Minimum Interference Channel Assignment in Multiradio Wireless Mesh Networks

In this paper, we consider multi-hop wireless mesh networks, where each router node is equipped with multiple radio interfaces and multiple channels are available for communication. We address the problem of assigning channels to communication links in the network with the objective of minimizing overall network interference. Since the number of radios on any node can be less than the number of available channels, the channel assignment must obey the constraint that the number of different channels assigned to the links incident on any node is atmost the number of radio interfaces on that node. The above optimization problem is known to be NP-hard. We design centralized and distributed algorithms for the above channel assignment problem. To evaluate the quality of the solutions obtained by our algorithms, we develop a semidefinite program and a linear program formulation of our optimization problem to obtain lower bounds on overall network interference. Empirical evaluations on randomly generated network graphs show that our algorithms perform close to the above established lower bounds, with the difference diminishing rapidly with increase in number of radios. Also, ns-2 simulations as well as experimental studies on testbed demonstrate the performance potential of our channel assignment algorithms in 802.11-based multi-radio mesh networks.     

Loss Tolerant Bandwidth Aggregation for Multihomed Video Streaming over Heterogeneous Wireless Networks

Bandwidth aggregation is a key research issue in integrating heterogeneous wireless networks, since it can substantially increase the throughput and reliability for enhancing streaming video quality. However, the burst loss in the unreliable wireless channels is a severely challenging problem which significantly degrades the effectiveness of bandwidth aggregation. Previous studies mainly address the critical problem by reactively increasing the forward error correction (FEC) redundancy. In this paper, we propose a loss tolerant bandwidth aggregation approach (LTBA), which proactively leverages the channel diversity in heterogeneous wireless networks to overcome the burst loss. First, we allocate the FEC packets according to the ‘loss-free’ bandwidth of each wireless network to the multihomed client. Second, we deliberately insert intervals between the FEC packets’ departures while still respecting the delay constraint. The proposed LTBA is able to reduce the consecutive packet loss under burst loss assumption. We carry out analysis to prove that the proposed LTBA outperforms the existing ‘back-to-back’ transmission schemes based on Gilbert loss model and continuous time Markov chain. We conduct the performance evaluation in Exata and emulation results show that LTBA outperforms the existing approaches in improving the video quality in terms of PSNR (Peak Signal-to-Noise Ratio).     

Distributed Channel Assignment and Routing in Multiradio Multichannel Multihop Wireless Networks

In this paper, we first identify several challenges in designing a joint channel assignment and routing (JCAR) protocol in heterogeneous multiradio multichannel multihop wireless networks (M³WNs) using commercial hardware [e.g., IEEE 802.11 Network Interface Card (NIC)]. We then propose a novel software solution, called Layer 2.5 JCAR, which resides between the MAC layer and routing layer. JCAR jointly coordinates the channel selection on each wireless interface and the route selection among interfaces based on the traffic information measured and exchanged among the two-hop neighbors. Since interference is one of the major factors that constrain the performance in a M³ WN, in this paper, we introduce an important channel cost metric (CCM) which actually reflects the interference cost and is defined as the sum of expected transmission time weighted by the channel utilization over all interfering channels (for each node). In CCM, both the interference and the diverse channel characteristics are taken into account. An expression for CCM is derived in terms of equivalent fraction of air time by explicitly taking the radio heterogeneity into consideration. Using CCM as one of the key performance measures, we propose a distributed algorithm (heuristic) that produces near-optimal JCAR solution. To evaluate the efficacy of our heuristics, we conduct extensive simulations using the network simulator NS2. To demonstrate implementation feasibility, we conducted various experiments for the proposed distributed JCAR algorithm on a multihop wireless network testbed with nine wireless nodes, each is equipped with single/multiple 802.11a/g cards. Both experimental and simulation results demonstrate the effectiveness and implementation easiness of our proposed software solution     

Power Efficient Video Multipath Transmission over Wireless Multimedia Sensor Networks

