802.11 DCF协议引入信道预约机制的必要性分析

论文对802.11 DCF协议引入信道预约机制的必要性问题进行了探讨.通过分析信道预约机制与隐藏/暴露终端问题之间的关系,提出一种比较隐藏终端和暴露终端出现概率大小的等效方法,并给出了相应的数值估算结果.理论分析结果验证了802.11 DCF协议引入信道预约机制的有效性.     

无线局域网WEP协议的安全性分析

本文介绍了无线局域网IEEE802.11标准中WEP协议的安全机制,分析了该协议的加密、解密和身份认证机制.在此基础上,从密钥管理、IV重用问题、CRC校验、身份认证、IP重定向攻击五个方面分析了WEP协议的漏洞,从而指出提出使用WEP协议是不安全的.     

用于无线网络中违规行为检测的退避算法

无线媒体访问控制协议通常使用分布式竞争机制来共享无线信道。通过对IEEE 802.11协议的分布式协调功能机制进行修改,提出一种改进的退避算法,可实现对网络中的违规行为节点的有效检测,并通过惩罚机制加以纠正。仿真结果表明,该方法能够更有效地检测出无线网络中的违规行为,提高整个网络的吞吐量。     

802.11无线局域网中的智能AP切换策略

在802.11协议内,站点有权选择将要连接的接入点,因此接入点选择机制的实现就成为了负载平衡的一个关键因素.新提出的AP切换策略可应用到新的兼容802.11e的无线网络.由于无需对原有的802.11和802.11e作修改,无论从实现成本和兼容性两个方面来看,都是很实用的方案.仿真实验表明该策略既能充分利用无线通信资源,又可以实现无线局域网内的负载平衡.     

无线网络协议的安全分析与测试

无线网络是目前网络发展的一个方向和趋势。借助对无线局域网802.11协议及其加密体制的安全性进行分析,从理论上得出原有的802.11协议及其加密体制存在的诸多漏洞。在Linux下对802.11协议中的WEP体制进行攻击实验的测试,尤其是注入式攻击实验,从实际上证明原有802.11协议及其加密体制的脆弱性。     

一种NTP协议隐蔽通道

网络隐蔽通道技术是一种被广泛应用的网络攻击技术.掌握隐蔽通道的构建机制,对制定相应网络防御策略具有指导意义.利用互联网不可或缺的NTP时间同步协议,提出了基于NTP协议的隐蔽通道构建机制.通过分析NTP协议查询/应答机制的特点,并研究可被用作载荷的NTP协议数据单元,设计了下行通道和上行通道分离的NTP隐蔽通道,它将隐藏信息伪装成普通NTP报文,进行隐秘消息的传递.NTP报文的普及性和不可替代性,使得基于NTP的隐蔽通道具有穿透能力强、隐蔽性好的优点.试验表明,提出的NTP隐蔽通道可以携带较多的秘密信息,穿透网络监测设备.下一步的工作将围绕NTP隐蔽通道的认证、加密等安全机制进行研究.     

DSRC中一种考虑剩余时间的信道访问退避算法

IEEE 802.11p协议是DSRC技术的下层标准,而该协议采用的仍然是传统的二进制指数退避算法（BEB）。BEB算法虽已广泛使用,但并不能很好地适应DSRC中车载节点的高速移动及其拓扑结构快速变化的特点,易出现信道访问不公平,网络丢包率增加等问题。针对这些问题,提出一种考虑剩余时间的退避算法,由车辆节点的当前速度计算其剩余时间,优化退避机制。实验表明,提出的机制在改善信道访问公平性,提高网络吞吐量等方面均有较好的改善。     

QoS敏感的802.11e分组调度算法

分析并总结无线网络中基于QoS的分组调度算法,针对802.11e EDCA机制中多媒体数据分组调度的不公平问题,提出QoS敏感的802.11e数据分组调度算法.首先,根据不同数据业务延时敏感性需求,提出新的基于紧急度的数据分组调度指标.然后,在802.11e协议中根据业务流的紧急度,调整不同业务流所对应AC队列的参数,改变AC队列信道访问优先级,使紧急业务流有更多机会竞争到信道访问权.最后,进行大量仿真实验,实验结果验证了所提算法的有效性.     

