A Novel Event Model for Performance Analysis of IEEE 802.11 DCF

After considering the memory effect among series events occurring on the channel, we propose a novel event model to analyze the channel status more precisely. The memory effect is caused by the backoff freezing regulation of IEEE 802.11 Distributed coordination function （DCF）, which has been ignored before and thus resulted in the inaccurate evaluation of the network performance. Based on our new event model, the network performance of IEEE 802.11 DCF, including throughput, packet delay distribution and energy efficiency is analyzed. Simulation results show that our model is highly accurate.     

DAWL: A Delayed-ACK Scheme for MAC-Level Performance Enhancement of Wireless LANs

The IEEE 802.11 MAC protocol provides a reliable link layer using Stop & Wait ARQ. The cost for high reliability is the overhead due to acknowledgement packets in the direction opposite to the actual data flow. In this paper, the design of a new protocol as an enhancement of IEEE 802.11 is proposed, with the aim of reducing supplementary traffic overhead and increasing the bandwidth available for actual data transmission. The performance of the proposed protocol is evaluated through comparison with IEEE 802.11 as well as with a SSCOP-based protocol. Results underline significant advantages of the proposed protocol against existing ones, thus confirming the value and potentiality of the approach.Dzmitry Kliazovich received his Masters degree in telecommunication science from Belarusian State University of Informatics and Radioelectronics in 2002. He is currently working towards the Ph.D. degree in University of Trento, Italy. His main research interest lies in wireless networking field with a focus on performance optimization and cross-layer design.Fabrizio Granelli was born in Genoa in 1972. He received the “Laurea” (M.Sc.) degree in Electronic Engineering from the University of Genoa, Italy, in 1997, with a thesis on video coding, awarded with the TELECOM Italy prize, and the Ph.D. degree in Electronic Engineering and Computer Science from the same university in 2001. Since 2000 he is carrying on his teaching activity as Assistant Professor at the Dept. of Information and Communication Technologies (DIT) of the University of Trento (Italy) within the B.Sc. and M.Sc. Degrees in Telecommunications Engineering.The research interests of Dr. Granelli are mainly focused on networking, with particular attention to network modeling and performance evaluation, wireless networks, access control, and next-generation telecommunication networks.He is author of more than 30 refereed papers, published in several international journals and conferences.Dr. Granelli is member of the IEEE Committee on “Communication Systems Integration and Modeling” (CSIM) and of the Technical Programme Committee of the “QoS and Performance Evaluation Symposium” of the International Conference on Communications (ICC 2003 and ICC 2004).     

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.     

Throughput Analysis and Admission Control for IEEE 802.11a

We propose a new Markov model for the distributed coordination function (DCF) of IEEE 802.11. The model incorporates carrier sense, non-saturated traffic and SNR, for both basic and RTS/CTS access mechanisms. Analysis of the model shows that the throughput first increases, and then decreases with the number of active stations, suggesting the need for an admission control mechanism.We introduce such a mechanism, which tries to maximize the throughput while maintaining a fair allocation. The maximum achievable throughput is tracked by the mechanism as the number of active stations increases. An extensive performance analysis shows that the mechanism provides significant improvements.Mustafa Ergen received the B.S. degree in electrical engineering from Middle East Technical University (METU) and was the METU Valedictorian in 2000. He received the M.S. and Ph.D. degrees in electrical engineering in 2002 and 2004, the MOT certificate of HAAS Business School in 2003, and the M.A. degree in International and Area Studies in 2004 from the University of California, Berkeley.Dr. Ergen has been conducting research in wireless communication networks with an emphasis on sensor networks, wireless LAN and OFDM systems and is the author of many works in the field, including the book (with A.R.S. Bahai and B.R. Saltzberg) Multi-Carrier Digital Communications: Theory and Applications of OFDM (New York: Springer, 2004).He is National Semiconductor Post Doctoral Fellow and was awarded eight times Bulent Kerim Altay Award by department of electrical engineering in METU and received Best Student Paper Award in IEEE ISCC 2003 and has an invited paper in IEEE GLOBECOM CAMAD 200.Pravin Varaiya is Nortel Networks Distinguished Professor in the Department of Electrical Engineering and Computer Sciences at the University of California, Berkeley. From 1975 to 1992, he was also Professor of Economics at Berkeley. His research is concerned with communication networks, transportation, and hybrid systems. He has taught at MIT and the Federal University of Rio de Janeiro, Varaiya has held a Guggenheim Fellowship and a Miller Research Professorship. He received an Honorary Doctorate from L’Institut National Polytechnique de Toulouse, and the Field Medal of the IEEE Control Systems Society. He is a Fellow of IEEE and a member of the National Academy of Engineering. He is on the editorial board of several journals, including “Discrete Event Dynamical Systems” and “Transportation Research-C.” He has co-authored three books and more than 250 technical papers. The second edition of “High-Performance Communication Networks” (with Jean Walrand) was published by Morgan-Kaufmann in 2000. “Structure and interpretation of signals and systems” (with Edward Lee) was published in 2002 by Addison-Wesley.     

