Orhan Tahir Yavascan | Searcharxiv

arXiv2021

MiSTA: An Age-Optimized Slotted ALOHA Protocol

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.

cs.IT↗

arXiv2021

Analysis of Slotted ALOHA with an Age Threshold

We present a comprehensive steady-state analysis of threshold-ALOHA, a distributed age-aware modification of slotted ALOHA proposed in recent literature. In threshold-ALOHA, each terminal suspends its transmissions until the Age of Information (AoI) of the status update flow it is sending reaches a certain threshold $Γ$. Once the age exceeds $Γ$, the terminal attempts transmission with constant probability $τ$ in each slot, as in standard slotted ALOHA. We analyze the time-average expected AoI attained by this policy, and explore its scaling with network size, $n$. We derive the probability distribution of the number of active users at steady state, and show that as network size increases the policy converges to one that runs slotted ALOHA with fewer sources: on average about one fifth of the users is active at any time. We obtain an expression for steady-state expected AoI and use this to optimize the parameters $Γ$ and $τ$, resolving the conjectures in \cite{doga} by confirming that the optimal age threshold and transmission probability are $2.2n$ and $4.69/n$, respectively. We find that the optimal AoI scales with the network size as $1.4169n$, which is almost half the minimum AoI achievable with slotted ALOHA, while the loss from the maximum throughput of $e^{-1}$ remains below $1\%$. We compare the performance of this rudimentary algorithm to that of the SAT policy that dynamically adapts its transmission probabilities.

cs.IT↗