Age of Information With Joint Packet Coding in Industrial IoT

This letter studies the information freshness in an industrial Internet of Things (IIoT) network, measured by Age of Information (AoI). We consider a scenario where a sink node collects information update packets from different sensors and then uploads the collected packets to an edge server. This scenario has two main requirements: high information freshness (low AoI) and high reliability (low packet error rate, PER). Since update packets are usually short in practice, previous works usually packed and encoded multiple short packets from different sensors into a long packet to improve PER performances. However, while such a joint coding approach improves reliability, it generally leads to longer delay and hence possibly higher AoI. This letter investigates the AoI performance tradeoff by examining the number of packets to be jointly encoded. We consider two AoI metrics, average AoI and bounded AoI. In particular, bounded AoI is the threshold below which the instantaneous AoI falls for a given percentage of the time. Our theoretical analysis and numerical results show that there exist optimal numbers of jointly coded packets that minimize the average AoI and the bounded AoI. Specifically, a smaller number of packets is usually sufficient to achieve both high information freshness and high reliability.