一种新型无线Mesh网络多信道MAC协议

在基于IEEE 802.11s无线Mesh网络中,Mesh网络接入点（MAP）和门户（MPP）在网络负载较重时会出现严重的流量瓶颈。为了保证MAP流量的优先传输,提出了基于节点优先级的新型多信道MAC协议（NPBM-MAC）;为了减少在小规模组网时各BSS间频率干扰,设计了基于地理位置信息和网络负载的频率分配方案（LLBFA）。仿真结果表明,NPBM-MAC协议和LLBFA频率分配方案能够有效解决重负载网络下的MAP/MPP瓶颈问题,最大限度地满足音视频等大业务流的QoS需求。     

支持多媒体业务的新型无线多跳网络MAC协议*

提出了一种单信道无线多跳网络同步媒体接入控制协议—M-TDMA。基于信道预约,协议采用分类调度机制以满足多媒体业务中各类业务的服务质量需求。协议采用信道使用列表（CUL）、预约控制时隙、划分竞争期和非竞争期等措施维护预约信道,降低分组冲突率,提高信道使用率。分析结果表明,协议在保证分组传输可靠性的同时,传输时延较低,能够较好地支持多媒体业务的服务质量需求。     

A decentralized MAC protocol for opportunistic spectrum access in cognitive wireless networks

Cognitive MAC protocols are designed to efficiently utilize the scarce spectral resources without affecting the performance characteristics of primary users. The use of spectrum opportunities can often require stochastic approaches due to difficulty in predicting their appearance. Infrastructure based coordinated access techniques are not viable for many applications and spectrum bands, especially in the case of wireless local area and sensor networks. In this article, we describe CogMAC, a decentralized cognitive MAC protocol, which is based on the multichannel preamble reservation scheme. The protocol dynamically selects an available communication channel using a distributed channel selection scheme and allows nodes to be completely asynchronous to each other. CogMAC does not require a common control channel or a cooperative infrastructure. The MAC design addresses practical issues such as network dynamics and traffic awareness. We have carried out the performance evaluation of our CogMAC protocol on Wireless Open Access Research Platform (WARP) SDR testbed. Experimental results indicate that our protocol is able to achieve reliable data communication by opportunistically utilizing the available spectrum holes even in harshly interfering environments.     

应用于桥梁监控的无线传感器网络MAC协议

为保证监控桥梁任务的实时性,提出了一种多优先级多信道的无线传感器网络MAC(MPMC-MAC)协议。MPMC-MAC协议结合节点接收的数据类型和节点发送信息频率为其分配优先级,再根据优先级及信道状况对节点进行信道分配,以确保优先级高的节点优先发送数据。当信道冲突或节点通信受到干扰导致信息需要重传时,采用信道再分配技术。该技术主要根据节点的优先级、节点的剩余能量及其重传次数重新对节点分配信道,保证了信道分配的公平性。另外,该协议通过动态调整节点的活跃周期和睡眠周期的时长以节省能量,并减少传播时延。仿真结果表明,MPMC-MAC协议在网络吞吐量、平均传播时延以及节点的能量消耗等性能方面均优于Hybrid MAC(HyMAC)、Zebra MAC(ZMAC)及IEEE802.15.4 MAC协议。     

Providing MAC QoS for multimedia traffic in 802.11e based multi-hop ad hoc wireless networks

