MiSTA: An Age-Optimized Sotted ALOHA Protocol

We introduce Mini Slotted Threshold-ALOHA (MiSTA), a slotted ALOHA modification designed to minimize the time average Age of Information (AoI) achieved in the network while also increasing throughput. In MiSTA, sources with age below a certain threshold stay silent. Nodes with age above the threshold that decide to transmit test the channel for possible collisions during a mini-slot placed ahead of each data slot. We derive the steady state distribution of the number of active sources and analyze its limiting behaviour. We show that MiSTA probabilistically converges to thinned slotted ALOHA, where the number of active users at steady state adjusts to optimize age. With an optimal selection of parameters, the AoI scales with the network size (i.e. the number of sources), n, as 0.9641n, in contrast to 1.4169n which is the lowest possible scaling with Threshold-ALOHA proposed in earlier literature. While achieving this reduction in age, MiSTA also increases achievable throughput to approximately 53%, from the 37% achievable by Threshold-ALOHA and regular slotted ALOHA.