Browsing by Author "Wang, YC"

Now showing 1 - 14 of 14

A fair scheduling algorithm with traffic classification for wireless networks
(2005-06-16)
Wang, YC
;
Ye, SR
;
Tseng, YC
;
資訊工程學系
;
Department of Computer Science
Wireless channels are characterized by more serious bursty and location-dependent errors. Many packet scheduling algorithms have been proposed for wireless networks to guarantee fairness and delay bounds. However, most existing schemes do not consider the difference of traffic natures among packet flows. This will cause the delay-weight coupling problem. In particular, serious queuing delays may be incurred for real-time flows. To resolve this problem, we propose a traffic-dependent wireless fair queuing (TD-FQ) algorithm that takes traffic types of flows into consideration when scheduling packets. The proposed TD-FQ algorithm not only alleviates queuing delay of real-time flows, but also guarantees bounded delays and fairness for all flows. (c) 2004 Elsevier B.V. All rights reserved.
A jamming-based MAC protocol for wireless multihop ad hoc networks
(2003)
Ye, SR
;
Wang, YC
;
Tseng, YC
;
資訊工程學系
;
Department of Computer Science
One critical issue in multihop ad hoc networks is the medium access control (MAC). The IEEE 802.11 MAC protocol is originally designed for fully connected, one-hop ad hoc networks but not for multihop ad hoc networks. In addition to the well known hidden-terminal problem, we found that IEEE 802.11 also suffers from an erroneous reservation problem which occurs when RTS-CTS exchange fails but the channel is incorrectly reserved. In this paper, we propose a jamming-based MAC (JMAC) protocol that is not only free from both hidden-terminal and the erroneous reservation problems but also allows more concurrent transmission/reception activities for stations within each other's transmission range. The idea behind the JMAC is to separate source stations' traffic from destination stations' traffic into different channels (i.e., dividing the shared medium into two channels), and explicitly signal the channel status by jamming the channels. Simulation results show that the JMAC can provide higher channel utilization when system is in high traffic load and the frame size is medium or large.
A jamming-based MAC protocol to improve the performance of wireless multihop ad-hoc networks
(2004-02-01)
Ye, SR
;
Wang, YC
;
Tseng, YC
;
資訊工程學系
;
Department of Computer Science
One critical issue in multihop ad-hoc networks is the medium access control (MAC). The IEEE 802.11 MAC protocol is originally designed for fully connected, one-hop ad-hoc networks but not for multihop ad-hoc networks. In addition to the well known hidden-terminal problem, we found that IEEE 802.11 also suffers from an erroneous reservation problem which occurs when RTS-CTS exchange fails but the channel is incorrectly reserved. In this paper, we propose a jamming-based MAC (JMAC) protocol that is not only free from both the hidden-terminal and the erroneous reservation problems but also allows more concurrent transmission/receipt activities for stations within each other's transmission range. The idea behind the JMAC is to separate source stations' traffic from destination stations' traffic into different channels (i.e. dividing the shared medium into two channels), and explicitly signal the channel status by jamming the channels. Simulation results show that although the channel division incurs some cost, the advantages of being free from the erroneous reservation and the hidden-terminal problems, and the benefits of more concurrent transmissions will compensate the cost and provide higher channel utilization when data frame size is median or large. Copyright (C) 2004 John Wiley Sons, Ltd.
Direct adaptive iterative learning control of nonlinear systems using an output-recurrent fuzzy neural network
(2004-06-01)
Wang, YC
;
Chien, CJ
;
Teng, CC
;
電控工程研究所
;
Institute of Electrical and Control Engineering
In this paper, a direct adaptive iterative learning control (DAILC) based on a new output-recurrent fuzzy neural network (ORFNN) is presented for a class of repeatable nonlinear systems with unknown nonlinearities and variable initial resetting errors. In order to overcome the design difficulty due to initial state errors at the beginning of each iteration, a concept of time-varying boundary layer is employed to construct an error equation. The learning controller is then designed by using the given ORFNN to approximate an optimal equivalent controller. Some auxiliary control components are applied to eliminate approximation error and ensure learning convergence. Since the optimal ORFNN parameters for a best approximation are generally unavailable, an adaptive algorithm with projection mechanism is derived to update all the consequent, premise, and recurrent parameters during iteration processes. Only one network is required to design the ORFNN-based DAILC and the plant nonlinearities, especially the nonlinear input gain, are allowed to be totally unknown. Based on a Lyapunov-like analysis, we show that all adjustable parameters and internal signals remain bounded for all iterations. Furthermore, the norm of state tracking error vector will asymptotically converge to a tunable residual set as iteration goes to infinity. Finally, iterative learning control of two nonlinear systems, inverted pendulum system and Chua's chaotic circuit, are performed to verify the tracking performance of the proposed learning scheme.
