Age of Information for Short-Packet Relaying Communications in Cognitive Internet of Things

Abstract

This paper investigates the age of information (AoI) with dual-hop short-packet communications in the cognitive Internet of Things (IoT) for monitoring and control. The AoI is adopted as a performance metric to characterize the freshness of received information at the remote server by measuring the value of the packet delay. Considering the packets error, we investigate the performance of dual-hop short-packet communications under classical automatic repeat-request (ARQ) protocol and truncated automatic repeat-request (TARQ) protocol, and obtain the approximated closed-form expressions of the average AoI, respectively. Accordingly, the blocklength and the retransmission times can be got by global search algorithm to minimize the average AoI under two protocols. Illustrative numerical results substantiate that the TARQ protocol can achieve lower average AoI in high packet generation rate scenarios. Moreover, when the interference from the primary user is large, the classical ARQ can obtain lower average AoI.