WLAN中MAC协议性能分析研究

对媒体接入控制(Media Access Control,MAC)协议进行性能分析,可以深入理解MAC协议的操作特点,发现吞吐量、数据包时延与丢失等性能遭受影响的本质原因。对当前马尔可夫链性能分析法加以详细地分析与总结,分别阐述了无线局域网络中分布式协调功能和增强的分布式信道接入两种MAC协议的性能分析研究工作。对进一步的研究工作进行了分析与展望。     

无线传感器网络MAC协议的设计研究

媒体访问控制(MAC)协议是无线传感器网络协议的重要组成部分,它的性能好坏直接关系到无线信道的利用效率和整个网络的性能。介绍了无线传感器网络MAC协议设计的主要问题,根据设计指标的不同对无线传感器网络MAC协议进行了分类,并在此基础上,分析研究了几种典型的无线传感器网络MAC协议采用的机制和方法。     

Extended EDCA for delay guarantees in wireless local area networks

Despite their very broad diffusion, IEEE 802.11 Wireless Local Area Networks (WLANs) are not able to provide service differentiation and to support real-time multimedia applications, due to their channel access methods. To overcome these limitations, the 802.11e working group has proposed the Enhanced Distributed Coordination Access (EDCA) scheme, which achieves service differentiation on a statistical basis by properly mapping user Quality of Service (QoS) requirements to channel contention parameters. Such a scheme will be included in the emerging 802.11n standard and in the revision of the 802.11 standard. However, it has been widely demonstrated that, especially at high network loads, EDCA does not provide an effective usage of the channel capacity. In particular, it is unable to provide a bounded delay service to all kinds of multimedia flow because flows with lower channel access priorities are starved to advantage only those with the highest priority. To fix this undesired behavior and improve wireless LAN performance, this paper proposes a new Extended EDCA (E²DCA) scheme, that is compliant with 802.11e specifications. By exploiting a closed-loop control algorithm, E²DCA performs a distributed dynamic bandwidth allocation, providing guarantees on average/absolute delays to real-time media flows, regardless of their priorities. Moreover, an innovative Call Admission Control (CAC) procedure has been developed. Using the ns-2 simulator, the effectiveness of the algorithm has been investigated in realistic network scenarios, involving a mix of audio, video, and FTP flows, at several network loads and with random losses. Results have shown that the proposed scheme is able to provide a bounded delay service to multimedia flows in a wide range of network loads and frame loss ratios.     

USIM-based EAP-TLS authentication protocol for wireless local area networks

Due to the rapid growth in popularity of Wireless Local Area Network (WLAN), wireless security has become one of many important research issues. For the WLAN security, the IEEE 802.1X standard provides an authentication framework that is based on the Extensible Authentication Protocols (EAP). In the EAP framework, there are many authentication protocols that have been proposed, in which each authentication protocol has some strengths and weaknesses, respectively. Most EAP authentication protocols lack two features: identity protection and withstanding man-in-the-middle attacks. In this paper, we first propose a novel symmetric-key based certificate distribution scheme based on Universal Subscriber Identity Module (USIM) cards in a cellular network. The symmetric-key based certificate distribution scheme allows mobile subscribers to obtain temporary certificates from the corresponding cellular network. Combining the proposed certificate distribution scheme with the EAP-TLS (Transport Layer Security) protocol, we present a new EAP authentication protocol called USIM-based EAP authentication protocol. The new EAP authentication protocol combining with USIM cards is an extension of the EAP-TLS protocol and also follows the EAP framework in the IEEE 802.1X standard. Compared to other EAP authentication protocols, the proposed protocol provides mutual authentication, strong identity protection and roaming capability between the cellular network and the WLAN networks.     

A novel re-authentication scheme based on tickets in wireless local area networks

Fast re-authentication schemes during handover of a mobile station are essential to seamless services for real-time multimedia applications in wireless local area networks. Although much research has been done to reduce re-authentication latency, the schemes developed so far either suffer from heavy burden problems or degrade the security level. In this paper, a novel ticket-based approach is proposed for re-authentication during handover. The mobile station receives handover tickets from the authentication server as a proof of authorization, and it presents the corresponding ticket when associating with a new access point. Our scheme reduces re-authentication delay to the delay of 2-way handshake between a mobile station and an access point. Furthermore, this scheme imposes less burden over the entities compared with other proactive key pre-distribution schemes, while satisfying 802.11i security requirements.     

