In IP-based mobile networks, a few of mobility agents (e.g., home agent, foreign agent, etc.) are used for mobility management. Recently, Hierarchical Mobile IPv6 (HMIPv6) was proposed to reduce signaling overhead and handoff latency occurred in Mobile IPv6. In HMIPv6, a new mobility agent, called mobility anchor point (MAP), is deployed in order to handle binding update procedures locally. However, the MAP can be a single point of performance bottleneck when there are a lot of mobile node (MNs) performing frequent local movements. This is because the MAP takes binding update procedures as well as data packet tunneling. Therefore, it is required to control the number of MNs serviced by a single MAP. In this paper, we propose a load control scheme at the MAP utilizing an admission control algorithm. We name the proposed load control scheme proactive load control scheme to distinct from the existing load control schemes in cellular networks. In terms of admission control, we use the cutoff priority scheme. We develop Markov chain models for the proactive load control scheme and evaluate the ongoing MN dropping and the new MN blocking probabilities. As a result, the proactive load control scheme can reduce the ongoing MN dropping probability while keeping the new MN blocking probability to a reasonable level.

We have determined the thickness and optical constants (refractive index and extinction coefficient) of each layer in the multi-layer organic light emitting diode (OLED) devices based on phosphorescent platinum octaethyl porphine (PtOEP) using a phase modulated spectroscopic ellipsometer. The thickness of each layer estimated from the ellipsometric measurement is different from the thickness measured with quartz oscillator during the evaporation of organic materials. The deviation of total multi-layer thickness is about 5%, while the deviation in each of N, N'-bis(1-naphtyl)-N, N'-diphenyl-1,1'-biphenyl-4,4'-diamine (α-NPD) and aluminum tris 8-hydroxyquinoline (Alq3) layers is about 20-25%. Additionally the spectra of refractive index and extinction coefficient of Alq3 and α-NPD layers are different from those that are measured using the single layer films. These results are understood by penetration of organic material from the neighboring layers in the multi-layer structure devices.

The IEEE 802.11 protocol is one of the most important standards for Wireless Local Area Networks. The primary MAC protocol of 802.11 is the distributed coordination function (DCF), which is Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) with binary slotted exponential backoff scheme. The basic access and the RTS/CTS access mechanisms are the two channel access methods defined in DCF. In real work environments, the common channel access method of 802.11 is the coexistence of the above two mechanisms, i.e., packets longer than a given threshold RTSthreshold are transmitted according to the RTS/CTS mechanism, otherwise, they are transmitted by means of basic mechanism. The common mechanism is called as hybrid access mechanism in this paper. Few analytical models have been proposed to evaluate the hybrid access mechanism up to now. The necessary condition which enables the hybrid mechanism to work is that the packets must be variable. But, almost all analytical models proposed for 802.11 DCF assume that the packet size is fix, so they can not study the hybrid access method. In this paper, we propose a detailed analytical model to evaluate the saturation performance of the hybrid access mechanism, in the assumption that the packet lengthes are sampled from a general distribution function f(x). Both the throughput and the delay performances are concerned. Our model is validated by extensive simulations. By means of the proposed model, we compare the performances of the above three mechanisms, i.e., basic, RTS/CTS and hybrid, under different network scenarios. Numerical results show that the hybrid access mechanism is the best choice in almost all scenarios.

A switched nonlinear system is considered, and the interval between two consecutive switchings is assumed to be greater than a value called "the dwell time." When switching among nonlinear systems, using a constant dwell time generally fails to lead to stability. In this letter, a state dependent dwell time function with convergence guarantees is presented for discrete-time stable nonlinear systems.

The Fourier integrals are treated as a rigorous extension of the Fourier series expansion. The reward for this is that so called, in the Fourier integrals, singular functions that are not absolutely integrable, e.g., trigonometric functions can be discussed within a field of ordinary function giving a foundation for the delta function as distribution.

In this paper, we introduce a new technology to extract the unique features from an iris image, which uses scale-space filtering. Resulting iris code can be used to develop a system for rapid and automatic human identification with high reliability and confidence levels. First, an iris part is separated from the whole image and the radius and center of the iris are evaluated. Next, the regions that have a high possibility of being noise are discriminated and the features presented in the highly detailed pattern are then extracted. In order to conserve the original signal while minimizing the effect of noise, scale-space filtering is applied. Experiments are performed using a set of 272 iris images taken from 18 persons. Test results show that the iris feature patterns of different persons are clearly discriminated from those of the same person.

