一种基于接收节点控制的无线传感器网络媒体访问控制协议

为了提高无线传感器网络数据包传输效率,提出一种基于时间同步、接收节点控制的无线传感器网络媒体访问控制协议。该协议在保持节点低功耗工作的前提下,使父节点在一个操作周期内,通过多次邀请机制和迸发传输机制,能够与多子节点进行数据包的多次传输。该多次邀请机制,使父节点具备了在单个操作周期内,从多个子节点接收数据包的能力,本质上减少了子节点之间的竞争、提高了信道利用率,增强了父节点对数据包传输的控制力。迸发传输机制,使得父节点可以在一次通讯中连续接收多个数据包,进一步提高了信道的利用率。仿真结果表明:当网络载荷强度增大时,该协议使网络中的节点能够充分利用信道,显著提高了网络中数据包的传输效率,随着网络载荷增加,使网络吞吐量增大近50%。     

保证无线上行链路TCP公平的调度算法

针对无线局域网中上行链路TCP流之间存在严重的无线信道资源分配不公平问题,提出一种上行链路TCP流的调度算法UFWFQ。该算法在接入节点上对上行TCP流采用与WFQ算法相同的轮询机制,根据流的传送速率动态计算其服务概率,分配给高速发送流较大的权重,使各上行TCP流占用的信道时间相等,以保证各流的加权公平性,提高网络的总吞吐率。仿真实验结果验证了该算法的有效性。     

基于线性网络编码的无线网络信道接入机制

为了提高无线自组织网络的通信性能,针对当前网络信道接入机制存在的不足,提出一种基于线性网络编码的信道接入机制(LNC)。首先对传统网络信道接入机制的工作原理和缺陷进行分析,然后采用线性网络编码方式提高数据包传输效率,最后运用马尔科夫链模型对LNC进行数学建模,并通过仿真实验对其性能进行分析。仿真实验结果表明,相对于传统网络信道接入机制,LNC不仅提高了网络的吞吐量,降低了节点的数据包丢失率,而且提高了信道利用率。     

基于Linux的无线局域网协议解析器的设计

无线局域网的快速发展使得对其安全性能的要求在不断提高。文中在对无线局域网安全机制分析的基础上,提出了一种基于Linux的无线局域网的协议解析器的设计方法。在Linux环境下,以目前运用最为普遍的无线局域网标准IEEE802.11b协议为基础设计协议解析器,详细介绍了系统的原理和体系组成。通过Libpcap数据包捕获开发包,捕获无线局域网传输过程中的数据包,并介绍了对所捕获到的符合过滤规则的数据包根据802.11b协议规范和TCP/IP协议簇中各协议的结构和特点进行解码。     

基于Linux的无线局域网协议解析器的设计

无线局域网的快速发展使得对其安全性能的要求在不断提高. 文中在对无线局域网安全机制分析的基础上,提出了一种基于Linux的无线局域网的协议解析器的设计方法.在Linux环境下,以目前运用最为普遍的无线局域网标准IEEE802.11b协议为基础设计协议解析器,详细介绍了系统的原理和体系组成.通过Libpcap数据包捕获开发包,捕获无线局域网传输过程中的数据包,并介绍了对所捕获到的符合过滤规则的数据包根据802.11b协议规范和TCP/IP协议簇中各协议的结构和特点进行解码.     

一种基于簇的无线传感器网MAC协议

MAC协议对无线传感网络的运行和性能具有重要的影响。为此,分析了基于簇的无线传感器网络的MAC协议,针对它们存在的缺陷,提出了一种新的基于簇的MAC协议(C-MAC)。该协议能够根据簇成员节点数目和通信负载动态地改变TDMA帧的长度,减少节点的空闲侦听时间,提高信道的利用率,从而延长网络的生命周期。模拟结果显示,该协议在数据包延迟、能量消耗和数据包接收率等性能上有很大提高。     

