A Video Streaming System for Mobile Phones: Practice and Experience

This paper presents a case of video streaming system for mobile phone which has actually been implemented and deployed for commercial services in CDMA2000 1X cellular phone networks. As the computing environment and the network connection of cellular phones are significantly different from the wired desktop environment, the traditional desktop streaming method is not applicable. Therefore, a new architecture is required to suit the successfully streaming in the mobile phone environment. We have developed a very lightweight video player for use in mobile phone and the related authoring tool for the player. The streaming server has carefully been designed to provide high efficiency, reliability and scalability. Based on a specifically-designed suite of streaming protocol, the server employs an adaptive rate control mechanism which transmits the media packets appropriately into the network according to the change in network bandwidth.Hojung Cha is currently a professor in computer science at Yonsei University, Seoul, Korea. His research interests include multimedia computing system, multimedia communication networks, wireless and mobile communication systems and embedded system software. He received his B.S. and M.S. in computer engineering from Seoul National University, Korea, in 1985 and 1987, respectively. He received his Ph.D. in computer science from the University of Manchester, England, in 1991.Jongmin Lee is a Ph.D. candidiate in computer science at Yonsei University, Seoul, Korea. His research interests include wireless multimedia system, QoS architecture, multimedia communication networks. He received his B.S. and M.S. in computer science from Kwangwoon University in 1999 and 2001, respectively.Jongho Nang is a professor in the Department of Computer Science at Sogang University. He received his B.S. degree from Sogang University, Korea, in 1986 and M.S. and Ph.D. degree from KAIST, in 1988 and in 1992, respectively. His research interests are in the field of multimedia systems, digital video library, and Internet technologies. He is a member of KISS, ACM, and IEEE.Sung-Yong Park is an associate professor in the Department of Computer Science at Sogang University, Seoul, Korea. He received his B.S. degree in computer science from Sogang University, and both the M.S. and Ph.D. degrees in computer science from Syracuse University. From 1987 to 1992, he worked for LG Electronics, Korea, as a research engineer. From 1998 to 1999, he was a research scientist at Telcordia Technologies (formerly Bellcore) where he developed network management software for optical switches. His research interests include high performance distributed computing and systems, operating systems, and multimedia.Jin-Hwan Jeong received the B.S. and M.S. degrees in computer science from Korea University, Seoul, Korea, in 1997, and 1999, respectively. He is currently in Ph.D. course at Korea University. His research interests include video processing for thin devices, multimedia streaming and operating systems.Chuck Yoo received the B.S. degree in electronics engineering from Seoul National University, Seoul, Korea and the M.S. and Ph.D. in computer science in University of Michigan. He worked as a researcher in Sun Microsystems Lab. from 1990 to 1995. He joined the Computer Science and Enginnering Department, Korea University, Seoul, Korea in 1995, where he is currently a professor. His research interests include high performance network, multimedia streaming, and operating systems.Jin-Young Choi received the B.S. degree from Seoul National University, Seoul, Korea, in 1982, the M.S. degree from Drexel University in 1986, and the Ph.D. degree from University of Pennsylvania, in 1993. He is currently a professor of Computer Science and Engineering Department, Korea University, Seoul, Korea. His current research interests are in real-time computing, formal methods, programming languages, process algebras, security, software engineering, and protocol engineering.     

Energy Efficient Broadcast in Wireless Ad hoc Networks with Hitch-hiking

In this paper, we propose a novel concept called Hitch-hiking in order to reduce the energy consumption of broadcast application for wireless networks. Hitch-hiking takes advantage of the physical layer design that facilitates the combining of partial signals to obtain the complete information. The concept of combining partial signals using maximal ratio combiner [15] has been used to improve the reliability of the communication link but has never been exploited to reduce energy consumption in broadcasting over wireless ad hoc networks. We study the advantage of Hitch-hiking for the scenario when the transmission power level of nodes is fixed as well as the scenario when the nodes can adjust their power level. For both scenarios, we show that Hitch-hiking is advantageous and have proposed algorithms to construct broadcast tree with Hitch-hiking taken into consideration. For fixed transmission power case, we propose and analyze a centralized heuristic algorithm called SPWMH (Single Power Wireless Multicast with Hitch-hiking) to construct a broadcast tree with minimum forwarding nodes. For the latter case, we propose a centralized heuristic algorithm called Wireless Multicast with Hitch-hiking (WMH) to construct an energy efficient tree using Hitch-hiking and also present a distributed version of the heuristic. We also evaluate the proposed heuristics through simulation. Simulation results show that Hitch-hiking can reduce the transmission cost of broadcast by as much as 50%. Further, we propose and evaluate a protocol called Power Saving with Broadcast Tree (PSBT) that reduces energy consumption of broadcast by eliminating redundancy in receive operation. Finally, we propose an algorithm that takes advantage of both Hitch-hiking and PSBT in conserving energy. Manish Agarwal is an engineer at Microsoft, Redmond. He received his Masters degree in Electrical and Computer Engineering from University of Massachusetts, Amherst in 2004. He received his undergraduate degree from Indian Institute of Technology, Guwahati. His research interest lies in the field of mobile ad hoc networks. Lixin Gao is an associate professor of Electrical and Computer Engineering at the University of Masschusetts, Amherst. She received her Ph.D. degree in computer science from the University of Massachusettes at Amherst in 1996. Her research interests include multimedia networking and Internet routing. Between May 1999 and January 2000, she was a visiting researcher at AT&T Research Labs and DIMACS. She is an Alfred P. Sloan Fellow and received an NSF CAREER Award in 1999. She is a member of IEEE, ACM, and Sigma Xi. Joon Ho Cho received the B.S. degree (summa cum laude) in electrical engineering from Seoul National University, Seoul, Korea, in 1995 and the M.S.E.E. and Ph.D. degrees in electrical and computer engineering from Purdue University, West Lafayette, IN, in 1997 and 2001, respectively. From 2001 to 2004, he was with the University of Massachusetts at Amherst as an Assistant Professor. Since July 2004, he has been with Pohang University of Science and Technology (POSTECH), Pohang, Korea, where he is presently an Assistant Professor in the Department of Electronic and Electrical Engineering. His research interests include wideband systems, multiuser communications, adaptive signal processing, packet radio networks, and information theory. Dr. Cho is currently an Associate Editor for the IEEE Transactions on Vehicular Technology. Jie Wu is a Professor at Department of Computer Science and Engineering, Florida Atlantic University. He has published over 300 papers in various journal and conference proceedings. His research interests are in the area of mobile computing, routing protocols, fault-tolerant computing, and interconnection networks. Dr. Wu served as a program vice chair for 2000 International Conference on Parallel Processing (ICPP) and a program vice chair for 2001 IEEE International Conference on Distributed Computing Systems (ICDCS). He is a program co-chair for the IEEE 1st International Conference on Mobile Ad-hoc and Sensor Systems (MASS'04). He was a co-guest-editor of a special issue in IEEE Computer on “Ad Hoc Networks”. He also editored several special issues in Journal of Parallel and Distributing Computing (JPDC) and IEEE Transactions on Parallel and Distributed Systems (TPDS). He is the author of the text “Distributed System Design” published by the CRC press. Currently, Dr. Wu serves as an Associate Editor in IEEE Transactions on Parallel and Distributed Systems and three other international journals. Dr. Wu is a recipient of the 1996–97 and 2001–2002 Researcher of the Year Award at Florida Atlantic University. He served as an IEEE Computer Society Distinguished Visitor. Dr. Wu is a Member of ACM and a Senior Member of IEEE.     

