A Novel Event Model for Performance Analysis of IEEE 802.11 DCF

After considering the memory effect among series events occurring on the channel, we propose a novel event model to analyze the channel status more precisely. The memory effect is caused by the backoff freezing regulation of IEEE 802.11 Distributed coordination function （DCF）, which has been ignored before and thus resulted in the inaccurate evaluation of the network performance. Based on our new event model, the network performance of IEEE 802.11 DCF, including throughput, packet delay distribution and energy efficiency is analyzed. Simulation results show that our model is highly accurate.     

移动ad hoc网络802.11 DCF性能分析

分析了移动ad hoc网络相关衰落信道下的802．11DCF的吞吐量以及帧长度对吞吐量的影响。研究表明移动速度越高,吞吐量越低;在一定的移动速度下存在最优的帧长使得系统吞吐量最大,并且该最优值与发送节点的数目无关。     

RWBO（pd, w）： A Novel Backoff Algorithm for IEEE 802.11 DCF

The Probability Distribution of Slot Selection (PDoSS) of IEEE 802.11 DCF is extremely uneven, which makes the packet collision probability very high. In this paper, the authors explore how to make the stations select the slots uniformly, and give an RWBO(pd,w) algorithm for 802.11 DCF to make the PDoSS even and decrease the packet collision probability. A Markov model is given to analyze the PDoSS of RWBO(pa, w). The performance of RWBO(pd, w) is evaluated by simulation in terms of saturation throughput and packet collision probability. The simulation results indicate that RWBO(pa, w) can decrease the packet contention probability to a large extent, and utilize the channel more efficiently as compared to the 802.11 DCF. Moreover, the relation between saturation throughput and walking probability (pd), the relation between saturation throughput and contention windows (w), the relation between packet collision probability and walking probability (pal), and the relation between packet collision probability and contention windows (w) are analyzed. The analysis indicates that RWBO(pd, w) has some remarkable features: its saturation throughout keeps high and packet collision probability keeps very low (under 0.1) in a large range of pd and w, which allow users to configure Pd and w more flexibly.     

光纤传输系统的色散补偿技术及其发展研究

首先给出色散的定义及色散补偿的基本原理,分别研究了光纤传输系统的几种色散补偿技术,包括已经发展成熟的色散补偿光纤、镜像相位阵列补偿技术,以及发展中的新型色散补偿技术如电色散补偿技术,最后给出了色散补偿技术的发展方向.     

路由特性对IEEE802．11 DCF多跳网络容量的影响

使用数学分析方法研究基于IEEE 802.11 DCF的Ad Hoc网络中节点传输半径和路由策略选择问题.在节点均匀分布的多跳网络中,使用四种路由策略以及不同的节点传榆半径设王,试图找出能够使网络容量最大化的方案组合.计算结果表明,在节点密度一定的情况下,减小网络节点的传输距离有利于增加网络的容量,而在传输半径一定的条件下,使用能够导致长跳路由的策略,有利于提高网络容量.     

生产阶段矿业投资评估模型建立的实物期权方法

文章在介绍传统矿业投资评估方法及其缺陷以及实物期权概念和定价方法的基础上，利用实物期权方法建立了生产阶段矿业投资评估模型。     

无线局域网DCF性能分析与仿真

主要分析了在无线局域网中应用比较广泛的MAC协议DCF(分布式协调功能)协议的性能.从DCF的基本接入模式和RTS/CTS模式出发,分析了不同的节点数下分别在低速、中速、高速下两种接入模式吞吐量和延时方面的比较.通过仿真验证了低速状态下RTS/CTS在大多数情况下比基本接入模式无论在吞吐量和延时方面都更加有效,而且节点数越多的时候,情况越明显.而在高速状态下,基本接入模式要比RTS/CTS方式有效.     

有限负载下802.11 DCF的性能分析及优化

利用三维马尔可夫链和M/G/1/K队列建立了有限负载下DCF机制的性能模型,分析了终端数量、传输负载、二进制指数回退机制及MAC层有限队列对系统性能的影响.基于该模型,推导了有限负载下最大化吞吐量的最优最小竞争窗口的闭式解.仿真结果表明,模型能够有效地预测有限负载下DCF的性能,根据传输负载调整最小竞争窗口大小能够获得最大化吞吐量.     

Modeling Channel Access Delay and Jitter of IEEE 802.11 DCF

With the ever-increasing requirement of WLAN to support real-time services, it is becoming important to study the delay properties of WLAN protocols. This paper constructs a new model to analyze the channel access delay and delay jitter of IEEE 802.11 DCF in saturation traffic condition. Based on this analytical model, average channel access delay and delay jitter are derived for both basic access and RTS/CTS-based access scheme. The accuracy of the analytical model is validated by simulations and furthermore we discuss the impact of initial contention window, maximal backoff stage, and packet size on channel access delay and delay jitter of 802.11 DCF using the proposed model.

基于全网冲突的自适应退避算法的研究

退避算法的设计对基于竞争的IEEE 802.11协议影响重大,而退避的前提取决于冲突的发生和正确判断。本文在DCF协议的基础上提出了一种基于全网冲突的自适应调整竞争窗口的新型退避算法(CWN-BEB),CWN-BEB算法通过统计全网冲突次数(即整个网络所有节点发生冲突的总次数),使全网冲突对节点透明,并引入一个新的变量全网冲突概率来自适应改变竞争窗口大小。此算法未引入额外开销,可以很好地与802.11 DCF协议兼容,实现复杂度低。仿真结果表明,在低负载情况下,CWN-BEB算法可以较好地向DCF协议收敛;在高负载情况下,CWN-BEB的时延和吞吐量等性能明显优于802.11 DCF协议。