Using Heuristics to the Controller Placement Problem in Software-Defined Multihop Wireless Networking

Solving the controller placement problem (CPP) in an SDN architecture with multiple controllers has a significant impact on control overhead in the network, especially in multihop wireless networks (MWNs). The generated control overhead consists of controller-device and inter-controller communications to discover the network topology, exchange configurations, and set up and modify flow tables in the control plane. However, due to the high complexity of the proposed optimization model to the CPP, heuristic algorithms have been reported to find near-optimal solutions faster for large-scale wired networks. In this paper, the objective is to extend those existing heuristic algorithms to solve a proposed optimization model to the CPP in software-defined multihop wireless networking (SDMWN).Our results demonstrate that using ranking degrees assigned to the possible controller placements, including the average distance to other devices as a degree or the connectivity degree of each placement, the extended heuristic algorithms are able to achieve the optimal solution in small-scale networks in terms of the generated control overhead and the number of controllers selected in the network. As a result, using extended heuristic algorithms, the average number of hops among devices and their assigned controllers as well as among controllers will be reduced. Moreover, these algorithms are able tolower the control overhead in large-scale networks and select fewer controllers compared to an extended algorithm that solves the CPP in SDMWN based on a randomly selected controller placement approach.

Jointly optimized congestion control, forwarding strategy,and link scheduling in a named-data multihop wireless network

As a promising future network architecture, named data networking(NDN) has been widely considered as a very appropriate network protocol for the multihop wireless network(MWN). In named-data MWNs, congestion control is a critical issue. Independent optimization for congestion control may cause severe performance degradation if it can not cooperate well with protocols in other layers. Cross-layer congestion control is a potential method to enhance performance. There have been many cross-layer congestion control mechanisms for MWN with Internet Protocol(IP). However, these cross-layer mechanisms for MWNs with IP are not applicable to named-data MWNs because the communication characteristics of NDN are different from those of IP. In this paper, we study the joint congestion control, forwarding strategy, and link scheduling problem for named-data MWNs. The problem is modeled as a network utility maximization(NUM) problem. Based on the approximate subgradient algorithm, we propose an algorithm called ‘jointly optimized congestion control, forwarding strategy, and link scheduling(JOCFS)'to solve the NUM problem distributively and iteratively. To the best of our knowledge, our proposal is the first cross-layer congestion control mechanism for named-data MWNs. By comparison with the existing congestion control mechanism, JOCFS can achieve a better performance in terms of network throughput, fairness, and the pending interest table(PIT) size.

Enhanced performance based on cross-layer design from physical to transport layers for multihop wireless networks

This paper puts forward a novel cognitive cross-layer design algorithms for multihop wireless networks optimization across physical,mediam access control （MAC）,network and transport layers.As is well known,the conventional layered-protocol architecture can not provide optimal performance for wireless networks,and cross-layer design is becoming increasingly important for improving the performance of wireless networks.In this study,we formulate a specific network utility maximization （NUM） problem that we believe is appropriate for multihop wireless networks.By using the dual algorithm,the NUM problem has been optimal decomposed and solved with a novel distributed cross-layer design algorithm from physical to transport layers.Our solution enjoys the benefits of cross-layer optimization while maintaining the simplicity and modularity of the traditional layered architecture.The proposed cross-layer design can guarantee the end-to-end goals of data flows while fully utilizing network resources.Computer simulations have evaluated an enhanced performance of the proposed algorithm at both average source rate and network throughput.Meanwhile,the proposed algorithm has low implementation complexity for practical reality.

Modelling and Analysis of TCP Performance in Wireless Multihop Networks

Researchers have used extensive simulation and experimental studies to understand TCP performance in wireless multihop networks. In contrast, the objective of this paper is to theoretically analyze TCP performance in this environment. By examining the case of running one TCP session over a string topology, a system model for analyzing TCP performance in multihop wireless networks is proposed, which considers packet buffering, contention of nodes for access to the wireless channel, and spatial reuse of the wireless channel. Markov chain modelling is applied to analyze this system model. Analytical results show that when the number of hops that the TCP session crosses is ?xed, the TCP throughput is independent of the TCP congestion window size. When the number of hops increases from one, the TCP throughput decreases ?rst, and then stabilizes when the number of hops becomes large. The analysis is validated by comparing the numerical and simulation results.

