A receiving system suitable for multipath fading channels with co-channel interference is described. This system is equipped with both an M-sectored directional antenna and an adaptive equalizer to mitigate the influence due to multipath propagation and co-channel interference. By using directional antennas, this receiving system can separate desirable signals from undesirable signals, such as multipath signals with longer delay time and co-channel interference. It accepts multipath signals which can be equalized by maximum likelihood sequence estimation, and rejects both multipath signals with longer delay time and co-channel interference. Based on computer simulation results, the performance of the proposed receiving system is analyzed assuming simple propagation models with Rayleigh-distributed multipath signals and co-channel interference.

A parallel quicksort algorithm in Ada is proposed and analyzed, its computational complexities are derived, and its performance profile is determined by simulation.

Reduction of the complexity of the NLMS algorithm has received attention in the area of adaptive filtering. A processing cost reduction method, in which the component of the weight vector is updated when the absolute value of the sample is greater than or equal to the average of the absolute values of the input samples, has been proposed. The convergence analysis of the processing cost reduction method has been derived from a low-pass filter expression. However, in this analysis the effect of the weignt vector components whose adaptations are skipped is not considered in terms of the direction of the gradient estimation vector. In this paper, we use an arbitrary value instead of the average of the absolute values of the input samples as a threshold level, and we derive the convergence characteristics of the processing cost reduction method with arbitrary threshold level for zero-mean white Gaussian samples. From the analytical results, it is shown that the range of the gain constant to insure convergence and the misadjustment are independent of the threshold level. Moreover, it is shown that the convergence rate is a function of the threshold level as well as the gain constant. When the gain constant is small, the processing cost is reduced by using a large threshold level without a large degradation of the convergence rate.

This paper proposes using an adaptive array in a base station for signal reception and transmission in order to increase the spectral efficiency without decreasing the cell radius. The adaptive array controls the directivity pattern of the base station to reduce co-channel interference during reception; the same array pattern is applied during transmission to prevent unnecessary illumination. Computer simulation results show that the cluster size can be reduced to one with time division duplexing (TDD), indicating that we can reuse the same frequency group at all cells. Thus, the improvement in spectral efficiency is as much as 16 fold that of an omni-antenna. Moreover, load sharing, which is expected to improve the channel utilization for unbalanced load situations, is available by cell overlapping. Frequency division duplexing (FDD) requires a weight adjust function to be applied for transmission since the difference in frequency between signal reception and transmission causes null positioning error. However, simple LMS-adjusting can provide a cluster size of one as well as cell overlapping when the frequency deference is 5%.

Many previous works state that a multiple Sidelobe canceller (MSLC) with two auxiliary antennas is successful in suppressing two interference signals received simultaneously by sidelobes of a main antenna. In this paper, we show that the MSLC does not always guarantee such capability in three dimensional applications where the incident direction of interference signals is defined by two angles (elevation and azimuth). We show the singularity of the autocorrelation matrix for the auxiliary channel signals induces the degradation of the capability by analyzing characteristics of MSLC's in three dimensional applications from the view point of the eigenvalue problem. To overcome this singularity, we propose a novel MSLC controlling the placement of auxiliary antennas by means of switching over three antennas arranged triangularly. Some simulations are conducted to show the effectiveness of the proposed MSLC.

This paper proposes a fast convergence algorithm for adaptive FIR filters with sparse taps. Coefficient values and positions are simultaneously controlled. The proposed algorithm consists of two stages： flat-delay estimation and tapposition control with a constraint. The flat-delay estimation is carried out by estimating the significant dispersive region of the impulse response. The constrained tap-position control is achieved by imposing a limit on the new-tap-position search. Simulation results show that the proposed algorithm reduces the convergence speed by up to 85% over the conventional algorithms for a white signal input. For a colored signal, it also converges in 40% of the convergence time by the conventional algorithms. The proposed algorithm is applicable to adaptive FIR filters which are to model a path with long flat delay, such as echo cancelers for satellite-link communications.

A technique to realize a transconductance which is relatively insensitive over temperature variations is reported. Simulation results with MOS and bipolar transistors indicate substantial improvement in temperature insensitivity over a range exceeding 100 degrees Celsius. It should find useful applications in analog LSI/VLSI systems operating over a wide range of temperature.

This paper proposes new algorithms for adaptive FIR filters. The proposed algorithms provide both fast convergence and small final misadjustment with an adaptive step size even under an interference to the error. The basic algorithm pays special attention to the interference which contaminates the error. To enhance robustness to the interference, it imposes a special limit on the increment/decrement of the step-size. The limit itself is also varied according to the step-size. The basic algorithm is extended for application to nonstationary signals. Simulation results with white signals show that the final misadjustment is reduced by up to 22 dB under severe observation noise at a negligible expense of the convergence speed. An echo canceler simulation with a real speech signal exhibits its potential for a nonstationary signal.