Roaming across wireless local area networks using SIM-based authentication protocol

Wireless local area networks provide high speed data transferring rate to a mobile device. And it is crucial to integrate together two critical issues, the authentication and roaming in heterogeneous networks. For this, Tsai and Chang proposed a SIM-based authentication mechanism for wireless local area networks in 2006. Tsai and Chang's scheme provides an integration method of mobile cellular networks and wireless local area networks. Unfortunately, we found that there are some weaknesses existing in their scheme. In this paper, we propose an improved version for a user roaming in heterogeneous networks. Besides, we also proposed a mobile IP model to provide a better efficiency for a mobile user in WLAN environment.     

基于有序竞争的传感器网络MAC协议

在定向扩散路由无线传感器网络中,为减轻竞争型MAC协议CSMA/CD的碰撞冲突问题,以及减小MAC协议引入的时延,对CSMA/CD协议进行改进,提出基于定向扩散与有序竞争的传感器网络MAC协议,即CSMA/CD-DDOC,通过将同跳梯度层次内的转发节点进行分组后实施各分组对共享信道的有序竞争,减少同时争用信道的节点数目,以达到减少碰撞和减小时延的目的。理论分析和仿真结果表明,CSMA/CD-DDOC协议具有优于CSMA/CD协议的时延性能。     

无线传感器网络MAC协议研究比较

无线传感器网络是微机电系统、通信、传感器、网络等技术相结合的产物。目前已经被预见具有广泛的应用领域和使用价值。介质访问控制（MAC）协议是一项构建网络底层基础结构的重要技术,结合目前国内外的研究成果,从技术方面对无线传感器器网络的MAC协议进行了分类,介绍了几种典型的MAC协议,对它们之间进行了分析和比较。     

基于矿井的无线传感器网络MAC协议的研究

介质访问控制(MAC)协议是一项构造底层基础网络结构的重要技术,其主要功能是为数据传输建立连接和在各网络节点间合理、高效地分配通信资源.从节能角度分析了当前几种比较典型的MAC协议,提出矿井下的无线网络拓扑结构,给出一种New-MAC协议,主要研究了节能问题、数据碰撞问题和同步问题.仿真实验表明:该协议较好地解决了节点能耗问题、延长了网络的生命周期.     

Dynamic adaptation of CSMA/CA MAC protocol for wide area wireless mesh networks

Though the popular IEEE 802.11 DCF is designed primarily for Wireless LAN (WLAN) environments, today it is being widely used for wide area wireless mesh networking. The protocol parameters of IEEE 802.11 such as timeout values, interframe spaces, and slot durations, sufficient for a general WLAN environment, need to be modified in order to efficiently operate in wide area wireless mesh networks. The current wide area wireless mesh network deployments use manual configuration of these parameters to the upper limit which essentially makes the networks operate at lower system efficiency. In this paper, we propose d802.11 (dynamic 802.11) which dynamically adapts the protocol parameters in order to operate at varying link distances. In fact, in 802.11, a transmitter can face ACK/CTS timeout even when it started receiving ACK/CTS packet before the timeout value. We present three strategies, (i) multiplicative timer backoff (MTB), (ii) additive timer backoff (ATB), and (iii) link RTT memoization (LRM), to adapt the ACK_TIMEOUT in d802.11 in order to provide better adaptation for varying link dimensions. Through extensive simulation experiments we observed significant performance improvement for the proposed strategies. We also theoretically modeled the maximum link throughput as a function of the link dimension for the proposed system. Our results show that the LRM technique provides the best adaptation compared to all other schemes.     

