Abstract:

In order to overcome the congestion in wireless Ad hoc networks,a novel congestion control algorithm,namely,medium contention-based fair congestion control ( MCFCC) algorithm,is proposed and compared with the typical algorithm LRED. In the MCFCC algorithm,the backoff ratio of the node is calculated according to the backoff times in competing for shared channels,and the corresponding packet dropping probability is further obtained. Thus,the packet transmission rate of the source nodes can be reasonably controlled,and both the collision of shared media and the throughput degradation caused by the congestion can be solved with the help of the fast and accurate judgements on the congestion statuses of nodes and networks. Moreover,the congestion information are sent to the neighbor nodes by means of request to send or clear to send frame,so that each node can know the congestion information about its neighbors and then adjust its congestion information and packet dropping probability,thus improving the fairness among traffic flows. Simulation results show that the MCFCC algorithm can significantly improve the performance of IEEE 802.11 DCF,greatly increase the network throughput,ameliorate the fairness among nodes and effectively avoid the network congestion at the medium access control layer.

Key words: wireless Ad hoc networks, congestion control, medium access control, traffic contention, fairness