This paper proposes a buried-LATID structure featuring a peaked vertical profile around gate edge for the n- drain unlike the reported conventional LATID structure. As compared to the conventional LATID FETs, the deep-submicron buried-LATID FETs achieve improved circuit speed by 7% (50% compared to LDD FETs) due to suppressed gate-to-drain capacitance and improved lifetime by 10 times (300 times compared to LDD FETs). The buried-LATID FETs are very promising for deep-submicron MOSFETs to achieve improved performance and hot-carrier reliability at the same time.

This paper describes modeling and simulation of submicron NMOSFET current drive focusing on carrier velocity-saturation effects. A new simple analytical model is proposed which predicts a significant degradation of drain current in sub- and quarter-micron NMOSFET's. Numerical two-dimensional simulations clarify that the degradation is namely caused by high lateral electric field along the channel, which leads to deep velocity-saturation of channel electrons even at the source end. Experimental data of NMOSFET's, with gate oxide thickness (Tox) of 9-20 nm and effective channel lengths (Leff) of 0.35-3.0 µm, show good agreement with the proposed model. It is found that the maximum drain current at the supply voltage of Vdd=3.3 V is predicted to be proportional to Leff0.54 in submicron NMOSFET's, and this is verified with experiments.

This paper describes a DBF (Digital Beamforming) technique as a spatial filtering in the radar systems. DBF for a beamformer and an adaptive processor are discussed. An architecture for the beamformer is proposed. The beamformer discussed consists of systolic arrays that can form beams arbitrarily. Antenna radiation patterns measured in an open site are shown. For the adaptive processor, Gram-Schmidt transformation method is attained by using systolic arrays. Proposed is a means to prevent target signals from being suppressed in cells of the systolic arrays and to achieve the convergent characteristics independent of the magnitude of undesired signal power. In order to demonstrate the performance of the proposed processor, a test model of the adaptive processor was developed and tested in multiple undesired signal environment. Test results are indicated.

This paper applies the principle of radar polarimetry to the synthetic aperture frequency modulated continuous wave radar. First, the principle of monochromatic wave radar polarimetry using scattering matrix and polarization ratio necessary for introducing polarimetric imaging is given. In order to accommodate this principle to a wideband radar, a scattering matrix must be introduced, because FM-CW radar utilizes a wideband signal. This paper points out that the polarimetric target reflection coefficient obtained by the synthetic aperture FM-CW radar works as the scattering matrix element. This replacement, i.e., polarimetric reflection coefficient = the scattering matrix element, was verified by an experiment based on the polarization ratio which maximizes and minimizes a target. A radar system operative in the microwave X-band was successfully applied to the polarimetric detection of a metallic pipe of different orientations, demonstrating the validity of FM-CW radar polarimetry, and indicating an establishment of full polarimetric radar system.

This paper proposes a new combined fast algorithm for transversal adaptive filters. The fast transversal filter (FTF) algorithm and the normalized LMS (NLMS) are combined in the following way. In the initialization period, the FTF is used to obtain fast convergence. After converging, the algorithm is switched to the NLMS algorithm because the FTF cannot be used for a long time due to its numerical instability. Nonstationary environment, that is, time varying unknown system for instance, is classified into three categories: slow time varying, fast time varying and sudden time varying systems. The NLMS algorithm is applied to the first situation. In the latter two cases, however, the NLMS algorithm cannot provide a good performance. So, the FTF algorithm is selected. Switching between the two algorithms is automatically controlled by using the difference of the MSE sequence. If the difference exceeds a threshold, then the FTF is selected. Other wise, the NLMS is selected. Compared with the RLS algorithm, the proposed combined algorithm needs less computation, while maintaining the same performance. Furthermore, compared with the FTF algorithm, it provides numerically stable operation.

