Collision chain mitigation and hidden device-aware grouping in large-scale IEEE 802.11ah networks

A new IEEE standard for large-scale wireless connectivity in IoT and M2M applications, called IEEE 802.11ah, has recently been introduced. A single access point (AP) of 802.11ah can provide connectivity to a large number of devices (up to 8192) with the communication range of up to 1 km. Due to such a large coverage area with a large number of connected devices, however, the hidden node problem of 802.11ah networks is severer than typical Wi-Fi networks. Especially, we observe that frequent occurrences of a collision chain results in significant deterioration of network performance even with the group-based access restriction mechanism of 802.11ah. To solve this problem, we propose a collision chain mitigation scheme that detects and interrupts a collision chain, lets a smaller number of devices contend thereafter and also provide the information from which a carrier-sensitivity table is constructed by AP. Although the proposed scheme mitigates performance deterioration due to a collision chain when occurred, collision chains still occur. So, we propose a grouping algorithm which can perform both initial grouping and regrouping from existing groups based on the carrier-sensitivity table constructed by the mitigation scheme so that only a negligible number of hidden devices remain in each group and the root cause of collision chain is obviated. Our simulation study shows that the mitigation scheme alone makes network throughput comparable to the case of no hidden devices and its combination with the grouping algorithm improves throughput performance over the 8-group case of the conventional mechanism by up to 146%.