Closed-form scheduling policies for delay-sensitive traffic over fading channels

Next-generation wireless networks for personal communication services should be designed to transfer delay-sensitive (possibly, heavy-tailed distributed) bursty traffic flows over energy-limited buffer-equipped faded connections. In this scenario, a still open question concerns the closed-form design of scheduling policies minimizing the average transfer-delay under constraints on both average and peak energies. The key-point of the novel approach we follow consists in the minimization (on a per step basis) of the queue-length averaged over the fading statistics and conditioned on the queue occupancy at the previous step. We prove that, under the considered energy constraints, the scheduler retains two optimality properties. First, its stability region is the maximal admissible one. Second, the scheduler also minimizes the unconditional average queue-length (over both queue and link state statistics). Finally, we explicitly derive the optimal scheduler expressions and performances for some systems of practical interest.