高吞吐量低时延的太赫兹无线个域网MAC协议

针对现有太赫兹无线个域网MAC协议存在的基于动态均衡思想的网络不稳定、不合理的竞争窗口导致退避时间过长,以及所分配CTA长度大于节点的时隙请求量时会导致时隙剩余3个问题,提出了一种高吞吐量低时延的太赫兹无线个域网MAC协议——HTLL-MAC(High Throughput and Low Latency MAC protocol)。HTLL-MAC协议通过基于动态均衡思想的接入机制提高网络稳定性,引入动态更改重传竞争窗口方法缩短了退避所需时间,并且启用CTA剩余时隙机制充分利用剩余时隙,从而达到增加网络吞吐量、降低数据传输时延的效果。理论分析验证了HTLL-MAC协议的有效性。仿真结果表明,相较于IEEE 802.15.3c和HTLD-MAC的MAC层,吞吐量提高了6.15%,数据平均时延降低了32.53%。     

Design and evaluation of a novel MAC layer handoff protocol for IEEE 802.11 wireless networks

In recent years, the IEEE 802.11 wireless network family has become one of the most important set of standards in the wireless communications industry. IEEE 802.11 compliant devices are inexpensive and easier to configure and deploy than other wireless technologies. In an IEEE 802.11 wireless network, wireless terminals can move freely. As a result, when the wireless terminal moves away from its current access point, it must switch to another access point to maintain the active connection. This is known as the MAC layer handoff process. MAC layer handoff latency should be minimized to support real-time applications and to provide mobile devices with seamless roaming in IEEE 802.11 wireless networks. This paper proposes a novel MAC layer handoff protocol over IEEE 802.11 wireless networks by introducing advertisement messages sent from other mobile nodes and from which wireless terminals are able to receive the information of access points in their neighborhood. A mobile node can try to associate with access points based on the prediction before starting the probe process. The experimental results demonstrate that our solution can reduce MAC layer handoff latency to meet the requirements of real-time applications.     

An expert system for real-time traffic management in wireless local area networks

The paper explores delay-based congestion and flow control and the offloading of real-time traffic from wireless local area networks (WLANs) to mobile cellular networks (MCNs) in multihomed devices. The control system developed is based on an embedded hierarchical expert system. It adjusts transceivers’ traffic flow(s) for prevailing network conditions to achieve application-dependent delay and throughput limits. In wireless networks, delay and throughput depend on the packet size, packet transmission interval, and node connection density. Therefore, the controller on the destination node monitors average one-way delay and the change of one-way delay of the incoming traffic. On this basis, it adjusts the packet size and transmission interval of the source node by transmitting a control command to the source. If the prevailing level of traffic in the network exceeds its capacity despite of the control actions taken, devices prepare for developed asynchronous offloading of traffic to another access network.The control model was validated via simulation of Voice over Internet Protocol (VoIP) traffic in the OMNeT++ network simulator. The results demonstrate that the expert system developed is able to regulate packet sizes to match the prevailing application-dependent optimum and transfer traffic to another network if the network exceed its capacity no matter the control actions taken. Although this work is motivated mainly by issues of congestion and flow control of WLAN systems and the simulations and results were prepared for the IEEE 802.11b system, the approach and techniques are not limited to these systems, but they are applicable for other packet switched access networks (PSANs), too.     

Expert system for open-loop power control of wireless local area networks

This paper considers an embedded fuzzy expert system for non-feedback uplink power control of wireless local area networks (WLANs). The main idea is to minimize the transmission power of the nodes while keeping the transmission errors at an acceptable level. In the developed method, receivers collect signal strength values which are used by the control systems to define an acceptable transmission power level. The functionality of the proposed solution is demonstrated with simulations, which prove that the use of the expert system to open-loop systems can significantly decrease transmission power, increase energy efficiency and decrease interference to adjacent access points and associated nodes.     

Enhanced cooperative communication MAC for mobile wireless networks

In this paper, we propose a new MAC (medium access control) protocol called enhanced cooperative communication MAC (ECCMAC) based on IEEE 802.11. The major objective of ECCMAC is to maximize the benefits of cooperative communication. We first propose a scheme for selecting and maintaining the best relay node. Second, since both cooperative communication and network coding rely on the selection of a relay node, we consider exploiting a network coding technique for additional throughput improvement. Third, to accommodate asymmetric link rates between a sender and a relay node, we employ ECCMAC to measure forward and reverse link rates, whereas prior works have simply assumed symmetric rates. ECCMAC is evaluated in this paper through theoretical analysis, extensive simulation, and simulation with measured data, and the results show that ECCMAC effectively improves wireless network performance.     