A Hybrid Error Recovery scheme for Scalable Video Transmission over 3G Cellular Broadcast Networks

The cdma2000 1xEV-DO mobile communication system provides broadcast and multicast services (BCMCS) to meet an increasing demand for multimedia data services. But the servicing of video streams over a BCMCS network faces a challenge from the unreliable and error-prone nature of the radio channel. BCMCS uses Reed-Solomon coding integrated with the MAC protocol for error recovery. We show that this is not effective for mobiles moving at the edge of service area, where the channel condition is bad, resulting in significantly lower video quality. To improve the playback quality of an MPEG-4 FGS (fine granularity scalability) video stream, we propose a hybrid error recovery scheme incorporating a packet scheduler, which uses slots saved by reducing the Reed-Solomon coding overhead. Packets to be retransmitted are prioritized by a utility function which reduces the packet error-rate in the application layer within a fixed retransmission budget by considering of the map of the error control block at each mobile node. Our error recovery scheme also uses the characteristics of MPEG-4 FGS to improve the video quality even for a slow-moving mobile which is experiencing a high error-rate in the physical channel because of error bursts. Kyungtae Kang received B.S. (1999) and M.S. (2001) degrees in computer engineering from Seoul National University, Korea. He received Ph.D. degree in Dept. of Electrical Engineering and Computer Science from Seoul National University, Korea in 2007. He is a member of IEEE and IEICE. His research interests include packet scheduling, error control, QoS provision, and energy minimization issues in nextgeneration wireless/mobile networks. In particular, he is researching the performance and energy requirements of 3G cellular broadcast services such as BCMCS and MBMS. Yongwoo Cho received the Premedical Degree from the College of Medicine, University of Ulsan, in 1997, a B.S. degree in Computer Science from Korea National Open University in 2004, while he was an military service, and an M.S. degree in Electrical Engineering and Computer Science from Seoul National University in 2006. He has worked as a researcher in Dooin Corp. and as a general manager in Bluecord Technology, Inc. His primary interests include multimedia systems, digital broadcasting, next-generation wireless/mobile networks, error control, real-time computing, and low-power design. He is currently a Ph.D. student in the School of Electrical Engineering and Computer Science at Seoul National University. Heonshik Shin received the B.S. degree in applied physics from Seoul National University, Korea, in 1973. Since he received Ph.D. degree in computer engineering from the University of Texas at Austin in 1985, he has actively involved himself in researches of various topics, ranging from real-time computing and distributed computing to mobile systems and software. He is currently a professor of School of Computer Science and Engineering at Seoul National University.     

Thyristor Input-Protection Device Suitable for CMOS RF IC’s

Based on simulation results and accompanying analysis, we suggest a thyristor-type ESD protection device structure suitable for implementation in standard CMOS processes to reduce the parasitic capacitances added to the input nodes, which is very important in CMOS RF ICs. We compare DC breakdown characteristics of the suggested device to those of a conventional NMOS protection device to show the benefits of using the suggested device for ESD protection. The characteristic improvements are demonstrated and the corresponding mechanisms are explained based on simulations. Structure dependencies are also examined to define the optimal structure. AC simulation results are introduced to estimate the magnitude of reduction in the added parasitic capacitance when using the suggested device for ESD protection. The analysis shows a possibility of reducing the added parasitic capacitance down to about 1/45 of that resulting with a conventional NMOS protection transistor, while maintaining robustness against ESD.Jin-Young Choi was born in Seoul, Korea in 1956. He received the B.S. degree in electrical engineering from the Seoul National University, Korea, in 1979, and the M.S. and Ph.D. degrees in electrical engineering from the University of Florida, USA, in 1986 and 1991, respectively. In 1991, he joined Samsung Electronics Memory Division, Korea, where he was engaged in high-speed SRAM development. In 1992, he moved to the Hongik University, Jochiwon, Korea, where he is now an associate professor. His recent research interests include the high-frequency modeling of CMOS devices, CMOS RF circuit design, and analysis & design for ESD protection.Woo Suk Yang was born in Seoul, Korea in 1957. He received the B.S. degree in electrical engineering from the Seoul National University, Korea, in 1979, and the Ph.D. degree in electrical and computer engineering from the North Calorina State University, USA, in 1990. His doctorial research was in the area of signal processing. In 1990, he joined LG Electronics Co. Korea. In 1991, he moved to the Hongik University, Jochiwon, Korea, where he is now a professor. His recent research interests include the high-frequency modeling and various topics in signal processing area.Dongmin Kim was born in Korea in 1956. He received the B.S. and M.S. degrees in electrical engineering from the Seoul National University, Korea, in 1979 and 1984, respectively and the Ph.D. degree in ECE from the University of Michigan, USA, in 1996. Now, he is an assistant professor of the Hongik University, Jochiwon, Korea. His recent research interests include circuit design and analysis.Youngju Kim was born in Seoul, Korea in 1957. He received the B.S. and M.S. degrees in electrical engineering from the Seoul National University, Korea in 1980 and 1985, respectively and the Ph.D. degree in electrical engineering from the Polytechnic University of New York, USA, in 1995, respectively. In 1996, he joined the Hongik University, Jochiwon, Korea, where he is now an assistance professor. His recent research interests include the RF circuit design and LIN wireless systems.     

Essential Considerations in Implementing the Smart Antenna System for Downlink Beamforming

This paper addresses some essential problems that have to be taken into consideration in implementing the smart antenna base station (SABS) for downlink beamforming. In order to provide proper downlink beamforming as well as uplink beamforming, a pragmatic procedure of automatic calibration is proposed. Through the experimental test, we confirm that the proposed calibration technique has eliminated the problem of the phase differences of the signal path associated with each antenna. Also, in this paper, we first analyze the multipath condition under which the auxiliary pilot becomes indispensable for detecting the data transmitted on the data channel and what happens if the auxiliary pilot is not available. Then, the performance of the downlink beamforming utilizing the auxiliary pilot is analyzed through the computer simulations. Finally, we present a comparison of downlink communications to uplink ones in terms of throughputs available at each of uplink and downlink communications. Weon-Cheol Lee received the B.S, M.S, and Ph.D. degree in Electronic Communication Engineering from Hanyang University, Korea, in 1992, 1994, 2005, respectively. From 1994 to 2000, he was with LG Electronic Inc., where he had worked for developing the digital VCR, digital cable modem, digital TV. Since 2001, he has been a professor with department of information and communications, Yong-in Songdam College, Korea. His research interests include smart antennas, mobile communications beyond the third generation, digital broadcasting technology, and communication signal processing. Dr. Lee also received the Best Research Paper Award and Excellent Research Engineer Award from LG Electronics, respectively. Seungwon Choireceived the BS degree from Hanyang University, Seoul, Korea, and the M.S. degree from Seoul National University, Korea, 1980 and 1982, respectively, both in electronics engineering, the MS degree (computer engineering) in 1985, and the PhD degree (electrical engineering), in 1988, both from Syracuse University, Syracuse, NY. From 1988 to 1989 he was with the Department of Electrical and Computer Engineering of Syracuse University, Syracuse, NY, as an Assistant Professor. In 1989 he joined the Electronics and Telecommunications Research Institute, Daejeon, Korea. From 1990 to 1992 he was with the Communications Research Laboratory, Tokyo, Japan, as a Science and Technology Agency fellow, developing the adaptive antenna array systems and adaptive equalizing filters. He joined Hanyang University, Seoul, Korea, in 1992 as an assistant professor. He is a professor in the School of Electrical and Computer Engineering of Hanyang University. Since 2003, Dr. Choi has been serving as a Vice Chairman and the representative of the ITU region 3 for SDR (Software Defined Radio) Forum and as a Director of the HY-SDR Research Center, MIC, Korea. His research interests include digital communications and adaptive signal processing with a recent focus on the implementation of the smart antenna systems for both mobile communication systems and wireless data systems. Jae-Moung Kim received the BS degree from Hanyang University, Korea in 1974, the MSEE degree from University of Southern California, USA in 1981, and the PhD degree from Yonsei University, Korea in 1987. He was a Vice President of Radio {&} Broadcasting Technology Laboratory and Director of Satellite Communication System Department at Electronics and Telecommunications Research Institute (ETRI) from September 1982 to March 2003. Since April of 2003, he has been a Professor in the Graduate School of Information Technology and Telecommunications, Inha University. He is a board member of directors of Korean Institute of Communication Science (KICS), a Vice President of Korea Society of Broadcast Engineers (KOSBE) and a senior member of IEEE. His research background is telecommunication systems modeling and performance analysis of broadband wireless access systems, mobile communications, satellite communications and broadcasting transmission technologies.     

