Repacking on Demand for Hierarchical Cellular Networks

In mobile telecommunications operation, radio channels are scarce resources and should be carefully assigned. One possibility is to deploy the hierarchical cellular network (HCN). This paper studies a HCN channel assignment scheme called repacking on demand (RoD). RoD was originally proposed for wireless local loop networks. We expend this work to accommodate mobile HCN. A simulation model is proposed to study the performance of HCN with RoD and some previously proposed schemes. Our study quantitatively indicates that RoD may significantly outperform the previous proposed schemes. Hsien-Ming Tsai was born in Tainan, Taiwan, R.O.C., in 1973. He received the double B.S. degrees in Computer Science & Information Engineering (CSIE) and Communication Engineering, the M.S. degree in CSIE, and the Ph.D. degree in CSIE from National Chiao-Tung University (NCTU), Taiwan, in 1996, 1997, and 2002, respectively. He is currently a research specialist in Quanta Research Institute, Quanta Computer Inc. His research interests are in the areas of cellular protocols (UMTS/GPRS/GSM/DECT), cellular multimedia (MPEG-4 Audio/Speech), and embedded systems. He is an IEEE member. Ai-Chun Pang was born in Hsinchu, Taiwan, R.O.C., in 1973. She received the B.S., M.S. and Ph.D. degrees in Computer Science and Information Engineering from National Chiao Tung University (NCTU) in 1996, 1998 and 2002, respectively. She joined the Department of Computer Science and Information Engineering, National Taiwan University (NTU), Taipei, Taiwan, as an Assistant Professor in 2002. Her research interests include design and analysis of personal communications services network, mobile computing, voice over IP and performance modeling. Yung-Chun Lin was born in Kaohsiung, Taiwan, R.O.C., in 1978. He received the B.S. and M.S. degrees in Computer Science and Information Engineering (CSIE) from National Chiao-Tung University (NCTU), Taiwan, in 2001, 2003, respectively. He is currently pursuing the Ph.D. degree in CSIE. His research interests include design and analysis of a personal communications services network, the cellular protocols (UMTS/GPRS/GSM), and mobile computing. Yi-Bing Lin received his BSEE degree from National Cheng Kung University in 1983, and his Ph.D. degree in Computer Science from the University of Washington in 1990. From 1990 to 1995, he was with the Applied Research Area at Bell Communications Research (Bellcore), Morristown, NJ. In 1995, he was appointed as a professor of Department of Computer Science and Information Engineering (CSIE), National Chiao Tung University (NCTU). In 1996, he was appointed as Deputy Director of Microelectronics and Information Systems Research Center, NCTU. During 1997-1999, he was elected as Chairman of CSIE, NCTU. His current research interests include design and analysis of personal communications services network, mobile computing, distributed simulation, and performance modeling. Dr. Lin has published over 150 journal articles and more than 200 conference papers. Lin is an Adjunct Research Fellow of Academia Sinica, and is Chair Professor of Providence University. Lin serves as consultant of many telecommunications companies including FarEasTone and Chung Hwa Telecom. Lin is an IEEE Fellow and an ACM Fellow.     