Study on Performance of Wireless Multihop Networks Using MIMO MRC and MIMO MRT

This paper presents the concepts of completely connected network,mean path length and cluster for analysis performance of wireless multihop network,where matrix are used to express topology of network and use a new algorithm to compute the number of cluster in the network.Multiple-input/multiple-output(MIMO) communication promises performance enhancement over conventional single-input/single-output(SISO) technology for the same radiated power,if leveraged in multihop network,MIMO may be able to provide significant network performance improvement in network robustness and in power consumption,this paper analyzes three types of multihop networks employing SISO, MIMO with maximum ratio combining(MRC) and MIMO with maximum ratio transmission(MRT) as link model respectively,and get that using MIMO link model can increase robust,decrease mean path length by simulation.

Full Duplex Media Access Control Protocol for Multihop Network Computing

Intelligent communication technologies beyond the network are pro-posed by using a new full-duplex protocol.The Media Access Control(MAC)is a data interaction network protocol,which outperforms the IEEE 802.15.4e.This research discusses the planning and execution of full-duplex(FD)pipeline MAC protocol for multihop wireless networks(MWN).The design uses a com-bination of Radio frequency and baseband methods to realize full-duplexing with smallest impact on cross layer functions.The execution and trial results specify that Pipeline Media Access Control(PiMAC)protocol considerably develops net-work implementation in terms of transmission protocol(TP)and transmission delay.The advantage of using FD-MAC will increase the range of nodes.Also takes benefit of the FD mode of the antenna,which outperforms additionally 80%for all assessed cases.In this analysis,it was considered of that Psz=8184 bits and Rc=1Mbps;that’s,T_(DATA) represents an excellent portion of total UTC.Tests on real nodes displays that the FD theme achieves a median gain of 90%in mix-ture throughput as equated to half-duplex(HD)theme for MWN.The energy con-sumption of proposed system method is 29.8%reduced when compared with existing system method.

BER Modified Decode-and-Forward Protocol for OFDM-Based Linear Multihop Networks

In orthogonal frequency division multiplexing （OFDM） based multihop communications, the conventional decodeand-forward （DF） relay scheme severely suffers from the error propagation problem. This drawback is serious in multihop networks as errors made by any relay node may fail the decoder at the destination in great chance. In this paper, we propose a bit error rate （BER） modified DF protocol （BMDF） which can be applied to systems where error correction channel coding and M-ary modulation are used. By modeling all links except the last one as a binary symmetric channel （BSC）, we derive a log likelihood ratio （LLR） modification function relying only on the accumulated BER of all previous links to be applied to the output of the soft demapper. Furthermore, to reduce the computational complexity and signaling overhead, the modification function is simplified from its original exponential expression and less BERs are delivered between nodes by making successive subcarriers share the same BER. In addition, for situations where the channel state information （CSI） of forward link is available, the proposed BMDF can be further enhanced by combining with subcarrier pairing （SP） and power allocation （PA）, where a sorted-channel gain SP scheme and a greedy PA algorithm are proposed. The simulation results verify thesignificant performance improvement to the conventional DF.

Centralized Quasi-Static Channel Assignment for Multi-Radio Multi-Channel Wireless Mesh Networks

Employing multiple channels in wireless multihop networks is regarded as an effective approach to increas-ing network capacity. This paper presents a centralized quasi-static channel assignment for multi-radio multi-channel Wireless Mesh Networks (WMNs). The proposed channel assignment can efficiently utilize multiple channels with only 2 radios equipped on each mesh router. In the scheme, the network end-to-end traffics are first modeled by probing data at wireless access points, and then the traffic load between each pair of neighboring routers is further estimated using an interference-aware estimation algorithm. Having knowledge of the expected link load, the scheme assigns channels to each radio with the objective of mini-mizing network interference, which as a result greatly improves network capacity. The performance evalua-tion shows that the proposed scheme is highly responsive to varying traffic conditions, and the network per-formance under the channel assignment significantly outperforms the single-radio IEEE 802.11 network as well as the 2-radio WMN with static 2 channels.

