“…The above works provide foundational understanding of temporal variations of AoI from the perspective of queuing theory for a point-to-point communication system. Inspired by these works, the AoI or similar age-related metrics have been used to characterize the performance of real-time monitoring services in a variety of communication systems, including broadcast networks [17]- [19], multicast networks [20], [21], multi-hop networks [22], [23], multi-server information-update systems [24], IoT networks [25]- [30], cooperative device-to-device (D2D) communication networks [31], [32], unmanned aerial vehicle (UAV)-assisted networks [33], [34], ultra-reliable low-latency vehicular networks [35], and social networks [36]- [38]. All these studies mostly focus on minimizing the AoI with the following design objectives: 1) design of scheduling policies [17]- [19], [22], [30], 2) design of cooperative transmission policies [20]- [23], [31], [32], 3) design of the status update sampling policies [27]- [29], [36], and 4) trade-off with other performances metrics in heterogeneous traffic/networks scenarios [23]- [25], [29], [37].…”