网络编码在无线Mesh网络中的研究与实现

Mesh网络沿用了Ad Hoc网络中的路由协议,但Mesh网络节点移动性高,路径的生存周期短,根据无线Mesh网络自身的动态特点进行路由协议的优化成为了研究的热点。COPE编码方案是针对Mesh网络中的单播特性提出的一种新的机会网络编码机制,能够提高网络的吞吐量。通过NS2仿真平台对AODV路由协议添加COPE网络编码方案,仿真结果表明在不同网络条件下,AODV和COPE的结合增加了无线节点的编码机会,使网络的吞吐量得到了有效的提高。     

丢包感知的线性编码在无线Mesh网络中的应用

采用网络编码提高无线Mesh网络的吞吐量己成为目前研究的热点.文献[1]中,作者提出了一种在无线Mesh网络中采用网络编码的MAC层先验式混合协议,它采用异或编码的算法,这种算法在低丢包环境下性能较好,但不适合高丢包率环境.文章提出了一种适用于无线Mesh网络的线性网络编码方法,并采用复合解码策略,能确保在高丢包的环境...     

无线自组织网络的网络编码技术

网络编码作为一种新的技术在宽带无线自组织网络中有很好的应用,通过网络编码,中间节点可以将接收信息进行编码并发送出去,提高了网络吞吐量和健壮性。为不对现有网络的软硬件设备和相应的协议做很大的修改,可以选择在高层实现网络编码。无线传感器网络、无线格状网（Mesh）等无线自组织网络都可以使用网络编码技术显著提高多跳链路的传输性能。目前网络编码的研究热点集中在网络编码节点选取方案、网络编码算法的设计、网络编码复杂度分析、网络编码的性能分析、网络编码与系统安全性分析、网络编码在无线分布式网络中的应用等方面。     

WMN中一种基于干扰感知的负载均衡路由协议

无线信道干扰和负载分布的不均衡严重影响无线Mesh网络吞吐量、端到端延时和资源利用率。在已有基于信噪比和邻居节点个数的干扰模型基础上,进一步研究了无线Mesh网络的链路干扰。在综合考虑了无线Mesh网络流间干扰和和流内干扰的基础上,提出路由判据PIL（Path Interfer-ence Level）。在此基础上,提出一种新的基于干扰感知的负载均衡路由协议IA-DSR（Interference-Aware DSR）。IA-DSR考虑无线网络拥塞并选择受到干扰最小的路径。仿真结果表明,在不显著增加开销的情况下,IA-DSR可以有效地提高网络的整体吞吐量,降低网络端到端时延和丢包率。     

无线网状网中基于信道预留的多信道媒体接入控制方案

目前多信道无线Mesh网络WMN(Wireless Mesh Network)的MAC(Medium Access Contro)l仍然存在信道利用率低的问题,因此提出了具有控制信道和数据信道的多信道WMN的MAC方案。方案采用数据信道预留机制来提高系统的吞吐量,并降低接入时延。该方案通过减小控制信道上的碰撞概率可以有效降低系统接入时延并提高控制信道的利用率。理论分析和性能估计表明此方案具有高的吞吐量和低的接入时延,性能明显优于现有的公共信道控制方案CCC(Common Control Channel)。     

多信道无线Mesh网络的性能研究

在无线Mesh网络中使用多信道可以减少碰撞和干扰,提高系统吞吐量。本文先介绍无线Mesh网络,然后介绍多信道在无线Mesh网络中的应用,分析了几种常用的多信道MAC协议。接着着重阐述了多信道无线Mesh网络所面临的问题与挑战,对信道分配、路由选择和隐蔽终端这3个主要问题进行分析,并对其研究设计方向进行了展望。     

多信道无线Mesh网络的性能研究

在无线Mesh网络中使用多信道可以减少碰撞和干扰,提高系统吞吐量.本文先介绍无线Mesh网络,然后介绍多信道在无线Mesh网络中的应用,分析了几种常用的多信道MAC协议.接着着重阐述了多信道无线Mesh网络所面临的问题与挑战,对信道分配、路由选择和隐蔽终端这3个主要问题进行分析,并对其研究设计方向进行了展望.     

