On-Demand-Sleep-Based Aloha for M2M Communication: Modeling, Optimization, and Tradeoff Between Lifetime and Delay

Slotted Aloha provides a simple solution for facilitating the massive access of machine-type-devices (MTDs). To prolong the battery lifetime of MTDs, on-demand sleep mechanisms are usually adopted, with which the lifetime and delay performance of MTDs crucially depends on the access and sleep parameters, and may significantly deteriorate if they are not properly selected. In this article, an analytical framework is proposed for on-demand-sleep-based slotted Aloha to optimize the lifetime and delay performance. Specifically, by establishing a novel node-centric model, explicit expressions of the expected lifetime of nodes and the mean queueing delay of data packets are derived, based on which the transmission probability of each node for maximizing the expected lifetime and minimizing the mean queueing delay is obtained. The tradeoff between the optimal lifetime and delay performance is also characterized. The practical insights of the analysis are further demonstrated by conducting a case study on the 2-step random-access-based small data transmission (RA-SDT) scheme with mobile initiated connection only (MICO)-based on-demand sleep mechanism.