基于单链路吞吐量建模的IEEE 802.11 DCF协议公平性研究
发布时间：2019-06-15 10:52
【摘要】：IEEE 802.11 DCF协议作为一种分布式的随机接入协议,旨在为网络中各链路提供均等的接入机会。尽管IEEE 802.11 DCF协议最初是为单跳网络而设计,随着无线网络技术的飞速发展,其基本接入思想现已被广泛应用于无线ad hoc网络、无线Mesh网络、无线传感网等多跳环境中。然而,当DCF协议应用于多跳网络时将出现严重的链路不公平性问题,即网络中有些链路可以取得较高的吞吐量而有些链路吞吐量几乎为零。自IEEE 802.11标准制定以来,对DCF协议的性能分析一直都是无线网络领域的热点问题。本文主要工作即围绕多跳网络中IEEE802.11 DCF协议的单链路吞吐量及链路公平性性能研究展开,主要创新性成果包括:(1)对多跳网络中IEEE 802.11 DCF协议单链路吞吐量建模难点进行分析,并在此基础上提出了适用于多跳网络中的定长时隙马尔科夫链模型。该模型可分为退避过程、挂起过程、冲突过程以及成功发送过程。退避过程模拟了DCF协议的二进制退避机制;在成功发送过程以及冲突过程中考虑了多跳网络中两种不同的冲突状况;利用连续时间马尔科夫链模型计算得出网络中各条链路发送节点的挂起概率以及每次挂起的时间期望,将其嵌入离散时间四维马尔科夫链中,进而得出马尔科夫链模型中各个稳定状态的概率。根据模型求解,即可得出多跳网络中各链路的发送概率、冲突概率以及吞吐量性能。Qual Net网络仿真环境下的仿真结果与模型推导所得的理论结果的对比验证了本文所提模型的有效性。(2)将多跳网络中DCF协议的链路不公平性问题的原因概括为发送概率的不平等和冲突概率的不平等,并且结合本文所提模型以及仿真实验,分析了竞争窗口的配置对链路的发送概率和冲突概率的影响。在多跳环境下,处于网络中间的链路可能因为不同的邻居干扰而无法监听到空闲的信道,从而缺乏发送数据的机会。另外,有些链路即使有足够的发送机会,仍可能因为隐藏终端的存在而使得发送的数据一直遭遇冲突,从而使其吞吐量几乎为零。在模型推导的基础上,本文以链路公平性为目标计算得出各链路竞争窗口的最优配置,增大了吞吐量较大链路的竞争窗口,使得吞吐量较小链路有更多的机会接入信道,并减小了冲突概率。Qual Net网络仿真环境下的仿真结果表明,两类链路不公平性问题均可通过对各链路竞争窗口的合理配置得到解决。
[Abstract]:As a distributed random access protocol, IEEE 802.11 DCF protocol aims to provide equal access opportunities for all links in the network. Although IEEE 802.11 DCF protocol was originally designed for single hop network, with the rapid development of wireless network technology, its basic access idea has been widely used in wireless ad hoc network, wireless Mesh network, wireless sensor network and other multi-hop environment. However, when DCF protocol is applied to multi-hop networks, there will be a serious link unfairness problem, that is, some links in the network can achieve higher throughput and some links have almost zero throughput. Since the establishment of IEEE 802.11 standard, the performance analysis of DCF protocol has been a hot issue in the field of wireless network. The main work of this paper is to study the single link throughput and link fairness performance of IEEE802.11 DCF protocol in multi-hop networks. The main innovative results are as follows: (1) the difficulties in modeling single link throughput of IEEE802.11 DCF protocol in multi-hop networks are analyzed, and a fixed length time slot Markov chain model suitable for multi-hop networks is proposed. The model can be divided into avoidance process, hanging process, conflict process and successful sending process. The avoidance process simulates the binary back-off mechanism of DCF protocol, and two different conflict situations in multi-hop networks are considered in the process of successful transmission and conflict. The hanging probability of each link sending node in the network and the time expectation of each suspension are calculated by using the continuous time Markov chain model, and it is embedded into the discrete time four-dimensional Markov chain, and then the probability of each stable state in the Markov chain model is obtained. According to the solution of the model, the transmission probability, conflict probability and throughput performance of each link in the multi-hop network can be obtained. The comparison between the simulation results in the Qual Net network simulation environment and the theoretical results derived from the model verifies the effectiveness of the model proposed in this paper. (2) the reasons for the link unfairness of the DCF protocol in the multi-hop network are summarized as the inequality of the transmission probability and the inequality of the conflict probability. Combined with the model and simulation experiments proposed in this paper, the influence of the configuration of competitive window on the transmission probability and conflict probability of the link is analyzed. In multi-hop environment, the link in the middle of the network may not be able to monitor the idle channel because of the interference of different neighbors, thus lacking the opportunity to send data. In addition, even if some links have enough transmission opportunities, the transmitted data may still encounter conflicts because of the existence of hidden terminals, so that their throughput is almost zero. Based on the derivation of the model, the optimal configuration of each link competition window is calculated with the goal of link fairness, which increases the competition window of the link with larger throughput, makes the link with smaller throughput have more opportunities to access the channel, and reduces the simulation results of the collision probability. Qual Net network simulation environment. The simulation results show that the two kinds of link unfairness problems can be solved by the reasonable configuration of each link competition window.
