Browsing by Author "Lee, CH"

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A fast motion estimation algorithm based on the block sum pyramid
(1997-11-01)
Lee, CH
;
Chen, LH
;
資訊工程學系
;
Department of Computer Science
In this correspondence, a fast approach to motion estimation is presented. The algorithm uses the block sum pyramid to eliminate unnecessary search positions. It first constructs the sum pyramid structure of a block. Successive elimination is then performed hierarchically from the top level to the bottom level of the pyramid. Many search positions can be shipped from being considered as the best motion vector and, thus, the search complexity can be reduced. The algorithm can achieve the same estimation accuracy as the full search block matching algorithm with much lass computation time.
A fast motion estimation algorithm based on the block sum pyramid
(1997-11-01)
Lee, CH
;
Chen, LH
;
資訊工程學系
;
Department of Computer Science
In this correspondence, a fast approach to motion estimation is presented. The algorithm uses the block sum pyramid to eliminate unnecessary search positions. It first constructs the sum pyramid structure of a block. Successive elimination is then performed hierarchically from the top level to the bottom level of the pyramid. Many search positions can be shipped from being considered as the best motion vector and, thus, the search complexity can be reduced. The algorithm can achieve the same estimation accuracy as the full search block matching algorithm with much lass computation time.
A new interpolative reasoning method in sparse rule-based systems
(1998-01-01)
Hsiao, WH
;
Chen, SM
;
Lee, CH
;
資訊工程學系
;
Department of Computer Science
In [7], Yan et al. analyzed Koczy and Hirota's linear interpolative reasoning method presented in [2,3] and found that the reasoning consequences by their method sometimes become abnormal fuzzy sets. Thus, they pointed out that a new interpolative reasoning method will be needed which can guarantee that the interpolated conclusion will also be triangular-type for a triangular-type observation. In this paper, we extend the works of [2,3,7] to present a new interpolative reasoning method to deal with fuzzy reasoning in sparse rule-based systems. The proposed method can overcome the drawback of Koczy and Hirota's method described in [7]. It can guarantee that the statement "If fuzzy rules A(1) double right arrow B-1, A(2) double right arrow B-2, and the observation A* are defined by triangular membership functions, the interpolated conclusion B* will also be triangular-type" holds. (C) 1998 Elsevier Science B.V.
A new interpolative reasoning method in sparse rule-based systems
(1998-01-01)
Hsiao, WH
;
Chen, SM
;
Lee, CH
;
資訊工程學系
;
Department of Computer Science
In [7], Yan et al. analyzed Koczy and Hirota's linear interpolative reasoning method presented in [2,3] and found that the reasoning consequences by their method sometimes become abnormal fuzzy sets. Thus, they pointed out that a new interpolative reasoning method will be needed which can guarantee that the interpolated conclusion will also be triangular-type for a triangular-type observation. In this paper, we extend the works of [2,3,7] to present a new interpolative reasoning method to deal with fuzzy reasoning in sparse rule-based systems. The proposed method can overcome the drawback of Koczy and Hirota's method described in [7]. It can guarantee that the statement "If fuzzy rules A(1) double right arrow B-1, A(2) double right arrow B-2, and the observation A* are defined by triangular membership functions, the interpolated conclusion B* will also be triangular-type" holds. (C) 1998 Elsevier Science B.V.
A new method for fuzzy information retrieval based on fuzzy hierarchical clustering and fuzzy inference techniques
(2005-04-01)
Horng, YJ
;
Chen, SM
;
Chang, YC
;
Lee, CH
;
資訊工程學系
In this paper, we extend the work of Kraft et al to present a new method for fuzzy information retrieval based on fuzzy hierarchical clustering and fuzzy inference techniques. First, we present a fuzzy agglomerative hierarchical clustering algorithm for clustering documents and to get the document cluster centers of document clusters. Then, we present a method to construct fuzzy logic rules based on the document clusters and their document cluster centers. Finally, we apply the constructed fuzzy logic rules to modify the user's query for query expansion and to guide the information retrieval system to retrieve documents relevant to the user's request. The fuzzy logic rules can represent three kinds of fuzzy relationships (i.e., fuzzy positive association relationship, fuzzy specialization relationship and fuzzy generalization relationship) between index terms. The proposed fuzzy information retrieval method is more flexible and more intelligent than the existing methods due to the fact that it can expand users' queries for fuzzy information retrieval in a more effective manner.
