Browsing by Author "Chou, C. L."

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Dynamic RCST grouping for achieving high link capacities in mobile DVB-RCS networks
(2007)
Chou, C. L.
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Wang, S. Y.
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資訊工程學系
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Department of Computer Science
A DVB-RCS system provides bidirectional connections between service providers and end users. Service providers deliver broadcast data through the forward link to end users while end users send back their data through the return link. The return link is composed of multiple access channels, which can be accessed by the MF-TDMA scheme. Over each channel, a time-slot includes a guard time duration for accommodating propagation delay uncertainties among RCSTs accessing the same channel. In a system with mobile RCSTs, the guard time duration may take a considerable portion of a time-slot for avoiding data collision. Guard time represents bandwidth overhead of the system and large guard time causes significant link capacity reduction. In this paper, we first investigate the problem of link capacity reduction when the DVB-RCS standard, which is originally designed for fixed RCSTs, is directly used with mobile RCSTs without modification. Then, we propose a dynamic RCST grouping mechanism for DVB-RCS to achieve high link capacity with mobile RCSTs.
Electrochemical Degradation of Nafion Ionomer to Functionalize Graphene As a Support for Core-Shell Palladium-Ruthenium Alloy @ Platinum Electrocatalysts
(2016-01-01)
Kuo, C. C.
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Chang, Y. C.
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Chou, C. L.
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Chou, S. C.
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Wu, P. W.
A simple but effective electrochemical route to functionalize graphene is demonstrated. Cyclic voltammetric sweeps are performed in H2SO4 aqueous solution on electrodes containing carbon cloth, graphene, and Nafion ionomer. With supply of ambient oxygen, the formation of hydroxyl radicals from the oxygen reduction reaction during CV cycles initiates the decomposition of Nafion ionomer that engenders oxygenated functional groups on the graphene surface. Raman analysis suggests a minor change for the graphene structure. Exploring various amounts of Nafion ionomer, we determine the optimized conditions for graphene functionalization. Contact angle is used to evaluate the effect of Nafion ionomer decomposition. X-ray photoelectron spectroscopy is employed to study relevant functional groups. Afterwards, nanoparticles of Pd9Ru are synthesized and impregnated on those functionalized graphene (FGN) via a wet chemical reflux process. X-ray diffraction patterns of the as-synthesized samples suggest successful formation of alloy. Images from transmission electron microscope confirm the average size of 3-4 nm. As expected, the Pd9Ru alloy are much more dispersive in FGN rather than in the one without functionalization.
Implementing and evaluating three routing protocols in dual-radio-dual-mode IEEE 802.11(b) wireless mesh networks
(2008-06-25)
Wang, S. Y.
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Lin, C. C.
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Chou, C. L.
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資訊工程學系
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Department of Computer Science
In a dual-radio-dual-mode IEEE 802.11(b) wireless mesh network (WMN), each mesh access point has two IEEE 802.11(b) interfaces. One interface operates in infrastructure mode to serve IEEE 802.11(b) client devices so that they can readily use the mesh network without any software modification or installation. The other interface operates in ad hoc mode to forward packets among mesh access points until they reach an Internet gateway or the access point with which the destination client device is associated. Compared with a single-radio WMN, such a WMN offers ease of use and higher network throughputs for client devices. In this paper, we implement and evaluate the performance of three routing protocols (OSPF, AODV, and STP) operating in dual-radio-dual-mode IEEE 802.11(b) WMNs. Our simulation results show that among the tested protocols, OSPF provides the highest system total througput and results in the largest number of stable connections in such a WMN. (c) 2008 Elsevier B.V. All rights reserved.
Improving the Channel Utilization of IEEE 802.11p/1609 Networks
(2009)
Wang, S. Y.
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Chou, C. L.
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Liu, K. C.
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Ho, T. W.
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Hung, W. J.
The IEEE 802.11p/1609 standards specify a suite of communication protocols for vehicular communication networks. A new operational mode, called the WAVE (Wireless Access in Vehicular Environments) mode, is defined to enable communication among high-speed vehicles or between a vehicle and a roadside infrastructure network. In the WAVE mode, a mobile/stationary station uses a combined FDMA/TDMA channel access scheme to switch its channel between the control channel and a service channel every 50 ms. The primary purpose of this design is to detect new services announced by other stations. However, if a station would like to use all of its service channel bandwidth to transmit a large volume of data to another station, switching back to the control channel every 50 ms without doing anything useful only unnecessarily reduces the maximum possible transmission throughput by a half. To overcome this problem, in this paper we propose an improved channel access scheme to allow a station to stay on a service channel as long as it requires before returning to the control channel. Our simulation results show that the proposed scheme significantly improves the service channel utilization under various network conditions.