无线传感器网络容错低功耗自适应分簇算法

针对成簇阶段因缺少容错性而无法保证数据可靠性的问题,提出基于局域世界的无线传感器网络容错分簇算法。以局域世界的社团理论和符号网络结构平衡理论为根本,构建由多个簇组成的局域世界下无线传感器网络拓扑结构。融入势博弈和最优刚性子图的概念,根据集聚系数较小边的所在位置,优化网络拓扑结构。以优先级理念与带宽预留技术为支撑,设计容错机制。将节点与簇的剩余能量作为簇头选择依据,采用低功耗自适应集簇分层型协议获取容错分簇簇头,实现无线传感器网络容错分簇。经实验检验,所提算法能够有效解决节点失效过早、失效速率过快等问题,容错分簇后减少死亡节点与节点能耗,增加运行周期,加强吞吐能力。

无线多跳网络中的机会路由

机会路由通过充分利用无线信道的广播特性,可以大大提高无线多跳网络的性能.从阐述机会路由的基本思想开始,介绍了机会路由协议的主要特点、适用环境和影响机会路由性能的重要因素.在此基础上,对重要机会路由协议进行了综述,讨论不同协议的工作机制及其优缺点.最后,探讨了机会路由的一些未来发展方向,以期为这一领域的发展提供一些有意义的借鉴.

多跳无线网络中具有时间意识的视频流控制协议

为了在多跳无线网络中对实时视频流提供高效的端到端服务质量支持,提出了一种具有时间意识的视频流控制协议(TACP).首先在网络层增加了独立的TACP子层,采用跨层设计方法将各协议层的参数映射至该子层.在此基础上,源节点通告视频同步信息,使中间节点形成时间意识;中间节点通过分布式时延估计方法限制超时视频数据的转发.随后,为了对高优先级视频数据提供保护,研究了一种基于GOP的路径探测机制,并将其与视频流控制协议协同工作.利用仿真实验,对TACP视频通信性能进行分析和评价.结果表明:TACP能够显著改善实时视频流质量,包括可解码帧率、端到端时延和时延抖动等性能指标;该协议极大地提高了网络带宽利用率,并能够有效适应实时性需求的变化.

一种基于多目标优化的交互式多跳分组无线网QoS路由算法

多跳分组无线网络是由一组具有路由和转发功能的移动节点组成的动态多跳的临时性自治系统 ,多用于军事战术系统。针对军事系统中一些特定业务对多个目标的同时性能要求以及战术网络环境的特点 ,选取带宽作为约束条件 ,把时延和丢失率作为 Qo S优化目标 ,建立了 Qo S路由选择的多目标整数优化模型 ,并给出了求解模型的交互式算法。实例计算结果表明了算法的可行性。

一种TDMA无线多跳网中新的传输调度算法

针对TDMA无线多跳网中的时隙分配问题,提出了一种新的传输调度算法,称为“碰撞避免正确稳健调度”(CA-PRS)。CA-PRS算法与以往PRS算法的区别是可以根据网络的拓扑变化,自适应选择分组发送时隙,实现了分组传输中的碰撞避免。该算法实现简单,协议开销小,不需要对节点度数进行约束。仿真结果表明与simple-PRS算法相比,该算法提高了无线资源的利用率。

