With an abstraction of serving rate-adaptive sources on a broadcast-type wireless channel as a utility maximization 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 oppurtunity 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.

Rajeev Agrawal is with Motorola where he is a fellow of the technical staff in the Network Advanced Technology group (part of Global Telecom Solutions Sector). Prior to joining Motorola in 1999, Rajeev was professor of Electrical and ComputerEngineering and Computer Science departments. He received his Ph.D. degrees in electrical engineering--systems from the University of Michigan, Ann Arbor, in 1988.

His research interest lie in the areas of wireless communication networks; network architectures; radio resource allocation and scheduling; traffic control, flow control, and routing; and stochastic control.