【学位授予单位】：南京航空航天大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN929.5
本文编号：2500163
[Abstract]:As a distributed random access protocol, IEEE 802.11 DCF protocol aims to provide equal access opportunities for all links in the network. Although IEEE 802.11 DCF protocol was originally designed for single hop network, with the rapid development of wireless network technology, its basic access idea has been widely used in wireless ad hoc network, wireless Mesh network, wireless sensor network and other multi-hop environment. However, when DCF protocol is applied to multi-hop networks, there will be a serious link unfairness problem, that is, some links in the network can achieve higher throughput and some links have almost zero throughput. Since the establishment of IEEE 802.11 standard, the performance analysis of DCF protocol has been a hot issue in the field of wireless network. The main work of this paper is to study the single link throughput and link fairness performance of IEEE802.11 DCF protocol in multi-hop networks. The main innovative results are as follows: (1) the difficulties in modeling single link throughput of IEEE802.11 DCF protocol in multi-hop networks are analyzed, and a fixed length time slot Markov chain model suitable for multi-hop networks is proposed. The model can be divided into avoidance process, hanging process, conflict process and successful sending process. The avoidance process simulates the binary back-off mechanism of DCF protocol, and two different conflict situations in multi-hop networks are considered in the process of successful transmission and conflict. The hanging probability of each link sending node in the network and the time expectation of each suspension are calculated by using the continuous time Markov chain model, and it is embedded into the discrete time four-dimensional Markov chain, and then the probability of each stable state in the Markov chain model is obtained. According to the solution of the model, the transmission probability, conflict probability and throughput performance of each link in the multi-hop network can be obtained. The comparison between the simulation results in the Qual Net network simulation environment and the theoretical results derived from the model verifies the effectiveness of the model proposed in this paper. (2) the reasons for the link unfairness of the DCF protocol in the multi-hop network are summarized as the inequality of the transmission probability and the inequality of the conflict probability. Combined with the model and simulation experiments proposed in this paper, the influence of the configuration of competitive window on the transmission probability and conflict probability of the link is analyzed. In multi-hop environment, the link in the middle of the network may not be able to monitor the idle channel because of the interference of different neighbors, thus lacking the opportunity to send data. In addition, even if some links have enough transmission opportunities, the transmitted data may still encounter conflicts because of the existence of hidden terminals, so that their throughput is almost zero. Based on the derivation of the model, the optimal configuration of each link competition window is calculated with the goal of link fairness, which increases the competition window of the link with larger throughput, makes the link with smaller throughput have more opportunities to access the channel, and reduces the simulation results of the collision probability. Qual Net network simulation environment. The simulation results show that the two kinds of link unfairness problems can be solved by the reasonable configuration of each link competition window.
【学位授予单位】：南京航空航天大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN929.5
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