DCCTA: Age of Information in Slotted ALOHA Under Duty Cycle Constraints

Slotted ALOHA has been receiving renewed interest due to its suitability as a channel access scheme in low-overhead IoT and LP-WAN scenarios. Threshold ALOHA (TA) is a modification of slotted ALOHA where users only become inactive when the Age of Information (AoI) of their respective packet flows rises above a certain threshold. TA, as well as related algorithms (e.g., SAT, MiSTA) proposed in recent literature, control the access to the channel to communicate fresh rather than stale data, without loss of throughput with respect to ordinary slotted ALOHA. This paper was motivated by the fact that many low power wide area network (LP-WAN) scenarios where TA and its variants are useful are bound in practice by mandatory duty cycle constraints. We observe that under such constraints the previously proposed TA variants run into duty cycle violations, when in fact these may be avoidable without sacrificing throughput or freshness. We propose a modification of TA, referred to as Duty Cycle Compliant Threshold ALOHA (DCCTA), that obeys a given duty cycle constraint and analyzes its performance.