A new method for generating fuzzy rules from numerical data for handling classification problems
(2001-08-01)
Chen, SM
;
Lee, SH
;
Lee, CH
;
資訊工程學系
;
Department of Computer Science
Fuzzy classification is one of the important applications of fuzzy logic. Fuzzy classification Systems are capable of handling perceptual uncertainties, such as the vagueness and ambiguity involved in classification problems. The most important task to accomplish a fuzzy classification system is to rnd a set of fuzzy rules suitable for a specific classification problem. In this article, we present a new method for generating fuzzy rules from numerical data for handling fuzzy classification problems based on the fuzzy subsethood values between decisions to be made and terms of attributes by using the level threshold value alpha and the applicability threshold value beta, where alpha is an element of [0, 1] and beta is an element of [0, 1]. We apply the proposed method to deal with the "Saturday Morning Problem,'' where the proposed method has a higher classification accuracy rate and generates fewer fuzzy rules than the existing methods.
A novel application of the phone card and its authentication in mobile communications
(1999-07-01)
Lee, CH
;
Hwang, MS
;
Yang, WP
;
資訊工程學系
;
Department of Computer Science
The Subscriber Identity Module (SIM) is conventionally used in wireless communication systems. However, several limitations involving SIM significantly reduce public access in wireless communications. This study examined the feasibility of using public telephone cards in wireless communications. This novel application retains the merits of SIM. Among the relevent issues addressed are location tracking of the user, authentication of the phone card, and the billing scheme. Moreover, two implementations of phone card authentication are presented.
A TCP-physical cross-layer congestion control mechanism for the multirate WCDMA system using explicit rate change notification
(2005)
Wang, LC
;
Lee, CH
;
電信工程研究所
;
Institute of Communications Engineering
In this paper we propose an explicit rate change notification (ERCN) mechanism to improve the transmission control protocol (TCP) performance in the wideband code-division multiple-access (WCDMA) system. The base station in the WCDMA system dynamically adapts transmission data rates according to the wireless channel condition. Therefore, if the TCP sender can not be notified about the rate change in the wireless channel, congestion in the radio link between the base station and mobile terminal occurs quite often. In this work, we first derive the relation between the bandwidth in the physical layer and the maximum queue size in the TCP layer and then obtain a closed-form expression for the average throughput in terms of average queue size, queue delay and channel capacity. We validate results by simulations. The analytical formula can facilitate the design of a cross-layer TCP-physical congestion control mechanism for the rate adaptive wireless system.
Adaptive tracking control of nonholonomic mobile robots by computed torque
(2003-07-01)
Lee, TC
;
Lee, CH
;
Teng, CC
;
電控工程研究所
;
Institute of Electrical and Control Engineering
A computed torque controller for a dynamic model of nonholonomic mobile robots with bounded external disturbance is proposed to treat the adaptive tracking control problem using the separated design method. A velocity controller is first designed for the kinematic steering system to make the tracking error approaching to zero asympotically. Then, a computed torque controller is designed such that the true mobile robot velocity converges to the desired velocity controller. In each step, the controllers are designed independently, and this will simplify the design of controllers. A novel stability analysis involving the estimation of some differential inequalities is also given to guarantee the stability of the closed-loop system. Moreover, the regulation problem and the tracking problem will be treated using the proposed controller. In particular, the mobile robots can globally follow any path such as a straight-line, a circle and the path approaching to the origin. Furthermore, the problems of back-into-garage parking and the parallel parking problem can also be solved using the proposed controller. Some interesting simulation results are given to illustrate the effectiveness of the proposed tracking control law.
An accurate method for approximating the interference statistics of DS/CDMA cellular systems with power control over frequency-selective fading channels
(2005-01-01)
Lee, CH
;
Chang, CJ
;
交大名義發表
;
National Chiao Tung University
This letter proposes an approximation method by characteristic function (AM-CF) method to approximate the distribution of interference in DS/CDMA cellular systems. This method considers the effects of frequency-selective multipath fading; it also assumes perfect power control and a rectangular/sinc chip waveform. the AM-CF method can yield results that fit the Monte Carlo simulation results more accurately than the conventional standard Gaussian approximation method.
