Quality of Service Guarantees in High Speed Networks A Research Project Funded by the National Science Foundation
Principal Investigator: R. L. Cruz
Summary of Results
- B. E. Collins and R. L. Cruz, "Transmission Policies for Time-Varying Channels with Average Delay Constraints," to appear in Proc. 1999 Allerton Conference on Communication, Control, and Computing, Monticello IL., Sept., 1999. (256K, pdf)
We consider the problem of transferring data with a fixed level of reliability over a discrete time channel whose characteristics vary with time, with a constraint on the average delay suffered by the data and a constraint on peak transmitter power. We assume that the channel state is known to the transmitter at the beginning of each slot, and seek transmission policies that minimize the average power expended by the transmitter. Using a dynamic programming formulation coupled with a duality argument, we find that good transmission policies will in general take action in accordance with how much data is queued at the transmitter, as well as in accordance with the channel state. In particular, if the backlog is sufficiently large the transmitter should use the channel even if it is in a "bad" state, and if the backlog is sufficiently small the transmitter should only use the channel when it is in a "good" state. However, we find that the time scale of the variations in the channel relative the maximum tolerable average delay is a crucial factor influencing the qualitative features of the optimal transmission policy.