Round-Robin is Provably Near-Optimal for Minimizing Age with HARQ over Heterogeneous Unreliable Multiaccess Channels

TL;DR

This paper proves that the simple round-robin scheduling policy is nearly optimal for minimizing Age of Information in multiaccess channels using practical HARQ schemes, with a small, explicitly quantified gap.

Contribution

The paper provides a rigorous analysis showing that RR-P is asymptotically near-optimal for AoI with HARQ in heterogeneous channels, with explicit tight bounds.

Findings

RR-P's AoI gap from optimal is within about 6.4% for fading channels.

RR-P's AoI gap is within about 6.2% in finite-blocklength regimes.

RR-P is simple, channel-unaware, and easy to implement.

Abstract

In a heterogeneous unreliable multiaccess network, wherein terminals share a common wireless channel with distinctive error probabilities, existing works have showed that a persistent round-robin (RR-P) scheduling policy (i.e., greedy policy) can be arbitrarily worse than the optimum in terms of Age of Information (AoI) under standard Automatic Repeat reQuest (ARQ), and one must resort to Whittle's index approach for optimal AoI. In this paper, practical Hybrid ARQ (HARQ) schemes which are widely-used in today's wireless networks are considered. We show that RR-P is very close to optimum with asymptotically many terminals in this case, by explicitly deriving tight, closed-form AoI gaps between optimum and achievable AoI by RR-P. In particular, it is rigorously proved that for RR-P, under HARQ models concerning fading channels (resp. finite-blocklength regime), the relative AoI gap compared with the optimum is within a constant of $(\sqrt{e}-1)^2/4\sqrt{e} \cong 6.4\%$ (resp. $6.2\%$ with error exponential decay rate of $0.5$). In addition, RR-P enjoys the distinct advantage of implementation simplicity with channel-unaware and easy-to-decentralize operations, making it favorable in practice.