In high-speed TDMA mobile communications, frequency-selective fading is a serious problem because a delay time difference between multipath signals is large in comparison with symbol duration. We have proposed a spatial-domain RAKE receiver using a multibeam adaptive antenna to reduce frequency-selective fading and to realize path-diversity. The multibeam adaptive antenna resolves multipath signals in the spatial domain, and combines array outputs. In this paper, we propose the application of MUSIC algorithm to estimation of the time delays of multipath signals to make the incident signals coincide with a common reference signal. Because the MUSIC algorithm can estimate the time delays accurately, the BER performance of the proposed scheme is improved. Furthermore, we propose weighting factors which easily realize the maximal-ratio combining.

Recent development of compact and powerful portable computers and mobile phones and proliferation of the Internet will enable mobile multimedia communications. From the viewpoint of implementing multimedia services into mobile communications, it allows us to predict that traffic characteristics of mobile networks change. For planning, designing, and operating mobile multimedia networks, it is important to investigate traffic models which take the effect of multimedia services into consideration. This paper investigates population of active users in a micro-cell and proposes a traffic model for mobile multimedia networks. This model describes a population process of active users in a micro-cell in diffusion model, and its characteristics include self-similarity and activity of mobility. We also made an evaluation of network performance by using simulation, in order to show that characteristics of the proposed traffic model have impact on planning and designing networks.

We present several challenging gridding problems for multi-dimensional device and process simulation and discuss how new strategies might contribute to their solution. Formulating grid quality requirements for the standard Scharfetter-Gummel box method discretization in device simulation, we demonstrate how the offsetting techniques compares with quadtree grid generation methods and how they apply to modern device designs. Further we present a grid adaptation approach which respects the grid quality criteria and touch upon the main adaptation difficulties within device simulation. For the 3D moving boundary grids in process simulation we present a new algorithm.

In this letter, we remark a well-known nonlinear filtering technique realize immediate effect to suppress the influence of the additive measurement noise in the input to a set theoretic linear blind deconvolution scheme. Numerical examples show ε-separating nonlinear pre-filtering techniques work suitably to this noisy blind deconvolution problem.

This paper reports a Monte Carlo calculation of the bimolecular reaction of arsenic precipitation. As the accuracy of the numerical solution for the coupled rate equations strongly depends on the size of grid spacing, it is necessary to choose adequate number of rate equations in order to understand the behavior of the extended defects. Therefore, we developed a general kinetic Monte Carlo model for the extended defects, which explicitly takes the time evolution of the size density of the extended defects into account. The Monte Carlo calculation exhibits a quantitative agreement with the experimental data for deactivation, and successfully reproduces the rapid deactivation at the beginning phase followed by slow deactivation in the subsequent steps.

This paper proposes radio resource control scheme for ABR service that execute flow-control on the transmission rate and assignable bandwidth according to the congestion conditions in both wireless and wired networks. The proposed scheme is useful in improving frequency utilization and meeting the QoS requirements. There are two methods to realize the proposed scheme: explicit rate control (ERC) and binary control (BC). We estimate the performance of the proposed scheme by simulation in comparison with a scheme without flow control in a wireless network under the conditions of a finite buffer, wired network congestion, and RM-cell errors. Consequently, we confirm that the proposed scheme is more effective than the scheme without flow-control under all service conditions. In addition, we clarify that both ERC and BC are effective under the conditions of a finite buffer, wired network congestion, and RM-cell errors.

This paper newly proposes radio-over-fiber systems using cascaded radio-to-optic direct conversion (ROC) scheme. The ROC system can convert a radio signal into an optical signal with the same signal format. The received carrier-to-noise ratio (CNR) performance of the radio-over-fiber systems using the ROC/heterodyne detection (HD) scheme and the ROC/self-heterodyne detection (SHD) scheme are theoretically analyzed. The optimization of an optical modulation index (OMI) in each radio base station (RBS) is also presented. By using the proposed OMI optimization method, the ROC/HD and the ROC/SHD schemes are shown to provide approximately 16 dB and 14 dB improvement over the intensity modulation/direct detection scheme when the number of RBS is 20 and the radio-frequency (RF) signal bandwidth is 150 MHz, respectively. The ROC/SHD scheme enables a receiver structure to become simple while still achieving high received CNR.

