Improving the Performance of Directional Medium Access Control Protocols with Smart Antennas for Mobile Ad hoc Network J.A. Guama, N.M. Saad Electrical and Electronics Department, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 31750 Tronoh, Perak, MALAYSIA Tel: +60 5 368 8000 Fax: +60 5 365 4075 Email: jackline_alphonse ,utp.edu.my, naufal saad petronas.com Abstract-In this paper, we conducted a comparison study of the existing directional MAC protocols that use Smart Antennas by contrasting their features. We found that, most of these protocols are not applicable in mobile environment. This investigation discusses the challenges in improving some of these Smart Antenna-based MAC protocols. We proposed to upgrade two protocols, Tone-DMAC protocol and Angular-MAC protocol. We proposed to model the behavior of these two protocols analytically and carry the improvement performance by using two omni-directional control packets. We suggested that using these two packets and Adaptive Array Antennas in the above protocols will make them applicable in mobile environment and as well as improve routing performance. Keywords-Smart Antennas, Mobile Ad-hoc Network, Medium Access Control, IEEE.802.11. I. INTRODUCTION Smart Antennas (or adaptive array antennas) have some unique properties that enable us to achieve high throughput in Mobile Ad hoc Network scenarios. A transmitter equipped with a Smart Antenna can form a directed beam towards its receiver and a receiver can similarly form a directed beam towards the sender thus resulting in very high gain. A receiver can also identify the direction of multiple simultaneous transmitters by running DOA (Direction of Arrival) algorithms and use this information to determine the directions in which it should place nulls. Placing nulls effectively cancels out the impact of interfering transmitters. [1].There are basically two types of Smart Antennas: Switched beam or fixed beam antennas and Adaptive Array antennas. Switched beam antenna generates a multiplicity of juxtaposed beams whose output may be switched to a receiver or a bank of receivers. In an Adaptive Array Antenna, which is more advanced than a Switched beam antenna, the beam structure is adapted to Radio Frequency (RF) signal environment and directs beams towards the desired signals, depressing the antenna pattern in the direction of the interferers, using algorithms (e.g. Least Mean Square Algorithm and Recursive Least Square Algorithm).[2] The difference between the two kinds of Smart antennas can be resumed as follows: fixed beam antennas focus their smartness in the strongest strength signal beam detection while Adaptive Array Antennas benefit from all the received information within all antenna elements to optimize the signal output through the adjustment of a weight vector. Mobile Ad hoc NETwork (MANET) is a system of wireless mobile nodes that can freely and dynamically self- organized in arbitrary and temporary network topologies without the need of a centralized administration. People and devices can seamlessly internetworked in areas without any preexisting communication infrastructure. MANET comprise of mobile devices (e.g. laptop, palmtop, internet mobile phone etc.) that use wireless transmission for communication. Medium Access Control protocol in Ad hoc Networks is called a contention based MAC protocol. Its role is to decide who has channel access on a shared medium. The main MAC protocol for MANET is IEEE 802.11.[3] Smart Antennas have been proposed as a means to enhance the performance of MANET including increasing capacity, increasing the range of communications, reducing the susceptibility to detection, interception, and jamming, conserving energy, and resolving collisions. Properties of Smart antennas that have been identified to support these benefits include: antenna directivity, increase gain, and signal processing technique including beamforming, null steering, diversity, spatial processing, and Multiple-Input Multiple -Output (MIMO). Unfortunately Smart Antennas cause some problems in MANET. Many protocols were designed to deal with these problems. These problems remain unsolved in some protocols. These protocols were classified and compared, but none have been upgraded. We proposed to improve two of these protocols based on some features. These protocols are Tone-DMAC and AN-MAC. The reminder of this paper is organized as follows; in the next section we briefly review IEEE 802.11. In section III. we classify directional MAC protocols and discuss some of the protocols based on the classification. Section IV presented the comparison of the directional MAC protocols. We discuss our proposed plan in section V. Concluding remarks are given in VI. II.IEEE 802.11 DISTRIBUTED COORDINATION FUNCTION IEEE 802.11 is a popular protocol that defines the functionality of MAC and physical layer of a wireless Ad Hoc Network. It introduces Distributed Coordination Function (DCF), which coordinates the medium occupancy using Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA). In IEEE 802.11 DCF protocol, an exchanged of request to send (RTS)/clear to send (CTS) precedes DATA communication. Both RTS and CTS packets contain the proposed duration of transmission. Nodes located in the vicinity of communicating nodes, which listen in either of these packets, must themselves defer transmission for the 1-4244-1005-3/07/$25.00 02007 IEEE.