Systems Seminar
Convergence and Optimality of Opportunistic Scheduling Algorithm
Dr. Vijay G. Subramanian
Global Telecommunications Solutions Sector
Motorola
Arlington Heights
Abstract
With an abstraction of serving rate-adaptive sources on a broadcast-type
wireless channel as a utility maximisation problem, it is shown how one
can design many intuitive online scheduling policies based upon the feedback
that one obtains at the scheduler. Using a stochastic approximation argument
it is then shown that the constructed algorithms converge to optimal
solutions of the utility maximization problem over different sets which
critically depend on the quality of the feedback information. We then apply
the theory developed above to the downlink in a CDMA based wireless network.
In terms of operational variables the problem is to select a subset of the
users for transmission at each transmission opportunity and for each of the
users selected, to choose the modulation and coding scheme, transmission
power, and number of codes used. We refer to this combination as the physical
layer operating point (PLOP). Each PLOP consumes different amounts of code
and power resources. Thus, the task is to pick the ``optimal'' PLOP taking
into account both system-wide and individual user resource constraints that
can arise in a practical system. Using an information theoretic model for the
achievable rate per code results in a tractable convex optimization problem.
By exploiting the structure of this problem, we give algorithms for finding
the optimal solution with geometric convergence. We also use insights
obtained from the optimal solution to construct low complexity near optimal
algorithms that are easily implementable. Numerical results comparing these
algorithms are also given.
Bio
Vijay G. Subramanian received a B.Tech. degree from the Department of
Electrical Engineering, Indian Institute of Technology, Madras in 1993,
a M.S. degree in Electrical Engineering from the Indian Institute of Science,
Bangalore in 1995, and a Ph.D. degree in Electrical Engineering from the
University of Illinois at Urbana-Champaign in 1999. Since November of 1999
he has been with the Global Telecommunications Solutions Sector, Motorola,
Arlington Heights working on radio resource allocation and channel-aware
schedulers for wireless data. His research interests include wireless and
communication networks, information theory and queuing theory.
Time and Place: Fri., Dec. 9, at 1 pm in 3534 Engr. Hall.
*** NOTE SPECIAL DAY, TIME, & ROOM ***
SYSTEMS SEMINAR WEB PAGE:
http://www.cae.wisc.edu/~gubner/seminar/