High Performance Wireless Switch Protocol for IEEE 802.11 Wireless Networks

All mobile stations (STAs) in IEEE 802.11 infrastructure wireless local area networks (IWLAN) are coordinated by an access point (AP). Within the 2.4 GHz unlicensed industry, science, and medicine (ISM) band defined in the IEEE 802.11 2.4 GHz physical layer (PHY) specifications, three channels are available for concurrently transferring data packets at the coverage area of an AP. In most of small/medium enterprises or home environments, an AP with one selected channel is sufficient for covering whole service area, but this implies that the radio resources for the remaining two channels are wasted. In order to overcome the drawback, we propose a new and simple media access control (MAC) protocol, named wireless switch protocol (WSP), for increasing the throughput of IEEE 802.11 IWLAN network to support high quality multimedia traffic. This is achieved by allowing any pair of STAs in IWLAN to exchange data packets in one of other idle channels after their handshake with each other in the common channel controlled by AP. Simulation results show that the total network throughput of WSP depends on the time taken by channel switching, and on the ‘Intranet’ and ‘Internet’ traffic distribution, where the Intranet and Internet mean data transmission between STAs in IWLAN and between the STA and wired host, respectively. When all data packets are Intranet traffic and the traffic load is heavy, the ratio of Goodput for the proposed WSP to that of IEEE 802.11 standard approximates 400%. In the worse case of all Internet traffic, the proposed WSP still obtains the similar throughput as that of IEEE 802.11 standard.Jenhui Chen was born on October 12, 1971 in Taipei, Taiwan, Republic of China. He received the Bachelor’s and Ph.D. degree in Computer Science and Information Engineering (CSIE) from Tamkang University in 1998 and 2003, respectively. In the Spring of 2003, he joined the faculty of Computer Science and Information Engineering Department at Chang Gung University and served as the Assistant Professor. He occupies the supervisor of Network Department in the Information Center, Chang Gung University. Dr. Chen once served the reviewer of IEEE Transactions on Wireless Communications, ACM/Kluwer Mobile Networks and Applications (MONET), and Journal of Information Science and Engineering. His main research interests include design, analysis, and implementation of communication and network protocols, wireless networks, milibots, and artificial intelligence. He is a member of ACM and IEEE.Ai-Chun Pang was born in Hsinchu, Taiwan, R.O.C., in 1973. She received the B.S., M.S. and Ph.D. degrees in Computer Science and Information Engineering from National Chiao Tung University (NCTU) in 1996, 1998 and 2002, respectively. She joined the Department of Computer Science and Information Engineering, National Taiwan University (NTU), Taipei, Taiwan, as an Assistant Professor in 2002. Her research interests include design and analysis of personal communications services network, mobile computing, voice over IP, and performance modeling.Shiann-Tsong Sheu received his B.S. degree in Applied Mathematics from National Chung Hsing University in 1990, and obtained his Ph.D. degree in Computer Science from National Tsing Hua University in May of 1995. From 1995 to 2002, he was an Associate Professor at the Department of Electrical Engineering, Tamkang University. Since Feb. 2002, he has become a Professor at the Department of Electrical Engineering, Tamkang University. Dr. Sheu received the outstanding young researcher award by the IEEE Communication Society Asia Pacific Board in 2002. His research interests include next-generation wireless communication, WDM networks and intelligent control algorithms.Hsueh-Wen Tseng received his B.S. degree in electrical engineering from Tamkang University, Taipei country, Taiwan, in 2001 and M.S. degree in electrical engineering from National Taiwan University of Science and Technology, Taipei, Taiwan, in 2003. He is currently pursuing the Ph. D. degree at the Department of Computer Science and Information Engineering, National Taiwan University, Taipei, Taiwan. His research interests include design, analysis and implementation of network protocols and wireless communications.     

An Adaptive and Fault-Tolerant Channel Set Allocation Algorithm for Microcell/Macrocell Cellular Networks

Microcell/macrocell architectures are generally deployed in current cellular networks, and involve allocating each cell to a preliminary channel set to support the communications of mobile subscribers. However, cellular networks suffer risks of base transceiver station (BTS) service failure and traffic load variation among BTSs. Both of these conditions impact traffic-carrying capacity and mobile subscriber satisfaction. This investigation presents a dynamic channel set allocation algorithm for ensuring continuous optimization of overall traffic-carrying capacity. This algorithm can tolerate BTSs failure and also resolve the traffic-adaptive problem. Additionally, analytical and simulation results are presented to demonstrate the efficiency of the algorithm.Chyi-Ren Dow was born in 1962. He received the B.S. and M.S. degrees in information engineering from National Chiao Tung University, Taiwan, in 1984 and 1988, respectively, and the M.S. and Ph.D. degrees in computer science from the University of Pittsburgh, U.S.A., in 1992 and 1994, respectively. Currently, he is a Professor in the Department of Information Engineering, Feng Chia University, Taiwan. His research interests include mobile ad-hoc networks, network agents, learning technologies, and embedded systems.Jong-Shin Chen was born in 1972. He received the B.Sc. and Ph.D. degrees in engineering from Feng Chia University, Taiwan, in 1996 and 2003, respectively. His research interests include mobile computing, wireless communications, capacity planning, and systems.Yi-Hsung Li was born in 1979. He received his B.S. degree and M.S. degree in information engineering from Feng Chia University, Taiwan, in 2001 and 2003. He is currently a graduate student for the Ph.D. degree in the Department of Information Engineering and Computer, Feng Chia University, Taiwan. His research interests include personal communications, mobile computing, learning technologies, and network agents.     