基于网络编码的无线Mesh网络启发式定向调度算法研究

网络编码技术是近年来网络通信研究领域的一项重大突破,允许网络节点在传统的“存储—转发”基础上参与数据处理,已成为提高网络吞吐量、鲁棒性和可靠性的有效方法。文章结合网络编码机制与定向天线技术,研究无线Mesh网络公平性优化问题。基于跨层设计的思想,文章给出基于网络编码与定向天线的线性规划模型,并进一步提出一种具有定向调度特点的链路调度机信道分配算法。实验仿真结果表明,该算法优于已有SP-omni,COPE,DDSR算法,吞吐量更大,公平性更好。     

认知无线Mesh网络中基于马氏决策模型的MAC协议

为解决认知无线Mesh网络中专用控制信道较难获得的问题,提出一种基于POMDP的机会式频谱接入MAC协议,在不需要中心控制器和专用控制信道的协调下,实现动态频谱感知和接入。仿真结果表明,基于POMDP的接入策略能够有效提高网络频谱利用率和吞吐量,性能最优,而基于贪心算法的接入策略,在降低计算复杂度的同时,获得了较好的性能,实用性较强。     

基于无线Mesh网络的多跳中继传输模式研究

无线Mesh网络(Wireless Mesh Network)简称WMN,是一种通过无线链路连接路由器和终端设备的无线多跳网络。文章对无线Mesh网络中IEEE802.11异常传输问题做出了深入分析,通过数学模型的分析,理论验证了在无线Mesh网络中只要有一个节点使用较低的发送速率,那么其他高速率的节点吞吐率都会显著下降,从而导致整个网络的吞吐性能下降。并且通过仿真实验,验证了多跳中继传输方案可以解决IEEE802.11异常传输问题,提高网络的整体吞吐性能。     

On-demand coding-aware routing in wireless Mesh networks

Network coding,which exploits the broadcast nature of wireless medium,is an effective way to improve network performance in wireless multi-hop networks,but the first practical wireless network coding system COPE cannot actively detect a route with more coding opportunities and limit the coding structure within two-hop regions.An on-demand coding-aware routing scheme(OCAR)for wireless Mesh networks is proposed to overcome the limitations specified above by actively detecting a route with more coding opportunities along the entire route rather than within two-hop regions.Utilizing more coding opportunities tends to route multiple flows 'close to each other' while avoiding interference requires routing multiple flows 'away from each other'.OCAR achieves a tradeoff by adopting RCAIA as routing metric in route discovery,which is not only coding-aware but also considers both inter and intra flow interference.Simulation results show that,compared with Ad-hoc on-demand distance vecfor routing(AODV)and AODV+COPE,OCAR can find more coding opportunities,thus effectively increase network throughput,reduce end to end delay and alleviate network congestion.     

一种环境感知的无线Mesh网络自适应QoS路径选择算法

本文针对如何改善无线多跳Mesh网络的服务质量,满足无线多媒体业务对数据传输的带宽、时延、抖动的要求等问题,研究了一种基于无线信道状态和链路质量统计的MAC层最大重传次数的自适应调整算法。该算法通过对无线Mesh网络的无线信道环境的动态感知,利用分层判断法区分无线分组丢失的主要原因是无线差错还是网络拥塞导致,实时调整MAC层的最佳重传次数,降低无线网络中的分组冲突概率。基于链路状态信息的统计和最大重传策略,提出了一种启发式的基于环境感知的QoS路由优化机制HEAOR。该算法通过动态感知底层链路状态信息,利用灰色关联分析法自适应选择最优路径,在不增加系统复杂度的基础上,减少链路误判概率,提高传输效率。NS2仿真结果表明,HEAOR算法能有效减少重路由次数,降低链路失效概率,提高网络的平均吞吐率。本文提出的方法不仅能够优化MAC层的重传,而且通过发现跨层设计的优化参数实现对路径的优化选择。      

无线Mesh网中基于网络编码的多路径TCP研究

在无线多跳网络中,本地重传和网络编码已经被成功地应用到多路径技术上以增加吞吐量并减少丢包。然而,在提高UDP传输性能的同时,也产生了数据包重排序和延迟等副作用,严重影响了TCP性能。针对此问题,主要提出一种基于网络编码的多路径传输方案NC-MPTCP,即在无线mesh网络的多条路径中引入网络编码、执行拥塞控制以及使用一个基于信用的方法控制节点的传输速率,提高网络的吞吐量以及增加网络传输的可靠性。该方案使用一个简单的算法,评估丢包率以及发送线性组合数据包的速率,用来降低目的节点的数据包解码延迟和防止TCP的超时重传。仿真结果表明设计的NC-MPTCP有效。     

