Status Update Control and Analysis under Two-Way Delay

TL;DR

This paper develops optimal control policies for status updating systems with two-way delays, analyzing different request policies and introducing pipelining to minimize the average age of information.

Contribution

It introduces pipelining-type status updating with up to two active requests and derives optimal policies using Markov decision processes.

Findings

Optimal policies for minimizing AoI under two-way delays are derived.

Pipelining with two active requests improves status update efficiency.

Analytical expressions for average AoI under various policies are provided.

Abstract

We study status updating under two-way delay in a system consisting of a sampler, a sink, and a controller residing at the sink. The controller controls the sampling process by sending request packets to the sampler. Upon receiving a request, the sampler generates a sample and transmits the status update packet to the sink. Transmissions of both request and status update packets encounter random delays. We develop optimal control policies to minimize the average age of information (AoI) using the tools of Markov decision processes in two scenarios. We begin with the system having at most one active request, i.e., a generated request for which the sink has not yet received a status update packet. Then, as the main distinctive feature of this paper, we initiate pipelining-type status updating by studying a system having at most two active requests. Furthermore, we conduct AoI analysis by deriving the average AoI expressions for the Zero-Wait-1, Zero-Wait-2, and Wait-1 policies. According to the Zero-Wait-1 policy, whenever a status update packet is delivered to the sink, a new request packet is inserted into the system. The Zero-Wait-2 policy operates similarly, except that the system holds two active requests. According to the Wait-1 policy, whenever a status update packet is delivered to the sink, a new request is sent after a waiting time which is a function of the current AoI. Numerical results illustrate the performance of each status updating policy under different system parameter values.