, Volume 11, Issue 3, pp 377-389
Date: 04 Apr 2006

Energy Efficient Schedulers in Wireless Networks: Design and Optimization

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Minimizing energy consumption is crucial for portable wireless stations because they operate on a limited battery supply. For example, the IEEE 802.11 standard includes a mechanism called power-saving mode (PSM), which allows a network interface on a mobile station to enter a sleep state whenever possible to reduce its energy consumption. We consider a generic wireless system composed of an access point (AP) and several stations that offer a PSM to its users. Our PSM is AP-centric (i.e., gives control to the AP) to save more energy. We formulate a downlink scheduling optimization problem aimed at saving energy and propose two heuristic scheduling policies to solve it. One of these policies is non-work-conserving, and it offers an interesting tradeoff between energy consumption and user performance.

We also study and show how the length of the Beacon Period (BP) has a significant impact on the energy and the delay performance of wireless stations. For each of our two scheduling policies, we derive simple approximate formulas for the length of the BP that minimizes the energy consumption and for the relationship between the delay performance and the length of the BP. Assuming the maximum allowable average packet delay is given by the users as a QoS requirement, we illustrate how to dimension the length of the BP for the two schedulers we have proposed and show that we can achieve significant energy savings while meeting the delay constraint with the non-work conserving one in many cases. Extensive simulations show that a fine-tuning of the length of the BP as well as well-designed scheduling disciplines is essential to saving energy in wireless stations.

A part of this paper was presented at WiOpt’04 (Modeling and Optimization in Mobile, Ad Hoc and Wireless Networks), March 24–26, 2004, Cambridge, UK.
Jeongjoon Lee received the B.S. and the M.S. degrees in Electrical Engineering from Seoul National University, Seoul, Korea, in 1988 and 1990, respectively, and the Ph.D. degree in the School of Electrical and Computer Engineering from Purdue, he is a project manager for LS Industrial System, Seoul, Korea (Now, it changes its name from LG Industrial Systems). His research interests include RFID, USN (Ubiquitous Sensor Networks), wireless PAN, wireless LAN,PLC (Power Line Communication), and home networking.
Catherine Rosenberg born and educated in France (Ecole Nationale Supérieure des Télécommunications de Bretagne, ‘Diplôme d’Ingénieur’ in EE in 1983 and University of Paris, Orsay, ‘Doctorat en Sciences’ in CS in 1986) and in the USA (UCLA, MS in CS in 1984), Dr. Rosenberg has worked in several countries including USA, UK, Canada, France and India. In particular, she worked for Nortel Networks in the UK, AT&T Bell Laboratories in the USA, Alcatel in France and taught at Purdue University (USA), Ecole Polytechnique of Montreal (Canada). Dr. Rosenberg is currently Chair of the Department of Electrical and Computer Engineering at the University of Waterloo, Canada, where she also holds a University Research Chair. Agencies and industries that have supported her research include NSF (National Science Foundation) NSERC (Natural Sciences and Engineering Research Council of Canada), FCAR (The Quebec counterpart of NSERC), CRC (Canadian Ministry of Communications), EEC (European Commission), ESA (European Space Agency), France-Telecom, CISCO, Bell Canada, and Nortel Networks. Her research interests are in broadband networks (IP and ATM), in wireless networking, in network security, in peer-to-peer networks, and in traffic engineering (Quality of Service, Network Design, and Routing). She has authored over 70 papers and has been awarded six patents in the USA.
Edwin K. P. Chong received the B.E.(Hons.) degree with First Class Honors from the University of Adelaide, South Australia, in 1987; and the M.A. and Ph.D. degrees in 1989 and 1991, respectively, both from Princeton University, where he held an IBM Fellowship. He joined the School of Electrical and Computer Engineering at Purdue University in 1991, where he was named a University Faculty Scholar in 1999, and promoted to Full Professor in 2001. Since August 2001, he has been a Professor of Electrical and Computer Engineering, and Professor of Mathematics, at Colorado State University. His current interests are in communication networks and optimization methods. He coauthored the best-selling book, An Introduction to Optimization, 2nd Edition, Wiley-Interscience, 2001. He received the NSF CAREER Award in 1995 and the ASEE Frederick Emmons Terman Award in 1998. Professor Chong is a Fellow of the IEEE. He was founding chairman of the IEEE Control Systems Society Technical Committee on Discrete Event Systems, and was an IEEE Control Systems Society Distinguished Lecturer. He has been on the editorial board of the IEEE Transactions on Automatic Control. He is currently on the editorial board of the journal Computer Networks. He has also served on the organizing committees of several international conferences, including the IEEE Conference on Decision and Control, the American Control Conference, the IEEE International Symposium on Intelligent Control, IEEE Symposium on Computers and Communications, and the IEEE Global Telecommunications Conference. He was the Conference (General) Chair for the Conference on Modeling and Design of Wireless Networks, part of SPIE ITCom 2001. An up-to-date vita is available at www.engr.colostate.edu/∼echong.