A Location Management Scheme Using Direction Characteristics of Mobile Terminals in Mobile Communication Networks

Recently, as the number of mobile terminals (or users) keeps explosively increasing, the location management to track the mobile terminals in mobile communication networks is becoming more important. However, previous schemes have used static location information without any consideration about the moving direction of a mobile terminal. For a fixed paging area, this results in unnecessary pagings, thus increasing the location management cost. In this paper, we propose a new location management scheme using the direction characteristics of a mobile terminal. The direction vector is defined to represent the moving direction of a mobile terminal and to compute a distance from the cell where a location update occurs to the current cell. The offset operation of direction vectors is also presented to represent the position of a mobile terminal in a paging area. This allows the mobile terminal to determine whether a location update will be performed or not. The mobile terminal can also vary its own paging area dynamically according to its moving direction whenever it moves across its paging area. In addition, we develop an analytical model for the proposed scheme which captures the direction characteristics of a mobile terminal based on the Markov model. Analytical results show that the proposed scheme can reduce location management cost by forming a dynamic paging area along the moving direction of a mobile terminal when compared to other schemes.Ui-Sung Song received his B.S and M.S. degrees in Computer Science and Engineering from Korea University, Seoul, Korea in 1997 and 1999, respectively. He is currently a Ph.D. candidate in Computer Science and Engineering from Korea University. Also, he is currently a researcher in the Research Institute of Computer Science and Engineering Technology at Korea University. His research interests include mobile IP, PCS networks, and ad-hoc networks.Joon-Min Gil received his B.S. and M.S. degrees in Computer Science from Korea University, Chochiwon, Korea in 1994 and 1996, respectively. He received his Ph.D. degree in Computer Science and Engineering from Korea University, Seoul, Korea in 2000. From 2001 to 2002, he was a visiting research associate in the Department of Computer Science at the University of Illinois at Chicago, U.S.A. He is currently a senior research engineer in Supercomputing Center at Korea Institute of Science & Technology Information, Daejeon, Korea. His recent research interests include distributed and mobile computing, wireless networks, Internet computing, P2P networks, and grid computing.Chong-Sun Hwang received his M.S. degree in Mathematics from Korea University, Seoul, Korea in 1970, and his Ph.D. degree in Statistics and Computer Science from the University of Georgia in 1978. From 1978 to 1980, he was an assistant professor at South Carolina Lander State University. He is currently a full professor in the Department of Computer Science and Engineering at Korea University, Seoul, Korea. Since 2004, he has been a Dean in the College of Information and Communications at Korea University. His research interests include distributed systems,distributed algorithm, and mobile computing systems     

On Downlink Beamforming Methods: Capacity and Error Probability Performance

In space-division multiple access (SDMA), different beamforming or space-domain precoding techniques can be applied. We investigate two different space-domain precoding methods, the maximum capacity (MC) and the minimum mean square error (MMSE) precoders, for the downlink channel. It is shown that the MMSE precoding, which is practically implementable, can provide a reasonable performance in terms of the capacity and error probability, while the MC precoding is not practical (although it is optimum in terms of the capacity). Space-domain precoding methods are also applied to code-division multiple access (CDMA) systems.This work was supported by the HY-SDR Research Center at Hanyang University, Seoul, Korea, under the ITRC Program of MIC, Korea.Jinho Choi was born in Seoul, Korea. He recieved the B.E. degree (magna cum laude) in electronics engineering from Sogang University in 1989 and the M.S.E. and Ph.D. degree in electrical engineering from the Korea Advanced Institute of Science and Technology in 1991 and 1994, respectively. Currently he is a Senior Lecturer in the School of Electrical Engineering and Telecommunications,University of New South Wales, Australia. Dr. Choi received the 1999 Best Paper Award of Signal Processing from EURASIP.Seungwon Choi received the B.S. degree from Hanyang University, Seoul, Korea, in 1980 and the M.S. degree from Seoul National University, Seoul, in 1982, both the electronic engineering. He received the M.S. degree in computer engineering in 1985 and the Ph.D degree in electrical engineering in 1988 from Syracuse University, Syracuse, NY.From 1982 to 1984, he was with LG Electronics Co. Ltd., Seoul, where he helped developed the 8-mm camcorder system. From 1988 to 1989, he was with the Department of Electrical and Computer Engineering, Syracuse University, as an Assistant Professor. In 1989, he joined the Electronics and Telecommunications Research Institute, daejeon, Korea, where he developed the adaptive algorithm for real-time application in secure telephone systems. From 1990 to 1992, he was with yhe Communication Research Laboratory, Tokyo, Japan, as a science and Technology Agency Fellow, developing adaptive antenna array system and adaptive equalizing filters for applications in land-mobile communications. He joined Hanyang University, Seoul, in 1992 as an Assistant Professor. He is a Professor in the School of Electrical and Computer Engineering, Hanyang University. His research interests include digital communications and adaptive signal processing with a recent focus on the real-time implementation of smart antenna system for 3G mobile communication system.     

