Interference Avoidance In WLAN Based On Reconfigurable Antennas

In recent years, along with the sharp increase in the demand for accessing to the Internet at anytime in anywhere, wireless LAN attracts great attention for its advantages such as flexibility and mobility. It has been widely deployed in daily life. The development of antenna technology makes great contribution to improve the performance of network. As one kind of antenna, reconfigurable antenna can switch among multiple operating modes with the electronic and mechanical methods. And it can adapt to the environment so as to optimize the performance of the system. Compared with the conventional omni-directional antennas, pattern reconfigurable antennas make full use of its characteristics that it can reconstruct the antennas’ pattern in real-time according to the channel. Due to its effect on suppressing the interference between nodes and increasing the number of parallel transmissions, inducing reconfigurable antenna technology into the wireless LAN has become a valuable research point.The specifies of traditional wireless LAN was proposed using the omni-directional antennas. As the most widely used protocol, IEEE 802.11 showed good performance. Pattern reconfigurable antenna has clear directions at multiple operating modes, thus it will bring in problems such as directional hidden node, deaf node and asymmetry in gain by using the existing protocol. Based on the study of typical media access control protocol for directional antennas, an idle node-assisted directional MAC protocol is proposed to solve the problems and to take advantages of the pattern reconfigurable antennas.The idle node-assisted directional MAC protocol uses the handshake signals which can reserve channels in existing protocols. Each node maintains a table which contains the network allocation vectors of different operating modes. Idle nodes in the network uses its own table to judge the current transmissions of the network, and send packets to the nodes that interfere the current communication. This mechanism for interference avoidance can bring the reconfigurable antennas into the wireless LAN successfully.In addition, combined with the features of reconfigurable antennas and WLAN co-channel interference, a mathematical model was established based on the traditional Markov model. The theoretical model takes the physical layer capture effect and hidden terminal problem into consideration. The effectiveness of IDA-DMAC mechanism is verified by using this model, and theoretical analysis shows that the reconfigurable antenna can enhance the throughput of the wireless LAN to as well as improving parallel transmission capability.