Peak age of information in slotted ALOHA network

In this paper, we concentrate on the peak age of information (PAoI) in a discrete-time slotted ALOHA network comprised of M buffer-less nodes, capable of keeping just one packet at each time. In this network, whenever some nodes transmit their packets simultaneously, a collision happens, thus there is interaction among queues and transmission delay of a packet might prolong more than one slot. The packets are generated at each node stochastically and independently. The nodes follow preemptive queueing policy. In this network, we propose a new trellis-based analytical model to represent the interaction among queues and derive exact average PAoI in closed form. Furthermore, we find average PAoI-constrained regions and minimize average PAoI for a symmetric network, numerically. As a byproduct of our analysis, the achievable throughput region of two slotted ALOHA networks with unlimited buffer and buffer-less nodes are compared. We observe that the latter is superior not only in AoI, but also in achievable throughput region. Simulation results confirm our analysis.