Scheduling for time-division based shared channel allocation for UMTS

The Universal Mobile Telecommunications System (UMTS) adopts the WCDMA technology as the radio access interface to provide variable transmission rate services. There are four classes of connections identified in UMTS, which are the conversational, streaming, interactive, and background connections. To efficiently utilize radio bandwidth, the shared channel approach is proposed to deliver the packets for the interactive and background connections. This paper proposes a “Shared-Channel Assignment and Scheduling” (SCAS) algorithm to periodically allocate shared channels to serve interactive and background connections. We conduct formal mathematical proofs and simulation experiments to investigate the performance of the SCAS algorithm. We formally prove that with SCAS, a shared channel can be fully utilized (i.e., the utilization of a shared channel can be up to 100%) to serve the interactive connections. Our analysis indicates that compared with the previously proposed shared channel allocation and scheduling algorithms, there are less computation and communication overheads introduced in the SCAS algorithm. The results of the simulation experiments indicate that it is preferred to set up the Transmission Time Interval (TTI; that is, the unit of time interval for shared channel allocation) smaller to optimize the performance of the SCAS algorithm, including the shared channel utilization and the average waiting time of a connection before getting transmission service. A preliminary version [11] of this work has been accepted by IEEE Wireless Communications and Networking Conference 2004. This paper is an extension of the proposed algorithm, and simulation and analysis are conducted to investigate the performance of the proposed algorithm. Chai-Hien Gan was born in Malaysia in 1971. He received his BS degree in computer science from Tamkang University in 1994, Taipei County, Taiwan, and both his MS. and Ph.D. degrees in computer science and information engineering from National Taiwan University, Taipei, Taiwan, in 1996 and 2005, respectively. Since March 2005, he has been a Research Assistant Professor in Department of Computer Science, National Chiao Tung University, R.O.C. His current research interests include wireless mesh networks, mobile computing, personal communications services, and wireless Internet. Phone Lin received his BSCSIE degree and Ph.D. degree from National Chiao Tung University, Taiwan, R.O.C. in 1996 and 2001, respectively. From August 2001 to July 2004, he was an Assistant Professor in Department of CSIE and Graduate Institute of Graduate of Networking and Multimedia, National Taiwan University, R.O.C. Since August 2004, he has been an Associate Professor in Department of CSIE and Graduate Institute Graduate of Networking and Multimedia, National Taiwan University, R.O.C. His current research interests include personal communications services, wireless Internet, and performance modeling. Dr. Lin is an Associate Editor for IEEE Transactions on Vehicular Technology, Editor for IEEE Wireless Communications special issue on Mobility and Resource Management and a Guest Editor for ACM/Springer MONET special issue on Wireless Broad Access. He is also an Associate Editorial Member for the WCMC Journal. P. Lin’s email and website addresses are plin@csie.ntu.edu.tw and http://www.csie.ntu.edu.tw/~plin, respectively. Nei-Chiung Perng is presently a Ph.D. student in the Department of Computer Science and Information Engineering, National Taiwan University. He received his Bachelor and Master degrees in the Department of Computer and Information Science, National Chiao Tung University in 1999 and 2001, respectively. His research interests include real-time systems and scheduling algorithms. Tei-Wei Kuo received B.S.E. degree in computer science and information engineering from National Taiwan University in Taipei, Taiwan, in 1986. He received the M.S. and Ph.D. degrees in computer sciences from the University of Texas at Austin in 1990 and 1994, respectively. He is currently a Professor and the Chairman of the Department of Computer Science and Information Engineering of the National Taiwan University, Taiwan, ROC. He was an Associate Professor in the Department of Computer Science and Information Engineering of the National Chung Cheng University, Taiwan, ROC, from August 1994 to July 2000. Dr. Kuo is a senior member of the IEEE computer society. His research interest includes embedded systems, real-time process scheduling, real-time operating systems, and real-time databases. He has over 100 technical papers published or been accepted in international journals and conferences and has a book “Real-Time Database Systems: Architecture and Techniques” published by Kluwer Academic Publishers (ISBN 0-7923-7218-2, USA). He is the Program Co-Chair of IEEE 7th Real-Time Technology and Applications Symposium, 2001, and an associate editor of the Journal of Real-Time Systems since 1998. He is an executive committee member of the IEEE Technical Committee on Real-Time Systems in 2005 and the steering committee chair of IEEE RTCSA’05. Dr. Kuo has consulted for government and industry on problems in various real-time and embedded systems designs. Dr. Kuo received several research awards in Taiwan, including the Distinguished Research Award from the ROC National Science Council in 2003 and the Young Scholar Research Award from Academia Sinica, Taiwan, ROC, in 2001. Ching-Chi Hsu was born in Taipei, Taiwan in 1949. He received his BS degree in physics from National Tsing Hwa. University in 1971, Hsishu, Taiwan, and both his MS. and Ph.D. degrees in computer engineering from EE department of National Taiwan University, Taipei, Taiwan, in 1975 and 1982, respectively. In 1977, he joined the faculty of the Department of Computer Science and Information Engineering at National Taiwan University and became an associate professor in 1982. During the years between 1987 and 2002, he was first engaged as a professor and became the chairman of the department. During his tenure in National Taiwan University, Dr. Hsu was a visiting scholar of Computer Science Department, Stanford University from 1984 to 1985. After serving in National Taiwan University for over 25 years, Dr. Hsu had left and was promoted as the president of Kai Nan University in 2002. Starting from February 2004, Dr. Hsu has been the executive vice president of the Institute for Information Industry in which he is mainly in charge of accelerating the growth of information industry in the whole nation. His research interests include distributed processing of data and knowledge, mobile computing and wireless networks.     

