Performance Evaluation of a Dynamic Medium Access Control Scheme for Mobile Ad-hoc Networks Using Different Mobility Models

Recently there have been considerable interests focusing on the enhancement of Mobile Ad-hoc NETworks (MANETs), which are a collection of wireless mobile stations forming a selfconfiguring network without using any existing infrastructure. The Distributed Coordination Function (DCF) of IEEE 802.11 Medium Access Control (MAC) protocol has been widely employed to control the shared wireless medium. The DCF utilizes a Binary Exponential Back-off (BEB) scheme to re duce the collision probability by doubling the contention window (cw ) upon a packet collision. In this paper, we propose a new back-off algorithm to enhance the performance of DCF in IEEE 802.11 MANETs, which is based on the idea of using a threshold of the collision rate to switch between two different increasing functions . This dynamic algorithm can be easily integrated into the traditional DCF protocol. The performance of the improved DCF is investigated and compared with the original DCF using the network simulator NS-2 under different mobility models . The performance results reveal that the improved DCF is able to achieve higher throughput as well as lower packet loss probability than the original DCF.