Ad hoc wireless networks with their widespread deployment, now need to support applications that generate multimedia and real-time traffic. Video, audio, real-time voice over IP, and other multimedia applications require the network to provide guarantees on the Quality of Service (QoS) of the connection. The 802.11e Medium Access Control (MAC) protocol was proposed with the aim of providing QoS support at the MAC layer. The 802.11e performs well in wireless LANs due to the presence of Access Points (APs), but in ad hoc networks, especially multi-hop ones, it is still incapable of supporting multimedia traffic.One of the most important QoS parameters for multimedia and real-time traffic is delay. Our primary goal is to reduce the end-to-end delay, thereby improving the Packet Delivery Ratio of multimedia traffic, that is, the proportion of packets that reach the destination within the deadline, in 802.11e based multi-hop ad hoc wireless networks.Our contribution is threefold: first we propose dynamic ReAllocative Priority (ReAP) scheme, wherein the priorities of packets in the MAC queues are not fixed, but keep changing dynamically. We use the laxity and the hop length information to decide the priority of the packet. ReAP improves the PDR by over 28% in comparison with 802.11e, especially under heavy loads. Second, we introduce Adaptive-TXOP (A-TXOP), where transmission opportunity (TXOP) is the time interval during which a node has the right to initiate transmissions. This scheme reduces the delay of video traffic by reducing the number of channel accesses required to transmit large video frames. It involves modifying the TXOP interval dynamically based on the packets in the queue, so that fragments of the same packet are sent in the same TXOP interval. A-TXOP is implemented over ReAP to further improve the performance of video traffic. ReAP with A-TXOP helps in reducing the delay of video traffic by over 27% and further improves the quality of video in comparison with ReAP without A-TXOP. Finally, we have TXOP-sharing, which is aimed at reducing the delay of voice traffic. It involves using the TXOP to transmit to multiple receivers, in order to utilize the TXOP interval fully. It reduces the number of contentions to the channel and thereby reduces the delay of voice traffic by over 14%. A-TXOP is implemented over ReAP to further improve the performance of voice traffic. The three schemes (ReAP, A-TXOP, and TXOP-sharing) work together to improve the performance of multimedia traffic in 802.11e based multi-hop ad hoc wireless networks.     

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。     

An adaptive QoS guaranteeing MAC protocol for real-time traffic in TDMA-based wireless ATM networks

This paper presents a new media access control (MAC) protocol based on forward error control (FEC), which is appropriate for supporting real-time traffic with strict QoS requirements in wireless ATM networks. As the channel BER in wireless environments is very high and varying 10⁻⁵–10⁻², previous schemes that use powerful FEC have combated to overcome this noisy channel condition at the cost of valuable bandwidth. As most previous works have been dedicated to maximize the channel efficiency, they were not able to meet QoS requirements of real-time applications in wireless networks. A new MAC protocol proposed in this paper is designed to guarantee the throughput requested by a real-time traffic user while keeping the bandwidth consumption at a minimum. The proposed scheme is for a TDMA system and uses adaptive FEC. We analyze the wireless channel and model it as a two-state error control system to design an efficient MAC protocol. We use simulation experiments to show how the proposed scheme provides QoS guarantees, and compare it with the CDMA system in terms of capacity, i.e. the number of users that can be supported.     

多信道无线Mesh网络的路由协议

针对单径路由协议不能充分利用多信道无线Mesh网络的信道资源的问题,提出了一种基于拥塞控制的并行多径路由协议PMRP。该协议将一个数据流分配到多条路径同时传输,当所有路径都发生中断时,才重新寻找路由;并采取相应的拥塞感知技术,避免拥塞节点再转发新的数据流。仿真结果证明：与无线自组网按需平面距离矢量路由协议（AODV）协议相比,PMRP在网络负载较大时,能有效地减小端到端延迟,提高数据包的成功投递率,增加网络的整体吞吐量。     

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。     

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.     

Coordination problem in cognitive wireless mesh networks

Due to their potential to create and extend pervasive communication applications to cognitive environments with distributed control, the emerging technology of cognitive wireless mesh networks is gaining significant attention from a growing research community. However, the major challenge in cognitive networks is the adaptation to time and space variability of the available resources, namely chunks of the frequency spectrum called channels. In particular, this problem is exacerbated in cognitive mesh networks because there exists no direct communication among devices which thereby cannot establish a global (common) control channel to coordinate the entire network. Instead, only local control channels that vary depending on the time instant and location, can be established to coordinate cognitive devices among themselves. This paper first analyzes the underlying challenges and existing approaches to address the absence of a static and global control channel, and then propose a novel Control channel formation protocol, called Connor. Our protocol Connor is a fully distributed coordination scheme where cognitive mesh devices self-organize into clusters based on the similarity of available channels and on topological constraints. Compared with the existing clustering algorithms, which requires synchronization, the proposed Connor performs better in most cases without imposing synchronization.     