It is important to predict serious deterioration of telecommunication quality. This paper investigates predicting such serious events by analyzing only a "short" period (i.e., a "small" amount) of teletraffic data. To achieve this end, this paper presents a method for analyzing the tail distributions of teletraffic state variables, because tail distributions are suitable for representing serious events. This method is based on Extreme Value Theory (EVT), which provides a firm theoretical foundation for the analysis. To be more precise, in this paper, we use throughput data measured on an actual network during daily busy hours for 15 minutes, and use its first 10 seconds (known data) to analyze the tail distribution. Then, we evaluate how well the obtained tail distribution can predict the tail distribution of the remaining 890 seconds (unknown data). The results indicate that the obtained tail distribution based on EVT by analyzing the small amount of known data can predict the tail distribution of unknown data much better than methods based on empirical or log-normal distributions. Furthermore, we apply the obtained tail distribution to predict the peak throughput in unknown data. The results of this paper enable us to predict serious deterioration events with lower measurement cost.

The luminance of about 10,000 cd/m2 at an applied voltage of 9.2 V and the external emission efficiency 5.5 cd/A at an injection current density of 50 mA/cm2 have been obtained from an organic light emitting diode (OLED) using starburst molecule doped with 5,6,11,12-tetraphenylnaphthacene fabricated by wet-processing. We demonstrate that the OLEDs fabricated by wet-processing can be applied to fields of short range optical communication as the electro-optical conversion device for transmitting the signals of moving picture.

To implement a fast and reliable question-answering system in Korean, we propose a two-pass answer indexer using co-occurrence information between answer candidates and adjacent content words. The two-pass indexer scans documents twice for obtaining local scores and global scores. Then, the two-pass indexer calculates the degrees of association between answer candidates and co-occurring content words. Using this technique, the proposed QA system shortens the response time and enhances the precision.

In this paper, we consider a data mining problem for semi-structured data. Modeling semi-structured data as labeled ordered trees, we present an efficient algorithm for discovering frequent substructures from a large collection of semi-structured data. By extending the enumeration technique developed by Bayardo (SIGMOD'98) for discovering long itemsets, our algorithm scales almost linearly in the total size of maximal tree patterns contained in an input collection depending mildly on the size of the longest pattern. We also developed several pruning techniques that significantly speed-up the search. Experiments on Web data show that our algorithm runs efficiently on real-life datasets combined with proposed pruning techniques in the wide range of parameters.

The partial projection filter gives optimal signal restoration in the presence of both the signal space and the observation space noises. In this paper, the filter has been characterized from the point of view of its signal restoration and noise suppression capabilities. The filter is shown to suppress the noise component in the restored signal while retaining the signal component, thus maximizing the signal-to-noise ratio. Further, a digital implementation of the filter is presented in matrix form in contrast to its original operator based derivation, for practical applications.

This paper introduces the problem of n mobile agents that repeatedly visit all n nodes of a given network, subject to the constraint that no two agents can simultaneously occupy a node. This paper first presents a self-stabilizing phase-based protocol for a tree network on a synchronous model. The protocol realizes agent traversal with O(Δn) time where n is the number of nodes and Δ is the maximum degree of any vertex in the communication network. The phase-based protocol can also be applied to an asynchronous model and a ring network. This paper also presents a self-stabilizing link-alternator-based protocol with agent traversal time of O(Δn) for a tree network on an asynchronous model. The protocols are proved to be asymptotically optimal with respect to the agent traversal time.

Latch-based circuits have advantages for timing and are widely used for high-speed custom circuits. ASIC design flows, however, are based on circuits with flip-flops. This paper describes a new timing optimization algorithm by replacing the flip-flops in high-end ASICs by latches without changing the functionality of the circuits. Timing is optimized by using a fixed-phase retiming minimizing the impact of clock skew and jitter. A formal equivalence verification method that assures the logical correctness of the latch-replaced circuits is also proposed. Experimental results show that the optimization algorithm decreases the delay of benchmark circuits by as much as 17%.

CDN (Content Delivery Networks) improves end-user performance by replicating web contents on a group of geographically distributed servers. However, repeatedly keeping the entire replica of the original objects into many content servers consumes too much server resource. This problem becomes more serious for the large-sized objects such as streaming media, e.g. high quality video. In this paper, we therefore propose an efficient replication method for layered video streams in CDN, which can reduce user response delays and storage costs simultaneously. Based on an analytical formulation of the cooperative replication of layers and segments of each video stream, we derive a replication algorithm which solves next three problems quantitatively. (1) How many servers should be selected to replicate a given video stream? (2) For a single video stream, how many layers and segments should be stored in a given server? (3) After selecting a group of servers for each video stream, how do we allocate the replication priority (i.e. order) to each server? Simulation results verify that the proposed algorithm efficiently resolves the above problems and provides much better performance than conventional methods.

