Improving the spatial reuse of IEEE 802.11 WLAN by adaptive carrier sense threshold of access points based on node positions

The IEEE 802.11 Distributed Coordination Function (DCF) is based on the Carrier Sense Multiple Access (CSMA) algorithm for avoiding collisions of frames. In CSMA, spatial reuse can be improved by suitably changing the carrier sense threshold (CST). If the increased CST does not incur collisions and helps concurrent transmissions from multiple devices, this improves the throughput of the wireless LAN. For example, when there are two APs and multiple devices exist near each of them, each AP can transmit a frame simultaneously without causing collisions of frames since each device can receive a frame from its associated AP with a high signal power and the interference from another AP is small. In this paper, we propose a system which improves the throughput in CSMA/CA based wireless LANs by controlling the CST values of APs according to positions of mobile hosts. In the system, the CST values of multiple APs are dynamically configured by a controller which has a camera for obtaining the current positions of mobile hosts. The proposed system improves the throughput in WLAN 58% in comparison with basic DCF in a LAN where two APs are arranged at an interval of 50 m and two devices exist within 10 m from each AP.