An Efficient Dictionary Organization for Maximum Diagnosis

The major problem of fault diagnosis with a fault dictionary is the enormous amount of data. The technique used to manage this data can have a significant effect on the outcome of the fault diagnosis procedure. If information is removed from a fault dictionary in order to reduce the size of the dictionary, its ability to diagnose stuck-at faults and unmodeled faults may be severely debased. Therefore, we focus on methods for producing a dictionary that is both small and lossless-compacted. We propose an efficient dictionary for maximum diagnosis, which is called SD-Dictionary. This dictionary consists of a static sub-dictionary and a dynamic sub-dictionary in order to make a smaller dictionary while maintaining the critical information needed for the diagnostic ability. Experimental results on ISCAS’ 85, ISCAS’ 89 and ITC’ 99 benchmark circuits show that the size of the proposed dictionary is substantially reduced, while the dictionary retains most or all of the diagnostic capability of the full dictionary. This work was supported by the “System IC 2010” project of Korea Ministry of Science and Technology and Ministry of Commerce, Industry and Energy. Editor: Y. Takamatsu Sunghoon Chun received the B.S. degrees in Electrical and Electronic Engineering from Yonsei University, Seoul, Korea, in 2002. He was a Reseach Engineer with ASIC Research Center in Yonsei University. He researched for test methodologies for SoC. He received the M.S. degrees in Electrical and Electronic Engineering from Yonsei University in 2005. He is currently working toward Ph.D. degree in Electrical and Electronic Engineering at Yonsei University. His area of interests includes SoC testing, delay testing, fault diagnosis, functional testing for processor based system and test methodologies for signal integrity faults. Sangwook Kim received the B.S., and M.S. degrees in Electrical and Electronic Engineering from Yonsei University, Seoul, Korea, in 1999, and 2001, respectively. He researched for Digital Signal Processor design and fault diagnosis of VLSI. He is a Research Engineer with SoC Design Group of System IC Division in LG Electronics, Inc. He is currently interested in SoC design for HDTV and design verification. Hong-Sik Kim was born in Seoul, Korea, on April 4, 1973. He received the B.S., M.S. and Ph.D. degrees in Electrical and Electronic Engineering from Yonsei University, Seoul, Korea, in 1977, 1999, and 2004, respectively. He was a Post-Doctorial Fellow with the Institute of Virginia Technology. He is currently working on System LSI Group in the Samsung Electronics. His current research interest includes design-for-testability, built-in self tests and fault diagnosis. Sungho Kang received the B.S. degree from Seoul National University, Seoul, Korea, and the M.S. and Ph.D. degrees in electrical and computer engineering from The University of Texas at Austin. He was a Post-Doctorial Fellow with the University of Texas at Austin, a Research Scientist with the Schlumberger Laboratory for Computer Science, Schlumberger Inc., and a Senior Staff Engineer with the Semiconductor Systems Design Technology, Motorola Inc. Since 1994, he has been an Associate Professor with the Department of Electrical and Electronic Engineering, Yonsei University, Seoul, Korea. His current research interests include VLSI design, VLSI CAD and VLSI testing and design for testability.     

Enhancement of a WLAN-Based Internet Service

A wireless LAN (WLAN)-based Internet service, called NESPOT, of Korea Telecom (KT), the biggest telecommunication and Internet service company in Korea, has been operational since early 2002. As the numbers of subscribers and deployed access points (APs) increase, KT has been endeavoring to improve its service quality as well as the network management. In this paper, we introduce a joint effort between Seoul National University (SNU) and KT to achieve it. We have been addressing two major issues as part of the joint project thus far: (1) a unified WLAN management/maintenance tool; and (2) real-time traffic support enhancement. We present our on-going efforts as well as some preliminary results. Some issues, which need further attention for the future NESPOT service enhancement, are also introduced.The work reported in this paper was financed and supported by KT. Any opinions, findings, and conclusions or recommendations expressed in this publication are those of the authors and do not necessarily reflect the views of KT. Youngkyu Choi is an M.S. candidate in the department of electrical engineering at Seoul National University (SNU), Seoul, Korea. He received his B.S. with honors in electrical engineering from SNU in 2002. He has a lot of project experiences related with system software development. His current research interests are the design of MAC layer from distributed system to centralized cellular system, resource management in next-generation (4G) cellular system, and mathematical analysis of system performance. He had served in the Korean Army for 3 years from 1998. Sekyu Park is a research staff at the Multimedia & Wireless Networking Lab. (MWNL), Seoul National University (SNU), Seoul, Korea. Before joining MWNL in September 2003, he was with MMC Technology, Seoul, Korea as a Research Staff for five years. His current research interests are in the area of wireless/mobile networks and embedded OS. Sunghyun Choi is an assistant professor at the School of Electrical Engineering, Seoul National University (SNU), Seoul, Korea. Before joining SNU in September 2002, he was with Philips Research USA, Briarcliff Manor, New York, USA as a Senior Member Research Staff and a project leader for three years. He received his B.S. (summa cum laude) and M.S. degrees in electrical engineering from Korea Advanced Institute of Science and Technology (KAIST) in 1992 and 1994, respectively, and received Ph.D. at the Department of Electrical Engineering and Computer Science, The University of Michigan, Ann Arbor in September, 1999. His current research interests are in the area of wireless/mobile networks with emphasis on the QoS guarantee and adaptation, resource management, wireless LAN and PAN, next-generation mobile networks, data link layer protocols, and connection and mobility management. He authored/coauthored over 45 technical papers and book chapters in the areas of wireless/mobile networks and communications. He is the technical program co-chair for ACM International Workshop on Wireless Mobile Applications and Services on WLAN Hotspots (WMASH’2004). He is currently serving on program committees of a number of leading wireless and networking conferences including IEEE INFOCOM, IEEE GLOBECOM, and IEEE VTC. He is also a guest co-editor for a special issue on “Emerging WLAN Applications and Technologies” of Wiley Wireless Communications and Mobile Computing Journal. He is an active participant and contributor of the IEEE 802.11 WLAN standardization committee. Dr. Choi was a recipient of the Korea Foundation for Advanced Studies Scholarship and the Korean Government Overseas Scholarship during 1997–1999 and 1994–1997, respectively. Go Woon Lee is a researcher at Service Development Laboratory, Korea Telecom (KT), Seoul, Korea. She received her B.S. degrees in computer science and material engineering from Korea Advanced Institute of Science and Technology (KAIST) in 1995. She was with Microsoft Korea R&D Group as a research staff in 1995. She received M.S. degree in information & communication from Kwang-Ju Institute of Science and Technology (K-JIST) in 1998. Her current research interests are in the area of wireless/mobile networks with emphasis on data link layer protocols, remote diagnosis, and wireless service management. Jaehwan Lee is a researcher at Korea Telecom (KT), Seoul, Korea. He received his B.S. and M.S. degrees in electrical engineering from Seoul National University (SNU) in 1998 and 2000, respectively. His master’s research was about estimation theory related to Global Positioning System (GPS) and image processing in robot soccer. His current research interest is to analyze and enhance the performance of wireless/mobile networks (IEEE 802.11, sensor networks and mobile ad-hoc networks) regarding QoS, energy-efficiency and high-throughput considering hand-off and inter-networking with heterogeneous networks. Before joining wireless LAN group in KT, he developed the Web-GIS (Geographical Information System) client-server system from 2000 to 2001. Hanwook Jung, Ph.D joined KT in 1985 and got his Ph.D degree with the company finalcial scholarship of KT from 1991 to 1996 at SUNY at Buffalo. His thesis is about “Wireless signal transmission over Fiber by subcarrier multiplexing” which is current heavily utilized for PCS and cellular repeater line. From 1985 to 1991, he had developed a Videotex service which is now known as Hitel. From 1996 to 1999, he developed 26GHz broadband wireless local loop system and contributed to get the license from the government. Since 1999, he has led a business model and service with wireless LAN. The KT Wi-Fi public service, “NESPOT” has 300,000 subscribers and 10,000 public hotspots. In 2003 he was promoted as an assistant vice president leading NESPOT research team to enhance KT’s broadband with 5,000,000 subscribers. His vision regarding next generation communications service is believed to be true by combining the broadband access and wireless technology including WiFi wireless LAN, UWB, and bluetooth in those areas such as wireless home-networking, device-to-device communications, and ubiqutous networking.This revised version was published online in August 2005 with a corrected cover date.     

