Please note the time change to 11am today, as well as for Friday morning, http://eecs.oregonstate.edu/graduate/colloquium/.
Wednesday March 2 11:00 - 11:50 AM Owen 106 Shuguang Cui Ph.D. Candidate Electrical Engineering Stanford University Cross-layer Optimization in Energy-Constrained Wireless Networks We consider wireless networks with hard energy constraints, where reducing the energy consumption becomes the most important network design consideration. An example of this type of network is a sensor network, where each node is powered by a non-rechargeable battery. Since all layers of the protocol stack affect the energy per bit consumed in its end-to-end transmission, energy minimization requires a joint design across all protocol layers as well as the underlying hardware, where the energy is actually expended. We show that the cross-layer design across the hardware, link, MAC, and routing layers is a beneficial and feasible approach to energy efficient wireless networking. We consider both the interference-free case (with TDMA-based orthogonal MAC) and the interference-limited case (with non-orthogonal MAC). For the first case, we start with a point-to-point link, where we show that dramatic energy savings is possible when the tradeoff between the transmission energy and the circuit processing energy is explored. The results tell us that for short-range applications, bursty transmissions minimize total energy consumption. We next consider a multiple access scenario, where multiple sensor nodes are sending data to a central node. We propose a variable-length TDMA scheme to minimize the total energy consumption through a joint design of the MAC and link layers. We demonstrate the energy savings of this approach relative to a non-optimized design. We then extend our analysis to a joint design optimized across the link, MAC, and routing layers considering the hardware processing energy. We show that if link adaptation is not allowed, the energy minimization problem is a LP problem and can be efficiently solved. The solution tells us how to optimally route the traffic to minimize the total energy consumption across the network. If link adaptation is allowed, the total energy consumption can be further reduced. The optimization is no longer convex in this case, but can be relaxed to a convex problem where efficient algorithms exist to obtain a near-optimal solution. For the energy-efficient TDMA solution we obtained, we show that there exists optimal scheduling or ordering of the time slot assignments to minimize the packet delay. In the link layer, we also show that by allowing multiple nodes to cooperate, we can construct virtual MIMO systems to reduce both energy and delay. For the interference-limited case with non-orthogonal channel usage, we decompose the non-convex cross-layer problem into two sub-problems: link scheduling with heuristics, and optimal rate adaptation with routing. We'll show how iterations between these two sub-problems lead to an energy-efficient solution. The talk will conclude with a brief discussion of joint estimation problems in sensor networks, where multiple sensors cooperate in an energy-efficient manner to estimate an unknown signal. The results will lead to a strategy where sensors with bad observation quality or bad transmission channels should be silenced to save energy. Biography Shuguang Cui received the B.Eng. degree in Radio Engineering with the highest distinction from Beijing University of Posts and Telecommunications, Beijing, China, in 1997, and the M.Eng. degree in Electrical Engineering from McMaster University, Hamilton, Canada, in 2000. He is currently working toward the Ph.D. degree in Electrical Engineering at Stanford University, California, USA. From 1997 to 1998 he worked at Hewlett-Packard, Beijing, P.R.China, as a system engineer. In the summer of 2003, he worked at National Semiconductor, Santa Clara, CA, as a wirless system researcher. His current research interests include cross-layer optimization for energy-constrained wireless networks, hardware and system synergies for high-performance wireless radios, and general communication theories. He is the winner of the NSERC graduate fellowship from the National Science and Engineering Research Council of Canada and the Canadian Wireless Telecommunications Association (CWTA) graduate scholarship. _______________________________________________ Colloquium mailing list [email protected] https://secure.engr.oregonstate.edu/mailman/listinfo/colloquium