802.11无线接入TCP连接本地延迟抖动的理论模型*

为了分析802.11接入网类型对延迟抖动的影响,基于对802.11DCF（distributed coordinated function）信道访问机制的分析与马尔可夫模型,提出一个802.11无线接入的TCP连接本地延迟抖动（local jitter,LJITTER）分布模型。实际网络的测试实验数据证明,该模型非常吻合802.11无线接入的TCP LJITTER实际分布。该模型可以用于接入网类型区分、数据包流量分类、TCP协议改进与非法AP检测。     

无线局域网MAC机制对TCP性能的影响分析

通过分析和比较IEEE802.11无线局域网分别采用3种典型MAC机制时的TCP性能,深入研究了MAC机制对无线局域网中TCP性能的影响.仿真结果表明,由MAC机制所决定的信道冲突率、MAC帧丢失率、MAC帧传输时延抖动幅度和频率、网络吞吐量和公平性将直接影响无线局域网中TCP的吞吐量、公平性和稳定性.     

网络编码感知的无线机会路由性能分析模型

结合基于优先级的ACK回复策略,提出网络编码感知的无线机会路由性能分析模型。该模型探讨多个中继节点时无线信道丢包对网络性能的影响。为此,建立二维马尔科夫链模型对802.11 DCF信道接入机制进行数学建模分析,从而得到数据包成功投递概率和网络吞吐量公式。数学分析结果表明:结合机会路由和网络编码,通过增加中继节点数量,可以提高数据包的投递概率和网络吞吐量。     

基于无线网络的智能酒店客房控制系统

本文以无线WIFI网络节点搭建的局域网为基础,使用C#语音编写的上位机软件通过TCP/IP协议与MT7681无线模块进行通信,使用sql server数据库来存储用户数据.登录智能酒店客房控制系统软件后,点击相应功能按键,上位机将会向所在局域网发送UDP数据包,MT7681无线模块识别并接收数据包后进行解析,通过IO口控制继电器工作状态来实现对客房内的"电源"和"热水器"的远程控制,提前控制,为酒店的管理与服务提供了便利,符合当前物联网趋势,实用性强.     

The performance evaluation of IEEE 802.11 DCF using Markov chain model for wireless LANs

During the past few years the widespread use of the wireless local area networks (WLANs) communication technique is one of the most popular technologies in data telecommunications and networking. The IEEE 802.11 protocol has achieved worldwide acceptance with WLANs with minimum management and maintenance costs. The theoretical performance and numerical results in terms of saturation throughput and delay of distributed coordination function (DCF) were finished by Ziouva and Antonakopoulous. It took into account of the busy medium conditions and how they affected the use of the backoff mechanism. However, the definition of their proposed channel busy probability is not suitable for the operating system architecture. In this paper, the channel busy conditions is modified and the Ziouva and Antonakopoulous's (ZA's) model is improved, and the more accurate analyses of the DCF are presented. Our analysis is also extended to the computation of the delay performance of both the request-to-send/clear-to-send (RTS/CTS) and basic access mechanisms. The numerical results show that the modified model has better performance than the ZA's model under ideal channel scenario.     

Maximizing multiuser diversity gains in IEEE 802.11 WLANs

Opportunistic scheduling monitors the receivers’ channel states and schedules packets to the receivers in relatively good channel conditions. Opportunistic scheduling can be easily implemented in cellular network systems that have embedded channel state report functions. To apply opportunistic scheduling to wireless LANs, deficient of channel report functions, we first devise an efficient channel probing mechanism. Prior opportunistic scheduling methods for WLANs limit the number of probed receivers and may not fully utilize the potential multiuser diversity gains. In this paper, we develop a new opportunistic scheduling scheme called WDOS (WLAN Distributed Opportunistic Scheduling). WDOS invites all receivers to channel probing and has a potential to fully realize the multiuser diversity gains. To reduce the overhead of probing all active receivers, we devise a contention based RTS/CTS exchange with early termination. A sender initiates channel probing by multicasting an MRTS (modified RTS) frame and each receiver responds with a CTS frame after a backoff delay. Hearing the first CTS frame, the sender terminates channel probing and transmits data frames to the first responder. WDOS attains the multiuser diversity gains by allocating a shorter backoff delay to a receiver in better relative channel conditions. We evaluate the performance of WDOS both via an analytic method and computer simulations. Our performance study shows that WDOS achieves the performance near optimal.     

