If the direction of arrival (DOA) of a source is perturbed due to some reasons in a statistical way as in the environment of wireless mobile communications, a new model appropriate for such environment should be used instead of the point source model. In this paper, an angle-perturbed source model is proposed and an estimation method based on the eigen-decomposition technique is investigated under the model. The asymptotic distribution of the estimation errors is obtained to see the statistical properties.

In this letter, the constant amplitude transmission for orthogonal multicode systems is discussed. In order to obtain the high power efficiency, we require the high power amplifier which has non-linear characteristic. The nonlinear distortion, however, may occur because of the multicode signals having large amplitude fluctuations. If we can achieve the constant amplitude transmission, the nonlinear distortion can be neglected. In this letter, I investigate the property of the information bit streams that can achieve the constant amplitude transmission and show that the bent sequences can achieve the constant amplitude transmission.

Numerous scientific and engineering fields extensively utilize optimization techniques for finding appropriate parameter values of models. Various optimization methods are available for practical use. The optimization algorithms are classified primarily due to the rates of convergence. Unfortunately, it is often the case in practice that the particular optimization method with specified convergence rates performs substantially differently on diverse optimization tasks. Theoretical classification of convergence rates then lacks its relevance in the context of the practical optimization. It is therefore desirable to formulate a novel classification framework relevant to the theoretical concept of convergence rates as well as to the practical optimization. This article introduces such classification framework. The proposed classification framework enables specification of optimization techniques and optimization tasks. It also underlies its inherent relationship to the convergence rates. Novel classification framework is applied to categorizing the tasks of optimizing polynomials and the problem of training multilayer perceptron neural networks.

A 50-Gbit/s demultiplexer IC module that uses 0.1-µm InAlAs/InGaAs/InP HEMTs is reported. The maximum error-free operation bit-rate of a fabricated module is 50 Gbit/s, and a wide phase margin of 170 degrees is obtained at 43 Gbit/s. 50-Gbit/s demultiplexing is the fastest performance of all packaged demultiplexer ICs yet reported.

We propose an agent-based grocery shopping system, which automates grocery shopping process. Agents gather grocery information from several store server agents and compare it with user's preferences of groceries and stores. The agents could adapt to user's up-to-date preferences by learning from his/her evaluation of previous shopping results. The proposed agent-based grocery shopping system is composed of three role agents: a user agent, an information management agent, and a store server agent. These role agents cooperate to buy the best groceries of user preference. A role agent is formed by an organization agent. The organization agent is responsible for organizing primitive agents and coordinating message delivery. A primitive agent executes a specific task/function using the accumulated knowledge to achieve user's goal. We have designed four agent communication protocols to facilitate cooperation between the user agent, the information management agent, and the store server agent. In this paper we focus on the protocols which support the user agent. By implementing a prototype of the agent-based grocery shopping system, we have verified that it is instrumental in purchasing the best groceries of user preference from several grocery stores. We have found that, (1) our agent-based grocery shopping system reduces the user's effort to buy groceries; (2) it saves user's time to buy groceries at a store; (3) it covers functional requirements of grocery shopping system from the user's viewpoint; (4) it supports the five stages of consumer buying behavior model.

This letter proposes a new detection method of human faces in gray scale image with cluttered background using a face template and elliptical structure of the human face. This proposed method can be applicable even in the cases that the face is much smaller than image size and several faces exist in one image, which is impossible in the existing one.

A novel adaptive algorithm based on pilot channel (PCA) for MMSE multiuser detection in downlink CDMA is proposed in this paper. This algorithm uses the information in pilot channel to compute the desired weight vector directly. Compared with conventional adaptive algorithms and blind algorithms, it does not require training sequences nor channel estimation. Analysis shows that the weight vector obtained by the PCA algorithm converges to the Wiener solution globally and its computational complexity is O(N2). Simulation results show that the PCA algorithm can adapt rapidly to the changing environment. The steady state performance can be enhanced by increasing the transmitted power in pilot channel, but is worse than that of conventional recursive least-square (RLS) algorithm in decision-directed mode. Also, performance of the adaptive MMSE detector is much better than that of conventional RAKE receiver.

We propose a new interference cancellation technique using reference signals for optical synchronous code-division multiple-access (CDMA) systems. In the proposed system, we use the signature code sequences composed of the group information codes and the modified prime code sequences. The group information codes are added in the forefront of the signature code sequences to estimate the amount of the multiple access interference (MAI). The proposed cancellation scheme can be realized with the simpler structure than the conventional canceller using the time division reference signal, because it can reduce the number of optical correlators from P to two where P is the prime number. We analyze the performance of the proposed system with considering the effects of the MAI, avalanche photodiode (APD) noise, and thermal noise. We show that the proposed canceller has better bit error probability than the conventional canceller.

