Energy-efficient Scheduling of Delay Constrained Traffic over Fading Channels

TL;DR

This paper investigates energy-efficient scheduling for delay-constrained data transmission over fading channels, deriving optimal and near-optimal policies to minimize energy use within deadlines.

Contribution

It provides a closed-form optimal policy for T=2 slots and develops simple, near-optimal policies for longer deadlines based on the structure of the problem.

Findings

Optimal policy for T=2 derived via dynamic programming.

Near-optimal policies for T>2 based on problem structure.

Channel-threshold policy optimal for single-slot transmission.

Abstract

A delay-constrained scheduling problem for point-to-point communication is considered: a packet of $B$ bits must be transmitted by a hard deadline of $T$ slots over a time-varying channel. The transmitter/scheduler must determine how many bits to transmit, or equivalently how much energy to transmit with, during each time slot based on the current channel quality and the number of unserved bits, with the objective of minimizing expected total energy. In order to focus on the fundamental scheduling problem, it is assumed that no other packets are scheduled during this time period and no outage is allowed. Assuming transmission at capacity of the underlying Gaussian noise channel, a closed-form expression for the optimal scheduling policy is obtained for the case T=2 via dynamic programming; for $T>2$, the optimal policy can only be numerically determined. Thus, the focus of the work is on derivation of simple, near-optimal policies based on intuition from the T=2 solution and the structure of the general problem. The proposed bit-allocation policies consist of a linear combination of a delay-associated term and an opportunistic (channel-aware) term. In addition, a variation of the problem in which the entire packet must be transmitted in a single slot is studied, and a channel-threshold policy is shown to be optimal.