This paper proposes a power efficient multipath video packet scheduling scheme for minimum video distortion transmission (optimised Video QoS) over wireless multimedia sensor networks. The transmission of video packets over multiple paths in a wireless sensor network improves the aggregate data rate of the network and minimizes the traffic load handled by each node. However, due to the lossy behavior of the wireless channel the aggregate transmission rate cannot always support the requested video source data rate. In such cases a packet scheduling algorithm is applied that can selectively drop combinations of video packets prior to transmission to adapt the source requirements to the channel capacity. The scheduling algorithm selects the less important video packets to drop using a recursive distortion prediction model. This model predicts accurately the resulting video distortion in case of isolated errors, burst of errors and errors separated by a lag. Two scheduling algorithms are proposed in this paper. The Baseline scheme is a simplified scheduler that can only decide upon which packet can be dropped prior to transmission based on the packet’s impact on the video distortion. This algorithm is compared against the Power aware packet scheduling that is an extension of the Baseline capable of estimating the power that will be consumed by each node in every available path depending on its traffic load, during the transmission. The proposed Power aware packet scheduling is able to identify the available paths connecting the video source to the receiver and schedule the packet transmission among the selected paths according to the perceived video QoS (Peak Signal to Noise Ratio—PSNR) and the energy efficiency of the participating wireless video sensor nodes, by dropping packets if necessary based on the distortion prediction model. The simulation results indicate that the proposed Power aware video packet scheduling can achieve energy efficiency in the wireless multimedia sensor network by minimizing the power dissipation across all nodes, while the perceived video quality is kept to very high levels even at extreme network conditions (many sensor nodes dropped due to power consumption and high background noise in the channel).     

无线Mesh网络组播研究分析

介绍了无线Mesh网络(WMN)中的组播协议,并分析了为WMN设计组播协议时要注意的一些因素,如Mesh路由器的有效性、多信道和信道分配的影响、负载均衡、组播路由性能指标的选择、保证QoS的影响和跨层优化.最后,分析了目前研究中存在的问题,并对未来的研究提出了自己的看法.     

Multicasting with Localized Control in Wireless Ad Hoc Networks

This paper investigates how to support multicasting in wireless ad hoc networks without throttling the dominant unicast flows. Unicast flows are usually congestion-controlled with protocols like TCP. However, there are no such protocols for multicast flows in wireless ad hoc networks and multicast flows can therefore cause severe congestion and throttle TCP-like flows in these environments. Based on a cross-layer approach, this paper proposes a completely-localized scheme to prevent multicast flows from causing severe congestion and the associated deleterious effects on other flows in wireless ad hoc networks. The proposed scheme combines the layered multicast concept with the routing-based congestion avoidance idea to reduce the aggregated rate of multicast flows when they use excessive bandwidth on a wireless link. Our analysis and extensive simulations show that the fully-localized scheme proposed in this paper is effective in ensuring the fairness of bandwidth sharing between multicast and unicast flows in wireless ad hoc networks.     

基于主动网络分级视频多播方案设计

提出了一种新的基于主动网络的视频分级传输解决方案SVM-AN,通过主动网络中间节点的处理能力,满足不同等级的QoS要求.仿真结果表明,与RLM方案相比,SVM-AN方案可以获得更好的性能.     

Algorithms for Energy-Efficient Multicasting in Static Ad Hoc Wireless Networks

In this paper we address the problem of multicasting in ad hoc wireless networks from the viewpoint of energy efficiency. We discuss the impact of the wireless medium on the multicasting problem and the fundamental trade-offs that arise. We propose and evaluate several algorithms for defining multicast trees for session (or connection-oriented) traffic when transceiver resources are limited. The algorithms select the relay nodes and the corresponding transmission power levels, and achieve different degrees of scalability and performance. We demonstrate that the incorporation of energy considerations into multicast algorithms can, indeed, result in improved energy efficiency.     

Channel Assignment Strategies for Multiradio Wireless Mesh Networks: Issues and Solutions

Next-generation wireless mobile communications will be driven by converged networks that integrate disparate technologies and services. The wireless mesh network is envisaged to be one of the key components in the converged networks of the future, providing flexible high- bandwidth wireless backhaul over large geographical areas. While single radio mesh nodes operating on a single channel suffer from capacity constraints, equipping mesh routers with multiple radios using multiple nonoverlap- ping channels can significantly alleviate the capacity problem and increase the aggregate bandwidth available to the network. However, the assignment of channels to the radio interfaces poses significant challenges. The goal of channel assignment algorithms in multiradio mesh networks is to minimize interference while improving the aggregate network capacity and maintaining the connectivity of the network. In this article we examine the unique constraints of channel assignment in wireless mesh networks and identify the key factors governing assignment schemes, with particular reference to interference, traffic patterns, and multipath connectivity. After presenting a taxonomy of existing channel assignment algorithms for WMNs, we describe a new channel assignment scheme called MesTiC, which incorporates the mesh traffic pattern together with connectivity issues in order to minimize interference in multi- radio mesh networks.     