A Scalable and Reliable Multicast Routing Protocol for Ad-hoc Wireless Networks

Multicasting is an essential service for ad-hoc wireless networks. In a multicasting environment with multiple senders, receivers or meeting members, traditional multicast routing protocols must pay great overhead for multiple multicast sessions. This work presents a scalable and reliable multicasting protocol for ad-hoc wireless networks. A virtual backbone is used as a shared structure for multiple sessions. A clustering scheme is used to reduce the routing path length. A novel scheme is developed to effectively multicast packets using forwarding gates. Furthermore, a lost packet recovery scheme is developed for reliable packet transmission. This scheme can be used to improve the reliability of traditional non-acknowledged multicasting approach. Experiments were conducted to evaluate the proposed multicasting scheme and the results demonstrate that our scheme outperforms other schemes in terms of packet delivery ratio, packet delivery time, control overhead, multicast efficiency, and cost effect. Furthermore, our approach is stable for networks with high mobility and the lost packet recovery scheme is cost-effective. Chyi-Ren Dow was born in 1962. He received the B.S. and M.S. degrees in information engineering from National Chiao Tung University, Taiwan, in 1984 and 1988, respectively, and the M.S. and Ph.D. degrees in computer science from the University of Pittsburgh, USA, in 1992 and 1994, respectively. Currently, he is a Professor in the Department of Information Engineering, Feng Chia University, Taiwan. His research interests include mobile computing, ad-hoc wireless networks, agent techniques, fault tolerance, and learning technology. Jyh-Horng Lin was born in 1975. He received the B.S. and M.S. degrees in information engineering from Feng Chia University, Taiwan, in 1998 and 2000, respectively. He is currently a candidate for the Ph.D. degree in the Department of Information Engineering, Feng Chia University, Taichung, Taiwan. His research interests include mobile computing and ad-hoc wireless networks. Kun-Tai Chen was born in 1978. He received the B.S. and M.S. degrees in information engineering from Feng Chia University, Taiwan, in 2000 and 2002, respectively. He is currently an engineer in the VIA technologies, Inc. Hsinchu branch, Taiwan. His research interests include mobile computing, ad-hoc wireless networks and video decoding. Sheng-Chang Chen was born in 1979. He received his B.S. degree and M.S. degree in information engineering from Feng Chia University, Taiwan, in 2001 and 2002. He is currently a Ph.D. degree in information engineering from Feng Chia University, Taiwan. His research interests include mobile computing, ad-hoc wireless network and fault tolerance technique. Shiow-Fen Hwang was born in 1963. She received her B.S., M.S. and Ph.D. degrees in Applied Mathematics from National Chiao Tung University, Taiwan, in 1985, 1987 and 1991, respectively. Currently, she is an Associate Professor in the Department of Information Engineering, Feng Chia University, Taiwan. Her research interests include interconnection networks, mobile computing, and computer algorithms.     

