  We introduce Mini Slotted Threshold ALOHA (MiSTA), a slotted ALOHA
modification designed to minimize the network-wide time average Age of
Information (AoI). In MiSTA, sources whose ages are below a certain threshold
stay silent. When a node with age above the threshold has data to send, it
becomes active in the next time frame with a certain probability. The active
node first transmits a short control sequence in a mini-slot ahead of actual
data transmission, and if collision is sensed, it backs off with a certain
probability. We derive the steady state distribution of the number of active
sources and analyze its limiting behaviour. We show that MiSTA
probabilistically converges to a "thinned" slotted ALOHA, where the number of
active users at steady state adjusts to optimize age. With an optimal selection
of parameters, MiSTA achieves an AoI scaling with the number of sources, n, as
0.9641n, which is an improvement over the Threshold ALOHA policy proposed
earlier (for which the lowest possible scaling is 1.4169n). 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.