In this paper, performance of a PN code acquisition scheme is analyzed and simulated for a DS/CDMA overlay system where a CDMA user and a narrowband user coexist in the same frequency band. A narrowband user is modelled as a narrowband interference (NBI) located at the fraction of a CDMA user's bandwidth. To suppress the NBI, an interference suppression filter is employed at the receiver frontend. Acquisition performance is evaluated in terms of mean acquisition time using state transition diagram for acquisition process. To apply for a DS/CDMA mobile cellular environments, multiple access interference and imperfection of power control are taken into account in the analysis of acquisition performance. The imperfect power control is considered by modelling the power of each user to be lognormally distributed about nominal received power. From the simulation results, it is shown that for the cases of perfect and imperfect power control, the interference suppression filter is very effective for supprssion of the NBI and rapid PN code acquisition in a DS/CDMA overlay environment. It is also shown that the one-sided tap number of 5 for interference suppression filter is sufficient to suppress the NBI. And, capacity estimates are compared based on acquisition and BER performance. The analysis in this paper can be applied to the practical situations for a DS/CDMA overlay environment.

Efficient radio resource utilization and fairness are important goals that must be achieved since wireless ATM systems support various services with different traffic characteristics such as CBR and UBR. This paper proposes a novel delay-and-queuing data size-based MAC protocol for broadband wireless ATM. The proposed MAC protocol relies on a new resource scheduling algorithm that decides the priority of channel assignment based on both the queuing delay and the queuing data size in the transmission buffer. Simulation results confirm that the proposed MAC protocol is able to provide throughput fairness and to achieve excellent throughput performance for ATM services that experience dynamic traffic fluctuations.

In this article, an efficient vector quantization (VQ) scheme called side-match finite-state vector quantization with adaptive block classification is presented for image compression. It makes use of edge information contained in image in additional to the average values of blocks forming the image. In order to achieve low bit rate coding while preserving good quality images, neighboring blocks are utilized to predict the class of current block. Image blocks are mainly classified as edge blocks and non-edge blocks in this coding scheme. To improve the coding efficiency, edge blocks and non-edge blocks are further reclassified into different classes, respectively. Moreover, the number of bits for encoding an image is greatly reduced by foretelling the class of input block and applying small state codebook in corresponding class. The improvement of the proposed coding scheme is attractive as compared with other VQ techniques.

Conventional multiuser interference canceling is always done in the uplink. In this paper, a novel multiuser interference canceling scheme is introduced. It can be used in the downlink of the TDD-CDMA systems. The multiuser interference canceling is done through the joint optimization of both the spreading and despreading waveform for different users, instead of the despreading code only. The idea is to take the advantages of exploitation, rather than mitigation, of the multipath propagation effects. In TDD-CDMA systems, the channel parameter of the downlink can be estimated from the uplink. We can calculate the spreading and despreading code by using the instantaneous channel parameters, so they can accommodate to the characteristic of the multipath channel. The maximum receive signal to interference plus noise ration (SINR) criterion is used to optimize the spreading and despreading code. An iteration algorithm is given to create the optimal spreading and despreading code. Numerical results show that our scheme can greatly decrease the multiple access interference (MAI), hence greatly increase the SINR, compared with the conventional spreading code such as Gold code. Numerical results of the proposed scheme assuming different number of active users, Doppler frequency and coefficient estimation error are also given.

This paper deals with the identification of system equation of the chaotic dynamics by using smaller number of data based upon the genetic programming (GP). The problem to estimate the system equation from the chaotic data is important to analyze the structure of dynamics in the fields such as the business and economics. Especially, for the prediction of chaotic dynamics, if the number of data is restricted, we can not use conventional numerical method such as the linear-reconstruction of attractors and the prediction by using the neural networks. In this paper we utilize an efficient method to identify the system equation by using the GP. In the GP, the performance (fitness) of each individual is defined as the inversion of the root mean square error of the spectrum obtained by the original and predicted time series to suppress the effect of the initial value of variables. Conventional GA (Genetic Algorithm) is combined to optimize the constants in equations and to select the primitives in the GP representation. By selecting a pair of individuals having higher fitness, the crossover operation is applied to generate new individuals. The crossover operation used here means the replacement of a part of tree in individual A by a part of tree in individual B. To avoid the meaningless genetic operation, the validity of prefix representation of the subtree to be embedded to the other tree is probed by using the stack count. These newly generated individuals replace old individuals with lower fitness. The mutation operation is also used to avoid the convergence to the local minimum. In the simulation study, the identification method is applied at first to the well known chaotic dynamics such as the Logistic map and the Henon map. Then, the method is applied to the identification of the chaotic data of various time series by using one dimensional and higher dimensional system. The result shows better prediction than conventional ones in cases where the number of data is small.

In this paper the application of a linear-quadratic processor is proposed for detection of each user's signal in a direct sequence code division multiple access scheme and, in particular, for W-CDMA systems. In this method, the knowledge of the user of interest, and some statistical knowledge of interfering transmitters' signals are used to detect the desired user's signal without needing exact "a priori" knowledge of the interfering signal parameters such as spreading sequences and signal powers. Parameters of the proposed processor, which are derived so as to maximise the signal-to-interference-plus-noise ratio (SINR), can generally be obtained by solving a system of linear equations for which many effective techniques exist. A model for this detection procedure is developed and shown--through analytical and numerical results--to offer a good compromise between complexity and quality of performance.