Ant-Based Distributed Topology Control Algorithms for Mobile Ad hoc Networks

By adjusting the transmission power of mobile nodes, topology control aims to reduce wireless interference, reduce energy consumption, and increase effective network capacity, subject to connectivity constraints. In this paper, we introduce the Ant-Based Topology Control (ABTC) algorithm that adapts the biological metaphor of Swarm Intelligence to control topology of mobile ad hoc networks. ABTC is a distributed algorithm where each node asynchronously collects local information from nearby nodes, via sending and receiving ant packets, to determine its appropriate transmission power. The operations of ABTC do not require any geographical location, angle-of-arrival, topology, or routing information, and are scalable. In particular, ABTC attempts to minimize the maximum power used by any node in the network, or minimize the total power used by all of the nodes in the network. By adapting swarm intelligence as an adaptive search mechanism, ABTC converges quickly to a good power assignment with respect to minimization objectives, and adapts well to mobility. In addition, ABTC may achieve common power, or properly assign power to nodes with non-uniform distribution. Results from a thorough comparative simulation study demonstrate the effectiveness of ABTC for different mobility speed, various density, and diverse node distributions.This work is supported in part by National Science Foundation under grant ANI-0240398.Chien-Chung Shen received his B.S. and M.S. degrees from National Chiao Tung University, Taiwan, and his Ph.D. degree from UCLA, all in computer science. He was a research scientist at Bellcore Applied Research working on control and management of broadband networks. He is now an assistant professor in the Department of Computer and Information Sciences of the University of Delaware, and a recipient of NSF CAREER Award. His research interests include ad hoc and sensor networks, control and management of broadband networks, distributed object and peer-to-peer computing, and simulation.Zhuochuan Huang received his B.E. degree in Computer Science and Technology from Tsinghua University, P.R. China, in 1998, and his M.S. degree in Computer Science from University of Delaware in 2000. He is currently a PhD candidate with the Department of Computer and Information Sciences at the University of Delaware. His current research interests include the design and simulation of protocols for mobile ad hoc networks.Chaiporn Jaikaeo received his B.Eng degree in computer engineering from Kasetsart University, Thailand, and his M.S. and Ph.D. degrees in computer and information sciences from the University of Delaware in 1996, 1999 and 2004, respectively. He is currently a lecturer in the Department of Computer Engineering at Kasetsart University. His research interests include unicast and multicast routing, topology control, peer-to-peer computing and network management for mobile wireless ad hoc and sensor networks.     

