Offline Delay-Optimal Transmission for Energy Harvesting Nodes

TL;DR

This paper develops a method to optimally minimize packet delay in energy harvesting communication systems by transforming a non-convex problem into a convex one, enabling analytical solutions and revealing a water-filling power allocation structure.

Contribution

It introduces a C2-diffeomorphic transformation to convert a non-convex delay minimization problem into a convex one, providing a tractable solution approach and analyzing the optimal policy structure.

Findings

Optimal transmission follows a weighted-directional-water-filling pattern.

More power is allocated in earlier time slots, less in later ones.

Simulation results confirm the analytical insights.

Abstract

This paper investigates the offline packet-delay-minimization problem for an energy harvesting transmitter. To overcome the non-convexity of the problem, we propose a C2-diffeomorphic transformation and provide the necessary and sufficient condition for the transformed problem to a standard convex optimization problem. Based on this condition, a simple choice of the transformation is determined which allows an analytically tractable solution of the original non-convex problem to be easily obtained once the transformed convex problem is solved. We further study the structure of the optimal transmission policy in a special case and find it to follow a weighted-directional-water-filling structure. In particular, the optimal policy tends to allocate more power in earlier time slots and less power in later time slots. Our analytical insight is verified by simulation results.