基于忙音多址的多信道无线Mesh网的MAC协议

无线Mesh网（WMN）是一种新型宽带无线接入技术,选择适当的MAC子层规范,根据网络业务特征有效地配置信道资源,可以提高Mesh网的无线资源使用效率以及系统传输性能。而现有的无线Mesh网络基本上是采用单信道MAC协议,不能满足日益俱增的用户需求,限制了整个网络的数据传输速率与网络容量。文中基于忙音多址访问的设计思想,结合无线Mesh网络的特点,提出了一种无线Mesh网MAC协议MCBTMA（Multi-Channel Busy Tone Multiple Access）。MCBTMA通过构建多个忙信号控制信道和多个数据信道,在MAC层进行多信道调度,使无线Mesh网络在吞吐量和时延方面性能有显著提高。     

基于忙音多址的多信道无线Mesh网的MAC协议

无线Mesh网(WMN)是一种新犁宽带无线接入技术,选择适当的MAC子层规范,根据网络业务特征有效地配置信道资源,可以提高Mesh网的无线资源使用效率以及系统传输性能.而现有的无线Mesh网络基本上是采用单信道MAC协议,不能满足日益俱增的用户需求,限制了整个网络的数据传输速率与网络容量.文中基于忙音多址访问的设计思想,结合无线Mesh网络的特点,提出了一种无线Mesh网MAC协议MCBTMA(Multi-Channel Busy Tone Multiple Access).MCBTMA通过构建多个忙信号控制信道和多个数据信道,在MAC层进行多信道调度,使无线Mesh网络在吞吐量和时延方面性能有显著提高.     

多信道无线网状网跨层优化研究

针对多网卡多信道无线Mesh网络容量问题,基于无线信道干扰模型,在给定各节点物理层发射功率的条件下,联合考虑无线Mesh网络传输层的流速控制、网络层的路由算法和MAC层的信道分配等问题,通过采用二次路由计算策略,提出了一个跨层联合优化算法,仿真结果表示,提出的算法能提高网络吞吐量。     

基于802.11DCF协作MAC的冲突分解算法

本文针对MAC层中由于采用二进制指数退避算法而存在的小尺度时间上的不公平性现象和网络资源浪费的现象,改进了基于协作MAC系统的冲突分解算法.     

无线Mesh网络入侵检测关键技术研究

本文研究了无线Mesh网络的结构和特点,以及入侵检测系统(IDS)在构建安全WMN中不可替代的作用。深入分析了AdHoc网络IDS、跨层和网络故障检测技术特点以及无线Mesh网络自身的安全需求。在此基础上,本文结合网络故障检测与跨层技术提出了一种基于代理的非对称分布式协作IDS结构,对代理模块设计原则进行了详细分析。最后以MAC自私行为攻击为例对该结构进行了模拟。结果显示,该结构能够很好地适应无线Mesh网络。     

面向编码机会路由的无线Mesh 网络广播信道接入

编码机会路由是有损无线Mesh网络中提供高吞吐量和高可靠性传输的理想方案.该路由机制建立在无线广播的多用户分集优势和随机网络编码的纠删特性之上,为广播MAC的设计引入了新的机会和挑战.基于最优停止理论,研究面向编码机会路由的机会广播信道接入问题,提出一种在接入延迟和信道交付能力之间加以折衷,以获得最优的平均有效速率的方法,并在IEEE 802.11 DCF协议基础上设计实现面向NCOR的广播MAC协议O-BCast.仿真结果表明,该协议显著提高了编码机会路由的端到端吞吐量,具有网络负载自适应的良好特性.     

Modeling and Optimization of Muiticast End-to-End Delay in Multi-Radio Wireless Mesh Networks

针对802.11多射频无线Mesh网络(MR-WMN)不能有效支持端到端低时延组播的问题,首先围绕MAC层传输时延和Mesh层排队时延建模分析,并提出低时延组播路由模型MR-MED(Multi-Radio Multicast End-to-End Delay).其次证明全局流干扰最小化问题是一个NP完全问题且全局流干扰和网络密度的数学关系符合dPIN分布,在此基础上提出有效减小MAC层流内和流间干扰的DCA算法.最后提出流量自适应的组播多径路由方案MMRA,有效减小Mesh层排队时延.仿真与常见算法的比较表明,提出的模型准确刻画了MR-WMN的组播时延,且联合运用DCA和MMRA有效降低了端到端时延.     