An On-Demand Routing Protocol with Backtracking for Mobile Ad Hoc Networks

A mobile ad hoc network (MANET) is characterized by multi-hop wireless links and frequent node mobility. Communication between non-neighboring nodes requires a multi-hop routing protocol to establish a route. But, the route often breaks due to mobility. The source must rediscover a new route for delivering the data packets. This wastes the resources that are limited in MANET. In this paper, a new on-demand routing protocol is proposed, named on-demand routing protocol with backtracking (ORB), for multi-hop mobile ad hoc networks. We use the multiple routes and cache data technique to reduce the rediscovery times and overhead. After executing the route discovery phase, we find out a set of nodes, named checkpoint, which has the multiple routes to the destination. When a checkpoint node receives a data packet, it caches this data packet in its buffer within a specific time period. When a node detects a broken route during the data packets delivery or receives an error packet, it will either recover the broken route or reply the error packet to the source. If a node can not forward the data packet to the next node, it replies an error packet to the source. This packet is backtracking to search a checkpoint to redeliver the data packet to the destination along other alternate routes. The main advantage of ORB is to reduce the flooding search times, maybe just delay and cost while a route has broken. The experimental results show that the proposed scheme can increase the performance of delivery but reduce the overhead efficiently comparing with that of AODV based routing protocols. Hua-Wen Tsai received the B.S. degree in Information Management from Chang Jung Christian University, Taiwan, in June 1998 and the M.B.A. degree in Business and Operations Management from Chang Jung Christian University, Taiwan, in June 2001. Since September 2001, he has been working towards the Ph.D. degree and currently is a doctoral candidate in the Department of Computer Science and Information Engineering, National Cheng Kung University, Taiwan. His research interests include wireless communication, ad hoc networks, and sensor networks. Tzung-Shi Chen received the B.S. degree in Computer Science and Information Engineering from Tamkang University, Taiwan, in June 1989 and the Ph.D. degree in Computer Science and Information Engineering from National Central University, Taiwan, in June 1994. He joined the faculty of the Department of Information Management, Chung Jung University, Tainan, Taiwan, as an Associate Professor in June 1996. Since November 2002, he has become a Full Professor at the Department of Information Management, Chung Jung University, Tainan, Taiwan. He was a visiting scholar at the Department of Computer Science, University of Illinois at Urbana-Champaign, USA, from June to September 2001. He was the chairman of the Department of Information Management at Chung Jung University from August 2000 to July 2003. Since August 2004, he has become a Full Professor at the Department of Information and Learning Technology, National University of Tainan, Tainan, Taiwan. Currently, he is the chairman of the Department of Information and Learning Technology, National University of Tainan. He co-received the best paper award of 2001 IEEE ICOIN-15. His current research interests include mobile computing and wireless networks, mobile learning, data mining, and pervasive computing. Dr. Chen is a member of the IEEE Computer Society. Chih-Ping Chu received the B.S. degree in agricultural chemistry from National Chung Hsing University, Taiwan, the M.S. degree in computer science from the University of California, Riverside, and the Ph.D. degree in computer science from Louisiana State University. He is currently a Professor in the Department of Computer Science and Information Engineering of National Cheng Kung University, Taiwan. His current research interests include parallel computing, parallel processing, component-based software development, and internet computing.     

An Efficient Adaptive Grouping for Single Code Assignment in WCDMA Mobile Networks

For achieving high utilization and efficient code management of the OVSF code tree in 3G WCDMA networks, several researches have extensively studied. Based on combining both the code assignment and the reassignment mechanisms, it increases obviously high utilization and reduces completely the code blocking. Nevertheless, the required rate of traffic should be powers of two of the basic rate, i.e. 1R, 2R, 4R, …, etc., which is impractical and results in wasting the system bandwidth while the required rate is not powers of two of the basic rate. Several multi-code assignment mechanisms have proposed to reduce the waste rate. Nevertheless, these methods bring two inevitable drawbacks including, high complexity of handling multiple codes, and increasing the cost of using more rake combiners at both the base stations and mobile nodes. Therefore, we propose an adaptive grouping code assignment herein to provide a single channelization code for any possible rate of traffic, even though the required rate is not powers of two of the basic rate. Based on the dynamic programming algorithm, the adaptive grouping approach forms several calls into a group. Then it allocates a subtree to the group and adaptively shares the subtree codes for these calls in the concept of time-sharing of slots during a group cycle time. Therefore, the waste rate and code blocking are thus reduced obviously while using a single rake combiner. Since the delay problem may be occurred in such a time-sharing approach, we propose two schemes of cycle interleaving methods to reduce delay. Numerical results indicate that the proposed adaptive grouping approach reduces significantly the waste rate and thus increases the system utilization. Moreover, the proposed cycle interleaving scheme reduces data delay significantly. Ren-Hung Hwang received his M.S. and Ph.D. degrees in computer science from University of Massachusetts, Amherst, Massachusetts, USA, in 1989 and 1993, respectively. He joined the Department of Computer Science and Information Engineering, National Chung Cheng University, Chia-Yi, Taiwan, in 1993, where he is now a full Professor and the Chair of the Department of Communication Engineering. His research interests include Internet QoS, peer-to-peer infrastructure design, and 3G QoS. Ben-Jye Chang received his M.S. degree in computer engineering from University of Massachusetts, Lowell, in 1991 and the Ph.D. degree in computer science and information engineering from National Chung-Cheng University, Taiwan, in 2001. He joined the Department of Computer Science and Information Engineering faculty at Chaoyang University of Technology, Taiwan, in 2002, where he is currently an Associate Professor. His research interests include QoS-based networks, QoS wirless networking, resource management for wireless networks and mobile cellular networks, and performance evaluation of networks. Min-Xiou Chen received the BS degree in computer science and information engineering from Tung Hai University, Tai-Chung, Taiwan, in 1996, and the MS and PhD degrees in computer science and information engineering from National Chung Cheng University, Chia-Yi, Taiwan, in 1998 and 2005, respectively. He is now an assistant professor at the Department of Computer Science and Information Engineering, Chung Hua University, Hsin-Chu, Taiwan. His research interests include wireless communication, SIP, sensor network and resource management in WCDMA systems. He is a member of the IEEE. Kun-Chan Tsai received the BS degree in information engineering and computer science from Feng Chia University, Taichung, Taiwan, in 2001, and the MS degree in computer science and information engineering from National Chung Cheng University, Chia-Yi, Taiwan, in 2003. His research interests include wireless communications and resource management in WCDMA systems.     

