Channel Access Scheduling for IEEE 802.11ah IoT Network Using Slot Length Adjustment

This paper proposes the Dynamic Slot Length Adjustment and Time-Stamp-based Scheduling (DSLA-TSS) method to improve the performance of IEEE 802.11ah Internet of Thing (IoT) network. The proposed method divides Restricted Access Window (RAW) into Claiming RAW and Data RAW. Each STA can send the claiming frame indicating it has uplinked data to send to AP in its associated Claiming RAW's claiming slot. AP uses the information about (i) STA's uplinked data, which is in the claiming frames of those STAs that have successfully claimed, and (ii) STA's downlinked data, which AP receives from Internet, to know the load condition of each data slot and then adjusts slots' lengths accordingly. For the issue of channel access's scheduling, the proposed method divides each data slot into two parts: (1) scheduled sub-slot, where AP schedules STAs that have successfully claimed their uplinked data and/or have downlinked data based on the time stamps of received claiming frames and downlinked data, and (2) remaining sub-slot, where STAs having uplinked data but unsuccessfully claimed can use the CSMA/CA control scheme to compete for the channel access privilege. Simulation results show that the proposed method improves overall network performance, including higher throughput, higher channel utilization and lower collision rate.