Design and Analysis of Optimal Multi-Level Hierarchical Mobile IPv6 Networks

Hierarchical Mobile IPv6 (HMIPv6) is an enhanced version of Mobile IPv6 designed to reduce signaling overhead and to support seamless handoff in IP-based wireless/mobile networks. To support more scalable services, HMIPv6 networks can be organized as the form of a multi-level hierarchy architecture (i.e., tree structure). However, since multi-level HMIPv6 networks incur additional packet processing overhead at multiple mobility agents, it is important to find the optimal hierarchy level to minimize the total cost, which consists of the location update cost and the packet delivery cost. In this paper, we investigate this problem, namely the design of an optimal multi-level HMIPv6 (OM-HMIPv6) network. To accomplish this, we design a function to represent the location update cost and the packet delivery cost in multi-level HMIPv6 networks. Based on these formulated cost functions, we calculate the optimal hierarchy level in multi-level HMIPv6 networks, in order to minimize the total cost. In addition, we investigate the effects of the session-to-mobility ratio (SMR) on the total cost and the optimal hierarchy. The numerical results, which show various relationships among the network size, optimal hierarchy, and SMR, can be utilized to design an optimal HMIPv6 network. In addition, the analytical results are validated by comprehensive simulations. Sangheon Pack received his B.S. (2000, magna cum laude) and Ph.D. (2005) degrees from Seoul National University, both in computer engineering. He is a post doctor fellow in the School of Computer Science and Engineering at the Seoul National University, Korea. He is a member of the IEEE and ACM. During 2002–2005, he was a recipient of the Korea Foundation for Advanced Studies (KFAS) Computer Science and Information Technology Scholarship. He has been also a member of Samsung Frontier Membership (SFM) from 1999. He received a student travel grant award for the IFIP Personal Wireless Conference (PWC) 2003. He was a visiting researcher to Fraunhofer FOKUS, German in 2003. His research interests include mobility management, wireless multimedia transmission, and QoS provision issues in the next-generation wireless/mobile networks. Yanghee Choi received B.S. in electronics engineering from Seoul National University, M.S. in electrical engineering from Korea advanced Institute of Science, and Doctor of Engineering in Computer Science from Ecole Nationale Superieure des Telecommunications (ENST) in Paris, in 1975, 1977 and 1984 respectively. Before joining the School of Computer Engineering, Seoul National University in 1991, he has been with Electronics and Telecommunications Research Institute (ETRI) during 1977–1991, where he served as director of Data Communication Section, and Protocol Engineering Center. He was research student at Centre National d'Etude des Telecommunications (CNET), Issy-les-Moulineaux, during 1981–1984. He was also Visiting Scientist to IBM T.J. Watson Research Center for the year 1988–1989. He is now leading the Multimedia Communications Laboratory in Seoul National University. He is also director of Computer Network Research Center in Institute of Computer Technology (ICT). He was editor-in-chief of Korea Information Science Society journals. He was chairman of the Special Interest Group on Information Networking. He has been associate dean of research affairs at Seoul National University. He was president of Open Systems and Internet Association of Korea. His research interest lies in the field of multimedia systems and high-speed networking. Minji Nam received her B.S. and M.S degrees in Computer Science and Engineering from Seoul National University in 2003 and 2005, respectively. From 2005, she has worked on Portable Internet Development Team for Korea Telecom. Her research interests are mobile networks, portable internet technology (IEEE 802.16) and Mobile IPv6.     

On-demand diversity wireless relay networks

There has been much recent attention on using wireless relay networks to forward data from mobile nodes to a base station. This network architecture is motivated by performance improvements obtained by leveraging the highest quality links to a base station for data transfer. With the advent of agile radios it is possible to improve the performance of relay networks through intelligent frequency assignments. First, it is beneficial if the links of the relay network are orthogonal with respect to each other so that simultaneous transmission on all links is possible. Second, diversity can be added to hops in the relay network to reduce error rates. In this paper we present algorithms for forming such relay networks dynamically. The formation algorithms support intelligent frequency assignments and diversity setup. Our results show that algorithms that order the sequence in which nodes join a relay network carefully, achieve the highest amount of diversity and hence best performance. This research is supported in part by NSF grant CNS-0508114. JaeSheung Shin received the B.S. and M.S. degree in Computer Science and Engineering from DongGuk University, Korea, in 1991 and 1993, respectively. He is currently working toward the Ph.D. degree in Computer Science and Engineering at the Pennsylvania State University, University Park. He is a research assistant at the Networking and Security Research Center (NSRC). Prior to joining Pennsylvania State University, he was with Electronics and Telecommunications Research Institute (ETRI), Korea, since 1993. He worked on development of 2G and 3G wireless cellular core network elements. His research interests include mobility management and signaling for wireless cellular and routing and resource allocation for multi-radio multi-hop wireless cellular networks. Kyounghwan Lee received the B.S. degree in Electrical and Electronics Engineering from University of Seoul, Seoul, Korea, in 2000, and the M.S. degree in Information and Communication Engineering from Gwangju Institute of Science and Technology, Gwangju, Korea, in 2002. He is currently a Ph.D candidate at the Electrical Engineering department at the Pennsylvania State University and a research assistant at the Wireless Communications and Networking Laboratory (WCAN@PSU). His research interests include wireless communication theory and relay networks. E-mail: kxl251@psu.edu Aylin Yener received the B.S. degrees in Electrical and Electronics Engineering, and in Physics, from Bogazici University, Istanbul, Turkey, in 1991, and the M.S. and Ph.D. degrees in Electrical and Computer Engineering from Rutgers University, NJ, in 1994 and 2000, respectively. During her Ph.D. studies, she was with Wireless Information Network Laboratory (WINLAB) in the Department of Electrical and Computer Engineering at Rutgers University, NJ. Between fall 2000 and fall 2001, she was with the Electrical Engineering and Computer Science Department at Lehigh University, PA, where she was a P.C. Rossin assistant professor. Currently, she is with the Electrical Engineering department at the Pennsylvania State University, University Park, PA, as an assistant professor. Dr. Yener is a recipient of the NSF CAREER award in 2003. She is an associate editor of the IEEE Transactions on Wireless Communications. Dr. Yener’s research interests include performance enhancement of multiuser systems, wireless communication theory and wireless networking. Thomas F. La Porta received his B.S.E.E. and M.S.E.E. degrees from The Cooper Union, New York, NY, and his Ph.D. degree in Electrical Engineering from Columbia University, New York, NY. He joined the Computer Science and Engineering Department at Penn State in 2002 as a Full Professor. He is the Director of the Networking Research Center at Penn State. Prior to joining Penn State, Dr. La Porta was with Bell Laboratories since 1986. He was the Director of the Mobile Networking Research Department in Bell Laboratories, Lucent Technologies. He is an IEEE Fellow and Bell Labs Fellow. Dr. La Porta was the founding Editor-in-Chief of the IEEE Transactions on Mobile Computing. He has published over 50 technical papers and holds 25 patents.     