A first-order investigation of the transport and energy-loss processes in silicon dioxide is worked out in the frame of the Spherical-Harmonics solution of the Boltzmann Transport Equation. The SiO2 conduction band is treated as a single-valley spherical and parabolic band. The relevant scattering mechanisms are modeled consistently: both the polar and nonpolar electron-phonon scattering mechanisms are considered. The scattering rates for each contribution are analyzed in comparison with Monte Carlo data. A number of macroscopic transport properties of electrons in SiO2 are worked out in the steady-state regime for a homogeneous bulk structure. The investigation shows a good agreement in comparison with experiments in the low-field regime and for different temperatures.

Since mobile communication systems using optical rays (optical mobile communication systems) do not radiate radio waves from the mobile terminals, they are expected to be used in environments containing sensitive electronic equipment. However, the placement and direction of the optical receivers must be suitably determined for mobile communication because light has high directivity. In optical mobile communication systems, the communication quality varies with the direction of the mobile terminal. Therefore, we examined the angle over which communication is possible at various measurement points and defined it as the communication angle. The mean opinion score (MOS) was obtained to assess the communication quality using the communication angle as a parameter. In this paper, the two situations, walking and sitting down, was considered the way optical mobile communication systems actually used. We found that for walking, when the communication angle was over 180 degrees, the MOS was over 3 and over 50% of users could communicate usefully. When used sitting down, the communication quality did not depend on the communication angle, but only on whether or not the user could communicate in the direction he/she was facing. Thus, if the communication angle in the service area is over 180 degrees, it is possible to communicate in practical situations, even while walking.

In MPEG standard, motion estimation (ME) is used to eliminate the temporal redundancy of video frames. This ME is the most time-consuming task in the encoding of video sequences and is also the one using the most power. Using low-bit images can save power of ME and a conventional architecture fixed to a certain bit width is used for low-bit motion estimator. It is known that there is a trade-off between power and image quality. ME may be used in various situations, and the relation between demands for power or image quality will depend on those circumstances. We therefore developed an architecture for a low-bit motion estimator with adjustable power consumption. In this architecture, we can select the bit width for the input image and adjust the amount of power for ME. To evaluate its effectiveness, we designed the motion estimator by VHDL and used the synthesis results to estimate the performance.

This paper proposes a method for extracting subimages from a huge reference image by learning lifting wavelet filters. Lifting wavelet filters are biorthogonal wavelet filters containing free parameters developed by Sweldens. Our method is to learn such free parameters using some training subimages so as to vanish their high frequency components in the y- and x-directions. The learnt wavelet filters have the feature of training subimages. Applying such wavelet filters to the reference image, we can detect the locations where the high frequency components are almost the same as those of the target subimage.

A generalized algorithm for designing an optimum VQ source codec in systems with channel coding is presented. Based on an AWGN channel model, the algorithm derives the distribution of the channel decoder soft-output and substitutes it in the expression for the system end-to-end distortion. The VQ encoder/decoder pair is then optimized by minimizing this end-to-end distortion. For a Gauss-Markov source, the proposed algorithm outperforms the conventional SOVQ source coding scheme by 5.0 dB in the decoded source SNR. Application of this algorithm for designing optimum low-bit-rate speech codec is given. A 4.0 kbps VQ based CELP codec is designed for performance evaluations, where all the CELP parameter encoder/decoder pairs are optimized by minimizing their end-to-end distortions, respectively. As a result, the speech distortion over the noisy channel is minimized. Subjective tests show that the proposed algorithm improves the decoded speech quality by 2.5 MOS relative to a regular SOVQ CELP speech coding system. The performances of the algorithm under channel mismatch conditions are also shown and discussed.

We present a simulation system which meets the requirements for practical application of inverse modeling in a professional environment. A tool interface for the integration of arbitrary simulation tools at the user level is introduced and a methodology for the formation of simulation networks is described. A Levenberg-Marquardt optimizer automates the inverse modeling procedure. Strategies for the efficient execution of simulation tools are discussed. An example demonstrates the extraction of doping profile information on the basis of electrical measurements.

We study the joint optimization problem of a transmitter with multiple transmit antennas and a receiver with multiple receive antennas in a narrow-band communication system. We discuss the problem of designing a pre-filter at the transmitter, a post-filter at the receiver, and a bit allocation pattern to multiple symbols in the sense of minimizing the average bit error rate. With the optimized filters and the bit allocation, we could realize high efficiency and high data rate in band-limited channels.