On the modulus of -convexity

In this paper, we prove that the moduli of W^*-convexity, introduced by Ji Gao [J. Gao, The W^*-convexity and normal structure in Banach spaces, Appl. Math. Lett. 17 (2004) 1381–1386], of a Banach space X and of the ultrapower of X itself coincide whenever X is super-reflexive. Moreover, we improve a sufficient condition for uniform normal structure of the space and its dual. This generalizes and strengthens the main results of [J. Gao, The W^*-convexity and normal structure in Banach spaces, Appl. Math. Lett. 17 (2004) 1381–1386].     

浅析无线局域网QoS机制

无线局域网（WLAN）技术的发展带来的多媒体业务流量的剧增,是无线网络的资源管理、服务质量（QoS）保障等问题日益突出,传统的媒体访问控制（MAC）协议需要重新设计才能对无线网络的QoS问题进行有效的解决。本文介绍了无限局域网QoS技术的发展,包括针对IEEE802．11MAC层协议进行的各种QoS增强技术。通过与传统的802．11标准的MAC层进行对比分析,讨论了IEEE802．11e的两个新的策略：增强的分布式协调功能和混合协调功能。通过对受控竞争机制的分析,指出了IEEE802．11e仍存在的不足及未来的发展方向。     

车载AdHoc网络

车载自组织网络（VANET）作为移动自组织网络（MANET）的特殊子类,因其在智能交通和车载娱乐方面的广阔应用前景,目前受到业界的普遍关注。VANET的主要特点是车辆高速行驶、信道快速衰落、多普勒效应严重、网络拓扑变化快,由此将带来许多传输和组网的问题。     

Two-level protection and guarantee for multimedia traffic in IEEE 802.11e distributed WLANs

In order to support multimedia applications such as voice and video over the wireless medium, a contention-based channel access function, called Enhanced Distributed Channel Access (EDCA), has been developed in the emerging standard IEEE 802.11e. In the EDCA, differentiated channel access is provided for different traffic classes. In this paper, we propose a two-level protection and guarantee mechanism for voice and video traffic in the EDCA-based distributed wireless LANs. In the first-level protection, the existing voice and video flows are protected from the new and other existing voice and video flows via a distributed admission control with tried-and-known and early-protection enhancements. In the second-level protection, the voice and video flows are protected from the best-effort data traffic by adopting frame-based and limit-based data control mechanisms. Performance evaluations are conducted in terms of throughput, delay, transmission limit, number of collisions, and throughput square relative difference. Extensive simulation results demonstrate that the proposed two-level protection and guarantee mechanism is very effective in terms of the protection and guarantee of existing voice and video flows as well as the utilization of the channel capacity. An early version of this paper was presented at IEEE INFOCOM 2004.     

浅谈WAPI较之于IEEE802．11i

文章首先介绍了现行的国内外无线局域网安全问题的解决方案——wAPI与IEEE802．11i,然后分别就两个标准的认证、密钥生成方式及加密算法做了分析,最后对发展WAPI提出了一些建议。     

路由特性对IEEE802．11 DCF多跳网络容量的影响

使用数学分析方法研究基于IEEE 802.11 DCF的Ad Hoc网络中节点传输半径和路由策略选择问题.在节点均匀分布的多跳网络中,使用四种路由策略以及不同的节点传榆半径设王,试图找出能够使网络容量最大化的方案组合.计算结果表明,在节点密度一定的情况下,减小网络节点的传输距离有利于增加网络的容量,而在传输半径一定的条件下,使用能够导致长跳路由的策略,有利于提高网络容量.