Medium Access Control Protocols for Wireless Networks using Switchable Directional Antennas

DoctorIn conventional infrastructure wireless local area networks (WLANs), all stations including access points (APs) use omni-directional antennas. As the number of wireless devices, especially recent smart phones, increases explosively, the throughput performance may suffer from significant deterioration, since the degree of competition for transmission is getting higher and higher, which may result in frequent collisions. If whole service area of an AP is divided into many small pieces and only stations in one of the pieces are allowed to access medium at a time, the collision chance can be reduced and furthermore, concurrent transmissions may be possible. Motivated by this observation, we exploit a switchable directional antenna with four sectors to divide service area. The carrier sense multiple access/collision avoidance (CSMA/CA) protocol for WLAN does not work well with directional antennas. To take advantage of directional antennas for infrastructure wireless networks, a new MAC protocol is required, including the way to make AP association and data transmission. In this dissertation, we suggest medium access control (MAC) protocols for two different networks. One for an infrastructure WLAN consisting of an AP equipped with a switchable directional antenna (directional AP) and stations equipped with omni-directional antennas (omni-directional station) and the other for a wireless network consisting of a directional AP and stations equipped with switchable directional antennas (directional station). Furthermore, we extend it for wireless networks consisting of two directional APs and directional stations. The main contribution of this dissertation is that we consider an infrastructure WLAN using directional antennas and propose the corresponding MAC protocols. To replace conventional WLANs by the ones using directional antennas, we believe that we need to make additional efforts on developing well-designed protocols