Age-Energy Tradeoff in Random-Access Poisson Networks

Energy efficiency and Age of Information (AoI) are two key performance metrics for many emerging battery-limited fresh-aware IoT networks, where random access protocols, such as Aloha, are usually adopted. Yet, in large-scale random access scenarios, the energy efficiency and AoI performance would degrade severely if the network is not configured properly. This paper aims to address this issue by studying the performance limit of energy efficiency under AoI constraint and how to achieve such limit in a slotted Aloha-based Poisson bipolar network. Specifically, we evaluate the energy efficiency via the lifetime throughput, which is defined as the number of update packets successfully decoded by the receiver during the lifetime of each transmitter. The explicit expression of the lifetime throughput is derived, based on which the maximum lifetime throughput with or without AoI constraint and the corresponding optimal channel access probability and packet arrival rate are characterized. The analysis reveals that both the maximum lifetime throughput and AoI-optimal lifetime throughput decline as the node density increases, while the gap between them would be non-negligible if the power ratio of the transmission state and the waiting state is large. Further with AoI constraint, it is shown that the AoI-constrained maximum lifetime throughput has to be sacrificed if the constraint is stringent. The effects of key system parameters on the optimal network configurations and age-energy tradeoff are also discussed, which provide important insights on practical battery-limited fresh-aware IoT network design.