Energy-Efficient Broadcast and Multicast Trees in Wireless Networks

The wireless networking environment presents formidable challenges to the study of broadcasting and multicasting problems. In this paper we focus on the problem of multicast tree construction, and we introduce and evaluate algorithms for tree construction in infrastructureless, all-wireless applications. The performance metric used to evaluate broadcast and multicast trees is energy-efficiency. We develop the Broadcast Incremental Power (BIP) algorithm, and adapt it to multicast operation by introducing the Multicast Incremental Power (MIP) algorithm. These algorithms exploit the broadcast nature of the wireless communication environment, and address the need for energy-efficient operation. We demonstrate that our algorithms provide better performance than algorithms that have been developed for the link-based, wired environment.     

Low-Latency Broadcast in Multirate Wireless Mesh Networks

In a multirate wireless network, a node can dynamically adjust its link transmission rate by switching between different modulation schemes. In the current IEEE802.11a/b/g standards, this rate adjustment is defined for unicast traffic only. In this paper, we consider a wireless mesh network (WMN), where a node can dynamically adjust its link-layer multicast rates to its neighbors, and address the problem of realizing low-latency network-wide broadcast in such a mesh. We first show that the multirate broadcast problem is significantly different from the single-rate case. We will then present an algorithm for achieving low-latency broadcast in a multirate mesh which exploits both the wireless multicast advantage and the multirate nature of the network. Simulations based on current IEEE802.11 parameters show that multirate multicast can reduce broadcast latency by 3-5 times compared with using the lowest rate alone. In addition, we show the significance of the product of transmission rate and transmission coverage area in designing multirate WMNs for broadcast     

Dynamic Rate and FEC Adaptation for Video Multicast in Multi-rate Wireless Networks

Video multicast over Wireless Local Area Networks (WLANs) faces many challenges due to varying channel conditions and limited bandwidth. A promising solution to this problem is the use of packet level Forward Error Correction (FEC) mechanisms. However, the adjustment of the FEC rate is not a trivial issue due to the dynamic wireless environment. This decision becomes more complicated if we consider the multi-rate capability of the existing wireless LAN technology. In this paper, we propose a novel method which dynamically adapts the transmission rate and FEC for video multicast over multi-rate wireless networks. In order to evaluate the system experimentally, we implemented a prototype using open source drivers and socket programming. Our experimental results show that the proposed system significantly improves the multicast system performance.     

Cross Layer Secure and Resource-Aware On-Demand Routing Protocol for Hybrid Wireless Mesh Networks

Secure routing is one of the challenges offered by hybrid wireless mesh networks (WMNs). Researcher are implementing different approaches for mesh routing, but still need more efforts in terms of security, efficiency, deployment and capability with different scenarios and applications. Cross layer secure and resource-aware on demand routing (CSROR) protocol for hybrid WMN is designed to ensure routing security and fulfil different applications specific requirements for multimedia delivery and real-time transmissions. CSROR selects an optimum route on the basis of route security taking in consideration the different cross layer parameters. CSROR is not only resource aware approach but also resilient to different packet dropping attacks. It is evaluated in diverse range of hostile hybrid WMN scenarios.     

A Cross-Layer Optimization Framework for Multihop Multicast in Wireless Mesh Networks

The optimal and distributed provisioning of high throughput in mesh networks is known as a fundamental but hard problem. The situation is exacerbated in a wireless setting due to the interference among local wireless transmissions. In this paper, we propose a cross-layer optimization framework for throughput maximization in wireless mesh networks, in which the data routing problem and the wireless medium contention problem are jointly optimized for multihop multicast. We show that the throughput maximization problem can be decomposed into two subproblems: a data routing subproblem at the network layer, and a power control subproblem at the physical layer with a set of Lagrangian dual variables coordinating interlayer coupling. Various effective solutions are discussed for each subproblem. We emphasize the network coding technique for multicast routing and a game theoretic method for interference management, for which efficient and distributed solutions are derived and illustrated. Finally, we show that the proposed framework can be extended to take into account physical-layer wireless multicast in mesh networks     

无线Mesh网络可靠多播路由

无线Mesh网络多播路由是无线路由必须解决的关键技术。部分研究者对网络资源和服务质量（QoS）进行研究,提出了建立最短路径树、最小开销树、负载感知、信道分配多播等多播算法;有的算法考虑链路可靠性,建立备用路径。将结合网络资源和可靠性对多播路由算法进行研究,提出了建立可靠多播树（RT,Reliable Tree）的多播路由算法：可靠多播树是一个多树结构,由一棵首选多播树和一棵多径树构成,多径树提供可靠多路径,以提高网络吞吐量。     

无线Mesh网络中的组播机会路由研究

 针对无线Mesh网络组播中包丢失严重的问题,提出了保持包的IP层不变,而改变包的目的MAC域,进而MAC层以单播形式向组成员发送包的M2U(Multicast to Unicast) 优化解决方案.为了满足组成员增加时不影响用户的性能,提出在M2U中引入了机会路由的M2UO（Multicast to Unicast Opportunistic Routing）算法,对候选节点采用单播形式发送包,对其它节点采用组播形式发送包.在实际网络环境中的大量实验表明,优化组播减小了数据包的丢失率,提高了网络的吞吐量,具有较好的组播视频流效果.     

