Age of Information: Basic Concepts and Its Theoretical Analysis

Abstract

For real-time monitoring systems, the primary performance objective is that sufficiently fresh information is displayed on monitors. As a result, information with an old timestamp has little value in such systems. In other words, the value of information decreases as time passes, and displayed information can be useful only if it is updated frequently enough. Although the delay of packets with new information has conventionally been used as a representative performance metric for monitoring systems, it is an indirect measure of information freshness. The age of information (AoI) is a new metric that quantifies the freshness of information directly, and considerable research efforts on it have been expended recently. In this article, we first introduce the basic concept of the AoI. We then present a mathematical basis for the theoretical analysis of the AoI, and we demonstrate its usefulness by providing some insights obtainable from theoretical results into the control of the AoI performance.