Dynamic Slot Allocations for M2M in IEEE 802.11ah Networks

Abstract

IEEE 802.11ah can support machine-to-machine (M2M) communications among many sensor devices, which is rapidly increasing with the Internet of Things (IoT). In 802.11ah, a restricted access window (RAW) is designed for a beacon interval (BI). RAW is divided into many slots that allow sensor devices to contend for transmission. This paper proposes a dynamic slot allocation scheme (DSAS) in 802.11ah networks. To alleviate the contention in crowded M2M environments, the DSAS defines two sets of thresholds, high and low, to determine the sleeping-time level of a machine and the contention level for a slot, respectively. The innovative aspect of the DSAS is that machines with short sleeping time are allocated to less congested slots whereas machines with long sleeping time are allocated to more congested slots. To avoid unnecessary slot reallocation, machines with sleeping-time levels or contention levels between the high and low thresholds continue to use their original transmission contention slots. Simulations performed on NS-3 show the DSAS can significantly improve average backoff time and packet delay and increase the overall system throughput by 30%.