Age of Computing: A Metric of Computation Freshness in Communication and Computation Cooperative Networks

In communication and computation cooperative networks (3CNs), timely computation is crucial but not always guaranteed. There is a strong demand for a computational task to be completed within a given time. The time taken involves both processing time and communication time. However, a measure of such timeliness in 3CNs is lacking. In this letter, we introduce the novel concept, Age of Computing (AoC), to capture computation freshness in 3CNs. We develop two methods for calculating this metric, applicable to a wide range of 3CNs. These calculations are applied to a queue-theoretic system comprising a task-initiating source, a task-executing computational node and a communication link, resulting in the derivation of two expressions for the AoC. Then a tight upper bound and a tight lower bound are derived. Subsequently, we investigate the communication-computation tradeoff and the AoC-delay tradeoff. While our models are simpler than their real-world counterparts, they provide comprehensive insight in understanding computation freshness in 3CNs and the relationships between computing and communications.