Adaptive random sampling for traffic volume measurement

Traffic measurement and monitoring are an important component of network management and traffic engineering. With high-speed Internet backbone links, efficient and effective packet sampling techniques for traffic measurement and monitoring are not only desirable, but also increasingly becoming a necessity. Since the utility of sampling depends on the accuracy and economy of measurement, it is important to control sampling error. In this paper, we propose an adaptive packet sampling technique for flow-level traffic measurement with stratification approach. We employ and advance sampling theory in order to ensure the accurate estimation of large flows. With real network traces, we demonstrate that the proposed sampling technique provides unbiased estimation of flow size with controllable error bound, in terms of both packet and byte counts for elephant flows, while avoiding excessive oversampling. Baek-Young Choi received her Ph.D. in 2003 in Computer Science and Engineering from the University of Minnesota, Twin Cities. She received her B.S. degree in 1993 from Pusan National University, Korea and M.S. degree in 1995 from Pohang University of Science and Technology, Korea. After her Ph.D. she was a post-doctoral researcher at Sprint Advanced Technology Labs, and a 3M McKnight Distinguished Visiting Assistant Professor at the University of Minnesota, Duluth. From 2005, Dr. Choi is an assistant professor at the University of Missouri, Kansas City. Zhi-Li Zhang received a B.S. degree in computer science from Nanjing University, China, in 1986 and his M.S. and Ph.D. degrees in computer science from the University of Massachusetts in 1992 and 1997. In 1997 he joined the Computer Science and Engineering faculty at the University of Minnesota, where he is currently a professor. From 1987 to 1990, he conducted research in Computer Science Department at rhus University, Denmark, under a fellowship from the Chinese National Committee for Education. He has held visiting positions at Sprint Advanced Technology Labs; IBM T.J. Watson Research Center; Fujitsu Labs of America, Microsoft Research China, and INRIA, Sophia-Antipolis, France.     

A low-power sigma-delta modulator for wireless communication receivers using adaptive biasing circuitry and cascaded comparator scheme

This paper represents the low-power signal-delta (ΣΔ) modulator for wireless communication receiver applications. The 2nd-order modulator has a single-loop structure with 11 quantization levels. An adaptive biasing scheme of the operational amplifier and cascaded comparator scheme are proposed in order to save the power consumption. The DAC with three-level references including the analog ground voltage can make the modulator be implemented with half of the input capacitances without degradation of linearity characteristics with the help of dynamic element matching technique. Peak SNR values of 74 dB and 68 dB are achieved with the input bandwidths of 615 kHz and 1.92 MHz for CDMA-2000 and WCDMA applications, respectively. The modulator is fabricated in a 0.13-μm standard digital CMOS technology and dissipates 4.3 mA for a single supply voltage of 2.8 V. Jinup Lim was born in Seoul, Korea, in 1973. He received the B.S. and the M.S. degrees in semiconductor engineering from University of Seoul, Seoul, Korea, in 1999 and 2001, respectively. From 2001 to 2002, he worked in GCT Semiconductor Inc., Seoul, Korea. He is currently working toward the Ph.D. degree in Electrical & Computer Engineering at the same university. He received the Best student paper award from IEEE SSCS/EDS Seoul Chapter in 2004 and the Samsung Best paper award third prize in ISOCC 2004. His research area is the design of high-performance discrete-time / continuous-time sigma-delta modulator circuits. Joongho Choi was born in Seoul, Korea, in 1964. He received the B.S. and the M.S. degrees in electronics engineering from Seoul National University, Seoul, Korea, in 1987 and 1989, respectively. In 1993, he received Ph.D. degree in electrical engineering from University of Southern California, CA, USA. From 1994 to 1996, he worked in IBM T. J. Watson Research Center, NY, USA. In 1996, he joined the University of Seoul, Seoul, where he is currently a professor in the Department of Electrical & Computer Engineering. His research area is the design of high-performance analog integrated circuits.     

A State-Space Approach to Multiuser Parameters Estimation Using Central Difference for CDMA Systems

In this paper, it is shown that a state-space model applies to the code-division multiple-access (CDMA) channel, and Central Difference Filter (CDF) produces channel estimates with the minimum mean-square error (MMSE). This result may be used as compare to Extended Kalman Filter (EKF) which used as channel estimator in CDMA system. The main purpose of this paper is to compare robustness of channel estimator for realistic rapidly time-varying Rayleigh fading channels. To overcome the highly nonlinear nature of time delay estimation and also improve the accuracy, consistency and efficiency of channel estimation, an iterative nonlinear filtering algorithm, called the CDF has been applied in the field of CDMA System. The proposed channel estimator has a more near-far resistant property than the conventional Extended Kalman Filter (EKF). Thus, it is believed that the proposed estimator can replace well-known filters, such as the EKF. The Cramer-Rao lower bound (CRLB) is derived for the estimator, and simulation result show that it is nearly near-far resistant and clearly outperforms the EKF. Jang Sub Kim was born June 15, 1974, in Yeongdeok, Korea. He received the M.S. degree in school of electrical and computer engineering from Sungkyunkwan University, Seoul, Korea. He is currently with the School of Information and Communication Engineering, Sungkyunkwan University, where he was a Ph. D. student since 1999. His research interests include code-division multiple access, channel estimation, position location, and wireless communications. Seokho Yoon (S‘99–M‘1) received the B.S.E. (summa cum laude), M.S.E., and Ph.D. degrees in electrical engineering from KAIST, Daejeon, Korea, in 1997, 1999, and 2002, respectively. From April 2002 to June 2002, he was with the Department of Electrical Engineering and Computer Sciences, Massachusetts Institute of Technology, Cambridge, MA, and from July 2002 to February 2003, he was with the Department of Electrical Engineering, Harvard University, Cambridge, MA, as a Postdoctoral Research Fellow. In March 2003, he joined the School of Information and Communication Engineering, Sungkyunkwan University, Suwon, Korea, where he is currently an Assistant Professor. His research interests include spread spectrum systems, mobile communications, detection and estimation theory, and statistical signal processing. Dr. Yoon is a member of the IEEK and KICS. He was the recipient of a Bronze Prize at Samsung Humantech Paper Contest in 2000. Dong-Ryeol Shin (M‘97) was born in Seoul, Korea, in 1957. He received the B.S., M.S. and Ph.D degree in electrical engineering from the Sungkyunkwan University in 1980, and the Korea Advanced Institute of Science and Technology (KAIST) in 1982 and the Georgia Institute of Technology in 1992, respectively. During 1992-1994, he had worked for Samsung Data Systems, Ltd., Korea. Since 1994, he has been with network research group at the Sungkyunkwan University, Korea, as a professor. His current research interests include wireless communications and ubiquitous computing.     