多跳无线传感器网络决策融合

研究了衰减信道下多跳无线传感器网络的决策融合规则,推导出了瑞利分布的信道模型下性能最优的似然比融合规则。该规则需要预知信道的实时状态信息,计算复杂,不适合资源受限的无线传感器网络。为此,提出了仅需要预知信道的统计分布信息的次优似然比融合规则,并分别在大信噪比和小信噪比情况下推导出了该规则的简化形式。理论分析和实验表明,次优规则性能损失轻微,显著降低运算量和信息消耗,适合在资源受限的多跳无线传感器网络决策融合系统中使用。

一种适用于多跳WMSNs的分布式图像压缩算法

在节点资源严重受限的无线多媒体传感器网络(WMSNs)中处理和传输大数据量的图像信息具有很大的挑战性。文章在研究基于小波变换的图像压缩算法SPIHT的基础上,提出了一种基于SPIHT算法的分布式并行图像压缩算法D-SPIHT,该算法具有复杂度低、设计简单、执行速度快、完全分布式并行执行的特点。仿真结果表明,文中提出的D-SPIHT算法,能够有效地平衡网络中各节点的能耗,从而延长网络的生命期,还能大大缩短图像压缩处理的时延,非常适合于对实时性要求较高的WMSNs中的图像压缩和传输。

提供QoS保障的无线多跳路径可用带宽估计模型与方法

该文对多跳路径的可用带宽估计问题进行了研究,提出了在估计过程中必须将全局QoS保障作为可用带宽的估计原则。对多跳路径的干扰进行了定性分析与定量计算,并利用排队网络理论建立了路径性能分析模型,利用该模型能得出路径中各个业务流的QoS参数。在此基础上设计了能提供QoS保障的可用带宽估计方法。该文所提出的估计方法以QoS需求不被破坏为约束条件,克服了现有工作将无约束的最大可达吞吐量作为可用带宽从而导致业务的QoS可能受到影响这一缺陷。仿真实验证明了分析模型与可用带宽估计方法的准确性。

基于最小路由数的多节点合作MRC系统的性能分析

提出了适用于多跳无线网络的基于最小路由数的多节点合作MRC(Maximum Ratio Combining)系统.在Nakagami衰落下研究了MRC合作方案和所提方案再生系统互信息的中断性能,运用矩生函数的方法推导了中断率的闭式解.仿真和理论分析表明MRC合作方案实现了全路由分集增益,其分集度为所有路由可能分集和的最小值,而所提合作系统实现了系统性能与目的节点的处理能力的良好折中,对降低目的节点接收机的信号处理功耗和复杂度很有好处.

一种用于多跳分布式无线网络的多址接入协议及其性能分析

为多跳分布式无线网络提出了一套灵活而有效的自适应获取冲突避免 (AACA)的多址接入协议 .它综合了多信道和随机附带预约的思想 ,有效地解决了多跳网络环境下出现的隐藏终端和暴露终端问题以及由于节点的移动而造成的侵入终端问题 .在该协议中 ,各节点自适应预约所要使用的空闲业务信道 ,预约之后的通信过程不会受到其它节点的干扰 .AACA协议有三种形式 ,即AACA SDT/MDT/RDT协议 ,它们使用任意确定数目的信道 。

基于两个中继的多跳无线网中的编码协同

本文针对使用两个中继的多跳无线网,提出了一种新的编码协同方案。利用有线的方式,两个距离很近的中继终端被联接后形成一对虚拟天线阵。由于分布式Turbo码被融合到该网中,该方案便于单天线中继与其他中继共享天线,并且以较低硬件实现复杂度提高了系统在准静态衰落中继信道下的性能。

基于多信道预约可冲突避免的多址接入协议

本文为多跳分布式无线网络提出了一套灵活而有效的自适应获取冲突避免(AACA)的多址接入协议。在该协议中,各节点竞争公共信道,利用RTS/CTS对话形式来预约各业务信道,成功预约后的分组传输不会受到其他节点的干扰。它使用任意确定数目的信道,以异步方式工作,并且使得各节点利用半双工无线电台就可以灵活、简便地实现资源预约。分析和比较结果说明,所提出的多信道预约协议可以有效地解决隐藏终端、暴露终端以及侵入终端的问题。