This paper describes an indexing framework for adaptive arrangement of mechanics problems in ITS (Intelligent Tutoring System). There have been some studies for adaptive arrangement of problems in ITS. However, they only choose a solution method in order to characterize a problem used in the practice. Because their target domains have been sufficiently formalized, this kind of characterization has sufficed to describe the relations between any two problems of such a class. In other words, here, it is enough to make students understand only the solution methods for the given class of problems. However, in other domains, it is also important to understand concepts used in the problems and not only to understand solution methods. In mechanics problems, concepts such as mechanical objects, their attributes, and phenomena composed of the objects and the attributes also need to be taught. Therefore, the difference between solution methods applied is not sufficient to describe the difference between two given problems. To use this type of problems properly in the practice, it is necessary to propose an advanced new characterization framework. In this paper, we describe a mechanics problem with three components: (1) surface structure, (2) phenomenon structure, (3) solution structure. Surface structure describes surface features of a problem with mechanical objects, their configuration, and each object's attributes given or required in the problem. Phenomenon structure is described by attributes and operational relations among them included in the phenomenon specific to the surface structure. Solution structure is described by a sequence of operational relations which compute required attributes from given attributes. We call this characterizing indexing because we use it as index of each problem. This paper also describes an application of the indexing to arrangement of problems. We propose two mechanisms of control: (a) reordering of a problem sequence, and (b) simplifying of a problem. By now, we have implemented basic functions to realize the mechanisms except for the part of interface.

This paper presents an adaptive rate error control scheme for digital communication over time-varying channels. The cyclic code with majority-logic decoding is used in a cascaded way as an inner code to create a simple and powerful hybrid-ARQ error control scheme. Inner code is used only for error correction and the outer code is used for both error correction and error detection. When an error is detected, retransmission is required. The unsuccessful packets are not discarded as with conventional schemes, but are combined with their retransmitted copies. Approximations for the throughput efficiency and the undetectable error probability are given. A high reliability coupled with a simple high-speed implementation makes it suitable for high data rate error control over both stationary and nonstationary channels. Adaptive error control scheme becomes the best solution for time-varying channels when the optimum code is selected according to the actual channel conditions to enhance the system performance. The main feature of this system is that the basic structure of the encoder and decoder need not be modified while the error-correction capability of the code increases. Results of a comparative analysis show that the proposed scheme outperforms other similar ARQ protocols.

This paper presents an equation capable of briefly evaluating the length of white noise sequence to be sent as a training signal. The equation is formulated by utilizing the formula describing the convergence property, which has been derived from the IIR filter expression of the NLMS algorithm. The result revealed that the length is directly proportional to I/[K(2-K)] where K is a step gain and I is the number of the adaptive filter taps.

A two-dimensional quasi-exact active imaging method for detecting the conducting objects buried in a dielectric half-space is proposed. In this imaging method, an image function which is a projection of buried object to an arbitrary direction, is introduced exactly by taking account of the presence of the planar boundary. The image function is synthesized from the scattering fields which are measured by moving a transmitting antenna (a current source) and a receiving antenna (an observation point) simultaneously along the ground surface. The scattering field is generated by the physical optics current assumed on the surface of buried object. Because the effectiveness of physical optics approximation has been confirmed for this problem, this is a quasi-exact active imaging method. The validity of this imaging method is confirmed by some numerical simulations and an experiment.

To make a fast Bi-CMOS SRAM yield high without speed degradation, three defect-repair methods, the address comparison method, the fuse decoder method and the distributed fuse method, were considered in detail and their advantages and disadvantages were made clear. The distributed fuse method is demonstrated to be further improved by a built-in fuse word driver and a built-in fuse column selector, and fuse analog switches. This enhanced distributed fuse scheme was examined in a fast Bi-CMOS SRAM. A maximun access time of 14 ns and a chip size of 8.8 mm17.4 mm are expected for a 4 Mb Bi-CMOS SRAM in the future.

The antennas for subsurface radar are usually covered with a conducting cavity to prevent the radiation field from affecting the electromagnetic environment and to protect the received field from external noises. Furthermore, radiowave absorber is attached to the interior wall of the cavity in order to suppress the multiple reflections in the cavity. In this paper, the characteristics of the two-dimensional cavity-backed antenna having the absorber and the over-all properties of this subsurface radar due to buried objects are numerically analyzed by the Finite-Difference Time-Domain method. It is shown that the pulse propagation in the ground is confined to the narrow region due to the cavity. It is also shown that the multiple reflections in the cavity are effectively suppressed by choosing the suitable absorber, and so that the distinctive pulse echo can be obtained.

This paper discusses methods and numerical simulations of one and two dimensional profilings for an arbitrary convex conducting target using the electromagnetic backscattering. The inversions for profile reconstructions are based upon the modified extended physical optics method (EPO). The modified EPO method assumes the modified physical optics current properly over the entire surface of conducting scatterers. First, the cross sectional area along a line of sight is reconstructed by performing iteratively the Fourier transform of the backscattering field in the frequency domain. Second, the two dimensional profile is reconstructed by synthesizing the above one dimensional results for several incident angles. Numerical simulation results of the target profiling are shown for spheroids and cone-spheroid.