Cycle-Accurate Energy Measurement and Characterization of FPGAs

Field Programmable Gate Arrays (FPGAs) play many important roles, ranging from small glue logic replacement to System-on-Chip (SoC) designs. Nevertheless, FPGA vendors cannot accurately specify the power consumption of their products on device data sheets because the power consumption of FPGAs is strongly dependent on the target circuit, including resource utilization, logic partitioning, mapping, placement and routing. Although major CAD tools have started to report average power consumption under given transition activities, power-efficient FPGA design demands more detailed information about power consumption. In this paper, we introduce an in-house cycle-accurate FPGA energy measurement tool and energy characterization schemes spanning low-level to high-level design. This tool offers all the capabilities necessary to investigate the energy consumption of FPGAs for operation-based energy characterization, which is applicable to high-level and system-wide energy estimation. It also includes features for low-level energy characterization. We compare our tool with Xilinx XPower and demonstrate the state-machine-based energy characterization of an SDRAM controller.The RIACT at Seoul National University provide research facilities for this study. This work was partly supported by the Brain Korea 21 Project.Hyung Gyu Lee received the B.S. degree in Dept. of Computer Engineering from DongGuk University, in 1999, M.S. degree in School of Computer Science and Engineering from Seoul National University, Seoul, Korea, in 2001, and is currently working toward the Ph.D. degree at Seoul National University. His research interests include device-level energy measurement and characterization, system-level low power design and low-power FPGA design.KyungSoo Lee is a M.S. student at the School of Computer Science and Engineering, Seoul National University. He received the B.S. degree in the School of Computer Science and Engineering from Seoul National University, Seoul, Korea, in 2004. He is currently working on low-power systems and embedded systems for his M.S. degree.Yongseok Choi received the B.S. and M.S. degree in the School of Computer Science and Engineering from Seoul National University, Seoul, Korea, in 2000 and 2002, respectively. He is currently working toward the Ph.D. degree in the School of Computer Science and Engineering at Seoul National University. His research interests include embedded systems and low power systems.Naehyuck Chang received his B.S., M.S. and Ph.D. degrees all from Dept. of Control and Instrumentation Engineering, Seoul National University, Seoul, Korea, in 1989, 1992 and 1996, respectively. Since 1997, he has been with School of Computer Science and Engineering, Seoul National University and currently is an Associate Professor. His research interest includes system-level low-power design and embedded systems design.     

Implementation of a Wireless Multimedia DSP Chip for Mobile Applications

This paper presents the implementation of a wireless multimedia DSP chip for mobile applications. The implemented DSP chip supports communication instructions for Viterbi, timing synchronization, etc. as well as multimedia instructions. The DSP can handle variable length data and perform four MACs in a cycle. The proposed DSP employs parallel processing techniques, such as SIMD, vector processing, DSP schemes and adopts low power features for wireless applications. The implemented DSP chip includes test circuits and various peripherals, such as DMA, bus arbitration, timer, etc. This chip has been modeled by Verilog HDL and implemented using the 0.35 m HCB60 library. The total gate count excluding memory is about 170,000 gates and the clock frequency is 100 MHz.Junghoo Lee received the B.S. degree in electronic engineering from Ajou University, Suwon, Korea in 2002. He is currently working toward the Ph.D. degree with School of Electrical and Computer Engineering, Ajou University. His main research interests include SOC design and application-specific DSP chip design.Myung H. Sunwoo received the B.S. degree in electronic engineering from the Sogang University in 1980, the M.S. degree in electrical and electronics from the Korea Advanced Institute of Science and Technology in 1982, and the Ph.D. degree in electrical and computer engineering from the University of Texas at Austin in 1990.He worked for Electronics and Telecommunications Research Institute (ETRI) in Daejeon, Korea from 1982 to 1985 and Digital Signal Processor Operations, Motorola, Austin, TX from 1990 to 1992. Since 1992, he has been a Professor with the School of Electrical and Computer Engineering, Ajou University in Suwon, Korea. In 2000, he was a Visiting Professor in the Department of Electrical and Computer Engineering, the University of California, Davis, CA. He is the Director of the National Research Laboratory sponsored by the Ministry of Science and Technology. His research interests include VLSI architectures, SOC design for multimedia and communications, and application-specific DSP architectures.Dr. Sunwoo has published more than 120 papers in international transactions/journals and conferences and also has 28 patents including five U.S. patents. He served as a Technical Program Chair of the IEEE Workshop on Signal Processing Systems (SIPS) in 2003 and a member of the technical program committee of various international conferences. He has received a number of research awards from the Ministry of Commerce, Industry and Energy, Samsung Electronics, and professional foundations. He served as an Associate Editor for the IEEE Transactions on Very Large Scale Integration (VLSI) Systems (2002–2003) and as a Guest Editor for the Journal of VLSI Signal Processing (Kluwer, 2004). Currently, He is a Senior Member of IEEE and a Chair of the IEEE CAS Society of the Seoul Chapter.     

Phase Noise Effects and Mitigation in OFDM Systems over Rayleigh Fading Channels

In this paper, we provide an exact analysis of phase-noise effects on orthogonal frequency division multiplexing (OFDM) performance. We focus on the phase-noise inter-carrier interference (ICI) and derive a closed-form expression for the signal-to-interference-noise ratio (SINR), which helps in understanding how system behavior changes with a certain parameter. An ICI reduction (ICIR) scheme was proposed in [14] and the algorithm performance over AWGN channel was thoroughly studied. In this paper, we further extend this work to Rayleigh fading channel and investigate the effects of multipath fading on the phase-noise mitigation. It is shown by the study that the ICIR algorithm reduces the phase-noise ICI a great deal before channel estimation and improves greatly system performance. Finally, numerical results show the effectiveness of the proposed approaches. Guanghui Liu was born in Sichuan, China, in 1976. He received the B.S. degree from Sichuan Teachers College, Nanchong, Sichuan, China in 1999, received the M.Sc. and Ph.D. degrees in electronic engineering from University of Electronic Science and Technology of China (UESTC), Chengdu, Sichuan, China, in 2002 and 2005 respectively. Dr. Liu serves as a reviewer for the IEEE Transactions on Communications, the IEEE Transactions on Broadcasting and the IEEE Transactions on Wireless Communications. As a research engineer, he is now with Samsung Electronics, Suwon, Republic of Korea. His research interests include synchronization, channel estimation and equalization, phase-noise suppression in OFDM communication systems. Weile zhu was born in Sichuan, China, in 1940. Since 1988 he has been a professor of signal processing with University of Electronic Science and Technology of China, Chengdu, China. He was a visiting scholar researching image processing in University of Illinois from 1980 to 1981, researching pattern recognition in Purdue University from 1982 to 1983, and researching intelligent robot in Stanford University from 1990 to 1991. His research interests include digital video codec and transmission, multicarrier modulation, and HDTV etc.     

Effective Paging Strategy based on Location Probability of Mobile Station and Paging Load Distribution of Base Station in Mobile Communication Networks

