On the Age of Information for Multicast Transmission with Hard Deadlines in IoT Systems

TL;DR

This paper analyzes the age of information in multicast IoT systems with hard deadlines, deriving formulas for average AoI and showing that hard deadlines can improve timeliness.

Contribution

It introduces a model for multicast transmission with hard deadlines, deriving closed-form expressions for average AoI, and identifies optimal deadline values for minimizing AoI.

Findings

Hard deadlines reduce average AoI compared to no deadlines.

An optimal hard deadline exists that minimizes AoI.

Simulation results validate the analytical expressions.

Abstract

We consider the multicast transmission of a real-time Internet of Things (IoT) system, where a server transmits time-stamped status updates to multiple IoT devices. We apply a recently proposed metric, named age of information (AoI), to capture the timeliness of the information delivery. The AoI is defined as the time elapsed since the generation of the most recently received status update. Different from the existing studies that considered either multicast transmission without hard deadlines or unicast transmission with hard deadlines, we enforce a hard deadline for the service time of multicast transmission. This is important for many emerging multicast IoT applications, where the outdated status updates are useless for IoT devices. Specifically, the transmission of a status update is terminated when either the hard deadline expires or a sufficient number of IoT devices successfully receive the status update. We first calculate the distributions of the service time for all possible reception outcomes at IoT devices, and then derive a closed-form expression of the average AoI. Simulations validate the performance analysis, which reveals that: 1) the multicast transmission with hard deadlines achieves a lower average AoI than that without hard deadlines; and 2) there exists an optimal value of the hard deadline that minimizes the average AoI.