“‘清华信息大讲堂’-诺基亚论坛”系列学术报告第五讲

报告时间:  2005年10月27日（周四）上午  9:00-12:00

报告地点:  信息大楼（FIT）1-312

报告题目: 

1.   802.11网络中实现可扩展容量并防止频带枯竭

2.   交叉层设计和资源分配

报 告 人： 香港中文大学教授 刘绍强，

         香港中文大学助理教授  张颖君

主    办： 信息学院 

协    办： IEEE清华大学学生分会

联 系 人:  电子工程系  曹志刚

Abstract 1:  

Two well known problems in IEEE 802.11 wireless networks are the exposed-node (EN) and hidden-node (HN) problems. This talk will report some of our recent research findings on EN and HN.

While it is well known that HN can cause unfair bandwidth allocation in the network, the performance implication of EN is less well studied. It turns out that EN has a direct impact on the scalability of network capacity. For example, with today’s 802.11 products, when there are too many client stations in a given geographical area and the network capacity runs out, a naïve proposal would be to install more Access Points (APs) to boost up capacity. Since APs are cheap, the argument goes, the solution is relatively cost-free. It turns out that this approach does not scale because EN is not properly taken care of in today’s 802.11 products. In particular, a point will be quickly reached wherein more APs do not increase the capacity anymore.

While there have been isolated and incidental studies of EN and HN, a comprehensive and fundamental treatment has not been attempted. The contributions of this work are three-fold:

n    We provide formal mathematical definitions for EN and HN

n    We establish the tie between EN and non-scalable network; and the tie between HN and unfair network bandwidth allocation.

n    We provide schemes to eliminate EN and HN entirely.

We thus show that it is possible to modify the CSMA/CA of 802.11 networks to achieve scalable capacity as well as to remove performance problems caused by HN. Capacity and performance then becomes scalable with the number of APs.

Abstract 2:

The next generation wireless systems are expected to provide universal personal and multimedia communications without regard to the users’ mobility and location. These services will include heterogeneous classes of traffics such as voice, file transfer, web browsing, wireless multimedia, teleconferencing, and interactive games, etc. The major challenges we are confronted with include the harsh wireless channel, scarce resources such as power and spectrum, and very diverse QoS (Quality of Services) requirements. This stimulates the development of intelligent resource management algorithms to achieve efficient utilization of radio resources, provide QoS differentiation and guarantees, and ultimately enable ubiquitous and high-rate communications over a limited frequency spectrum.

In this talk, I will present joint MAC-PHY layer resource allocation algorithms for OFDM systems. Building our work upon a multiuser OFDM architecture, we maximize the overall power or spectral efficiency by exploiting the inherent system diversity in the frequency, time, space, and user domains through an intelligent management of bandwidth allocation, multiple access, adaptive modulation and coding, along with power allocation. Particularly, I will present dynamic resource allocation algorithms for four multiuser OFDM systems. These are 1) uncoded system; 2) coded system; 3) MIMO system; and 4) packet-switched system.

Biography 1:

Soung Liew received his  S.B., S.M., E.E., and Ph.D. degrees from the Massachusetts Institute of Technology. From 1984 to 1988, he was at the MIT Laboratory for Information and Decision Systems, where he investigated Fiber-Optic Communications Networks. From March 1988 to July 1993, Soung was at Bellcore (now Telcordia), New Jersey, where he engaged in Broadband Network Research. Soung is currently Professor at the Chinese University of Hong Kong.

Soung’s research interests include wireless networks, Internet protocols, multimedia communications, optical networks, and broadband packet switch design. He has over 100 publications in these areas combined. Most recently, he has been working on 1) applications and communications protocols over wireless networks, focusing on performance, security, and mobility issues; and 2) wireless LAN and ad-hoc network designs.

Soung initiated and coordinated the first inter-university ATM network testbed in Hong Kong in 1993. He is currently co-Director of the Area of Excellence in Information Technology (AoE-IT) of Hong Kong, a multimillion-dollar joint project with participations from the Chinese University, University of Science and Technology, and University of Hong Kong.  Currently, two main themes for research at AoE-IT are 1) Pervasive Multimedia Content Delivery of Heterogeneous Internet and 2) Intrusion Detection on Internet.

Besides academic activities, Soung is also active in the industry. He co-founded two technology start-ups in Internet Software. He was instrumental in raising VC funding for TradeCity Cybersoft and was the CEO of the company during its initial phase of operation. The company’s J2EE application server achieves record-breaking performance in Chinese text processing and delivery. Soung was also a co-founder of Nexcel Limited, which was contracted by Hutchison Telecom to build the first residential Intranet in Hong Kong in mid 90’s.

Soung has also been serving as consultant to many other companies and industrial organizations. He is currently consultant for the Hong Kong Applied Science and Technology Research Institute, helping to formulate R&D directions and strategies in the areas of Wireless Internetworking, Applications, and Services. In this capacity, Soung has also contributed to the technical ideas behind several pending patents. 

Soung is the holder of three U.S. patents and Fellow of IEE and HKIE. He is listed in Marquis Who’s Who in Science and Engineering. He is the recipient of the first Vice-Chancellor Exemplary Teaching Award at the Chinese University of Hong Kong.

Biography 2:

Ying Jun Zhang received her BEng degree with Honors in Electronic Engineering from Fudan University, Shanghai, China, in 2000, and the PhD degree in Electrical and Electronic Engineering from The Hong Kong University of Science and Technology (HKUST), Hong Kong, in 2004. From 2000 to 2004, she was a research assistant in the Center for Wireless Information Technology(CENWIT) at HKUST, where she worked on adaptive resource allocation for wireless OFDM networks. Since Jan. 2005, she has been with The Chinese University of Hong Kong, where she is currently an assistant professor of the Department of Information Engineering. Her research interests include broadband multi-carrier/OFDM techniques, adaptive coding and modulation, optimal resource allocation for wireless networks, cross-layer design and optimization, MIMO antenna techniques, and wireless LAN. Dr. Zhang serves on the Technical Program Committee for IEEE ICCCAS and IEEE ICC. She has been serving on the review board of various journals and conferences such as IEEE Transactions on Communications, IEEE Transactions on Wireless Communications, IEEE Transactions on Vehicular Technology, and IEEE Communications Letters. Dr. Zhang is currently a member of IEEE and IEEE Communications Society.