Rate avalanche: Effects on the performance of multi-rate 802.11 wireless networks

Originally designed to deal with the hidden node problem, the Request-to-Send/Clear-to-Send (RTS/CTS) exchange is often turned off in most infrastructure-based 802.11 networks with the belief that the benefit it brings might not even be able to pay off its transmission overhead. While this is often true for networks using fixed transmission rate, our investigation leads to the opposite conclusion when multiple transmission rates are exploited in WLANs. Through extensive simulations using realistic channel propagation and reception models, we found out that in a heavily loaded multi-rate WLAN, a situation that we call rate avalanche often happens if RTS/CTS is turned off: high collision rates not only lead to retransmissions but also drive the nodes to switch to lower date rates; the retransmissions and the longer channel occupation caused by lower rates will further deteriorate the channel contention, which yields more collisions. This vicious circle could significantly degrade the network performance even no hidden node presents. Our investigation also reveals that, in the absence of effective and practical loss differentiation mechanisms, simply turning on the RTS/CTS could effectively suppress the rate avalanche effect. Various scenarios/conditions are extensively examined to study the impact of RTS/CTS on the network performance. Our study provides some important insights about using the RTS/CTS exchange in multi-rate 802.11 WLANs.     

一种平均噪声功率预估计的自组网节能机制

基于IEEE 802.11 DCF MAC协议提出了一种适用于移动无线自组网的功率控制节能方案,在该方案中节点通过一种接收过程中的噪声功率预估计方法和RTS/CTS握手机制的反馈,动态调节待发送数据分组的发射功率。协议分析和NS2仿真表明,该方案在不明显降低网络吞吐量的同时,可以有效降低分组发射的平均功耗,从而达到节能的目的。     

Reliable beacon transmission based MAC protocol for LR-WPANs over WLAN interferences

The use of IEEE 802.15.4 standard based application systems has been rapidly increasing, for example, in medical services, sensor networks, public safety systems, and home automation systems. However, issues arise from the fact that IEEE 802.15.4 standard based low rate wireless personal area networks （LR-WPANs） use the same frequency bands as wireless local area networks （WLANs）, and they interfere with each other. Based on past research on this issue, the interference has a more serious impact on LR-WPANs＇ performance than on WLANs＇ performance. In this paper we propose a method to improve LR-WPANs＇ performance while coexisting with WLANs, which is called the reliable beacon transmission based medium access control （MAC） protocol. Since the reliability of a beacon frame is important, in this method, only the beacon frame is transmitted in interference-free channels, and the data packets are transmitted in interfered channels instead of abandoning the channels altogether. This method increases the reliability of beacon frames as well as overall channel utilizations. The effectiveness of the proposed method was evaluated through extensive simulations, and this paper proves that this method improves the performance of IEEE 802.15.4 based wireless sensor networks （WSNs） over WLANs＇ interferences.     

无线局域网中一种自适应RTS门限调整算法

媒体访问控制是无线局域网的重要部分,决定了具有受限通信带宽的无线信道的共享效率.IEEE 802.11系列标准基于现有以太网技术,具有良好的操作性和兼容性,已发展成为WLAN的主要标准.IEEE 802.11 DCF中有两种接入方式:基本方式和RTS/CTS方式.RTS/CTS方式是IEEE 802.11无线网络的可选握手过程,用于减小碰撞的可能性.决定使用RTS/CTS握手方式的RTS门限值是研究的重要参数,不同的取值对数据传送会产生不同的性能特点.文章通过分析IEEE 802.11 DCF分组发送成功和碰撞的持续时间,获得了RTS和基本方式下分组传输时间开销与分组长度的关系.给出了以最小化分组传输时间代价为优化目标的最优RTS门限的计算公式.通过对当前信道分组发送的冲突概率的预测实现了最优RTS门限的计算;给出了一个具体的RTS门限自适应调整算法,使终端能自动调整其RTS门限以达到或接近最优值.仿真表明RTS门限自适应调整算法明显减小了分组传送时收发器发送单位比特数据的时间开销.     

