Energy Efficient Packet Scheduling For Fading Channels and Delay Constraints

This paper focuses on energy-efficient packet transmission with individual packet delay constraints over a fading channel. The problem of optimal offline scheduling (vis-à-vis total transmission energy), assuming information of all packet arrivals and channel states before scheduling, is formulated as a convex optimization problem with linear constraints. The optimality conditions are analyzed. From the analysis, a recursive algorithm is developed to search for the optimal offline scheduling. The optimal offline scheduler tries to equalize the energy-rate derivative function as much as possible subject to causality and delay constraints, in contrast to the equalization of transmission rates in static channels. It is shown that the optimal offline schedulers over a fading channel and over a static channel have a similar symmetry property. However, the optimal scheduling over fading channels may observe idle periods that are not seen in the static channel case. Combining the symmetry property with potential idling periods, upper and lower bounds of the average packet delay are derived. A heuristic online scheduling algorithm, which tries to equalize the energy-rate derivatives using causal traffic and channel variations, is proposed. The online scheduler is shown via simulations to achieve comparable energy and delay performance to the optimal offline scheduler in a wide range of scenarios.