This paper proposes a novel dual-mode ring bandpass filter (BPF) using defect ground structure (DGS). The proposed filter provides wide stopband characteristic resulted from the bandgap characteristic of DGS for suppressing spurious response of the dual-mode ring BPF. The H shaped DGS cell is modeled as a parallel LC resonator and the equivalent circuit parameters are extracted. The relationship between bandgap characteristic and design parameters of DGS dimension is discussed and the bandgap characteristic of DGS on the filter performance is also investigated. The novel proposed filter has the frequency characteristics with a central frequency f0 = 7.7 GHz, a 3-dB bandwidth of 4.5% and wider stopband from 9 to 15.5 GHz at the level of -35 GHz. Measured results of experimental filter has good agreement with the theoretical simulation results.

Displaying a 3D geometric model of a user in real time is an advantage for a telecommunication system because depth information is useful for nonverbal communication such as finger-pointing and gesturing that contain 3D information. However, the range image acquired by a rangefinder suffers from errors due to image noises and distortions in depth measurement. On the other hand, a 2D image is free from such errors. In this paper, we propose a new method for a shared space communication system that combines the advantages of both 2D and 3D representations. A user is represented as a 3D geometric model in order to exchange nonverbal communication cues. A background is displayed as a 2D image to give the user adequate information about the environment of the remote site. Additionally, a high-resolution texture taken by a video camera is projected onto the 3D geometric model of the user. This is done because the low resolution of the image acquired by the rangefinder makes it difficult to exchange facial expressions. Furthermore, to fill in the data occluded by the user, old pixel values are used for the user area in the 2D background image. We have constructed a prototype of a high presence shared space communication system based on our method. Through a number of experiments, we have found that our method is more effective for telecommunication than a method with only a 2D or 3D representation.

This study aims to identify grammatical relations (GRs) in Korean sentences. The key task is to find the GRs in sentences in terms of such GR categories as subject, object, and adverbial. To overcome this problem, we are faced with the structural ambiguity and the grammatical relational ambiguity. We propose a statistical model, which resolves the grammatical relational ambiguity first, and then resolves structural ambiguity by using the probabilities of the GRs given noun phrases and verb phrases in sentences. The proposed model uses the characteristics of the Korean language such as distance, no-crossing and case property. We showed that consideration of such characteristics produces better results than without consideration by experiments. We attempt to enhance our system by estimating the probabilities of the proposed model with the Maximum Entropy (ME) model, and with Support Vector Machines (SVM) classifiers and we confirm that SVM classifiers improved the performance of our proposed model through experiments. Through an experiment with a tree and GR tagged corpus for training the model, we achieved an overall accuracy of 84.8%, 94.1%, and 84.8% in identifying subject, object, and adverbial relations in sentences, respectively.

We propose a practical blind channel identification algorithm based on the principal component analysis. The algorithm estimates (1) the channel order, (2) the noise variance, and then identifies (3) the channel impulse response, from the autocorrelation of the channel output signal without using the eigenvalue and singular-value decomposition. The special features of the proposed algorithm are (1) practical method to find the channel order and (2) reduction of computational complexity. Numerical examples show the effectiveness of the proposed algorithm.

In wide-area wireless access systems such as satellite communications systems and stratospheric platform systems, electric power supplies for radio communications are realized using solar photovoltaic cells and/or fuel cells. However, the on-board weight limits restrict the number of cells that can be equipped. In addition, the transmission power of such systems is limited taking account of issues and regulations on sharing the same frequency band with other systems. Hence, both the frequency band and electric power is limited, which are crucial radio resources for those systems. Although radio channel allocation methods taking account of the frequency constraint only or the power constraint only have been proposed, radio channel allocation methods taking account of both constraints simultaneously have been insufficiently studied. This paper proposes a radio channel allocation method that provides global optimum allocation results by utilizing the linear programming method. The proposed method has features such that the method first allocates radio channels in proportion to the traffic demand distributed over the service coverage area and then maximizes the total radio channels allocated to systems. Numerical results are presented for a stratospheric platform system that covers an area of Japan, as an example, to demonstrate that the proposed method optimally allocates radio channels taking account of both constraints while efficiently allocating excess resources. In addition, whether a system reaches either the frequency or power limit can be estimated, by investigating the radio channel allocation results. Furthermore, enhanced linear programming models based on a method aiming at practical use of the radio channel allocation results in operation are also introduced. The enhanced model is demonstrated to work effectively to avoid unbalanced radio channel allocations over geographical areas. The proposed method and linear programming models are useful not only for making pre-plans but also for determining the amount of necessary frequency and power resources in designing systems.

Loss compensation in a RF CMOS active inductor with using a capacitor is proposed. This simple compensation technique yields a negative conductance characteristic that can compensate for the constant internal loss of active devices. Simulation results show that the inductor obtains a maximum Q-value of 1.2E8, an inductance value in the range of 50 nH to 450 nH, and a 1.4E-6 Ω of minimum total equivalent loss in the range of 0.6 GHz to 1.3 GHz.