Optimal Scheduling for OFDM Systems

Speaker: Dr.Rajeev Agrawal, MOTOROLA
Abstract: This talk will consider the problem of downlink scheduling in OFDM systems. The scheduling problem is to determine the sub-channels allocated to each user, and for each sub-channel the modulation and coding scheme (MCS) and power level for the user to whom it is allocated. We have shown earlier that scheduling for elastic traffic for a broad class of channels can be asymptotically solved by a gradient-based policy. The gradient optimization problem can be viewed as a weighted rate optimization problem over a suitably defined rate region that depends on the "channel" state and system and user parameters. For an OFDM system the "channel" state depends on the channelization structure, feedback granularity, etc. Given the "channel" state we formulate the weighted rate maximization problem as a convex optimization problem. The solution is obtained by solving the dual problem through a combination of analytic steps and a one-dimensional numerical search with geometrically fast convergence to the optimal. The dual approach also reveals key structural properties and a finite-time algorithm for optimal power allocation when the sub-channel allocation is given. Using the general solution we specialize to different channelization and feedback schemes used in practice. We also consider a channel model where the channel response is not completely known; this induces a model with self noise that upper bounds the achievable SINR. This work is joint with Vijay Subramanian, Randall Berry and Jianwei Huang.
Biography: Rajeev Agrawal is a Fellow of the Technical Staff in the Networks Advanced Technology organization of Motorola's Networks and Enterprise Business. He heads the Advanced Networks and Performance Department and his responsibilities include the architecture, design and optimization of Motorola's next generation wireless systems. Prior to joining Motorola in 1999, Rajeev was Professor of Electrical and Computer Engineering and Computer Science departments at the University of Wisconsin - Madison. While at UW-Madison, he conducted research on stochastic control, traffic control and QoS in communication networks, scheduling and resource allocation in wireless systems. He also spent a sabbatical year at IBM TJ Watson Research, British Telecom Labs, and INRIA-Sophia Antipolis. Rajeev received his M.S. (1987) and Ph.D. (1988) degrees in electrical engineering-systems from the University of Michigan, Ann Arbor and his B.Tech. (1985) degree in electrical engineering from the Indian Institute of Technology, Kanpur.
Presentation On: Wednesday,12 May, 2006,
11:00 a.m. in room 1115, CSIC