Distribution of AoI in EH-powered Multi-source Systems under Non-preemptive and Preemptive Policies

In this paper, we study a multi-source updating system in which a transmitter powered by energy harvesting (EH) has multiple sources generating status updates about several physical processes. The status updates are then sent to a destination node where the freshness of each status update is measured in terms of Age of Information (AoI). The harvested energy packets and the status updates of each source are assumed to arrive at the transmitter according to independent Poisson processes, and the service time of each status update is assumed to be exponentially distributed. We focus on understanding the distributional properties of AoI under both non-preemptive and preemptive in service queueing disciplines at the transmitter. In particular, we use the stochastic hybrid systems (SHS) framework to derive closed-form expressions of the moment generating function (MGF) and average AoI under each queueing discipline. To the best of our knowledge, this paper is the first to characterize the AoI performance in EH-powered multi-source updating systems under both non-preemptive and preemptive queueing models. The generality of our results is demonstrated by recovering several existing results as special cases. Our results reveal a fundamental trade-off between obtaining a minimum sum of average AoI values associated with different sources (average sum-AoI) and achieving fairness among the average AoI values of different sources. They also reveal the impact of system design parameters on the achievable AoI performance.