Increasing wide-area download throughputs on the roads by trunking multiple cellular channels over a vehicular ad hoc network
(2009-02-12)
Wang, S. Y.
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Chou, C. L.
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Lin, C. C.
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資訊工程學系
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Department of Computer Science
To obtain infotainment services (e.g., traffic, maps, accidents, weather, etc.) on the roads, vehicle drivers and back-seat passengers may want to use wide-area networks (e.g., GPRS) to download useful information from the Internet when needed. In this paper. we design and implement a scheme to increase GPRS download throughput for a vehicle user while he (she) is moving on the roads. This scheme integrates inter-vehicle communication with trunking mechanisms to achieve this goal. This scheme can be readily deployed for any real-world GPRS network or any 3G network without any support from the network operator. Our field trial results show that when this scheme is applied in a motorcade of four vehicles and all of the GPRS channel provided by each vehicle are used to download a file simultaneously, the download speed is 3.92 times faster than that achieved when only one GPRS channel is used. (C) 2008 Elsevier B.V. All rights reserved.
NCTUns 4.0: An integrated simulation platform for vehicular traffic, communication, and network researches
(2007)
Wang, S. Y.
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Chou, C. L.
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Chin, Y. H.
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Tzeng, Y. S.
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Hsu, M. S.
In this paper, we present an integrated simulation platform, called NCTUns, for vehicular traffic, communication, and network researches. This platform combines the capabilities supported by a network simulator and those supported by a traffic simulator. With these simulation capabilities, NCTUns can be used to design protocols for Intelligent Transportation Systems (ITS) communication networks such as a wireless vehicular communication network. Besides, the novel architecture of the platform enables the real-world Linux protocol stack and any real-world application to be used in simulations of such networks. In this paper, we present the design of NCTUns for supporting ITS researches and show its scalability.
NCTUns 5.0 Network Simulator for Advanced Wireless Vehicular Network Researches
(2009)
Wang, S. Y.
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Chou, C. L.
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資訊工程學系
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Department of Computer Science
NCTUns is a high-fidelity network simulator and emulator By using a novel kernel re-entering simulation methodology, it provides many unique advantages over traditional network simulators and emulators. For this reason, since its public release on November 1, 2002, as of February 2, 2009, more than 13,838 people from. 130 countries in the world have registered at its web site to download it and these numbers are still fast increasing. NCTUns is open-source and runs on Linux. It can simulate many different types of networks. In this paper, we will present its supports for wireless vehicular network researches. In particular it supports IEEE 802.11(p)/1609 standards, which are proposed for wireless vehicular networks. More information about this tool is available at its web site at (http://NSL.csie.nctu.edu.tw/nctuns.html).
NCTUns tool for wireless vehicular communication network researches
(2009-08-01)
Wang, S. Y.
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Chou, C. L.
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資訊工程學系
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Department of Computer Science
Several goals such as improving road safety and increasing transport efficiency are being pursued in intelligent transportation systems (ITS). Wireless vehicular communication is one technology to achieve these goals. Conducting vehicular experiments on the roads is an approach to studying the effectiveness of wireless vehicular communication. However, such an approach is costly, hard-to-control (repeat), dangerous, and infeasible when many vehicles and people are involved in the field trial. In contrast, the simulation approach does not have these problems. It is a very useful approach and complements the field trial approach. This paper presents NCTUns, an open source integrated simulation platform, for wireless vehicular communication network researches. This tool tightly integrates network and traffic simulations and provides a fast feedback loop between them. Therefore, a simulated vehicle can quickly change its driving behavior such as moving speed and direction when it receives a message from the wireless vehicular communication network. This capability is required by several novel ITS applications such as active collision avoidance systems. In this paper, we present the design, implementation, validation, and performance of this tool. (C) 2009 Elsevier B.V. All rights reserved.
On the characteristics of information dissemination paths in vehicular ad hoc networks on the move
(2008-11-01)
Wang, S. Y.
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Chou, C. L.
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資訊工程學系
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Department of Computer Science
Recently, Intelligent Transportation Systems (ITS) is becoming an important research topic. One goal for ITS is to disseminate important information among vehicles in a timely and efficient manner. In the ITS research community, inter-vehicle communications (IVC) is considered a way that may be able to achieve this goal. An information network built on top of vehicles using IVC can be viewed as a type of mobile ad hoc networks. Although several information dissemination protocols for mobile ad hoc networks have been proposed, how well they can be applied to a vehicle-formed mobile ad hoc network is still poorly studied. Without doubt, no matter what methodology is taking for designing an IVC suitable information dissemination protocol, the protocol performance is fundamentally limited by the potential degree of physical-link connectivity. Thus, in this paper, some potential link attributes of IVC networks, such as the lifetime of a transmission path between two vehicles, are studied based on reasonable vehicle traces generated by a microscopic traffic simulator. Although no specific protocol is focused on in this paper, the studied results can potentially contribute to performance improvement and/or protocol efficiently for any existed or developing protocol.
