A Dual-Cluster-Head Based Medium Access Control for Large-Scale UAV Ad-Hoc Networks

Unmanned Aerial Vehicle(UAV)ad hoc network has achieved significant growth for its flexibility,extensibility,and high deployability in recent years.The application of clustering scheme for UAV ad hoc network is imperative to enhance the performance of throughput and energy efficiency.In conventional clustering scheme,a single cluster head(CH)is always assigned in each cluster.However,this method has some weaknesses such as overload and premature death of CH when the number of UAVs increased.In order to solve this problem,we propose a dual-cluster-head based medium access control(DCHMAC)scheme for large-scale UAV networks.In DCHMAC,two CHs are elected to manage resource allocation and data forwarding cooperatively.Specifically,two CHs work on different channels.One of CH is used for intra-cluster communication and the other one is for inter-cluster communication.A Markov chain model is developed to analyse the throughput of the network.Simulation result shows that compared with FM-MAC(flying ad hoc networks multi-channel MAC,FM-MAC),DCHMAC improves the throughput by approximately 20%~50%and prolongs the network lifetime by approximately 40%.

Virus spreading in wireless sensor networks with a medium access control mechanism

In this paper, an extended version of standard susceptible-infected （SI） model is proposed to consider the influence of a medium access control mechanism on virus spreading in wireless sensor networks. Theoretical analysis shows that the medium access control mechanism obviously reduces the density of infected nodes in the networks, which has been ignored in previous studies. It is also found that by increasing the network node density or node communication radius greatly increases the number of infected nodes. The theoretical results are confirmed by numerical simulations.

Medium Access Control： A Physical Layer Network- Coded Approach

This paper investigates the medium access control （MAC） stratifies for communication systems. Since the signals are naturally superposed in public medium, we introduce physical layer network coding into MAC system and propose the physical layer network coded MAC （PNC-MAC） to utilize the collisions occurring in the MAC process. The implicit expressions of the throughput and average delay of the system operated with the new algorithm are derived in an iterative way. To show the performance of the algorithm, we compare the throughput and average delay induced by the new algorithm with current schemes via simulations. The results show that when operated with our proposed PNC-MAC, MAC system can achieve a larger throughput while the frames bear shorter average delay. Moreover, in many users case, the throughput increases slightly while the average delay ascends drastically.

Performance Analysis of WLAN Medium Access Control Protocols in Simulcast Radio-Over-Fiber-Based Distributed Antenna Systems

The performance of three wireless local-area network(WLAN) media access control(MAC) protocols is investigated and compared in the context of simulcast radioover-fiber-based distributed antenna systems(RoF-DASs) where multiple remote antenna units(RAUs) are connected to one access point(AP) with different-length fiber links.The three WLAN MAC protocols under investigation are distributed coordination function(DCF) in basic access mode,DCF in request/clear to send(RTS/CTS) exchange mode,and point coordination function(PCF).In the analysis,the inter-RAU hidden nodes problems and fiber-length difference effect are both taken into account.Results show that adaptive PCF mechanism has better throughput performances than the other two DCF modes,especially when the inserted fiber length is short.

IEEE 802.11e Medium Access Control层QoS机制的改进研究

针对IEEE802.11e Medium Access Control层的QoS机制高负载时存在远端节点冲突和低优先级业务资源被耗尽的问题,提出在牺牲较小带宽的基础上增加一条忙音信道,取代CTS帧在数据信道上的广播,减少远端节点的冲突.仿真结果表明,该方案具有较小的冲突概率,有效地减少了远端节点冲突.同时提出一个解决公平性问题的新思路:在避退时间发送忙音抢占信道,以期提高低优先级业务的接入概率.

Distributed multichannel medium access control protocol without common control channel for single-hop cognitive radio networks

A novel distributed cognitive radio multichannel medium access protocol without common control channel was proposed.The protocol divided a transmission interval into two parts for exchanging control information and data,respectively.In addition to evaluating system saturation throughput of the proposed protocol,a three-dimensional multi channel Markov chain model to describe the sate of the cognitive users (CUs) in dynamic spectrum access was presented.The proposed analysis was applied to the packet transmission schemes employed by the basic,RTS/CTS access mechanism adopted in the normal IEEE 802.11.Analyzing the advantage of the two methods,a hybrid access mechanism was proposed to improve the system throughput.The simulation results show that the experiment results are close to the value computed by the model (less than 5%),and the proposed protocol significantly improves the performance of the system throughput by borrowing the licensed spectrum.By analyzing the dependence of throughput on system parameters,hybrid mechanism dynamically selecting access mechanism can maintain high throughput.

