Optimizing freshness of information: On minimum age link scheduling in wireless systems

There is a growing interest in age of information, which is a newly introduced metric that measures the freshness of information in communication systems. We investigate the age of information in wireless networks and propose the novel approach of optimizing the scheduling strategy to deliver the information as timely as possible. We consider a set of links that share a common channel, each containing a number of packets with time stamps, and address the scheduling problem with the objective of minimizing the overall information age. We model this problem mathematically and prove it is NP-hard in general. Fundamental insights including tractable cases and optimality conditions are presented. An integer linear programming formulation is provided for performance benchmarking. Moreover, a steepest age decent algorithm with better scalability is developed. Numerical study shows that, by employing the optimal schedule, the overall information age is significantly reduced in comparison to other scheduling strategies.

I. Introduction

In a wireless network with a common shared medium, scheduling is one of the fundamental aspects of access coordination [1], [2]. It amounts to deciding which links, i.e., pairs of transmitters and receivers, are allowed to be activated simultaneously and for how long they should do so. Due to the broadcast nature of wireless media, a set of links that can be activated together is constrained by the interference they cause on each other [3], [4]. Usually, the selection of a schedule is driven by the goal of optimizing a cost criterion, such as maximizing throughput, or minimizing the completion time for all the links. The investigation of scheduling has a long history that has ranged from simple transmission models to fully cross-layered ones that combine rate and power control with overall network resource allocation (e.g., [5]–[8]). In this paper, we consider the scheduling problem with a new objective towards the freshness of information, which differs significantly from conventional performance metrics, such as transmission time or delay.