无线数据通信网中的信道接入协议研究

信道接入协议（MAC）是无线数据通信协议的重要组成部分。由于无线信道是一个开放、共享的信道，网络节点在通信过程中存在隐终端和暴露终端问题。基于目前无线通信常用的MAC协议存在的问题，着重分析了基于扩频码的信道接入协议，该协议利用扩频码的正变特性，使得网络中各节点可以同时占用信道而互不干扰，较好地解决了信道争用问题，提高了系统效率。同时指出，在选择MAC协议时，应根据无线网络的拓扑结构及特点灵活选择，以提高网络性能。     

采用定向天线Ad Hoc网络MAC协议关键问题研究

介绍基于定向天线的MAC协议,阐述使用定向天线所面临的隐藏终端、暴露终端以及聋节点问题。重点分析定向天线的MAC协议造成隐藏终端和暴露终端的原因以及解决这些问题的相应策略,在此基础上提出了新的改进CSMA协议。通过仿真表明,改进CSMA协议能提高基于定向天线Ad Hoc网络的整体性能。     

短波自组织网络HFMACA协议研究

在研究无线多路访问碰撞回避协议MACAW的基础上,针对短波无线自组织网络的分布式控制、网络拓扑结构动态变化、存在隐藏终端和暴露终端等特点,对MACAW进行了适当改进,提出了短波多路访问碰撞回避协议HFMACA,详细介绍了其基本思想、运行机制,并对其网络容量、业务成功率、业务传输时延等性能进行了仿真分析,给出了网络业务量与业务成功率及传输时延之间的关系,对短波自组织网MAC协议的研究和设计具有一定的参考意义。     

Ad Hoc网中的一种新型MAC协议

在移动Ad Hoc网络中,一个最基本的问题就是如何在避免隐藏终端和暴露终端问题的同时,增加信道利用率．．针对这个问题．在现有的DBTMA协议以及采用定向天线的一些协议的基础上．提出了一种把信道划分与定向天线相结合的新型MAC协议．DC／A协议（Dual Channel／Directional Antennas)一仿真结果表明这种新的MAC协议可以有效改善网络性能.     

一种适合无线多跳Mesh网络的MAC协议研究

提出了一种适合全分布方式无线多跳网络的MAC层协议,使用带外信号来调度媒体接入,以解决隐藏终端和暴露终端问题。仿真结果显示,网络吞吐量和端到端延迟都得到了明显改善。     

一种基于功率控制的无线传感器网络MAC协议

提出了一种基于功率控制机制的无线传感器网络MAC协议 Distance Prediction Power Control MAC (DPPC-MAC).DPPC-MAC协议基于目前十分成熟的SMAC协议[1-2],引入了功率控制机制以降低数据包发送时的能耗,并且提出了一种新的通过功率预测距离来解决暴露终端和隐藏终端的方法.仿真结果表明,DPPC-MAC能有效降低网络能耗,同时吞吐量性能也得到了一定的改善.     

Ad Hoc网络中MAC协议的研究与展望

MAC协议是无线AdHoc网络的一个重要研究领域，特别是暴露终端和隐终端问题的解决尤为重要。文中介绍了当前AdHoc网络中MAC协议研究的最新成果，并对这些协议进行了分析比较，最后给出了进一步的研究方向。     

Ad-hoc网络的关键技术——MAC层协议研究

介绍了无线Ad-hoc网络MAC层协议面临的问题，重点分析了隐蔽终端问题和暴露终端问题产生的原因以及解决这些问题相应的策略。在此基础上提出了一种结合了定向天线、RTS／C3S握手和信道分割的新的MAC协议。     

一种基于全双工的分布式认知无线电MAC协议

现有的MAC协议在认知无线电环境下都存在"隐藏"终端和"暴露"终端问题,这降低频谱资源利用率和多信道环境下的系统性能,文章提出一种基于全双工的分布式认知无线电MAC(CR-MAC)协议,该协议在不影响授权用户前提下,认知用户通过侦听控制信道的消息,动态的使用授权信道,并通过两根天线同时进行发送数据和接收数据,以此解决"隐藏"终端和"暴露"终端的问题。通过仿真验证,并与现有的MAC协议进行比较,CR-MAC协议可以有效的提高系统的吞吐量。     

双忙音多址接入-Ad Hoc网络中的多址接入控制机制的研究

在Ad Hoc网络中,隐藏终端和暴露终端的存在,严重影响了网络的通信能力。但是通常只采用RTS／CTS对话的MAC层机制不能完全解决隐藏终端和暴露终端的影响,正如单纯的分组侦听的MAC机制在全连通的网络中并不安全一样。为了解决这些问题,介绍一种新的MAC层协议——双忙音多址接入(DBTMA)机制。他的运行借助2个窄带带外忙音。通过使用RTS分组和接收端的接收忙音完全解决了隐藏终端的影响,接收端的CTS分组和接收忙音解决了暴露终端的影响。发送端建立的忙音保护了RTS分组,提高了接收RTS成功的概率,因此也就提高了吞吐量。     

Does the IEEE 802.11 MAC protocol work well in multihop wireless adhoc networks?