无线多跳网络中一种基于网络编码的机会路由

近年来机会路由和网络编码是两种利用无线信道广播特性提高网络性能的新兴技术。相比传统的静态路由决策,机会路由利用动态和机会路由选择减轻无线有损链路带来的影响。网络编码可以提高网络的资源利用率。但编码机会依赖于多个并发流所选路径的相对结构。为了创造更多的网络编码机会和提高网络吞吐量,本文提出了一种基于流间网络编码的机会路由(ORNC)算法。在ORNC中,每个分组转发的机会路径选择是基于网络编码感知的方式进行的。当没有编码机会时,采用背压策略选择下一跳转发路径以平衡网络负载。仿真结果表明本文提出的ORNC算法能够提高无线多跳网络的吞吐量。     

An adaptive opportunistic retransmission control scheme environment-aware-based for wireless multimedia Mesh networks

In this paper, we propose an aware-based adaptive opportunistic retransmission control scheme for wireless multimedia Mesh networks. The proposed scheme provides maximum retransmission count optimization based on environment-aware to improve packet relay probability. The scheme discriminates the types of packet loss in wireless link by means of environment information and selects the retransmission count by taking the IEEE 802.11 wireless channel characteristics into consideration. Furthermore, the maximum retransmission count of MAC is adjusted adaptively. Extensive simulations demonstrate that the proposed scheme significantly reduces packet collision probability and packet loss rate, and thus improves network throughput.     

无线Mesh网络可信路由协议THWMP研究

为了使节点在网络中存在恶意节点和自私节点时能够选择安全可靠的路由,降低恶意节点和自私节点对无线Mesh网络带来的影响,文中通过对无线Mesh网络混合路由协议HWMP(Hybrid Wireless Mesh Protocol)和信任模型的研究,提出了基于主观逻辑信任模型的无线Mesh网络可信路由协议THWMP(Trusted HWMP),大大降低了因为信任的传递带来的网络开销,同时保证了路由的可信度。与HWMP路由协议相比较,在网络中存在恶意节点时,THWMP路由协议能够在增加有限的额外开销的情况下保证全网有较高的数据传递成功率和吞吐量。     

To‐send‐or‐not‐to‐send: An optimal stopping approach to network coding in multi‐hop wireless networks

Network coding is all about combining a variety of packets and forwarding as much packets as possible in each transmission operation. The network coding technique improves the throughput efficiency of multi‐hop wireless networks by taking advantage of the broadcast nature of wireless channels. However, there are some scenarios where the coding cannot be exploited due to the stochastic nature of the packet arrival process in the network. In these cases, the coding node faces 2 critical choices: forwarding the packet towards the destination without coding, thereby sacrificing the advantage of network coding, or waiting for a while until a coding opportunity arises for the packets. Current research works have addressed this challenge for the case of a simple and restricted scheme called reverse carpooling where it is assumed that 2 flows with opposite directions arrive at the coding node. In this paper, the issue is explored in a general sense based on the COPE architecture requiring no assumption about flows in multi‐hop wireless networks. In particular, we address this sequential decision making problem by using the solid framework of optimal stopping theory and derive the optimal stopping rule for the coding node to choose the optimal action to take, ie, to wait for more coding opportunity or to stop immediately (and send packet). Our simulation results validate the effectiveness of the derived optimal stopping rule and show that the proposed scheme outperforms existing methods in terms of network throughput and energy consumption.     

Performance analysis of slotted ALOHA and network coding for single-relay multi-user wireless networks

Deployment of wireless relay nodes can enhance system capacity, extend wireless service coverage, and reduce energy consumption in wireless networks. Network coding enables us to mix two or more packets into a single coded packet at relay nodes and improve performances in wireless relay networks. In this paper, we succeed in developing analytical models of the throughput and delay on slotted ALOHA (S-ALOHA) and S-ALOHA with network coding (S-ALOHA/NC) for single-relay multi-user wireless networks with bidirectional data flows. The analytical models involve effects of queue saturation and unsaturation at the relay node. The throughput and delay for each user node can be extracted from the total throughput and delay by using the analytical models. One can formulate various optimization problems on traffic control in order to maximize the throughput, minimize the delay, or achieve fairness of the throughput or the delay. In particular, we clarify that the total throughput is enhanced in the S-ALOHA/NC protocol on condition that the transmission probability at the relay node is set at the value on the boundary between queue saturation and unsaturation. Our analysis provides achievable regions in throughput on two directional data flows at the relay node for both the S-ALOHA and S-ALOHA/NC protocols. As a result, we show that the achievable region in throughput can be enhanced by using network coding and traffic control.