一种基于空间相关性的无线传感器网络MAC协议

在大规模无线传感器网络中传输的监测数据具有较大的空间相关性,数据的传输存在一定冗余.如何有效的减少冗余数据的传输来改善网络性能成为一个重要的研究课题.本文以环状空间相关性模型为基础,从节点的筛选策略研究入手,提出一种能量高效的无线传感器网络MAC协议SEMAC.SEMAC协议采用信号强度优先的节点选择算法和冲突避免机制...     

认知无线电网络分布式多信道MAC协议*

在认知无线电网络中,MAC协议用于信道感知、选择和接入控制。以单网卡多信道MAC（MMAC）协议为基础,依据IEEE 802.22标准定义的静默期管理的两阶段感知策略,提出一种认知无线电网络分布式多信道MAC（CR-MMAC）协议。将两阶段感知机制和分布式协商融入MMAC协议,利用空闲频谱进行数据传输,并在MMAC协议ATIM窗的数据信道协商阶段引入预约机制,以避免选择同一信道的认知节点对在后续数据传输阶段再利用CSMA/CA造成的竞争碰撞。仿真对比分析表明,CR-MMAC协议能提高网络吞吐量、降低通信时     

认知无线电网络双天线多信道MAC协议

在认知无线电网络中,媒体接入控制(MAC)协议的主要功能包括信道感知、选择和接入控制,其中感知时间和传输时间的长度对网络的性能有着重要的影响。在动态无线网络环境下,如何合理分配感知时间和传输时间是个挑战性问题。提出了一种双天线多信道分布式认知无线电MAC（TM-MAC）协议,不需要在传输之前对信道进行感知。节点可以在其它节点传输数据的同时对频谱资源进行检测,然后利用空闲的频谱资源通信。建立了数学模型分析在饱和网络状况下MAC协议的吞吐量。仿真分析表明TM-MAC协议能够有效提高网络的吞吐量。     

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。     

基于预约调度的无线传感器网络的MAC协议

提出了一种基于预约调度的用于无线传感器网络的MAC协议--SSMAC.该协议采用分布式竞争接入和预约调度发送,提供高能量效率的信道接入和支持QoS业务的传输,较好地解决了隐藏终端和暴露终端问题.仿真结果表明SSMAC协议在保持节能的同时,在降低媒体接入时延、提高报文投递成功率和提供QoS保障上较TRAMA协议性能有很大的提高.     

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.     

接收端发起的异步无线传感器网络MAC协议

为了减少无线传感器网络中由于空闲侦听而产生的能量消耗,在接收端发起的介质访问控制(RI-MAC)协议基础上提出一种新的接收端发起的异步RP-MAC。该协议通过预测接收节点唤醒时间,采用随机数作为唤醒间隔,改进RI-MAC的重传机制,从而减少了空闲侦听和网络冲突。NS2仿真结果表明,改进后的MAC协议在在高负载网络中显著降低了节点工作的占空比,提高了包交付率,从而减少了网络能耗。     

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 integrated traffic model for multimedia wireless networks

Multimedia wireless networks are seen today as one of the key factors for the success of the global communication infrastructure in the near future. Such networks will have to handle a range of heterogeneous traffic classes with different QoS requirements. Their design, planning and control must be supported by suitable traffic models capable of dealing with a new set of constraints where QoS management and mobility play an important role.This paper proposes a traffic model for a cellular multimedia wireless network characterized by the integration of mobility and traffic management aspects. User mobility is modeled through a Markov renewal process, which allows for non-exponential cell residence times and may restrict the user mobility to existent paths in the system. A Markov-modulated fluid process is used to describe the changes in the bandwidth requirements of each mobile over the duration of its calls, including the periods where the mobile is inactive (without call).Based on the proposed model, the number of mobiles per class of traffic in a cell and the handoff processes are characterized. System performance results, such as new and handoff call blocking probabilities, for network planning are derived. Also, the distribution of the required capacity in a short time interval for network control is obtained. Simulations were carried out to validate the analytical results. The comparisons have shown that the integrated model may be regarded as a good basis to build useful teletraffic engineering tools for multimedia wireless networks.