An IEEE 802.3 Compatible Real Time Medium Access Control with Length-based Priority

A new medium access control method is proposed over the predominant Ethernet broadcast channel. Taking advantages of intrinsic variable length characteristic of standard Ethemet frame, message-oriented dynamic priority mechanism is established. Prioritized medium access control operates under a so-called block mode in event of collisions. High priority messages have a chance to preempt block status incurred by low priority ones. By this means, the new MAC provides a conditional detrministic real time performance beyond a statistical one. Experiments effectiveness and attractiveness of the proposed scheme.Moreover,this new MAC is completely compatible with IEEE802.3 .

DQCA:a New Medium Access Control Protocol for MANs

A new medium access control protocol for MANs named DQCA(Distributed QueueCyclic Access)is presented in this paper.When the users of DQCA MAN transfer long files,the network will reach a steady state which is fair after a transient period.The transient pe-riod is shorter than that of DQDB.DQCA MAN has the flexibility in bandwidth allocation:the users can achieve different throughputs if the parameters,Pmax(i),are set to be differ-ent.The implementation of priority mechanism is simpler than that of DQDB.

Mobility Conscious Medium Access Control Scheme for Wireless Sensor Networks: A Conceptual Approach

Mobility in Wireless Sensor Network (WSN) presents distinctive challenges in Medium Access Control (MAC) scheme. Numerous MAC protocols for sensor networks assume that sensor nodes are static and focus primarily on energy efficiency. This work seeks to develop an improved mobility conscious medium access control scheme for wireless sensor networks with a view to enhance energy conservation on mobile sensor nodes. On this note, mobility patterns of different scenarios are modelled using Gauss Markov Mobility Model (GMMM) to determine the position and distance of the sensor nodes and how they are correlated in time.

Modified Distributed Medium Access Control Algorithm Based on Multi-Packets Reception in Ad Hoc Networks

Based on the Multi-Packet Reception (MPR) capability at the physical layerand the Distributed Coordination Function (DCF) of the IEEE 802.11 MAC protocol, we propose amodified new solution about WAITING mechanism to make full use of the MPR capability in this paper,which is named as modified distributed medium access control algorithm. We describe the details ofeach step of the algorithm after introducing the WAITING mechanism. Then, we also analyze how thewaiting-time affects the throughput performance of the network. The network simulator NS-2 is usedto evaluate the throughput performance of the new WAITING algorithm and we compare it with IEEE802.11 MAC protocol and the old WAITING algorithm. The experimental results show that our newalgorithm has the best performance.

Design and Analysis of Prioritized Medium Access Control Protocol for Backbone Routers in Wireless Mesh Networks

A Prioritized Medium Access Control （P-MAC） protocol is proposed for wireless routers of mesh networks with quality-of-service provisioning. The simple yet effective design of P-MAC offers strict service differentiation for prioritized packets. A Markov model is developed to yield important performance matrices including the packet blocking probability due to queue overflow and the packet reneging probability due to delay bound. It is further proved that the service time of P-MAC approximates exponential distribution, and can be effectively estimated. The analytic models with preemptive and non-preemptive schemes, validated via simulations, show that P-MAC can effectively support traffic differentiation and achieve very low packet dropping （both reneging and blocking） probabilities when the traffic load is below the channel capacity. When the network is overloaded, P-MAC can still maintain extremely stable and high channel throughput. Moreover, it is demonstrated that P-MAC performs superior in multihop networks, further proving the advantages of the proposed protocol.

A Novel Medium Access Control for Ad hoc Networks Based on OFDM System

Recently, hosts of Medium Access Control （MAC） protocols for Ad hoc radio networks have been proposed to solve the hidden terminal problem and exposed terminal problem. However most of them take into no account the interactions between physical （PHY） system and MAC protocol. Therefore, the current MAC protocols are either inefficient in the networks with mobile nodes and fading channel or difficult in hardware implementation. In this paper, we present a novel media access control for Ad hoc networks that integrates a media access control protocol termed as Dual Busy Tone Multiple Access （DBTMA） into Orthagonal Frequency Division Multiplexing （ OFDM ） system proposed in IEEE 802.11 a standard. The analysis presented in the paper indicates that the proposed MAC scheme achieves performance improvement over IEEE 802.11 protocol about 25% -80% especially in the environment with high mobility and deep fading. The complexity of the proposed scheme is also lower than other implementation of similar busy tone solution. Furthermore, it is compatible with IEEE 802. 11a networks.

