The Role of Early Sampling in Age of Information Minimization in the Presence of ACK Delays

TL;DR

This paper investigates optimal sampling strategies to minimize age of information considering random ACK delays, revealing that early sampling can be optimal and that the optimal policy may be a mixture of threshold policies.

Contribution

It characterizes the structure of optimal sampling policies under ACK delays, showing that early sampling can be beneficial and that the optimal policy can be a mixture of thresholds.

Findings

Early sampling can be optimal even without immediate ACKs.

Optimal policies may be a mixture of two threshold strategies.

The structure depends on the distribution of ACK delays.

Abstract

We study the structure of the optimal sampling policy to minimize the average age of information when the channel state (i.e., busy or idle) is not immediately perceived by the transmitter upon the delivery of a sample due to random delays in the feedback (ACK) channel. In this setting, we show that it is not always optimal to wait for ACKs before sampling, and thus, early sampling before the arrival of an ACK may be optimal. We show that, under certain conditions on the distribution of the ACK delays, the optimal policy is a mixture of two threshold policies.