The IEEE 802.11 MAC protocol is the standard for wireless LANs; it is widely used in testbeds and simulations for wireless multihop ad hoc networks. However, this protocol was not designed for multihop networks. Although it can support some ad hoc network architecture, it is not intended to support the wireless mobile ad hoc network, in which multihop connectivity is one of the most prominent features. In this article we focus on the following question: can the IEEE 802.11 MAC protocol function well in multihop networks? By presenting several serious problems encountered in an IEEE 802.11-based multihop network and revealing the in-depth cause of these problems, we conclude that the current version of this wireless LAN protocol does not function well in multihop ad hoc networks. We thus doubt whether the WaveLAN-based system is workable as a mobile ad hoc testbed     

一种自组网功率控制算法及分析

无线自组网中的移动节点大多依靠电池提供能量,因此能量是影响无线自组网性能的一个很大的瓶颈,作为事实上的无线自组网媒体接入协议,802.11并没有动态调整传输功率的能力,大大限制了网络的生存时间。采用功率控制可以提高节点的功率使用效率,减少相邻节点间的干扰,改善网络的性能。在802.11基础上提出一种基于信噪比的动态传输功率控制算法。通过进行计算机仿真,与802.11协议相比,在保持吞吐量性能的前提下,大大减少了节点的功率消耗,提高了节点的能量利用率。     

无线Ad Hoc网络中基于业务感知的多信道MAC协议(英文)

Existing multi-channel Medium Access Control (MAC) protocols have been demonstrated to significantly increase wireless network performance compared to single channel MAC protocols. Traditionally, the channelization structure in IEEE 802.11 based wireless networks is pre-configured, and the entire available spectrum is divided into subchannels and equal channel widths. In contrast, this paper presents a Traffic-Aware Channelization MAC (TAC-MAC) protocol for wireless ad hoc networks, where each node is equipped with a single half duplex transceiver. TAC-MAC works in a distributed, fine-grai-ned manner, which dynamically divides variable-width subchannels and allocates subchannel width based on the Orthogonal Frequency Division Multiplexing (OFDM) technique according to the traffic demands of nodes. Simulations show that the TAC-MAC can significantly improve network throughput and reduce packet delay compared with both fixed-width multi-channel MAC and single channel 802.11 protocols, which illustrates a new paradigm for high-efficient multi-channel MAC design in wireless ad hoc networks.     

Performance issues with IEEE 802.11 in ad hoc networking

Although 802.11 is initially designed for infrastructure-based networks, the distributed coordination function allows mobiles to access the radio medium without the need for a base station. Thus, studies in wireless multihop networks, also called ad hoc networks, often rely on the use of IEEE 802.11 for the physical and MAC layers. However, for a couple of years the use of 802.11 in ad hoc networks has been discussed. Different scenarios show serious performance issues. The performance offered by 802.11 is often low and directly impacts the performance of higher-layer protocols. In this article we provide a summary of the different performance issues extracted so far. We classify basic situations according to the main effects. We then present a quick survey of the possible solutions to these problems. This classification is intended to help design appropriate MAC protocols dedicated to ad hoc networks.     

Power-Controlled MAC Protocols with Dynamic Neighbor Prediction for Ad hoc Networks

1　IntroductionMobileadhocnetworksareasetofmobilenodeswhichformandself configurethenetworkwithoutthepre deployedcentraladministrativein frastructure (e.g .thebasestationofWLAN) .Thedemandforadhocnetworkshasbeenbloominginthepastyearsinthecommercialandmilitaryappli cations ,becauseonlyadhocnetworkscanbeappliedinthesituationswherethecentraladministrativein frastructurecan tbe pre installed (e .g .battlefields,disasterrescue)orisnoteconomicaltoinstallbecauseoftemporaryuse (e .g .ameetingintherent…     

