乔平安　李峰杰　颜景善

(西安邮电大学计算机学院　西安　710121)



Ad hoc网络双忙音多址访问协议的研究与仿真*

乔平安李峰杰颜景善

(西安邮电大学计算机学院西安710121)

摘要由于移动Ad hoc网络没有固定控制中心,信道访问冲突十分严重。论文通过对双忙音多址访问(DBTMA)协议的仿真,发现当网络中存在暴露接收节点时,DBTMA协议出现了严重的不公平性问题,有些节点甚至可以垄断信道。论文提出了一种针对DBTMA协议不足进行改进的策略,该策略通过设计一种基于竞争节点数目的自适应竞争窗口调整因子,以达到根据网络竞争状况动态调整退避窗口的目的。仿真结果表明,改进后的DBTMA协议有效地解决了原协议存在的不公平性问题。

关键词Ad hoc网络; 公平性; 调整因子; 退避窗口

Research and Simulation of DBTMA Protocol for Ad hoc Network

QIAO Ping’anLI FengjieYAN Jingshan

(School of Computer Science, Xi’an Univerity of Posts and Telecommunications, Xi’an710121)

AbstractChannel access conflict is very serious as mobile Ad hoc network has no fixed control center. By emulating dual busy tone multiple access(DBTMA) protocol, it is found that when there is receiving node in the network, DBTMA agreement appeared a serious problem of unfairness, some node can even monopolize the channel. An improve strategy is proposed in this paper aiming at the shtorage if the DBTMA protocol. By designing a kind of adaptive contention window adjument factor based on the number of node, in order to adjust the backoff window according to dynamic network competition. The simulation results show that the improved DBTMA agreement effectively solve the unfairness problem exists in orginal agrement.

Key WordsAd hoc network, fairness, adjustment factor, backoff window

Class NumberTP393

1引言

目前在无线Ad hoc网络的研究工作中,多数采用IEEE802.11DCF[1]作为媒体接入控制(MAC)层协议。该协议大多利用载波监听技术(CSMA)[2]来减少数据碰撞,但这样就会带来隐藏节点和暴露节点的问题,从而影响节点访问信道的公平性。一些研究表明节点在访问信道时可能出现单个数据流独占信道而其他数据流完全处于“饥饿”的状态,这就是所谓的公平性问题。现有的公平性改进方案大都以退避算法为基础,文献[3]提到一种针对信道访问的乘数递增线性递减(Multiplicative Increase Linear Decrease,MILD)退避算法,在一定程度上改善了节点的公平性,但会使节点较长时间处于较大竞争窗口状态,这样反而会降低网络吞吐量。文献[4]提出一种改进的指数递增指数递减算法,递增和递减指数参数可以灵活配置,但如何准确配置参数还需认真考虑。……