Age of Information Minimization in Fading Multiple Access Channels

Freshness of information is an important requirement in many real-time applications. The age of information (AoI), a metric for measuring the freshness of information, is the time elapsed since the generation of the last successful update received by the destination. We consider $M$ sources (users) updating their statuses over a block-fading multiple access channel to a base station (BS). At the start of each fading block, the BS acquires perfect information about channel power gain realizations of all the users in the block. Using this information, a centralized scheduling policy at the BS in a block decides whether to idle or select a user to receive a packet from, in order to minimize a long-term weighted average AoI across all users subject to long-term average power constraint at each user. In this work, we propose a simple age-independent stationary randomized policy (AI-SRP), with which the minimum achievable weighted average AoI across the users is at most two times the AoI of the optimal policy.