A system for frame collision detection based on power sensing and time-domain signal processing in wireless LAN

With the increase of wireless local area networks (WLAN) using the IEEE 802.11 protocol, the interference between WLAN devices has become a significant problem. Access control in IEEE 802.11 is based on Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) to avoid collisions that could prevent transmitted frames from being successfully received. However CSMA/CA cannot completely avoid all collisions which cause transmission failure, because it is possible for different devices to initiate transmissions simultaneously after Clear Channel Assessment (CCA), and because there may be interference from transmissions that are too weak to be detected by the CCA. Moreover, because the IEEE 802.11 has no function to distinguish the cause of transmission failure, counter-measures specific to the cause cannot be taken. In this paper, we propose a novel frame collision detection system based on power-sensing and signal-processing in the time-domain, which can detect frame collisions under variable conditions of frame transmission power, frame sizes and frame transmission rates. Performance of the proposed method was evaluated using collision signals obtained in experiments.