基于IEEE802.11的无线Ad Hoc网络的接入性能研究及算法改进

Research on Access Performance of Wireless Ad Hoc Network Based on IEEE802.11 and its Algorithm Improvement

在研究IEEE802.11标准的基础上,查阅了Ad Hoc网络信道接入的相关资料,分析了IEEE 802.11信道接入协议的优缺点,提出了对IEEE 802.11DCF工作模式的改进建议,以提高整个系统的性能.本文所作的主要工作包括以下几个方面:1.对IEEE802.11所采用的BEB退避机制,在分析了其缺点的基础上,参照了相关的改进算法,如MILD、LMILD、EIED等,提出了基于信道状况,根据信道忙闲程度的不同来设定相应的竟争窗口的退避机制,缓解了信道接入时发生的不公平性,提高了系统吞吐量.2.对DCF的工作机制进行了改动,在延迟阶段对信道进行探测,以避免出现错误的阻塞,同时,根据节点收发RTS/CTS的情况,探测信道的状况,来确定是否可以并行传送数据,以提高吞吐量.3.对原有的IEEE8 02.11中RTS/CTS和DATA报文的重传门限进行了改进,引入了一种自适应机制来进行门限值得设定,以减少报文被丢弃的可能性,从而达到减少触发TCP拥塞控制机制可能性的目的,从而提高系统的吞吐量.4.使用网络仿真器NS2对相关的改进进行了模拟仿真,仿真结果表明,与原有的接入方案相比,改进后的方案在网络性能方面有所提高.本文针对IEEE802.11的缺陷,提出了一些改进,为Ad Hoc网络的研究,提供了一些参考,具有一定的参考价值和借鉴意义.

Based on the research of IEEE802.11,referring to information related to the channel access control of Ad hoc network and analyzing the strongpoint and shortcoming of IEEE802.11, we provide some kinds of new improved methods for IEEE8 02.11 DCF to improve the performance of the system. The main work of this paper includes the following several aspects：1. Based on analyzing the shortcoming of the BEB backoff mechanism used in IEEE802.11 and referring to related improved methods, such as MILD,EIED and so on, we put forward a new backoff mechanism which is based on the status of the channel. This method is based on the busy or idle degree of the channel to certain the parameter of the contention window then can relieve the unfairness during the period of the channel access and enhance the throughput of the system.2. After analyzing the problem of the hidden terminal,exposed terminal and blocking in IEEE802.11＇s channel ac cess control, we modify the mechanism of DCF.During the period of deferring, we detect the channel to avoiding the false blocking. At the same time, based on the status of receiving and sending RTS/CTS we decide to transfer data parallelly to improve throughput.3. Modifying the threshold of the retransmission for RTS/CTS and DATA packet in IEEE802.11, an adaptive mechanism is used to set the threshold of the retransmission, so that the probability of packet loss is minimized and TCP＇s congestion control mechanism is triggered fewer.4. The NS2 network simulator is used to simulate the modified scheme. The results of the simulation show that with the modified scheme, the throughput of network is better than IEEE802.11. In this paper, we take into account the shortcoming of the IEEE802.11 and put forward some improvement. The results of this paper providesa valuable reference for the research of Ad hoc network.