Broadcast versus Distributed Short-Packet Transmission: An Age of Information Perspective

We study the age of information (AoI) performance of a multiuser downlink system where a base station generates and transmits status updates to multiple user equipments (UEs). The question of whether to adopt broadcast transmission or distributed transmission for the optimal AoI performance is addressed analytically. In the broadcast transmission scheme, the status update for all UEs is jointly encoded into a packet for transmission, while in the distributed transmission scheme, the status update for each UE is encoded individually and transmitted by following the round robin policy. We first derive new closed-form expressions for the average AoI achieved by two transmission schemes. Then, we provide a criterion for selecting the better transmission scheme for a remote control system. Aided by simulation results, we investigate the impact of system parameters on the average AoI. For example, the distributed transmission scheme is more appropriate for the system with a large number UEs; otherwise, the broadcast transmission scheme is more appropriate.