Age of Information in Downlink Systems: Broadcast or Unicast Transmission?

TL;DR

This paper analytically compares broadcast and unicast transmission schemes for minimizing the age of information in multiuser systems, considering different packet management strategies and system parameters.

Contribution

It provides new closed-form expressions for average AoI under various schemes and strategies, and offers insights into optimal transmission choices based on system size and conditions.

Findings

Unicast is better for large numbers of UEs.

Broadcast is preferable for smaller systems.

System parameters significantly influence AoI performance.

Abstract

We analytically decide whether the broadcast transmission scheme or the unicast transmission scheme achieves the optimal age of information (AoI) performance of a multiuser system where a base station (BS) generates and transmits status updates to multiple user equipments (UEs). In the broadcast transmission scheme, the status update for all UEs is jointly encoded into a packet for transmission, while in the unicast transmission scheme, the status update for each UE is encoded individually and transmitted by following the round robin policy. For both transmission schemes, we examine three packet management strategies, namely the non-preemption strategy, the preemption in buffer strategy, and the preemption in serving strategy. We first derive new closed-form expressions for the average AoI achieved by two transmission schemes with three packet management strategies. Based on them, we compare the AoI performance of two transmission schemes in two systems, namely, the remote control system and the dynamic system. Aided by simulation results, we verify our analysis and investigate the impact of system parameters on the average AoI. For example, the unicast transmission scheme is more appropriate for the system with a large number UEs. Otherwise, the broadcast transmission scheme is more appropriate.