What’s My Age of Information Again? The Role of Feedback in AoI Optimization Under Limited Transmission Opportunities

Real-time applications in the Internet of things (IoT) commonly require to schedule status updates from remote sensors to minimize age of information (AoI), a metric that captures the freshness of received data. Oftentimes, this problem is tackled assuming that sensors operate over an indefinite time horizon and can decide when to transmit data leveraging the knowledge of the current AoI level at the receiver, even when the communication channel is unreliable. Such a modeling approach, however, neglects some key aspects of most practical IoT systems, where the frequency of status reporting is limited due to resource constraints, such as energy limitations, and tracking the outcome of the updates would require additional consumption of resources to acquire a feedback. In this paper, instead, we investigate the optimal schedule of updates over a finite time horizon for a resource-constrained sensor that is allowed to perform a limited number of updates. We discuss the role of the feedback from the receiver, and whether it is convenient to ask for it whenever this causes additional energy consumption and consequently allows the transmission of a lower number of updates. We analytically identify regions for the feedback cost and the reliability of the channel where making use of feedback may or may not be beneficial. Our study covers both the generate-at-will case, in which a sensor can produce a fresh reading whenever it wants to communicate with the receiver, and an exogenous setting, where the transmitter cannot decide when new status updates are produced. The results highlight some interesting trade-offs, providing useful design hints for the protocol operation of IoT remote sensing systems.