DeviceNet的无线节点适配器设计

将802.11b引入到DeviceNet从站适配器的开发。介绍DeviceNet和802.11b协议的基本内容和特点,给出无线节点适配器的设计思路;以变频器从站的适配器为例,从硬件、链路层和应用层三个方面介绍具体的实现方法,并概述该设计方法的特点。     

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。     

一种用于WLAN的自适应发射功率控制方案

为降低无线网络中工作站的能量消耗、延长工作时间,在分析IEEE802.11协议的基础上,提出一种用于WLAN的自适应发射功率控制方案。利用IEEE802.11协议中规定的ACK信息,引入效率因子和加权因子,使移动终端根据信道环境自适应地调整发射功率,从而降低能耗。仿真结果验证了该方案的有效性。     

Leveraging 802.11n frame aggregation to enhance QoS and power consumption in Wi-Fi networks

The Wi-Fi technology, driven by its tremendous success, is expanding into a wide variety of devices and applications. However, many of these new devices, like handheld devices, pose new challenges in terms of QoS and energy efficiency. In order to address these challenges, in this paper we study how the novel MAC aggregation mechanisms developed in the 802.11n standard can be used to enhance the current 802.11 QoS and power saving protocols. Our contribution is twofold. First, we present a simulation study that illustrates the interactions between 802.11n and the current 802.11 QoS and power saving protocols. This study reveals that the 802.11n MAC aggregation mechanisms perform better when combined with the power save mode included in the original 802.11 standard than with the 802.11e U-APSD protocol. Second, we design CA-DFA, an algorithm that, using only information available at layer two, adapts the amount of 802.11n aggregation used by a Wi-Fi station according to the level of congestion in the network. A detailed performance evaluation demonstrates the benefits of CA-DFA in terms of QoS, energy efficiency and network capacity with respect to state of the art alternatives.     

A simple recursive scheme for adjusting the contention window size in IEEE 802.11e wireless ad hoc networks

The IEEE 802.11e standard has been introduced recently for providing Quality of Service (QoS) capabilities in the emerging wireless local area networks. This standard introduces a contention window based Enhanced Distributed Channel Access (EDCA) technique that provides a prioritized traffic to guarantee the minimum bandwidth needed for time critical applications. However, the EDCA technique resets the Contention Window (CW) of the mobile station statically after each successful transmission. This static behavior does not adapt to the network state since it reduces the network usage and results in bad performance and poor link utilization whenever the demand for link utilization increases. This paper proposes a new adaptive differentiation technique for IEEE 802.11e Wireless Local Area Networks that takes into account the network state before resetting the contention window. In the new technique, the congestion level of the network is sensed by using previous CW values. Three other enhancement techniques that focus on network adaptation are also discussed. Their main limitations are the high complexity of the implemented algorithms and their slow adaptation to the network state when the channel experiences bursty traffic. The proposed technique is compared to the original differentiation techniques of IEEE 802.11a and IEEE 802.11e standards, as well as to the enhancement schemes. Results show that the proposed adaptive technique outperforms IEEE 802.11e and is comparable to the other enhancement schemes while maintaining relatively low complexity requirements.     