Dopant profile engineering by near-infrared femtosecond laser activation
(2006-03-27)
Wang, YC
;
Pan, CL
;
Shieh, JM
;
Dai, BT
;
光電工程學系
Femtosecond laser annealing (FLA) was employed for activation of phosphorus (P)- and boron (B)-implanted silicons with negligible dopant diffusion. Preamorphizing implantation is not required. We found that the dopant profiles in FLA-activated samples essentially duplicate those of as-implanted ones even for junctions as deep as 100 nm below the surface. The measured sheet resistances and activation efficiencies of P- and B-implanted samples were in the range of 100-400 Omega/square and 28%-35%, respectively. Moreover, thermal-energy-assisted dopant diffusion by heating was observed for substrate temperature as low as 100 degrees C. The shallow activated-depth feature associated with FLA reduces the separation between end-of-range defects and high-concentration portion of dopants. This generates a steep interstitial gradient responsible for observed B and P uphill diffusions at a depth of about 60 nm below the surface. (c) 2006 American Institute of Physics.
Efficient deployment algorithms for ensuring coverage and connectivity of wireless sensor networks
(2005)
Wang, YC
;
Hu, CC
;
Tseng, YC
;
資訊工程學系
;
Department of Computer Science
Sensor deployment is a critical issue since it reflects the cost and detection capability of a wireless sensor network. Although lots of work has addressed this issue, most of them assume that the sensing field is an open space and there is a special relationship between the communication range and sensing range of sensors. In this work, we consider the sensing field as an arbitrary-shaped region possibly with obstacles. Besides, we allow an arbitrary relationship between the communication range and sensing range, thus eliminating the constraints of existing results. Our approach is to partition the sensing field into smaller sub-regions based on the shape of the field, and then to deploy sensors in these sub-regions. Simulation results show that our method requires fewer sensors compared to existing results.
Experience in designing a using TCP as transport protocol VOD system over a dedicated network
(1998-11-01)
Lu, DJ
;
Wang, YC
;
Ho, JM
;
Chen, MC
;
Ko, MT
In this paper we address the problem of designing a TCP[11] and IP[10] (TCP/IP for short) based video on demand (VOD for short) system over a dedicated network based on standard internet protocols, ie., Transmission Control Protocol (TCP for short, IETF RFC 793[11]) and Internet Protocol (IP for short, IETF RFC 791[10]). TCP and IP are usually refered together as TCP/IP. Despite of the general belief that TCP/IP is not suitable for real-time multimedia applications, after testing in laboratory environment for about one year we are confident in announcing that our prototype is both efficient and reliable. This success depends on several important factors. First of all, the system operates on a dedicated network in which there exists no other traffic except a light of background traffic generated by the Ether Switch the major network component used by our prototype. Second system overhead due to the VOD server and the network adaptor card is minimized Third, we maximize disk bandwidth by implementing a proprietary disk file system. Our experiment shows that it requires only about 330 KBytes at the client buffer to smooth packet delay jitters. In our experimental environment, due to resource limitations, up to 40 clients had been tested successfully. By looking at network bandwidth and CPU utilization, we estimate that a single VOD sewer should be able to handle more than 40 interactive clients playing MPEG-1 system streams simultaneously.
MR-FQ: A fair scheduling algorithm for wireless networks with variable transmission rates
(2005-01-01)
Wang, YC
;
Tseng, YC
;
Chen, WT
;
Tsai, KC
;
資訊工程學系
Wireless networks are characterized by bursty and location-dependent errors. Although many fair scheduling methods have been proposed to address these issues, most of them assume a simple two-state channel model, where a channel can be either good or bad. However, the situation is not so pessimistic since different modulation techniques can be adapted to different channel conditions. Multi-rate transmission is a common technique for wireless networks nowadays. This leads to a dilemma: should fairness be built based on the amount of medium time that a user utilizes or the amount of services that a user receives? In this work, we propose a Multi-rate wireless Fair Queueing (MR-FQ) algorithm that allows a flow to transmit at different rates according to its channel condition and lagging degree. MR-FQ takes both time and service fairness into account. It not only guarantees fairness and bounded delays for packet flows, but also increases the overall system throughput.
