Mobile Intelligence

3.1 INTRODUCTION

In wireless network, performance is dependent on medium access control protocol. Carrier sense multiple access (CSMA) is commonly used for its simplicity. But CSMA is unable to handle the hidden terminal problem, especially in ad hoc networks, where multihop communication among nodes is common. To overcome this problem, a frame exchange protocol is used, called request to send/clear to send (RTS/CTS) handshaking. It was first proposed in Ref. [1].

There have been a lot of researches on developing the wireless medium access control (MAC) that efficiently shares limited resources between all stations [1, 2]. At present, IEEE 802.11 MAC is clearly the most accepted and widely used wireless technology. The IEEE 802.11 works based on carrier sense multiple access with collision avoidance (CSMA/CA) and adopts a random access scheme where packets are sent randomly to reduce the number of collisions as much as possible. In addition, IEEE 802.11 introduces a mechanism called RTS/CTS handshaking and virtual carrier sensing to further reduce the chance of collisions that can occur due to hidden terminal problems.

However, it is observed [3] that hidden and exposed terminal problems are exacerbated in mobile ad hoc network (MANET) while using IEEE 802.11. The ultimate result is heavy degradation in throughput and instability of networks. In Ref.[4], it is shown that this problem is more severe in large and dense ad hoc networks. So, improvement of performance degradation for ...