QoS enhanced channel access in IEEE 802.11ah networks

摘要

Recently, the IEEE 802.11ah protocol has been released for communication between low power IoT devices. IEEE 802.11ah is a wireless LAN technology that operates in the unlicensed low frequency band of 1GHz or lower and is a technology created for network communication between IoT devices. IEEE 802.11ah has a new feature called RAW (Restricted Access Window) to handle large numbers of nodes in a long range. The RAW mechanism groups the nodes and allows only the nodes belonging to the RAW selected by the access point (AP) to have channel access. The RAW mechanism is an effective way to reduce collisions between nodes. However, 802.11ah supports a long transmission range and many sensor nodes will try to access the channel. If RAW size is set small, there will be many collisions between nodes, and delays will occur. If RAW size is set large, delay will occur because RAW Turn Around time increases. As a result, the quality of service cannot be guaranteed. So we proposed two new algorithms. First, we propose a method to reduce the maximum delay by allocating the nodes that cannot access the channel to the reserved slots preferentially. Second, we propose a method to change reservation slot duration for nodes that cannot access channel by detecting collision frequency. We implemented this through the NS-3 simulator and confirmed the effect of reducing the actual maximum delay.