In recent decades, rapid growth of wireless Ad Hoc networks, has led to network connectivity with complete lack of central control and wired backbone. Increasing demand for accessing information, has made undeniably essential increase in the wireless Ad Hoc networks. This expansion is impossible without efficient use of bandwidth and network capacity increment. In addition to limited bandwidth in all wireless networks, power limited batteries in wireless Ad Hoc networks result in power consumption constraint. Many solutions have been proposed to solve these problems. Conventionally, Omni directional antennas are used. Omni directional antennas spread energy over a large region of space, while small portion is received by the intended receiver. Furthermore, Omni directional transmission results in higher interference and lower network capacity. Therefore, the battery is used inefficiently and the network lifetime decreases. It causes not only unnecessary interference to other nodes but also network capacity reduction. It is shown that directional antennas reduce interference and consequently increase network capacity. Besides, directional antennas significantly enhance power consumption. Nevertheless, using directional antennas in wireless Ad Hoc networks inherently introduce new kinds of problems arising from directivity and some other serious challenges. Thus, directional transmission, sometimes decays network throughput. A solution to this problem is to modify traditional protocols or design a new protocol which is suitable for support of directional antenna features. Therefore, there is a strong demand for the design of a new protocol which will be efficient enough. In this thesis, the effort is made to modify IEEE 802.11 standard and enhance network throughput and reduce power consumption reduction by using multi beam directional antennas. In the proposed scheme, each node is equipped with a switched beam antenna system which can switch between M fixed beam patterns. The antenna system can operate in two separate modes: Omni and Directional. Neighbor’s information such as appropriate beam for communication, minimum transmission power level, deafness status is maintained in Neighbor Table. Initially, the Neighbor Table is empty and it is continuously updated upon overhearing any transmission. Transmission will take place based on this information. There is no need for acquiring this information in the upper layer or use additional hardware. Each node keeps maximum admissible power and NAV duration for each of its beams dynamically through the Angle Table. If the channel is busy and required transmission power is less than admissible power in that direction, new communication is allowed. Simulation results in NS-2 show remarkable performance improvement in comparison with IEEE 802.11 protocol.