On Channel Assignment for Multicast in Multi-Radio Multi-Channel Wireless Mesh Networks:A Survey

The major challenge faced by wireless mesh networks is the capacity reduction caused by interference,and interference can be reduced or even eliminated through appropriate channel assignment.This article presents a comprehensive survey of channel assignment schemes for multicast in multi-radio multi-channel wireless mesh networks.We analyze the state-of-the-art channel assignment schemes for multicast and provide comprehensive taxonomy of the latest work.In general,we classify the channel assignment schemes for multicast into two types,that is,sequential multicast routing and channel assignment(SMRCA)and joint multicast routing and channel assignment(JMRCA).Detailed review of channel assignment schemes in each category is provided.Possible future research directions and corresponding solutions are also explored to motivate research interests in the field of channel assignment for multicast in wireless mesh networks.     

无线Mesh技术和网络

无线网状网（WMN）是近年被高度重视和快速发展的新型网络技术,支持宽带高速多媒体业务服务。文章就无线Mesh网络技术和应用进行讨论,综述无线Mesh网络的发展由来、基本技术、典型应用和现在的发展。随着未来无线分布技术和无线分布网络的发展,无线Mesh技术和网络将会成为无线移动通信的基本网络技术和网络结构,渗透到各种无线网络中,发挥更大作用。     

3G移动网络中的组播与广播

手机电视业务可以使用户在移动终端上观看电视节目。目前的手机电视都是以点到点(PtoP)的方式通过流媒体技术来实现的。但是,随着手机电视业务市场的不断拓展,简单的点到点方式已经无法满足需求,因此移动网络需要具有点到多点(PtoM)实现方式的广播,组播能力。本文简单介绍了3GPP和3GPP2中定义的新移动广播,组播业务,详细说明了其网络架构和具体的无线承载方式。     

Multicast and Broadcast Multimedia Services in Mobile WiMAX Networks

Multicast and broadcast services in WiMAX are downlink point-to-multipoint access services optimized for transmission of a common set of multimedia data packets to a group of users. This capability enables low-cost delivery of large volumes of popular contents (e.g., for video/audio streaming and file sharing) in a mobile network. The MCBCS framework in WiMAX allows multicast/broadcast of data in a radio channel that is time shared with unicast services. In a single-frequency network, where MCBCS transmissions are synchronized or coordinated across BSs in the designated service area, the mobile stations can use macro-space diversity to improve achievable data rates and also maintain service continuity and power saving across cells with minimal interaction with the network.     

Energy-Aware Broadcast Trees in Wireless Networks

In this paper we address the problem of broadcasting in wireless networks, so that the power consumed by any node is as small as possible. This approach is motivated by the fact that nodes in such networks often use batteries and, hence, it is important to conserve energy individually, so that they remain operational for a long time. We formulate the problem as a lexicographic node power optimization one. The problem is in general NP-complete. We provide an optimal algorithm which runs in polynomial time in certain cases. We also provide a heuristic algorithm whose performance relative to the optimal one is fairly satisfactory. We next show that these algorithms can also be used to solve the problem of broadcasting so that the residual energy of any node after the broadcast process is as large as possible. Finally, we discuss the issues of implementing the above algorithms distributively, as well as their multicast extensions.     

Multicast Routing in Wireless Mesh Networks: Minimum Cost Trees or Shortest Path Trees?

There exist two fundamental approaches to multicast routing: shortest path trees (SPTs) and minimum cost trees (MCTs). The SPT algorithms minimize the distance (or cost) from the sender to each receiver, whereas the MCT algorithms minimize the overall cost of the multicast tree. Due to the very large scale and unknown topology of the Internet, computing MCTs for multicast routing in the Internet is a very complex problem. As a result, the SPT approach is the more commonly used method for multicast routing in the Internet, because it is easy to implement and gives minimum delay from the sender to each receiver, a property favored by many real-life applications. Unlike the Internet, a wireless mesh network (WMN) has a much smaller size, and its topology can be made known to all nodes in the network. This makes the MCT approach an equally viable candidate for multicast routing in WMNs. However, it is not clear how the two types of trees compare when used in WMNs. In this article we present a simulation-based performance comparison of SPTs and MCTs in WMNs, using performance metrics, such as packet delivery ratio, end-to-end delay, and traffic impacts on unicast flows in the same network.     