具有介质访问约束的网络化控制系统H∞状态估计

研究了一类存在介质访问约束和信号量化的网络化控制系统的H∞状态估计问题。首先,考虑到介质访问约束和信号量化的影响,将信号量化误差转化为扇形有界的不确定性,对由于访问约束而未获得网络传输的系统输出采用加权补偿策略,根据网络介质的随机访问机制将网络化系统建模为具有不确定性的马尔可夫跳跃系统。然后,在此基础上借助李雅普诺夫稳定性理论和H∞性能约束条件,利用线性矩阵不等式(linear matrix inequality,LMI)方法给出状态估计器存在的充分条件,所设计的状态估计器使得估计误差系统渐近稳定且具有给定的H∞性能。最后,通过仿真实例验证了该设计方法的有效性。

具有访问约束和数据丢包的网络化系统H_(∞)鲁棒控制

针对同时存在访问约束和数据丢包的网络化控制系统,研究了H_(∞)鲁棒控制方法的设计问题.首先,采用Bernoulli随机过程来描述系统的数据丢包过程,并根据介质访问约束的随机访问机制建立了离散时间马尔可夫跳变系统模型;其次,通过Lyapunov稳定性理论和LMI技术导出闭环系统随机稳定的充分条件,并设计了相应的H_(∞)鲁棒控制器,使得闭环系统随机稳定并具有给定的H_(∞)性能;最后,通过仿真算例验证了所提控制方案的正确性和有效性.

含网关节点的高时隙复用率TDMA协议

针对网络收敛慢、拓扑表不完整时导致的信道冲突以及空闲时隙浪费问题,提出一种提高节点时隙利用率和网络可靠性的多跳时分多址接入协议。该协议提出3种新机制,使用时隙请求时期快速收敛机制,加快时隙请求时期的收敛;使用空闲时隙公平重用机制,消除中心节点调度时隙碰撞问题,提高空闲时隙利用率;使用一跳邻居多层次调度机制,降低数据重传的时延。仿真结果表明,在时隙请求时期收敛时间、数据传输平均时延及数据传输成功率方面,该协议较现有协议性能更优。

空基网络中定向自组网关键技术研究综述

基于定向天线的移动自组织网络被广泛应用于军事领域,尤其对于具有易实施、高隐蔽性、高保密性要求的空基网络,定向天线比全向天线更具有优势,它具有更远的传输范围,减小了节点间的相互干扰,能够实现空间复用能力的提升。但是定向天线的引入在增加通信距离的同时也会带来一些问题,给许多协议层带来破坏性的副作用。目前,国内外研究人员已提出多种算法来解决这些问题。结合空基网络的复杂性,研究了国内外提出的基于定向天线的移动自组网数据链路层和网络层的各类算法和协议,总结对比近年来定向邻居发现算法、媒体访问控制协议和定向路由协议三种关键技术,并提出更适合用于空基网络的技术与协议,最后对这些算法和协议的下一步研究提供了一些方向。

A Media Access Control Scheme for Service Differentiation in Ad hoc Networks

IEEE 802.11 distributed coordination function(DCF)can alleviate the collision and hidden station problem,but it doesn't differentiate traffic categories(TC).Therefore,it can't provide sufficient quality of service(QoS)support for different TC.Recently,a new contention-based enhanced distributed channel access(EDCA)scheme is proposed which provides a probabilistic QoS support.In this paper,an improved EDCA scheme for service differentiation in ad hoc networks is proposed.In this scheme,signal channel resistance coefficient is used to adjust the contention window(CW).It proves that the scheme provides the traffic differentiation,high throughput and low delay through simulation.

基于Access的MIS系统的快速开发与实现

文章针对一些中小企业资金短缺没有能力开发和维护昂贵的MIS系统的问题，介绍了如何利用Access快速、方便地自行设计并开发自己所需要的小型MIS系统。文中以开发一个小型的图书信息管理系统为例，详细介绍了系统开发中的需求分析、功能分析、数据库设计以及各项功能的实现，以期对一些中小企业的信息化建设起借鉴作用。

基于行为交互的集群编队网络自组织算法

针对恶劣条件下对集群编队网络自组织构建的要求,对无线自组织网络组网算法进行了研究,将几种媒体接入控制(Medium Access Control, MAC)协议进行深度融合,提出了基于行为交互的集群编队网络自组织算法。该算法通过随机竞争的方式来竞争主节点,避免装订节点身份过程繁琐或主节点被损毁导致网络陷入瘫痪的问题,提升编队组网的安全性;通过行为交互,每个节点获得专有的传输时隙,实现全网节点无冲突的数据传输,最终达到固定分配MAC协议的传输性能。最后,通过仿真对算法进行验证,结果表明16个节点在6s内完成组网,可有力支撑未来协同探测、协同制导等典型场景下对编队网络自组织构建的需求。

5G环境下具有介质访问控制感知的无线网络编码方案

为优化5G无线网络环境下单波流的网络编码,提出一种具有介质访问控制(MAC)感知的随机线性网络编码方案。由于流间网络编码假设条件是即时解码和反馈信道可靠,其在5G环境下不多常见。因此,所提方案使用随机化处理方式,从有限域GF(2)中均匀随机地选择出数据包变量,源节点不需要采集来自接收器的反馈帧,通过优化MAC开销来缓解数据包相关信息的影响。在TelosB motes试验台进行验证,结果表明,对于单跳数据发布和多跳无线路由,所提方案使用Block ACK握手,可以高效采集反馈信息,且能够大幅降低数据包传输时间,最高降低42%。