Peak Age of Information Analysis of Status Update Strategies in Cache-Enabled IIoT Networks

This article investigates the Peak Age of Information (PAoI) violation probability of status update strategies in cache-enabled Industrial Internet of Things (IIoT) networks. Specifically, a PAoI characterization framework for PAoI violation probability analysis in cache-enabled IIoT networks is presented for status updates with and without a zero wait (ZW) policy. Furthermore, multicast-aware (MA) and hierarchical-aware (HA) status update strategies are also proposed for cache-enabled IIoT networks. Using newly derived PAoI cumulative distribution functions (CDFs) and a status update transmission delay probability density function (PDF), closed-form PAoI violation probability expressions are obtained for the MA and HA status update strategies. Extensive analysis shows that the ZW policy for status updates in cache-enabled IIoT networks can experience high PAoI violation probability when high transmission delay is encountered during the delivery of acknowledgement messages. Furthermore, the PAoI violation probability of the proposed MA and HA status update strategies are dependent upon the status update transmission delays, PAoI violation threshold, wireless link timeout threshold, and the popularity of wireless sensors (WSs). We show that the proposed MA and HA status update strategies exhibit lower PAoI violation probability over other benchmark strategies. Importantly, the proposed MA status update strategy with and without the ZW policy attains the lowest PAoI violation probability even in scenarios where status updates are requested from a large pool of WSs. Therefore, the analysis shows both the proposed MA and HA status update strategies as promising solutions toward the monitoring and control of mission-critical IIoT applications.