MR-FQ: A fair scheduling algorithm for wireless networks with variable transmission rates
(2005-08-01)
Wang, YC
;
Tseng, YC
;
Chen, WT
;
資訊工程學系
;
Department of Computer Science
Wireless networks are characterized by bursty and location-dependent errors. Although many fair scheduling algorithms have been proposed to address these issues, most of them assume a simple two-state channel model, where a channel can be either good or bad. In fact, the situation is not so pessimistic because different modulation techniques can be used to adapt to different channel conditions. Multirate transmission is a common technique forwireless networks nowadays. This leads to a dilemma: should fairness be built based on the amount of time that a user utilizes the medium or the amount of services that a user receives? In this work, the authors propose a multitate wireless fair queueing (MR-FQ) algorithm that allows a flow to transmit at different rates according to its channel condition and lagging degree. MR-FQ takes both time and service fairness into account. They demonstrate that MR-FQ can guarantee fairness and bounded delays for packet flows by mathematical modeling and analyses. Besides, simulation results show that MR-FQ can also increase the overall system throughput compared to other scheduling methods.
Near-infrared femtosecond laser activation of shallow B and P doped layers
(2005)
Wang, YC
;
Zaitsev, A
;
Pan, CL
;
光電工程學系
;
Department of Photonics
Femtosecond Ti:sapphire laser was employed for ultrashallow junction formation in the dopant activation process. Activation of both p-type and n-type dopants were studied, and only very short diffusion length was observed after activation process.
Near-infrared femtosecond laser-induced crystallization of amorphous silicon
(2004-08-16)
Shieh, JM
;
Chen, ZH
;
Dai, BT
;
Wang, YC
;
Zaitsev, A
Amorphous silicon (a-Si) was crystallized by femtosecond laser annealing (FLA) using a near-infrared (lambdaapproximate to800 nm) ultrafast Ti:sapphire laser system. The intense ultrashort laser pulses lead to efficient nonlinear photoenergy absorption and the generation of very dense photoexcited plasma in irradiated materials, enabling nonlinear melting on transparent silicon materials. We studied the structural characteristics of recrystallized films and found that FLA assisted by spatial scanning of laser strip spot constitutes superlateral epitaxy that can crystallize a-Si films with largest grains of similar to800 nm, requiring laser fluence as low as similar to45 mJ/cm(2), and low laser shots. Moreover, the optimal annealing conditions are observed with a significant laser-fluence window (similar to30%). (C) 2004 American Institute of Physics.
Synthesis and characterization of thiophene-containing liquid crystals
(2000-11-01)
Wu, LH
;
Wang, YC
;
Hsu, CS
;
應用化學系
;
Department of Applied Chemistry
Six series of liquid crystal materials containing a 2,5-disubstituted thiophene unit were synthesized. The liquid crystal compounds obtained were characterized by NMR, differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction techniques. The properties of liquid crystalline phases were investigated as a function of spacer units, number of aromatic core rings and different terminal moieties. Cyano, methoxy and iodo groups were used as terminal groups. It is found that: (i) compounds having one thiophene ring and one phenyl ring connected by an ester group, with a length/breadth value of 2.1, exhibit no mesophase, while other compounds containing two biphenyl rings, with a length/breadth ratio of 2.7, show mesophases; ( ii) the polarity of terminal groups and the flexible spacer length significantly affect the thermal behaviour of these compounds; (iii) the nematic transition range of cyano-containing compounds decreases with increasing length of the flexible spacer, and long alkenyloxy chains tend to facilitate the formation of the smectic phase and suppress the nematic phase in all the mesogenic compounds synthesized.
Takagi-Sugeno recurrent fuzzy neural networks for identification and control of dynamic systems
(2001)
Wang, YC
;
Chien, CJ
;
Teng, CC
;
電控工程研究所
;
Institute of Electrical and Control Engineering
In this paper, we propose a Takagi-Sugeno recurrent fuzzy neural networks (TSRFNN) for identification and control nonlinear dynamic systems. The TSRFNN combines the recurrent multilayered connectionist network with dynamic Takagi-Sugeno (TS) fuzzy model. The temporal information are embedded in the recurrent structure by adding feedback connections between the states layer and inputs layer of the fuzzy neural networks (FNN). Based on the derived dynamic backpropagation (DBP) and recursive least squares (RLS) algorithms, the parameters in the TSRFNN are on-line adjusted. Compared with the traditional recurrent fuzzy neural networks (RFNN), the proposed TSRFNN has not only a smaller network structure and a smaller number of network parameters, but also a fast convergence speed and a better learning performance.
Web-based unsupervised learning for query formulation in question answering
(2005)
Wang, YC
;
Wu, JC
;
Liang, T
;
Chang, JS
;
資訊工程學系
Converting questions to effective queries is crucial to open-domain question answering systems. In this paper, we present a web-based unsupervised learning approach for transforming a given natural-language question to an effective query. The method involves querying a search engine for Web passages that contain the answer to the question, extracting patterns that characterize fine-grained classification for answers, and linking these patterns with n-grams in answer passages. Independent evaluation on a set of questions shows that the proposed approach outperforms a naive keyword-based approach in terms of mean reciprocal rank and human effort.