An adaptive digital image watermarking technique for copyright protection
(1999-11-01)
Lee, CH
;
Lee, YK
;
資訊工程學系
;
Department of Computer Science
An adaptive digital image watemarking technique is proposed in this paper. The proposed method exploits the sensitivity of human eyes to adaptively embed a visually recognizable watermark in an image without affecting the perceptual quality of the underlying host image. In addition, the watermark will still be present if some lossy image processing operations such as low-pass filtering, median filtering, resampling, requantization, and lossy JPEG image compression are applied to the watermarked image. Experimental results show the effectiveness of the proposed watermarking method.
An Equal-Strength/Power-Suspended power control scheme for a DS/CDMA cellular system
(2000)
Lee, CH
;
Chang, CJ
;
電信工程研究所
;
Institute of Communications Engineering
The paper proposes a closed-loop equal-strength/power-suspended power control scheme for uplinks in a DS/CDMA cellular system. In this scheme, MS (mobile station) suspends ifs transmission as the short-term channel fading is less than a preset threshold; otherwise, MS transmits with power adapting to combat the channel fading so that the received signal power level is constant. We analyze this power control schemes and obtain performance measures such as the system capacity total transmission rate. and MSs power consumption. Numerical results show that the proposed equal-strength/power-suspended power control scheme has the best performance, compared with other closed-loop power control schemes such as the equal-strength power control scheme (also known as perfect power control), the equal-strength/power-limited power control scheme, and the equal-strength/power-limited+rate-adapted power control scheme.
Automatic Chinese unknown word extraction using small-corpus-based method
(2003)
Chang, TH
;
Lee, CH
;
資訊工程學系
;
Department of Computer Science
Chinese unknown word extraction is an important problem for Chinese language processing. There are troublesome difficulties in the problem. First, almost any Chinese character can either represent a word or be a part of other words. Secondly, there is no blank between Chinese words for identifying the boundaries. Although some approaches have been proposed, there are some drawbacks in these methods. In this paper, we present and develop a method to extract Chinese unknown words more efficiently and precisely. It retains efficiency and accuracy even though the size of document set is small for training. It can also extract the unknown words occur rarely. Based on these advantages, it is very practical for real applications.
Automatically constructing multi-relationship fuzzy concept networks for document retrieval
(2003-04-01)
Horng, YJ
;
Chen, SM
;
Lee, CH
;
資訊工程學系
;
Department of Computer Science
Although the knowledge bases incorporated in existing information retrieval systems can enhance retrieval effectiveness, many of them are built by domain experts. It is obvious that the construction of such knowledge bases requires a large amount of human effort. In this paper, an intelligent fuzzy information retrieval system with an automatically constructed knowledge base is presented; the knowledge base is represented by a multi-relationship fuzzy concept network. The multi-relationship fuzzy concept network can describe four kinds of context-independent and context-dependent fuzzy relationships, i.e., "fuzzy positive association" relationship, "fuzzy negative association" relationship, "fuzzy generalization" relationship, and "fuzzy specialization" relationship between concepts. The users of the fuzzy information retrieval system can submit a fuzzy contextual query which specifies the search context in the query formula. The fuzzy information retrieval system retrieves documents whose contents are relevant to the user's query by some kinds of fuzzy relationships for the specified search context of the user's query. The proposed fuzzy information retrieval method is more intelligent and more flexible than the existing methods due to the fact that it can construct multi-relationship fuzzy concept networks automatically and it can provide contextual search capability to allow the users to specify fuzzy contextual queries in a more intelligent and flexible manner.
Automatically constructing multi-relationship fuzzy concept networks in fuzzy information retrieval systems
(2001)
Horng, YJ
;
Chen, SM
;
Lee, CH
;
資訊工程學系
;
Department of Computer Science
In this paper, an intelligent fuzzy information retrieval system with an automatically constructed knowledge base is presented. The knowledge base is represented by a multi-relationship fuzzy concept network that can depict the relationships and their associating relevance degrees between concepts clearly. Based on the multi-relationship fuzzy concept network architecture, the users of the fuzzy information retrieval system can submit a fuzzy contextual query that specifies; the search context in the query formula. The fuzzy information retrieval system retrieves documents whose contents are relevant to the user's query by some required relationships beneath a specified search context The proposed fuzzy information retrieval method is more intelligent and more flexible than the existing methods since it can automatically construct knowledge bases (i.e, multi-relationship fuzzy concept networks) and it provides contextual search capability that allows users to specify fuzzy contextual queries in a more flexible manner.