多射频无线Mesh网络组播端到端时延建模与优化

针对802.11多射频无线Mesh网络(MR-WMN)不能有效支持端到端低时延组播的问题,首先围绕MAC层传输时延和Mesh层排队时延建模分析,并提出低时延组播路由模型MR-MED(Multi-Radio Multicast End-to-End Delay).其次证明全局流干扰最小化问题是一个NP完全问题且全局流干扰和网络密度的数学关系符合dPlN分布,在此基础上提出有效减小MAC层流内和流间干扰的DCA算法.最后提出流量自适应的组播多径路由方案MMRA,有效减小Mesh层排队时延.仿真与常见算法的比较表明,提出的模型准确刻画了MR-WMN的组播时延,且联合运用DCA和MMRA有效降低了端到端时延.     

EMSM:一种有效的无线Mesh网络流媒体组播策略

采用网络编码的方法能够提高无线Mesh网络流媒体组播的吞吐量,但也引发了不公平性和延迟增加的问题.针对这两个问题,提出一种有效的无线Mesh网络流媒体组播策略EMSM.EMSM基于用户积分值来控制信道质量好与差的用户之间的公平性,采用网络编码感知获得节点解码的能力,有效地选择信宿集,降低对信道质量好的用户带来的不公平性.在每个Mesh路由器节点采用双队列机制和有效的原始编码选取策略降低系统延迟.仿真实验结果表明我们提出的EMSM策略不仅降低了系统的延迟,而且质量好与差的信道之间的不公平性得到了很好的解决.     

无线自组网络中TCP流公平性的分析与改进

研究了TCP(transmission control protocol)流在多跳无线自组网络中的公平性问题,发现IEEE802.11DCF协议在此环境下会导致严重的不公平性,即部分节点垄断了网络带宽而其他节点被饿死.首先,通过仿真分析了产生TCP流不公平性的原因,指出其根源在于MAC(media access and control)协议的不公平性,同时,TCP的超时机制加剧了不公平性的产生;然后,利用概率模型定量分析了TCP不公平性与MAC协议参数之间的关系,发现TCP流的公平性与TCP报文长度直接相关,并且增加MAC协议初始竞争窗口的大小能够有效提高公平性.据此,提出了一种根据TCP报文长度动态调节初始回退窗口大小的自适应回退MAC协议改进算法.理论分析和仿真表明,该算法在很大程度上可以有效缓解不公平性问题的产生,并且不会引起网络吞吐量的严重降低.     

Interworking wireless mesh networks: Problems,performance characterization,and perspectives

Wireless broadband networks based on the IEEE 802.11 technology are being increasingly deployed as mesh networks to provide users with extended coverage for wireless Internet access. These wireless mesh networks, however, may be deployed by different authorities without any coordination a priori, and hence it is possible that they overlap partially or even entirely in service area, resulting in contention of radio resources among them. In this paper, we investigate the artifacts that result from the uncoordinated deployment of wireless mesh networks. We use a network optimization approach to model the problem as resource sharing among nodes belonging to one or different networks. Based on the proposed LP formulation, we then conduct simulations to characterize the performance of overlaying wireless mesh networks, with the goal to provide perspectives for addressing the problems. We find that in a system with multiple overlaying wireless mesh networks, if no form of inter-domain coordination is present, individual mesh networks could suffer from capacity degradation due to increased network contention. One solution toward addressing the performance degradation is to “interwork” these wireless mesh networks by allowing inter-domain traffic relay through provisioning of “bridge” nodes. However, if such bridge nodes are chosen arbitrarily, the problems of throughput sub-optimality and unfairness may arise. We profile the impact of bridge node selection and show the importance in controlling network unfairness for wireless mesh network interworking. We conclude that mesh network interworking is a promising direction to address the artifacts due to uncoordinated deployment of wireless mesh networks if it is supplemented with appropriate mechanisms.     

基于速度与状态感知的车载网络接入退避算法

IEEE 802.11p协议是针对车载无线接入技术制定的MAC层和物理层标准,仍采用二进制指数退避算法,该算法不能根据车辆速度和密度作出调节,在V2I通信中,会造成严重的信道访问不公平和碰撞等现象,无法很好地适用于车载网络。针对上述问题,提出的算法在退避重传阶段,采用固定的最优竞争窗口,并能够根据车速和从路边单元获取的网络信息实时调整竞争窗口大小。模型分析和仿真实验表明,该算法可明显改善信道访问的吞吐量、公平性与可靠性。     

Revealing the problems with 802.11 medium access control protocol in multi-hop wireless ad hoc networks