Scheduling Combined Unicast and Multicast Traffic in Broadcast WDM Networks

This paper studies the performance of various strategies for scheduling a combined load of unicast and multicast traffic in a broadcast WDM network. The performance measure of interest is schedule length, which directly affects both aggregate network throughput and average packet delay. Three different scheduling strategies are presented, namely: separate scheduling of unicast and multicast traffic, treating multicast traffic as a number of unicast messages, and treating unicast traffic as multicasts of size one. A lower bound on the schedule length for each strategy is first obtained. Subsequently, the strategies are compared against each other using extensive simulation experiments in order to establish the regions of operation, in terms of a number of relevant system parameters, for which each strategy performs best. Our main conclusions are as follows. Multicast traffic can be treated as unicast traffic, by replicating all multicast packets, under very limited circumstances. On the other hand, treating unicast traffic as a special case of multicast traffic with a group of size 1, produces short schedules in most cases. Alternatively, scheduling and transmitting each traffic component separately is also a good choice.     

QoS Routing in Wireless Mesh Networks

An H-hop interference model is proposed, where the transmission is successfully received if no other nodes that are within H hops from the receiver are transmitting on the same channel simultaneously. Based on this model. the interference-free property in the Time division multiple access Wireless mesh networks is analyzed. A heuristic algorithm with max-rain time slots reservation strategy is developed to get the maximum bandwidth of a given path. And it is used in the bandwidth guaranteed routing protocol to find a path for a connection with bidirectional bandwidth requirement. Extensive simulations show that our routing protocol decreases the blocking ratios significantly compared with the shortest path routing.     

Battery-Aware Scheduling in Wireless Mesh Networks

Wireless mesh networks recently emerge as a flexible, low-cost and multipurpose networking platform with wired infrastructure connected to the Internet. A critical issue in mesh networks is to maintain network activities for a long lifetime with high energy efficiency. As more and more outdoor applications require long-lasting, high energy efficient and continuously-working mesh networks with battery-powered mesh routers, it is important to optimize the performance of mesh networks from a battery-aware point of view. Recent study in battery technology reveals that discharging of a battery is nonlinear. Batteries tend to discharge more energy than needed, and reimburse the over-discharged energy later if they have sufficiently long recovery time. Intuitively, to optimize network performance, a mesh router should recover its battery periodically to prolong the lifetime. In this paper, we introduce a mathematical model on battery discharging duration and lifetime for wireless mesh networks. We also present a battery lifetime optimization scheduling algorithm (BLOS) to maximize the lifetime of battery-powered mesh routers. Based on the BLOS algorithm, we further consider the problem of using battery powered routers to monitor or cover a few hot spots in the network. We refer to this problem as the Spot Covering under BLOS Policy problem (SCBP). We prove that the SCBP problem is NP-hard and give an approximation algorithm called the Spanning Tree Scheduling (STS) to dynamically schedule mesh routers. The key idea of the STS algorithm is to construct a spanning tree according to the BLOS Policy in the mesh network. The time complexity of the STS algorithm is O(r) for a network with r mesh routers. Our simulation results show that the STS algorithm can greatly improve the lifetime, data throughput and energy consumption efficiency of a wireless mesh network.     

无线网状网技术与应用

无线网状网(WMNs)由网状路由器节点和客户机节点组成,其中的网状路由器节点组成了无线网状网的网络骨干,其移动性很小。他们一起为无线网状网和其他常规无线网络的客户机节点提供网络的无线接入。WMNs技术结合了中心式控制的蜂窝网与分布式控制的无线自组织网的优点,可有效克服这两种技术的缺陷并显著提高无线网络的性能,已经成为下一代无线通信网络的研究热点之一。WMNs可为无线个域网、局域网、校园网、城域网的一系列应用提供高速无线宽带接入服务。虽然目前WMNs技术发展很快,但其协议栈各层仍存在许多有待研究的课题。首先简要介绍了无线网状网的结构与特点;随后重点分析了其主要的几个应用领域;最后探讨了WMNs各协议层的研究现状与关键技术,并分析了该技术存在的问题及未来的研究方向。     

Interference Nomenclature in Wireless Mesh Networks

The Quality of Service of Multi-Channel Multi-Radio Wireless Mesh Networks is adversely affected by the complex behavior of interference patterns present between the sender and receiver of a link. This behavior is usually captured using wireless channel interference models. The accuracy of the interference model is highly dependent on the interaction of the Carrier Sense Multiple Access with Collision Avoidance Medium Access Control (CSMA/CA MAC) protocol based on the geometric location of the sender and receiver of the link. Therefore, this paper presents a nomenclature of interference modeling schemes available in Wireless Mesh Network (WMN) literature with respect to the geometric location of the sender and receiver of a link. The behavior and limitations of each model are analyzed with the help of empirical examples. The results indicate that Garetto’s model of interfering links is the best choice to model wireless channel interference in WMNs. In addition, this study provides an interference analysis of Garetto’s model for the two link case by computing the conditional packet loss probability of each class of interfering link. The probability analysis concluded that the links with disconnected senders are highly interfering compared to sender connected links. Further, the analysis will assist researchers and engineers in relay node placement, capacity analysis, channel assignment, and topology control schemes in the WMN.