“…The age of information was proposed to measure timeliness of information in communication systems, and has been studied in the context of queueing systems [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 ], multi-hop and multi-cast networks [ 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 ], social networks [ 18 ], timely remote estimation of random processes [ 19 , 20 , 21 , 22 , 23 , 24 , 25 ], energy harvesting systems [ 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 ], wireless fading channels [ 41 , 42 ], scheduling in networks [ 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , ...…”