An efficient spatial group restricted access window scheme for IEEE 802.11ah networks

The development of Internet of Things (IoT) is expected to be more rapid after the introduction of IEEE 802.11ah wireless local area network (WLAN) standard. IEEE 802.11ah standard is applicable to high-density WLAN system operating at sub 1 GHz band. In order to deal with the serious channel contention, collisions and hidden-node problems in the legacy distributed coordination function (DCF) protocol with large size networks, 802.11ah adopts the restricted access window (RAW) mechanism. RAW is defined as an access interval which contains several time slots, and a station is expected to contend for medium access during a time slot. However, since the hidden-node problem is not in the range of consideration when the time slots of a RAW are allocated, stations belonging to the same time slot may not detect each other, and thus a large number of stations may collide seriously with each other. In this paper, an efficient spatial group RAW media access control (MAC) scheme based on the location of STAs is proposed. It provides an effective way to reduce the influence of hidden nodes and collision problems by optimizing the strategy of STAs allocation. The joint performance evaluation of 802.11ah on the MAC layer and physical layer (PHY) with the proposed scheme is implemented by MATLAB simulator. It is shown in the simulation results that the throughput performance of the proposed scheme improves substantially compared with legacy DCF and conventional RAW.