Minimizing age-of-information in multi-hop wireless networks

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Timely exchange of information over multi-hop wireless networks is gaining increasing relevance with growing interests in applications such as internet of things (IoT) and autonomous vehicular networks. Age-of-information (AoI) is a recently proposed performance metric that measures information freshness at the destination node. AoI at a destination node is the time since last update was received. We study AoI for multi-hop networks with general interference constraints with R source-destination pairs, and derive simple stationary policies in which links are activated according to a stationary probability distribution. We first consider a line network with a single source-destination pair, and characterize AoI as a convex function of link activation rates. We then use this result to obtain the optimal policy, in the class of stationary policies, for multi-hop network, with several source-destination pairs. We prove an important separation principle, which says that the optimal scheduling policy for the multi-hop problem can be obtained by solving an equivalent problem in which all source-destination pairs are single-hop away.