An asynchronous MAC protocol for wireless sensor networks

The MAC protocol for wireless sensor network plays a very important role in the control of energy consumption. It is a very important issue to effectively utilize power under the condition of limited energy. The most energy-wasting part of the MAC protocol for wireless sensor network is at the idling condition. Therefore it is crucial for power saving to be able to turn off the signal transducer of the wireless network when the equipment is idling. Pattern-MAC (PMAC) allows sensors that did not transfer for a long period of time to quickly enter a dormant state, so that the problem of sensor overhearing can be greatly improved, and the whole network structure can fully respond to the actual transfer rate without too much energy consumption, but this type of design requires precise time synchronization mechanism. Achieving time synchronization is a very energy consuming and very expensive mechanism in the sensor network structure, achieving the goal is coupled with excess energy consumption and reduction of the lifespan of the sensor. Additionally, the exchange action with the neighboring pattern after each cycle, not only generates additional energy consumption for data transfer, but is also accompanied by factors such as competition, collision and pattern exchange failure. We propose an asynchronous MAC protocol (AMAC) in this paper and expect to improve the problem of energy wasting and time synchronization due to sleeping schedule exchange under the PMAC basic protocol.     

Contention-free MAC protocols for asynchronous wireless sensor networks

A MAC protocol specifies how nodes in a sensor network access a shared communication channel. Desired properties of a MAC protocol are: it should be contention-free (avoid collisions); it should be distributed and self-stabilize to topological changes in the network; topological changes should be contained, namely, affect only the nodes in the vicinity of the change; it should not assume that nodes have a global time reference, that is, nodes may not be time-synchronized. We give a set of TDMA-based MAC protocols for asynchronous wireless sensor networks satisfying all of these requirements. The communication complexity, number and size of messages, for the protocols to stabilize is small, poly-logarithmic in the network size. A preliminary version of the paper appears in the Proceedings of the 18th Annual Conference on Distributed Computing (DISC 2004), LNCS 3704, pp 245–259, Trippenhuis, Amsterdam, The Netherlands, October 2004.     

一种低延时的无线传感器网络MAC协议

针对典型无线传感器网络X-MAC协议在多跳环境下累积延迟问题,提出一种具有低时延的Ex-MAC协议。利用管理邻居节点工作周期和虚通道算法,使得虚通道中的所有节点近似于同步,从而减少数据传输延迟,而且不需要交换同步控制帧。仿真结果与X-MAC协议相比,减少了端到端的延迟和数据包冲突的几率,提高了网络的吞吐量。     

Energy efficient smart-relay-based cooperative MAC for wireless networks

An enormous number of papers investigated wireless cooperative networks over the last few years. Almost all have shown that cooperative transmission improves network performance significantly. However, none of these studies have considered the hidden and exposed terminal problems which appear due to the cooperative mechanisms of relay selection and transmission processes. The hidden terminal problems increase collisions and the exposed terminal problems increase bandwidth wastage, degrading the expected performance of cooperative networks. This paper addresses these problems of traditional wireless cooperative networks. We also propose a protocol called smart-relay-based-cooperative (SRcoop) MAC to optimally reduce the impacts of hidden and exposed terminal problems. We also illustrate an efficient relay selection mechanism that uses a back-up relay to increase transmission reliability. Our innovative model significantly improves the network throughput, end-to-end delay and energy efficiency over traditional cooperative MAC, 2rcMAC, LC-MAC, C-ARQ and Adere et al. protocols.     

基于生成树的无线传感器网络MAC协议

简要分析了无线传感器网络(W SNs)MAC层协议,针对MAC协议在节能和时延方面的不足,提出了一种基于生成树的MAC协议(ST-MAC)。以汇聚点为根节点,创建一个由网络中所有节点组成的生成树。ST-MAC采用TDMA接入方式,其固有的低工作周期提高了网络性能。性能分析和实验结果表明:相对S-MAC,ST-MAC在能量节省和时延方面有较好的效果。