Research On The Fairness Of MAC Layer In Ad Hoc Network

Ad hoc network compared with other wireless mobile networks are very different. All nodes in the network without any central control node, and they are equal. All the nodes in the Ad hoc networks have abilities of routing and forwarding data packets to all the other nodes, thereby extending the range and the coverage of communications links among nodes, due highly flexibility and ease of setting up, so it can be applied to family entertainment, commercial telecommunication, modern battle field and disaster rescue and other environment. In Ad hoc Networks, fair distribution of bandwidth and maximization of resource utilization are in conflict in nature, hence it is necessary to design a MAC protocol based on the tradeoff of Throughput and Fairness.MAC protocol, which is at the bottom layer of the Ad hoc network protocol, determines the channel used by nodes and has a great impact on network performance. Many current MAC protocols use this exponential backoff mechanism. In that mechanism, a node need to backoff for a random period of time, which is uniformly selected from the Contention Window (CW) and it is doubled after each collision and immediately reduces to a minimum value after a single successful transmission. The BEB algorithm essentially favors the last transmitter to aggressively contend for the channel again and thus it can cause unfairness problem to some nodes. Based on the analysis of the domestic and overseas research on MAC protocol of Ad hoc network, in this paper, we propose an adaptive (ATFTB) backoff algorithm, which provides a tradeoff between fairness and the throughput. In order to attain both throughput and fairness in node channel competition, ATFTB depends on the current collision rate and transmission time rate on the shared channel contending nodes dynamically chose the random waiting time interval, and evaluates the fairness of node channel competition by calculating the fairness index for channel competition.Under the NS2platform, simulation experiments are carried out to get contrast between ATFTB algorithm and other MAC protocols. The simulation results show that, compared with the other MAC protocols, the proposed ATFTB algorithm improve fairness of node channel competition under the circumstances of a high throughput of the network.