Balancing energy efficiency and throughput fairness in IEEE 802.11 WLANs

The proliferation of wireless networks based on IEEE 802.11 has resulted in a heterogenous set of devices using a variety of applications to compete for the desired service performance. Most notably, the class of highly mobile and energy constrained devices is showing high growth rates. Yet, fairness of resource allocation is still only considered in terms of achievable throughput and without considering energy efficiency. In this paper we first show that performing an energy efficient and fair resource allocation in current IEEE 802.11 WLANs is challenging, given the diversity of power consumption figures among mobile devices. We then propose a criterion to objectively balance between the most energy-efficient configuration (where all resources are given to one station) and the throughput-fair allocation (where the power consumption is not considered). We derive a closed-form expression for the optimal configuration of 802.11 with respect to this criterion. Our analysis is validated through simulations, showing that our approach betters the prevalent allocation schemes discussed in literature in terms of energy efficiency, while maintaining the notion of fairness among devices. Experimental results obtained in a real-world testbed confirm the main results derived from our analysis and simulations.     

无线802.11蜜罐研究综述

介绍了典型的无线802.11蜜罐,并对其进行了比较和评估.分析了目前无线802.11蜜罐的主要应用领域,对无线802.11蜜罐面临的主要挑战和发展方向进行了讨论.     

一种功率自适应控制方案在移动自组网的应用

介绍了移动自组网的特点和802．11 DCF传输方式,论述了自组网的动态节能机制,提出了一种通过交换控制信息来预测最小发射功率的功率自适应调整MAC协议。仿真实验证明了该方案能有效降低系统的能量消耗,提高了网络的利用率。     

基于STM32的太阳能光热实验系统

采用STM32设计实现了一种太阳能光热实验系统, 介绍了系统的构成及功能, 给出系统终端软、硬件系统设计. 分析了温度传感器PT1000调理电路、AD转换及隔离电路、人工光源调光电路等单元电路的结构和工作原理. 架构了多任务的软件体系, 采用最小二乘法对温度实测数据进行分段线性化拟合, 并引入误差评估原理来确定适用于PT1000的最佳校正方程. 相关技术已应用于福建师范大学新能源工程中心的太阳能光热实验教学系统中, 实际应用表明, 该终端的性能指标满足设计要求.     

无线局域网MAC协议研究及实时业务QoS实现

随着无线网络的迅速发展,网络上的业务流量与日俱增,如何保证无线局域网实时业务服务质量的问题也越来越突出。本文介绍了提供QoS保障的IEEE802.11e协议,着重研究了一种基于标准PCF的增强QoS保证的媒体接入机制——动态PCF,讨论了它在802.11WLAN中支持IP话音及一般非实时数据业务的QoS控制流程。     

下一代高速无线局域网标准IEEE802．11n的关键技术

IEEE802．11系列标准代表了WLAN技术的主流发展方向。1EEE802．11n作为下一代高速无线局域网标准,物理层采用MIMO—OFDM技术,并对MAC层性能进行优化,大大提高了数据的传榆速率。文中讨论了IEEE802．11n的关键技术。     

A novel Effective Capacity-based framework for providing statistical QoS guarantees in IEEE 802.11 WLANs

This article proposes a performance model of the IEEE 802.11 MAC layer that employs the notion of Effective Capacity. In particular, the paper establishes that an IEEE 802.11 mobile station can be regarded as a Semi-Markovian bursty server of the On/Off type, with known distributions for the On and Off periods, and subsequently applies known results for Semi-Markovian models to derive the Effective Capacity function of this On/Off server. The general Effective Bandwidth/Capacity theory can then be used for computing buffer overflow probabilities and for employing simple traffic control policies to enforce related QoS guarantees. The policies guarantee a soft bound on the buffer overflow probability and are suitable for real-time traffic control over WLANs. The Effective Capacity model of IEEE 802.11 stations is originally developed by assuming that the other competing stations are saturated. This is a conservative assumption that becomes very accurate in a highly loaded network. Subsequently, the model is adapted to encompass lightly loaded networks as well. In the adapted model, each mobile station directly measures a few model parameters, instead of calculating them on the basis of the saturation assumption, and uses these measurements in the computation of its Effective Capacity function. The theoretical results are checked against simulations, validating the appropriateness of the model.