On the characteristics of routing paths and the performance of routing protocols in vehicle-formed mobile ad hoc networks on highways
(2010-02-01)
Wang, S. Y.
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Chou, C. L.
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Lin, C. C.
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資訊工程學系
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Department of Computer Science
Recently, intelligent transportation systems (ITS) is becoming an important research topic. One goal of ITS is to exchange information among vehicles in a timely and efficient manner. In the ITS research community, inter-vehicle communications (IVC) is considered a way that may be able to achieve this goal. An information network built on the top of vehicles using IVC can be viewed as a type of mobile ad hoc networks (MANETs). In the past, several unicast routing protocols for MANET have been proposed. However, most of them are designed for general MANETs rather than for IVC networks. In this paper, we first used more realistic vehicle mobility traces generated by a microscopic traffic simulator (VISSIM) to understand the characteristics of routing paths in an IVC network. Based on the insights gained from the derived path characteristics, we designed and implemented an intelligent flooding-based routing protocol for small-scale IVC networks. Via several field trials conducted on highways, we compared the performance of ad hoc on-demand distance vector (AODV) and our protocol. Our experimental results show that (1) our protocol outperforms AODV greatly in IVC networks and (2) our protocol can provide text, image, audio, and video services for small-scale IVC networks (e.g., a platoon) quite well. Copyright (C) 2009 John Wiley & Sons, Ltd.
Optical coupling from InGaAs subcell to InGaP subcell in InGaP/InGaAs/Ge multi-junction solar cells
(2013-01-14)
Shu, G. W.
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Lin, J. Y.
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Jian, H. T.
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Shen, J. L.
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Wang, S. C.
Spatially-resolved electroluminescence (EL) images in the triple junction InGaP/InGaAs/Ge solar cell have been investigated to demonstrate the subcell coupling effect. Upon irradiating the infrared light with an energy below bandgap of the active layer in the top subcell, but above that in the middle subcell, the EL of the top subcell quenches. By analysis of EL intensity as a function of irradiation level, it is found that the coupled p-n junction structure and the photovoltaic effect are responsible for the observed EL quenching. With optical coupling and photoswitching effects in the multi-junction diode, a concept of infrared image sensors is proposed. (C)2012 Optical Society of America
Shape Design Optimization of a Robot Arm Using a Surrogate-Based Evolutionary Approach
(2020-04-01)
Hsiao, J. C.
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Shivam, Kumar
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Chou, C. L.
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Kam, T. Y.
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機械工程學系
In the design optimization of robot arms, the use of simulation technologies for modeling and optimizing the objective functions is still challenging. The difficulty is not only associated with the large computational cost of high-fidelity structural simulations but also linked to the reasonable compromise between the multiple conflicting objectives of robot arms. In this paper we propose a surrogate-based evolutionary optimization (SBEO) method via a global optimization approach, which incorporates the response surface method (RSM) and multi-objective evolutionary algorithm by decomposition (the differential evolution (DE ) variant) (MOEA/D-DE) to tackle the shape design optimization problem of robot arms for achieving high speed performance. The computer-aided engineering (CAE) tools such as CAE solvers, computer-aided design (CAD) Inventor, and finite element method (FEM) ANSYS are first used to produce the design and assess the performance of the robot arm. The surrogate model constructed on the basis of Box-Behnken design is then used in the MOEA/D-DE, which includes the process of selection, recombination, and mutation, to optimize the robot arm. The performance of the optimized robot arm is compared with the baseline one to validate the correctness and effectiveness of the proposed method. The results obtained for the adopted example show that the proposed method can not only significantly improve the robot arm performance and save computational cost but may also be deployed to solve other complex design optimization problems.
The design and implementation of the NCTUns network simulation engine
(2007-01-01)
Wang, S. Y.
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Chou, C. L.
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Lin, C. C.
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資訊工程學系
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Department of Computer Science
NCTUns is a network simulator running on Linux. It has several unique advantages over traditional network simulators. This paper presents the novel design and implementation of its simulation engine. This paper focuses on how to combine the kernel re-entering and discrete-event simulation methodologies to execute simulations quickly. The performance and scalability of NCTUns are also presented and discussed. (C) 2006 Elsevier B.V. All rights reserved.