes the computer simulation impossible at LGA for a stable result. However, when the extrapolation is used for calculating the scattered field, an accurate result can be estimated. If we want to obtain the ratio of backscattering between the horizontal and vertical polarization, we do not need the large number of sampling points.

In this paper, the electromagnetic scattering from a cylinder with a computer-generated random rough surface is analyzed by a numerical simulation method. The validity of the proposed numerical method is confirmed by comparing the present numerical results with those calculated by the perturbation method to second order and its Pade approximation. It is shown that the present proposed method can be applied to the case where the surface roughness becomes relatively large.

This paper deals with the scattering problem of a layer where many spherical lossy particles of high dielectric constant are randomly distributed. A radiative transfer equation is used to calculate the scattering cross section of the layer. Four different multiple scattering methods are applied to determine the coefficients of the equation. The scattering cross sections of the four methods are compared by changing the incident angle and polarization of incident waves and the layer thickness. The comparison shows that the scattering cross section fairly depends on the multiple scattering methods and that we need to use an appropriate multiple scattering method for a scattering problem when using a radiative transfer equation.

In this paper we report the results of a study regarding the backscattering from wind-roughened water surfaces. The reference profile data has been deducted by an experiment held at the University of Heidelberg circular wave tank facility. The scattering theory is based on a fractal description of the surface and a combined use of the Kirchhoff approximation and the small perturbation method (SPM). The scattering results are tested versus the ones obtained via the periodic-surface moment method. The study shows the reliability of the novel approach.

To make clear numerically the scattering characteristics for a body embedded in a random medium, we need to analyze the bistatic cross-section (BCS). The scattering problem can be analyzed as a boundary value problem by using current generator method. The fourth moment of Green's functions in the random medium, which is necessary for the analysis, is obtained approximately by two-scale method. We analyze numerically the BCS of conducting circular cylinders in continuous random media, which are assumed to fluctuate about the dielectric constant of free space. The numerical results agree well with the law of energy conservation. The effects of random media on the BCS are also clarified numerically.

The mean reflection and transmission coefficients of electromagnetic waves incident onto a two-dimensional slightly random dielectric surface are investigated by means of the stochastic functional approach. We discuss the shift of Brewster's scattering angle using the Wiener kernels and numerical calculations. It is also shown that the phase shift at the reflection into Brewster's angle for a flat surface does not depend on the rms height of the surface, but does on the correlation length of the surface.

In designing a field-programmable gate array (FPGA)-based processor for motion stereo, a parallel memory system and a simple interconnection network for parallel data transfer are essential for parallel image processing. This paper, firstly, presents an FPGA-oriented hierarchical memory system. To reduce the bandwidth requirement between an on-chip memory in an FPGA and external memories, we propose an efficient scheduling: Once pixels are transferred to the on-chip memory, operations associated with the data are consecutively performed. Secondly, a rectangular memory allocation is proposed which allocates pixels to be accessed in parallel onto different memory modules of the on-chip memory. Consequently, completely parallel access can be achieved. The memory allocation also minimizes the required capacity of the on-chip memory and thus is suitable for FPGA-based implementation. Finally, a functional unit allocation is proposed to minimize the complexity between memory modules and functional units. An experimental result shows that the performance of the processor becomes 96 times higher than that of a 400 MHz Pentium II.

An Off-line mammography screening system is used in pre-screening mammograms to separate high-risk mammograms from most normal cases. Off-line system can run before radiologist's review and is particularly useful in the national breast cancer screening program which usually consists of high percentage of normal cases. Until now, the shortcomings of on-line detection of clustered microcalcifications from a mammogram remain in the necessity of manual selection of regions of interest. The developed technique focuses on detection of microcalcifications within a region of interest indicated by the radiologist. Therefore, this kind of system is not efficient enough to process hundreds of mammograms in a short time without a large number of radiologists. In this paper, based on a "hierarchically-coarse-to-fine" approach, an off-line mammography screening system for the detection and segmentation of clustered microcalcifications is presented. A serial off-line procedures without any human intervention should consider the complexity of organization of mammograms. In practice, it is impossible to use one technique to obtain clustered microcalcifications without consideration of background text and noises from image acquisition, the position of breast area and regions of interest. "Hierarchically-coarse-to-fine" approach is a serial procedures without any manual operations to reduce the potential areas of clustered microcalcifications from a mammogram until clustered microcalcifications are found. The reduction of potential areas starts with a mammogram, through identification of the breast area, identification of the suspicious areas of clustered microcalcifications, and finally segmentation of clustered microcalcifications. It is achieved hierarchically from coarse level to fine level. In detail, the proposed system includes breast area separation, enhancement, detection and localization of suspicious areas, segmentation of microcalcifications, and target selection of microcalcifications. The system separates its functions into hierarchical steps and follows the rule of thumb "coarse detection followed by fine segmentation" in performing each step of processing. The decomposed hierarchical steps are as follows: The system first extracts the breast region from which suspicious areas are detected. Then precise clustered microcalcification regions are segmented from the suspicious areas. For each step of operation, techniques for rough detection are first applied followed by a fine segmentation to accurately detect the boundaries of the target regions. With this "hierarchically-coarse-to-fine" approach, a complicated work such as the detection of clustered microcalcifications can be divided and conquered. The effectiveness of the system is evaluated by three experienced radiologists using two mammogram databases from the Nijmegen University Hospital and the Taichung Veterans General Hospital. Results indicate that the system can precisely extract the clustered microcalcifications without human intervention, and its performance is competitive with that of experienced radiologists, showing the system as a promising asset to radiologists.

An averaged intensity peak profile of light scattered from a random medium depends on a thickness of a sample as well as parameters such as a volume fraction and a size of particles composing the medium. We used this dependence to measure a depth profile varied in the random medium. We demonstrated the possible simultaneous measurement of a transport mean free path and a depth of an aqueous suspension of titanium particles.

In this study, we propose a simple multipoint-to-point ABR mechanism that can be implemented easily in existing ATM networks. The proposed scheme can provide fair bandwidth allocation among the sources in multipoint-to-point connection.

Multicast ATM switch is in great demand for the future communication network. We have proposed the Batcher banyan network with cell copy preparation stages as a transit switch. It performs cell replication with small hardware increase. On the trunkline, multicast traffic is quite little, thus hardware for cell copy can be sustained small. In those previous works, the effect of the external blocking was omitted. In this paper, we propose a multicast switching network which adopts the incomplete copy network that we have proposed, and examine several strategies to prevent the external blocking for this switching network. Namely, the input buffer method with an arbitration network is applied. For multicast usage, we propose two modifications. One is to arbitrate after cell replication for the sake of simple control and small hardware. The other is to annex a cell distribution network for smoothing biased cell arrival. Biased cell arrival occurs because the output of the incomplete copy network is not uniform. Simulation results show the effectiveness of the proposed method.

This letter points out some flaws in the previous works on UKS (unknown key-share) attacks. We show that Blake-Wilson and Menezes' revised STS-MAC (Station-to-Station Message Authentication Code) protocol, which was proposed to prevent UKS attack, is still vulnerable to a new UKS attack. Also, Hirose and Yoshida's key agreement protocol presented at PKC'98 is shown to be insecure against public key substitution UKS attacks. Finally, we discuss countermeasures for such UKS attacks.