When the cells in a location area are sequentially paged based on specific information, such as the last registered area or a mobile speed, the paging load may be non-uniformly distributed among the cells. This non-uniform paging traffic causes an additional paging delay due to the increased waiting time in cells that have a high paging load. In this paper, we introduce a new paging strategy in which the paging sequence in a location area is optimized according to both the location probability of a mobile terminal and the paging load distribution among the cells. In addition, we propose a simple polynomial-time heuristic algorithm to determine sub-optimal paging sequence. Numerical results show that our proposed strategy has almost an equivalent optimal performance and outperforms the conventional paging scheme with respect to a paging delay. Dong-Jun Lee received the B.S., M.S., and Ph.D. degrees in electrical engineering from the Korea Advanced Institute of Science and Technology (KAIST), Daejeon, Korea, in 1994, 1996, and 2000, respectively. Since 2000 to 2004, he was with Samsung Electronics Co., Ltd., Korea and participated in developing cdma2000 systems. Since 2005, he has been with Hankuk Aviation University, where he is a professor with School of Electronics, Telecommunications and Computer Engineering. His research interests include radio resource management and location management of 3G and 4G wireless systems. HyeJeong Lee has received the B.S. and M.S. degrees, both in Electrical and Electronics Engineering from the Korea Advanced Institute of Science and Technology (KAIST), in 2000 and 2002, respectively. She is currently working toward the Ph. D. degree in Electrical Engineering at the KAIST. Her current research interests include mobility and resource management and reverse link performance in the high data rate mobile communication networks. Dong-Ho Cho received the B.S. degree in Electrical Engineering from the Seoul National University in 1979, and the M.S. and Ph.D. degrees, both in Electrical and Electronics Engineering from the Korea Advanced Institute of Science and Technology (KAIST), in 1981 and 1985, respectively. From 1987 to 1997, he was Professor of Computer Engineering at the Kyunghee University. Since 1998, he has been Professor of Electrical Engineering at KAIST. He is active as a Technical Program Committee and Chair of several conferences, and a reviewer for IEEE journals. He is a Technical Program Committee of the IEEE WCNC 2005 and Globecom 2005. His research interests include 3G/4G wireless communication network, protocol and services.     

Markov model of link connectivity in mobile ad hoc networks

This paper proposes a Markov model of link connectivity for mobile ad hoc networks. Under a random behavior, the model provides a unified approach to describe many different mobility models including entity mobility models and group mobility models. Using the model, we can predict the time dependence of link connectivity, and estimate a settling time for which node movements are considered in a transient state. We verify the model with the simulation results of four different mobility models using a global connectivity and a link duration distribution. This research was supported in part by the National Science Foundation under grant CCF-0514975. Seok K. Hwang received the B.S. degree in Control and Instrumentation Engineering from Korea University, Korea in 1998. He received the M.S. degreeand the Ph.D.degree in Electrical Engineering at POSTECH, Korea in 2000 and 2006, respectively.His research interests include intelligence controls and computational intelligence for multi-objective optimization problems. He is working on multimedia communication as a senior researcher at Korea Telecom since 2006. Dongsoo Stephen Kim received the B.S. degree from Korean University in 1987, the M.S. degree in computer science from the University of Texas in 1994, and the Ph.D. degree in computer science and engineering from the University of Minnesota in 1998. During 1986–2002, he was a Research Associate at Electronic and Telecommunication Research Institute, Taejon, Korea. In 1998–2000, he was a project manager at Megaxess Inc., Germantown, Maryland. He joined the Department of Electrical and Computer Engineering at Purdue School of Engineering and Technology, IUPUI in 2000. His current research interests include mobile wireless networks, mobility modeling, traffic modeling, and performance evaluation of communication networks.     

Performance of a burst-frame-based CSMA/CA protocol: Analysis and enhancement

In this paper, we develop an analytical model to evaluate the delay performance of the burst-frame-based CSMA/CA protocol under unsaturated conditions, which has not been fully addressed in the literature. Our delay analysis is unique in that we consider the end-to-end packet delay, which is the duration from the epoch that a packet enters the queue at the MAC layer of the transmitter side to the epoch that the packet is successfully received at the receiver side. The analytical results give excellent agreement with the simulation results, which represents the accuracy of our analytical model. The results also provide important guideline on how to set the parameters of the burst assembly policy. Based on these results, we further develop an efficient adaptive burst assembly policy so as to optimize the throughput and delay performance of the burst-frame-based CSMA/CA protocol. Kejie Lu received the B.E. and M.E. degrees in Telecommunications Engineering from Beijing University of Posts and Telecommunications, Beijing, China, in 1994 and 1997, respectively. He received the Ph.D. degree in Electrical Engineering from the University of Texas at Dallas in 2003. In 2004 and 2005, he was a postdoctoral research associate in the Department of Electrical and Computer Engineering, University of Florida. Currently, he is an assistant professor in the Department of Electrical and Computer Engineering, University of Puerto Rico at Mayagüez. His research interests include architecture and protocols design for computer and communication networks, performance analysis, network security, and wireless communications. Jianfeng Wang received the B.E. and M.E. degrees in electrical engineering from Huazhong University of Science and Technology, China, in 1999 and 2002, respectively, and the Ph.D. degree in electrical engineering from University of Florida in 2006. From January 2006 to July 2006, he was a research intern in wireless standards and technology group, Intel Corporation. In October 2006, he joined Philips Research North America as a senior member research staff in wireless communications and networking department. He is engaged in research and standardization on wireless networks with emphasis on medium access control (MAC). Dapeng Wu received B.E. in Electrical Engineering from Huazhong University of Science and Technology, Wuhan, China, in 1990, M.E. in Electrical Engineering from Beijing University of Posts and Telecommunications, Beijing, China, in 1997, and Ph.D. in Electrical and Computer Engineering from Carnegie Mellon University, Pittsburgh, PA, in 2003. Since August 2003, he has been with Electrical and Computer Engineering Department at University of Florida, Gainesville, FL, as an Assistant Professor. His research interests are in the areas of networking, communications, multimedia, signal processing, and information and network security. He received the IEEE Circuits and Systems for Video Technology (CSVT) Transactions Best Paper Award for Year 2001, and the Best Paper Award in International Conference on Quality of Service in Heterogeneous Wired/Wireless Networks (QShine) 2006. Currently, he serves as the Editor-in-Chief of Journal of Advances in Multimedia, and an Associate Editor for IEEE Transactions on Wireless Communications, IEEE Transactions on Circuits and Systems for Video Technology, IEEE Transactions on Vehicular Technology, and International Journal of Ad Hoc and Ubiquitous Computing. He is also a guest-editor for IEEE Journal on Selected Areas in Communications (JSAC), Special Issue on Cross-layer Optimized Wireless Multimedia Communications. He served as Program Chair for IEEE/ACM First International Workshop on Broadband Wireless Services and Applications (BroadWISE 2004); and as a technical program committee member of over 30 conferences. He is Vice Chair of Mobile and wireless multimedia Interest Group (MobIG), Technical Committee on Multimedia Communications, IEEE Communications Society. He is a member of the Best Paper Award Committee, Technical Committee on Multimedia Communications, IEEE Communications Society. Yuguang Fang received a Ph.D. degree in Systems Engineering from Case Western Reserve University in January 1994 and a Ph.D. degree in Electrical Engineering from Boston University in May 1997. He was an assistant professor in the Department of Electrical and Computer Engineering at New Jersey Institute of Technology from July 1998 to May 2000. He then joined the Department of Electrical and Computer Engineering at University of Florida in May 2000 as an assistant professor and got an early promotion to an associate professor with tenure in August 2003 and to a full professor in August 2005. He has published over 200 papers in refereed professional journals and conferences. He received the National Science Foundation Faculty Early Career Award in 2001 and the Office of Naval Research Young Investigator Award in 2002. He has served on several editorial boards of technical journals including IEEE Transactions on Communications, IEEE Transactions on Wireless Communications, IEEE Transactions on Mobile Computing and ACM Wireless Networks. He have also been actively participating in professional conference organizations such as serving as The Steering Committee Co-Chair for QShine, the Technical Program Vice-Chair for IEEE INFOCOM’2005, Technical Program Symposium Co-Chair for IEEE Globecom’2004, and a member of Technical Program Committee for IEEE INFOCOM (1998, 2000, 2003–2007). He is a senior member of the IEEE.