The IEEE 802.11 medium access control (MAC) protocol is a standard for wireless LANs, it is also widely used in almost all test beds and simulations for the research in wireless mobile multi-hop ad hoc networks. However, this protocol was not designed for multi-hop networks. Although it can support some ad hoc network architecture, it is not intended to support the wireless mobile ad hoc network, in which multi-hop connectivity is one of the most prominent features. In this paper, we focus on the following question: can IEEE 802.11 MAC protocol function well in multi-hop networks? By presenting several serious problems encountered in transmission control protocol (TCP) connections in an IEEE 802.11 based multi-hop network, we show that the current TCP protocol does not work well above the current 802.11 MAC layer. The relevant problems include the TCP instability problem found in this kind of network, the severe unfairness problem, and the incompatibility problem. We illustrate that all these problems are rooted in the MAC layer. Furthermore, by revealing the in-depth cause of these problems, we conclude that the current version of this wireless LAN protocol does not function well in multi-hop ad hoc networks. We thus doubt whether the current WaveLAN based system is workable as a mobile multi-hop ad hoc test bed. All the results shown in this paper are based on NS2 simulations, and are compatible with the results from the OPNET simulations.     

无线自组织网络中的IEEE802．11 MAC协议的研究

IEEES02．11 DCF作为无线局域网的MAC层规范被广泛应用于无线自组织网络的仿真和测试中。通过研究发现即使在拓扑不变的条件下，使用表驱动路由协议DSDV，TCP流仍然存在不稳定和不公平现象，本文分析了问题产生的原因，提出了基于网络负载的解决问题方法。     

Mechanisms for centralized flow rate control in 802.11-based wireless mesh networks

Cross-layer interaction between TCP and CSMA/CA-based MAC in multihop wireless networks produces suboptimal network performance, including flow rate unfairness and starvation. Rate control mechanisms can mitigate this behavior. Of particular interest are centralized mechanisms that enforce rate limits at traffic aggregation points, without modifying individual mesh routers or client devices. In this paper, we propose, design, and evaluate a framework of zero-overhead, feedback-driven centralized rate controllers. These controllers are implemented at gateway mesh routers. We use existing data traffic as capacity probes with a feedback-driven response to adapt to changes in network and traffic conditions. Using simulations and experiments on a testbed, we show an improvement in fairness by a factor of 2–3 over networks without any rate control. Further, our fairness metrics are within 2% of those achieved by a centralized controller with an omniscient knowledge of network conditions.     

基于赤字轮询算法的无线Mesh网络公平性研究*

无线Mesh网络在负载较重时会出现严重的空间不公平现象,即远离网络中心的节点很难将其数据传送到网关。赤字轮询算法能够保证节点数据传输的公平性要求,但却存在吞吐量平均化的问题。在分析无线Mesh网络公平性问题的基础上,提出基于最小均方的动态赤字轮询算法,其核心思想是动态调整轮询权重值。仿真在IEEE 802.11 DCF机制下将所提出的算法与传统的赤字轮询及弃尾算法进行比较,结果表明,所提出的方法能够保证吞吐量需求不同的业务流之间的公平性,并使网络总吞吐量获得提高。     

Joint scheduling and routing algorithm with load balancing in wireless mesh network

Wireless mesh network (WMN) is a promising solution for last mile broadband internet access. Mesh nodes or mesh routers are connected via wireless links to form a multi-hop backbone infrastructure and improving throughput is the primary goal. While previous works mainly focused on either link level protocol design or complex mathematical model, in this paper, we investigate the performance gains from jointly optimizing scheduling and routing in a multi-radio, multi-channel and multi-hop wireless mesh network. Then, two optimization objectives are addressed by considering wireless media contention and spatial multiplexing. The first objective is to maximize throughput by exploiting spatial reuse while the second one is to ensure fairness among different links. We design a cross-layer algorithm by considering both MAC layer and network layer. Simulation results show that our joint optimization algorithm can significantly increase throughput as well as fairness.     

无线接入网络中TCP流的上下行信道公平算法

在无线接入网络中,上行TCP流会极大地压制下行TCP流,导致严重的上下行信道TCP流不公平问题.本文指出TCP流的ACK包在接入节点下行缓存中的侵占性是上下行TCP不公平问题的直接原因,从限制缓存大小的新角度提出了MBA(Maximum Buffer for ACKs)算法.MBA算法基于上下行TCP流的不公平比例和缓存大小的关系,自适应地调节ACK包的最大缓存空间.理论分析和仿真实验结果表明MBA算法不但能通过限制ACK包的缓存空间实现上下行TCP流公平,还能通过减少无线信道ACK包传输概率提高网络总有效吞吐率.