A Fault-Tolerant Scheme for Mobility Management in PCS Networks

One of the most important and challenging issues in the design of personal communication service (PCS) systems is the management of location information. In this paper, we propose a new fault-tolerant location management scheme, which is based on the cellular quorum system. Due to quorum's salient set property, our scheme can tolerate the failures of one or more location server(s) without adding or changing the hardware of the systems in the two-tier networks. Meanwhile, with a region-based approach, our scheme stores/retrieves the MH location information in the location servers of a quorum set of the local region as much as possible to avoid long delays caused by the possible long-distance of VLR and HLR. Thus, it yields better connection establishment and update delay. Ming-Jeng Yang received the M.S. degree in computer science from the Syracuse University, New York, in 1991, and the Ph.D. degree in computer science from National Taiwan Normal University, Taiwan, in 2004. He is an associate professor in the Department of Information Technology, Takming College, Taiwan. His research interests include wireless networks, mobile computing, fault-tolerant computing, and distributed computing. He is a member of the IEEE Computer Society and the ACM. Yao-Ming Yeh received the B.S. degree in computer engineering from National Chiao-Tung University, Taiwan, in 1981, and the M.S. degree in computer science and information engineering from National Taiwan University, Taiwan, in 1983. In August 1991, he received the Ph.D. degree in the Department of Electrical and Computer Engineering, The Pennsylvania State University, Pa., U.S.A. He is a professor in the Department of Information and Computer Education, National Taiwan Normal University, Taiwan. His research interests include fault-tolerant computing, web and XML computing, and distributed computing.     

Private Authentication Techniques for the Global Mobility Network

Numerous authentication approaches have been proposed recently for the global mobility network (GLOMONET), which provides mobile users with global roaming services. In these authentication schemes, the home network operators can easily obtain the authentication key and wiretap the confidentiality between the roaming user and the visited network. This investigation provides a solution of authentication techniques for GLOMONET in order to prevent this weakness from happening and presents a secure authentication protocol for roaming services. In addition, a round-efficient version of the same authentication protocol is presented. Comparing with other related approaches, the proposed authentication protocol involves fewer messages and rounds in communication. Tian-Fu Lee was born in Tainan, Taiwan, ROC, in 1969. He received his B.S. degree in Applied Mathematics from National Chung Hsing University, Taiwan, in 1992, and his M.S. degree in Computer Science and Information Engineering from National Chung Cheng University, Taiwan, in 1998. He works as a lecturer in Leader University and pursues his Ph.D. degree at Department of Computer Science and Information Engineering, National Cheng Kung University, Taiwan. His research interests include cryptography and network security. Chi-Chao Chang received the BS degree in Microbiology from Soochow University in 1990 and the MS degree in Computer Science from State University of New York at Albany in 1992. He is currently working as an instructor in Chang Jung Christian University and a graduate student in National Cheng Kung University. His research interests are information security, mobile agent systems, anonymous digital signatures and quantum cryptography. Tzonelih Hwang was born in Tainan, Taiwan, in March 1958. He received his undergraduate degree from National Cheng Kung University, Tainan, Taiwan, in 1980, and the M.S. and Ph.D. degrees in Computer Science from the University of Southwestern Louisiana, USA, in 1988. He is presently a professor in Department of Computer Science and Information Engineering, National Cheng Kung University. His research interests include cryptology, network security, and coding theory.