# Age-Minimal Transmission in Energy Harvesting Two-hop Networks

## TL;DR

This paper addresses minimizing the age of information in an energy harvesting two-hop network by optimizing update transmissions under energy and data causality constraints, using a novel problem transformation approach.

## Contribution

It introduces a method to solve the two-hop age minimization problem by transforming it into a single-hop problem through parameter adjustments.

## Key findings

- Optimal transmission schedules minimize age of information.
- The two-hop problem reduces to a single-hop problem via parameter transformation.
- The approach effectively handles energy and data causality constraints.

## Abstract

We consider an energy harvesting two-hop network where a source is communicating to a destination through a relay. During a given communication session time, the source collects measurement updates from a physical phenomenon and sends them to the relay, which then forwards them to the destination. The objective is to send these updates to the destination as timely as possible; namely, such that the total age of information is minimized by the end of the communication session, subject to energy causality constraints at the source and the relay, and data causality constraints at the relay. Both the source and the relay use fixed, yet possibly different, transmission rates. Hence, each update packet incurs fixed non-zero transmission delays. We first solve the single-hop version of this problem, and then show that the two-hop problem is solved by treating the source and relay nodes as one combined node, with some parameter transformations, and solving a single-hop problem between that combined node and the destination.