移动Ad Hoc网络中应用智能天线的多址协议及其性能分析

对智能天线在移动Ad Hoc网络(MANET)中的应用进行研究．提出了自适应波束形成CSMA／CA(ABF—CSMA／CA)协议．该协议利用RTS／CTS对话实现信道预约；在RTs与CTS分组中设置了训练序列，收发节点的智能天线基于训练序列进行自适应波束形成以传输数据分组与ACK．提出改进的“虚拟载波监测”机制进行冲突避免(CA)．每个节点中设置两类网络分配矢量(NAV)，用一个oNAV记录邻节点以全向模式占用信道的时间，用多个bNAV分别记录各邻节点以波束形成模式传输分组的时间．推导了信道利用率的近似计算公式并进行了仿真，考察了节点传输距离、训练序列长度及天线模式切换时间对网络性能的影响．结果表明，ABF-CSMA／CA协议与智能天线的结合能有效实现信道的空分复用(SDMA)，显著提高整个网络的信道利用率．     

Comparing the results from various performance models of IEEE 802.11g DCF

IEEE 802.11 DCF is the most widely-used CSMA/CA access control mechanism. Recent analytic performance models for DCF have received acclaim for both their simplicity and reported accuracy. Most of these models share the assumptions of full single-hop connectivity among all stations, that DCF back-off may be modeled as a Markov process and that the network is saturated with traffic. In order to verify the accuracy of existing analytic models we developed a discrete-event simulator to record the performance of the DCF protocol and ensure that every detail of the standard is represented. Simultaneously we set up a hardware test bed to measure the same performance metrics in an environment that makes none of the simplifying assumptions of either the analytic models or the simulation. In the test bed, as in the simulator, we used the same physical parameter settings prescribed by the standard. As is the case for the analytic models we used, we subjected the simulator and the test bed to the same saturated workload for both basic and RTS/CTS access modes. Finally, we also implemented a non-saturating Markov Modulated Arrival Process (MMAP) workload model for our simulator to test the performance of DCF subject to more realistic internet traffic conditions. We describe both the simulator and the test bed in some detail in order to testify to the accuracy and detail of our results. The results show that the analytic models are mostly pessimistic for small numbers of nodes and optimistic for larger numbers of nodes. The performance measurements from the test bed, in turn, indicate that the simulation results are similarly optimistic when large numbers of nodes are concerned. Since the test bed uses an error-prone wireless channel, this latter result is, in principle, not surprising. The rate of deterioration in the actual performance is however something that is not widely known and is much more rapid than analytic models would suggest.     

基于模糊逻辑的多速率WLAN自适应MAC协议

针对DCF应用在多速率无线局域网中存在吞吐量异常和严重不公平性问题,提出了一个基于信道状态和节点速率的模糊自适应退避算法——RCFAB算法。仿真结果表明,RCFAB能够适应多速率WLAN,并有效地改善系统的吞吐量和接入公平性。     

IEEE 802.11ax密集WLAN的干扰协调策略

无线局域网(WLAN)中设备数量的指数级增长,导致激烈的信道争用及严重的同频干扰。当运行在同一频段上的两个WLAN在彼此感知范围内时,使用先监听后发送的分布式信道接入方式会引起资源浪费,降低网络吞吐率。提出一种密集WLAN场景下的干扰协调策略。根据IEEE 802.11ax中的基本服务集颜色对站点进行分组,提出协调交替目标唤醒时间策略(CAT),安排不同组内站点在不同的时间接收数据,从而避免信道争用,最小化干扰,同时通过优化下行数据包大小提高网络吞吐率。仿真结果表明,当两个WLAN距离很近时,CAT方案能够保证网络吞吐率。此外,在考虑误码率的情况下,吞吐率并非随着数据包的增大单调递增,而是存在一个阈值,超过该阈值后网络吞吐率即呈下降趋势。