Age-of-Information Dependent Random Access in Multiple-Relay Slotted ALOHA

With the advent and rapidly consolidating of the Internet of Things (IoT), multiple applications arise with different performance requirements, such as the timeliness of information, which can be quantified by the age-of-information (AoI) metric. Furthermore, allowing the coexistence of massive numbers of low-complexity IoT devices is often desirable, and modern random access methods have been explored as a way of achieving it. In this paper, we investigate the performance of a random access two-hop network with multiple relays, focusing on the AoI metric. We evaluate the average age of the network under two age-dependent approaches, namely ADRA-MRU, in which users evaluate their age against a threshold before transmitting, and ADRA-MRD, where this responsibility belongs to relays. As a result, we show through analytical and numerical results that ADRA-MRU can considerably reduce the average AoI of an age-independent random access scheme with multiple relays (AIRA-MR) by more than 60%, while the performance of ADRA-MRD is slightly better than that of AIRA-MR. Moreover, we also provide insights on the optimal number of relays as well as other parameters that influence the AoI.