In DS-CDMA (including W-CDMA), a received signal can be resolved into multiple paths to be Rake combined. An important design problem of the Rake receiver is how to accurately search the paths with a sufficiently large signal-to-interference plus background noise power ratio (SIR). This paper investigates the performance of a coherent Rake receiver using pilot symbol-assisted channel estimation with fast transmit power control, and thereby optimizes three key parameters: the total averaging period, Tavg, consisting of a combination of coherent summation and power summation; each period of the summations for measuring the average power delay profile; and path-selection threshold M from the generated power delay profile. We used a path search algorithm, which searches the paths that have M times greater average signal power than the interference plus background noise power measured in the average power delay profile generated using time-multiplexed pilot symbols. It was clarified by both simulation and laboratory experiments that when M = 4, Tavg = 50-100 msec, and the number of slots for coherent accumulation R = 2, the required average transmit Eb/N0 for obtaining the average BER of 10-3 is almost minimized with and without antenna diversity for both ITU-R Vehicular-B and average equal power L-path delay profile model, in which each path suffered independent Rayleigh fading. The paper also shows that based on the field experiments, the path search algorithm with optimized path-selection parameters is robust against actual dynamic changes in the power delay profile shape.

In CDMA mobile system, network connection is constructed with orthogonal spreading codes assigned to each user in order to distinguish one from the other. The number of distinguishable codes and the process speed are different according to the orthogonal spreading factors which, in another literature, can be described as the tree structure. In this paper, we investigate methods to improve the quality of services (QoS) of communication, by changing the spreading factors of orthogonal spreading codes according to the number of users. We propose the effective method to reconstruct the tree structure of orthogonal spreading codes for supporting various data rates transmission in DS-CDMA mobile system. We compare spreading factors with and without the reconstruction and evaluate the effectiveness of the reconstruction method.

In this paper, we discuss the access control in multimedia CDMA ALOHA protocol. We introduce a new algorithm for the access control based on Modified Channel Load Sensing Protocol (MCLSP) in an integrated voice and two different classes of data users, high bit rate and low bit rate, exist in a multi-code CDMA Slotted ALOHA system. With our new algorithm, we show that the throughput of high bit rate data users, as well as, the total throughput of the data medium can be optimized and take a maximum value even at high values of offered loads. We also investigate the performance when voice activity detection (VAD) is considered in voice transmission.

In this paper, a novel chaos circuit with long working-life is proposed. The proposed circuit consists of NMOS-coupled discrete-time chaotic cell circuits. By employing chaos synchronization phenomenon, the proposed circuit can achieve long working-life. Since the proposed circuit is less susceptible to breakdown, the rate of the acceptable product for chaos IC can be improved. Furthermore, thanks to the coupling by using NMOSFET's, the loss of the connection line between chaotic cell circuits can be controlled electronically. Therefore, the proposed system designed by using switched-current (SI) techniques is useful as an experimental tool to analyze chaos synchronization phenomena. The validity of the proposed circuits is confirmed by computer simulations and experiments.

We propose a unique word detection scheme having the correction of the phase ambiguity that remains in the output of a carrier recovery circuit for QPSK systems. The performance of the proposed scheme is analyzed by obtaining the probability generating function (PGF) for the output of the detector. The PGF is obtained from the z-transform of the probability density function (PDF) for each matched symbol with the reference symbol and by using the characteristics at this time that the random variables for matched symbols are independent and identically distributed. Then the total PGF for a unique word is obtained from powering the PGF for the individual symbol. From the total PGF, the length of a UW and the threshold value for detection can be obtained with a detection probability defined in a required system specification.

Despite their attractive properties, networked virtual environments (net-VEs) are notoriously difficult to design, implement and test due to the concurrency, real-time and networking features in these systems. The current practice for net-VE design is basically trial and error, empirical, and totally lacks formal methods. This paper proposes to apply a Petri net formal modeling technique to a net-VE: NICE (Narrative Immersive Constructionist/Collaborative Environment), predict the net-VE performance based on simulation, and improve the net-VE performance. NICE is essentially a network of collaborative virtual reality systems called CAVE-(CAVE Automatic Virtual Environment). First, we present extended fuzzy-timing Petri net models of both CAVE and NICE. Then, by using these models and Design/CPN as the simulation tool, we have conducted various simulations to study real-time behavior, network effects and performance (latencies and jitters) of NICE. Our simulation results are consistent with experimental data.

Most distributed systems are based on either the C/S (Client/Server) model or the P-to-P (Peer to Peer) model. In C/S based distributed systems, a client invokes a server and waits for the server reply. Because of this sequential nature, C/S based distributed systems can be implemented by the RPC (Remote Procedure Call) scheme. Most tools for developing distributed objects are based on the RPC scheme. Whereas, in P-to-P based distributed systems, each distributed objects work concurrently, by exchanging asynchronous messages, without waiting for the receiver's action. To implement these P-to-P distributed systems, the RPC scheme is not powerful enough, and the active object model using asynchronous messages is suitable. This paper explains the pure Java library CAPE for developing P-to-P based distributed active object systems.