MAC protocols using directional antennas in IEEE 802.11 based ad hoc networks

Using directional antennas can be beneficial for wireless ad hoc networks consisting of a collection of wireless hosts. The most important benefit includes a reduction of the radio interference. Thus, it can significantly increase the spatial reuse, thereby improving the network throughput. To best utilize directional antennas, a suitable Medium Access Control (MAC) protocol must be designed. Current MAC protocols, such as the IEEE 802.11 standard, do not benefit when using directional antennas, because these protocols have been designed for omnidirectional antennas. In this paper, we present modified MAC protocols suitable for 802.11 based ad hoc networks using directional antennas. Our comprehensive simulation results demonstrate the performance improvement obtained with the proposed protocols. Copyright © 2007 John Wiley & Sons, Ltd.     

On designing MAC protocols for wireless networks using directional antennas

We investigate the possibility of using directional antennas for medium access control in wireless ad hoc networks. Previous research in ad hoc networks typically assumes the use of omnidirectional antennas at all nodes. With omnidirectional antennas, while two nodes are communicating using a given channel, MAC protocols such as IEEE 802.11 require all other nodes in the vicinity to remain silent. With directional antennas, two pairs of nodes located in each other's vicinity may potentially communicate simultaneously, increasing spatial reuse of the wireless channel. Range extension due to higher gain of directional antennas can also be useful in discovering fewer hop routes. However, new problems arise when using directional beams that simple modifications to 802.11 may not be able to mitigate. This paper identifies these problems and evaluates the tradeoffs associated with them. We also design a directional MAC protocol (MMAC) that uses multihop RTSs to establish links between distant nodes and then transmits CTS, DATA, and ACK over a single hop. While MMAC does not address all the problems identified with directional communication, it is an attempt to exploit the primary benefits of beamforming in the presence of some of these problems. Results show that MMAC can perform better than IEEE 802.11, although we find that the performance is dependent on the topology and flow patterns in the system.     

A range-adaptive directional MAC protocol for wireless ad hoc networks with smart antennas

Using smart antennas in wireless ad hoc networks can offer tremendous potential for improving the network performance. This paper proposes a range-adaptive MAC protocol, called Ra-MAC, for wireless ad hoc networks using smart antennas. In contrast to the previous MAC protocols with only single-fold directional transmission range, we propose to use multi-fold transmission ranges, i.e., LD (Low-distance), MD (Mid-distance) and HD (High-distance), to arrange efficient communications between the senders and receivers. The transmission range is selected dynamically according to the distance between the communicating node-pair. Building on the multiple transmission ranges, we extend directional network allocation vector (DNAV) to range-based DNAV (R-DNAV) to make full use of wireless channels. Moreover, in order to deal with the basic problems (i.e., hidden terminals, deafness and capture) within smart antenna-based wireless networks, we further equip some optimizations such as half-sweeping start of dialog (SOD), extended directional virtual carrier sensing (DVCS) and so on to Ra-MAC, and then detailedly discuss how these optimizations contribute to address the problems. Simulation results indicate that Ra-MAC outperforms the existing directional MAC protocols and 802.11 DCF. Finally, we also make a brief qualitative comparison between all these protocols.     

Medium access control protocols for wireless mobile ad hoc networks: issues and approaches

In this article, a comprehensive survey of the medium access control (MAC) approaches for wireless mobile ad hoc networks is presented. The complexity in MAC design for wireless ad hoc networks arises due to node mobility, radio link vulnerability and the lack of central coordination. A series of studies on MAC design has been conducted in the literature to improve medium access performance in different aspects as identified by the different performance metrics. Tradeoffs among the different performance metrics (such as between throughput and fairness) dictate the design of a suitable MAC protocol. We compare the different proposed MAC approaches, identify their problems and discuss the possible remedies. The interactions among the MAC and the higher layer protocols such as routing and transport layer protocols are discussed and some interesting research issues are also identified. Copyright © 2003 John Wiley & Sons, Ltd.     

无线多跳Ad hoc网络中MAC机制的公平性与网络容量利用率

高效、公平的MAC协议是目前无线多跳Ad hoc网络研究的关键问题之一。该文在给出一种新的无线多跳Ad hoc网络的网络模型前提下,定义了MAC协议公平性、网络容量利用率两个性能参数。给出了一种能在竞争节点间公平共享无线信道并充分利用网络容量的MAC协议(FMAC),仿真比较了FMAC和IEEE 802.11 DCF的公平性和网络容量利用率。结果表明FMAC能在充分利用网络容量的前提下,实现无线信道在竞争节点间的公平共享。