Investigation On QoS Based Backoff Algorithm For Channel Access In Ad Hoc Networks

Ad hoc Network is a network formed by a series of mobile hosts with wireless transceivers. It is a multi-hop and instant self-organizing network without the aid of any established infrastructure or centralized administration. Ad hoc Network can be built up rapidly and flexibly, and it is free from the restriction of wired network, therefore, it can be widely applied to such situations as: military action, emergency search, disaster rescue. In Ad hoc Network, the channel resource is limited due to all of the mobile nodes sharing the same wireless channel under the condition of single channel. Therefore, an effective MAC protocol is required to coordinate the access of the nodes to the channel. At the same time, the application environments and potential applications in commerce require that wireless ad hoc networks should support Quality-of-Service (QoS). A QoS-aware MAC protocol is a key factor for QoS supporting components at upper layers. The simple effective and providing service differentiation MAC protocols are therefore very important, and the backoff algorithm is the key of restricting MAC fairness and providing service differentiation.At first, the characteristics of Ad hoc Network and its related techniques are reviewed in this thesis. Afterwards, the relevant research results and the problems of Ad hoc Network's MAC protocols are studied deeply. Great attentions are paid to fair scheduling issues and service differentiation. Then proposes a Fair Service Differentiation Dynamic Backoff (FSDDB) algorithm, which can provide service differentiation of the traffic flows dynamically while achieving fair access to all mobile nodes. Simulation is operated with NS2 under Linux, and the simulation results show that, the presented algorithm is simpler and more practical, while it can improve the fairness index of Ad hoc Network to a large extent compared with the IEEE802.11 Binary Exponential Backoff (BEB) algorithm. It can make better use of the wireless channel by dynamically adjusting its backoff timer according to the network's contest situation. In addition, service differentiation can be achieved among flows with different QoS requirements and thus the QoS for Medium Access Control in Ad hoc network is improved.