A constant amplitude transmission scheme for multicode wideband CDMA systems is proposed. Multicode wideband CDMA systems result in large amplitude fluctuation because the multicode signal is the sum of constituent code channel signals. This large amplitude fluctuation brings out large non-linear distortion and then, if unaccounted, can significantly degrade the bit error rate (BER) performance. Constant amplitude transmission, achieved by using a Walsh code and parity generator, is proposed to combat the large amplitude fluctuation and reduce the peak-to-average power ratio (PAPR). Unlike other constant amplitude transmission scheme, the proposed scheme does not use a redundant code channel. Computer simulation results show that the proposed scheme improves BER performance significantly and that the proposed scheme is extremely effective to the non-linear distortion of high power amplifier (HPA).

A hybrid system in which mobile terminals (MTs) themselves select whether to communicate directly or via base stations (BSs) from communication conditions, "cellularad-hoc united communication system," has been proposed by the authors. It has been confirmed to have effective channel usage and battery consumption, especially for MTs which tend to communicate with partners which are close together, such as operational mobile robots. In this paper, the hybrid system is examined with respect to handoff rate. This hybrid system uses two modes, a cellular mode and an ad-hoc mode. The former mode is for communication using BSs and the latter is for direct communication. Thus, there will be two kinds of handoffs. One is the ordinary one between BSs and the other is between the two modes. Such a system may suffer from frequent handoffs. Thus the handoff rate of the system was examined. However, by the addition of a simple hysteresis characteristic, the handoff rate was held down closer to that of a pure cellular system in a multipath environment.

This paper investigates the influence of the number of antennas, the angle difference between the direction of arrival (DOA) of the desired signal and those of interfering signals, and the antenna arrangement on the BER performance of the coherent adaptive antenna array diversity (CAAAD) receiver in the wideband DS-CDMA (W-CDMA) reverse link. Experiments assuming high-rate interfering users were conducted in a radio anechoic room using a three-sectored antenna with a 120-degree beam (maximum number of antennas was six). The experimental results showed that the degree to which the interference was suppressed from high-rate users of the CAAAD receiver was significantly increased by increasing the number of antennas, especially when the number of interfering users was larger than degree of freedom of the CAAAD. It was also verified that although the BER performance of the CAAAD receiver significantly improved compared to a single sectored antenna, the improvement remarkably decreased when the DOA difference between the desired signal and interfering signals was within approximately 10-15 degrees irrespective of the number of antennas. Finally, we show that the BER performance difference between the linear and conformal arrangements was small when using the three-sectored antenna.

A new timing estimation algorithm for asynchronous DS/CDMA multiuser communication system is proposed in this paper. The algorithm is based on the Minimum Variance Distortionless Response (MVDR) beamforming technique that minimizes the beamformer's output power with the constraint that only the signal with exact timing is distortionlessly passed. Exploiting the characteristics that the MVDR beamformer's output power is severely degraded according to erroneous timing estimation, we develop an efficient algorithm to estimate each user's timing by scanning the beamformer's output power variation. Compared to the maximum a posteriori (MAP) or maximum likelihood (ML) based multiuser timing estimator, the complexity is extensively reduced by separating the multi-dimensional optimization problem into several one-dimensional optimization problems. Furthermore, the algorithm is computationally feasible than the subspace-based timing estimator since no eigendecomposition (EVD) is required. Moreover, the proposed algorithm is near-far resistant since the MVDR beamformer is inherently energy independent to the interferers.

We described short time span idiotype immune network reactions by rigorous mathematical equations. For each idiotype, we described the temporal changes in concentration of (1) single bound antibody, one of its two Fab arms has bound to the complemental receptor site on the B cell. (2) double bound antibody, both of its two Fab arms have bound to the complemental receptor sites on the B cell and (3) an immune complex which is a product of reaction among the antibodies. Stimulation and secretion processes of an antibody in the idiotype network were described by non linear differential equations characterized by the magnitude of cross-linking of the complemental antibody and B cell receptor. The affinity between the mutually complemental antibody and receptor was described by an weighted affinity matrix. The activating process was expressed by an exponential function with threshold. The rate constant for the linkage of the second Fab arm of an antibody was induced from the molecular diffusion process that was modified by the Coulomb repulsive force. By using reported experimental data, we integrated 60 non linear differential equations for the idiotype immune network to obtain the temporal behavior of concentrations of the species in hour span. The concentrations of the idiotype antibody and immune complex changed synchronously. The influence of a change in one rate constant extended to all the members of the idiotype network. The concentrations of the single bound antibody, double bound antibody and immune complex oscillated as functions of the concentration of the free antibody particularly at its low concentration. By comparing to the reported experimental data, the present computational approach seems to realize biological immune network reactions.