MobiHoc 2005



Tutorial 1  Friday 27 May 2005, 1:00pm-5:00pm, 2405 Siebel Center
Cross-Layer Design for Multi-hop Wireless Networks: A Loose-Coupling Perspective
Instructor: Ness B. Shroff (Purdue University)


The layered networking architecture has been key to the enormous success and widespread usage of the Internet, as well the initial development of wireless systems. The success of the layered architecture has been its ability to provide modularity and transparency between the layers. However, it is becoming increasingly clear that optimizing within layers is insufficient to obtain the orders-of-magnitude performance gains necessary to fuel major growth in next-generation wireless services. To achieve these performance gains, it is imperative that network protocols and designs are engineered by optimizing across the layers (cross-layer design). The idea is that by jointly optimizing the control over two or more layers, cross-layer solutions can yield significantly improved performance by exploiting the tight coupling between the layers in wireless systems. However, the Achilles heel of cross-layer design is its potential to destroy modularity, and make the overall system fragile. Thus, there is a fundamental tradeoff between efficiency and modularity that needs to be carefully taken into account in any cross-layer solution.

In this talk, we will emphasize the importance of taking a "loose-coupling" approach in the development of cross-layer solutions for wireless systems. By loose-coupling we mean that that there must be only a minimal amount of interaction between the layers, and the overall solution must be robust to imperfect decisions/information at each layer. Thus, the goal is to obtain a high degree of efficiency while retaining modularity. We will provide three relevant case studies to demonstrate the importance and efficacy of this approach, starting with cross-layer design between the MAC and physical layer, and work our way up to the transport layer.

Intended Audience:

This tutorial is intended for researchers and engineers in both industry and academia that would like to have a deeper understanding of the issues and challenges involved in the development of cross-layer design for wireless networks. Researchers with either a CS or EE background will be able to follow and benefit from this tutorial.


Ness B. Shroff is a Professor of Electrical and Computer Engineering at Purdue University. He is also the director of the Center for Wireless Systems and Applications (CWSA), a university-wide multi-disciplinary center on wireless systems and applications.

His research interests span the areas of wireless and wireline communication networks.  He is especially interested in fundamental problems in the design, performance, pricing, and security of these networks.  His research is funded by various companies such as Intel, Hewlett Packard, Nortel, AT&T, BAE systems, and L. G. Electronics; and government agencies such as the National Science Foundation (NSF), Defense Advanced Research Projects Agency (DARPA), Indiana Dept. of Transportation, and the Indiana 21st Century fund.

Dr. Shroff is an editor for IEEE/ACM Trans. on Networking and the Computer Networks Journal, and past editor of IEEE Communications Letters. He has served on the technical and executive committees of several major conferences and workshops. He was the technical program co-chair of IEEE INFOCOM'03, the premier conference in communication networking. He was also the conference chair of the 14th Annual IEEE Computer Communications Workshop (CCW'99), the program co-chair for the symposium on high-speed networks, Globecom 2001, and the panel co-chair for ACM Mobicom'02. Dr. Shroff was also a co-organizer of the NSF workshop on Fundamental Research in Networking, held in Arlie House Virginia, in 2003. He received the NSF CAREER award in 1996 and the best paper of the year award for Computer Networks, in 2003. See for further details.


Tutorial 2  Saturday 28 May, 8:00am-12:00pm, 2405 Siebel Center    Back to Top
Algorithm and Graph Issues in Wireless Ad-hoc and Sensor Networks
Instructor: Xiang-Yang Li (Illinois Institute of Technology)



Wireless ad hoc and sensor networks have drawn a considerable amount of research interests from a number of researchers from electronic engineering to computer scientists including computer systems, architecture, and theoretician. This tutorial will cover some basics of applying graph and algorithmic techniques to solve some interesting and challenging questions from wireless ad hoc and sensor networks. The tutorial will cover three important areas of wireless ad hoc and sensor networks, namely, power assignment and management, topology control, and energy efficient routing.

The power assignment and management problem is to assign power to each wireless node such that the resulting communication graph has a certain property such as being connected, being k-connected, having a small diameter and so on. We will survey the current state of the art of power assignment results for random deployed networks (this is beneficial for studying the mobile networks) and for fixed static networks.

The topology control problem in wireless ad hoc networks is to either, for each wireless node, choose a certain subset of neighbors to communicate, or to choose a certain subset of nodes as the backbone of the network, in such a way that energy consumption is reduced and a certain property (such as being planar, fault-tolerant and so on) of the resulted communication graph is maintained. Topology control could reduce the energy consumption; increase the capacity of the network by implicitly reducing contention to access the wireless channel through using shorter links.

The energy efficient routing is to find the best route for unicast, multicast, and broadcast when the underlying routing structure is fixed either via the topology control mechanism or some other means. In this tutorial, we will summarize some recent theoretical results on energy efficient unicast, multicast and broadcast under a certain energy consumption model and link reliability model. In addition, we will briefly talk about how to do energy efficient routing when the possible relay nodes are selfish and will not follow the prescribed protocols unless it could not do better otherwise.

This tutorial has three major goals:

  • To give the attendees a brief overview of the considerable body of literature devoted to algorithmic and graph theoretical approaches in wireless networks.
  • To provide the attendees with an algorithmic and graph theoretical toolkit (including computational geometry, distributed systems, graph theory, algorithm design and analysis and game theory), i.e., with the expertise needed in the design and analysis of effective heuristics and mechanisms for wireless ad hoc and sensor networks.
  • To outline the limitations of the current model for wireless networks, and to bridge the gap between the theoretician and engineers.


The tutorial will address both theoretical and technological aspects related to wireless ad hoc and sensor networks in terms of graph theoretical and algorithmic design and analysis, such as power assignment and management, topology control (including flat structures and hierarchical structures), and energy efficient routing. For this reason, we believe this tutorial is appealing for researchers with both a computer science or engineering background, as well as for people from the industrial community. Graduate and undergraduate students, and any professional who is interested in entering into this fundamental field of wireless ad hoc networking research, are especially welcome.


Dr. Xiang-Yang Li has been an Assistant Professor of Computer Science at the Illinois Institute of Technology since 2000. He received MS (2000) and PhD (2001) degree at Department of Computer Science from University of Illinois at Urbana-Champaign. He received his Bachelor degree at Department of Computer Science and Bachelor degree at Department of Business Management from Tsinghua University, P.R. China in 1995. He is a member of the Chinese national team prepared for the International Mathematics Olympics (IMO) from 1988 to 1990.

His research interests span the computational geometry, wireless ad hoc networks, game theory, cryptography and network security. Recently, he focuses on performing research on the cooperation, energy efficiency, and distributed algorithms for wireless ad hoc and sensor networks. He has published over 30 journal papers and over 60 conference papers in wireless networks, computational geometry, non-cooperative computing and optical networks. He is a Member of the ACM, IEEE, and IEEE Communication Society.

Dr. XiangYang Li served various positions (such as conference chair, local arrangement chair, financial chair, session chair, TPC member) at a number of international conferences. Dr. Li recently also co-organized a special issue of ACM MONET on non-cooperative computing in wireless networks.

For more information, please see


Last modified 06-Apr.-2005