Calculation of PID controller parameters by using a fuzzy neural network
(2003-07-01)
Lee, CH
;
Teng, CC
;
電控工程研究所
;
Institute of Electrical and Control Engineering
In this paper, we use the fuzzy neural network (FNN) to develop a formula for designing the proportional-integral-derivative (PID) controller. This PID controller satisfies the criteria of minimum integrated absolute error (IAE) and maximum of sensitivity (M-s). The FNN system is used to identify the relationship between plant model and controller parameters based, on IAE, and M-s. To derive the tuning rule, the dominant pole assignment method is a applied. to simplify our optimization processes. Therefore, the FNN system is used to automatically tune the PID controller for different system parameters so that neither theoretical methods not numerical methods need be used. Moreover; the FNN-based formula can modify the controller to meet our specification when the system model changes. A simulation result for applying to the motor position control problem is given to demonstrate the effectiveness of our approach. (C) 2003 ISA-The Instrumentation, Systems, and Automation Society.
Document retrieval using fuzzy-valued concept networks
(2001-02-01)
Chen, SM
;
Horng, YJ
;
Lee, CH
;
資訊工程學系
;
Department of Computer Science
This paper presents a new method for document retrieval using fuzzy-valued concept networks, where the relevant degrees between the concepts in a fuzzy-valued concept network are represented by arbitrary shapes of fuzzy numbers. There are two kinds of relevant relationships between any two concepts in a fuzzy-valued concept network, i.e., fuzzy positive association and fuzzy negative association. The relevant matrices and the relationship matrices are used to model the fuzzy-valued concept network. The elements in a relevant matrix represent the relevant degrees between concepts. The elements in a relationship matrix represent the relevant relationships between concepts. Furthermore, we also allow users' queries to be represented by arbitrary shapes of fuzzy numbers and to use fuzzy positive association relationship and fuzzy negative association relationship for formulating their queries for increasing the flexibility of fuzzy information retrieval systems. We also present an information retrieval method in the Internet environment based on the network-type fuzzy-valued concept network architecture.
Enhanced privacy and authentication for the global system for mobile communications
(1999)
Lee, CH
;
Hwang, MS
;
Yang, WP
;
資訊工程學系
;
Department of Computer Science
The Global System for Mobile Communications (GSM) is widely recognized as the modern digital mobile network architecture. Increasing market demands point toward the relevancy of security-related issues in communications. The security requirements of mobile communications for the mobile users include: (1) the authentication of the mobile user and Visitor Location Register/Home Location Register; (2) the data confidentiality between mobile station and Visitor Location Register, and the data confidentiality between Visitor Location Register and Visitor Location Register/Home Location Register (VLR/HLR); (3) the location privacy of mobile user. However, GSM does not provide enough security functions to meet these requirements. We propose three improved methods to enhance the security, to reduce the storage space, to eliminate the sensitive information stored in VLR, and consequently to improve the performance of the system. Proposed methods include an improved authentication protocol for the mobile station, a data confidentiality protocol, and a location privacy protocol. The merit of the proposed methods is to improve but not to alter the existing architecture of the system. Furthermore, this study also performs computational and capacity analyses to evaluate the original GSM system and proposed approaches on a comparative basis.
Formation of D(-) centers in GaAs/AlGaAs quantum wells
(1998-06-01)
Lee, CH
;
Chang, YH
;
Lin, HH
;
Lee, CP
;
電子工程學系及電子研究所
Three different experiments were employed to study the behaviors of neutral (D(0)) and negatively charged donors (D(-)) in doped GaAs/AlGaAs multiple quantum wells. The existence of the D(-) centers in such structures were demonstrated, and its optical properties were investigated. The spectral responses of such systems under different experimental conditions, such as different barrier doping concentration, different temperature, and different exposure to light illumination were studied. A potential fluctuation model was proposed to explain the experimental results.
Formation of D- centers in GaAs/AlGaAs quantum wells
(1998-06-01)
Lee, CH
;
Chang, YH
;
Lin, HH
;
Lee, CP
;
電子工程學系及電子研究所
Three different experiments were employed to study the behaviors of neutral (D-0) and negatively charged donors (D-) in doped GaAs/AlGaAs multiple quantum wells. The existence of the D- centers in such structures were demonstrated, and its optical properties were investigated. The spectral responses of such systems under different experimental conditions, such as different barrier doping concentration, different temperature, and different exposure to light illumination were studied. A potential fluctuation model was proposed to explain the experimental results.