Joint Channel Assignment and Routing for Throughput Optimization in Multiradio Wireless Mesh Networks

Multihop infrastructure wireless mesh networks offer increased reliability, coverage, and reduced equipment costs over their single-hop counterpart, wireless local area networks. Equipping wireless routers with multiple radios further improves the capacity by transmitting over multiple radios simultaneously using orthogonal channels. Efficient channel assignment and routing is essential for throughput optimization of mesh clients. Efficient channel assignment schemes can greatly relieve the interference effect of close-by transmissions; effective routing schemes can alleviate potential congestion on any gateways to the Internet, thereby improving per-client throughput. Unlike previous heuristic approaches, we mathematically formulate the joint channel assignment and routing problem, taking into account the interference constraints, the number of channels in the network, and the number of radios available at each mesh router. We then use this formulation to develop a solution for our problem that optimizes the overall network throughput subject to fairness constraints on allocation of scarce wireless capacity among mobile clients. We show that the performance of our algorithms is within a constant factor of that of any optimal algorithm for the joint channel assignment and routing problem. Our evaluation demonstrates that our algorithm can effectively exploit the increased number of channels and radios, and it performs much better than the theoretical worst case bounds     

基于无线视频服务器自适应带宽算法

针对无线网络上行带宽有限的情况,提出了无线视频传输带宽的自适应算法.采用双卡发送采集的视频流数据,这样大大增加了无线视频传输带宽.解决了公共无线网络带宽资源有限的问题.使得无线视频传输码率能够达到500 ～ 900 kbit/s.在接收端采取双缓冲区的设计,在客户端能够得到清晰、流畅的视频图像.从而解决了无线视频传输和带宽不足的问题.     

基于无线视频服务器的自适应带宽算法

针对无线通信的特殊性,无线视频传输图像可能出现马赛克、拖影等现象,提出了无线视频传输带宽的自适应算法,从系统总体结构、硬件设计、软件设计、自适应算法分析及测试分析几方面进行了较全面的介绍.该算法能在客户端得到清晰、流畅的视频图像,从而解决了无线视频传输和带宽不足的问题.     

ATM网中图像分组的带宽分配算法

用两个节点各复用几个图像终端的ＡＴＭ网为例，研究五种图像源的带宽分配算法，静态时隙分配算法，缓冲区基础动态时隙分配算法，自适应时隙分配算法，先来先服务时隙分配算法和速度基础动态时隙分配算法，用计算机仿真和比较确定了五种算法的平均信元时延及时延偏差系数。     

无线Ad Hoc网络中动态的带宽管理

基于已有的带宽管理机制,采用加权公平对竞争的流分配带宽,不仅可以对流实现准入控制,以保证每条流的最低信道时间需求,同时也能动态地调节流所分配的信道时间。另外,我们的方案,也适用于多跳的情况,通过例子说明,在考虑到用户需求的同时,也提高了网络的吞吐量。     

Dynamic Bandwidth Management in Single-Hop Ad Hoc Wireless Networks

Distributed weighted fair scheduling schemes for Quality of Service (QoS) support in wireless local area networks have not yet become standard. Therefore, we propose an Admission Control and Dynamic Bandwidth Management scheme that provides fairness and a soft rate guarantee in the absence of distributed MAC-layer weighted fair scheduling. This scheme is especially suitable for smart-rooms where peer-to-peer multimedia transmissions need to adapt their transmission rates co-operatively. We present a mapping scheme to translate the bandwidth requirements of an application into its channel time requirements. The center piece of our scheme is a Bandwidth Manager, which allots each flow a share of the channel, depending on the flow's requirements relative to the requirements of other flows in the network. Admitted flows control their transmission rates so they only occupy the channel for the fraction of time allotted to them. Thus co-operation between flows is achieved and the channel time is fair shared. As the available channel capacity changes and the traffic characteristics of various flows change, the Bandwidth Manager dynamically re-allocates the channel access time to the individual flows. Our simulation experiments show that, at a very low cost and with high probability, every admitted flow in the network will receive at least its minimum requested share of the network bandwidth. We also present extensive testbed experiments with our scheme using a real-time audio streaming application running between Linux laptops equipped with standard IEEE 802.11 network cards.     

Auction-Based Bandwidth Allocation in Multi-Hop Wireless Ad Hoc Networks

In this paper, we propose a multi-hop auction-based bandwidth allocation mechanism to address the flow contention problem in wireless ad hoc networks. By modeling the problem as an iterative auction-based structure, it enables us to derive fair and efficient bandwidth allocation to each node on the basis of only local information. Further, a multi-hop flow coordination mechanism is then developed to optimize the network performance. Simulation results suggest that the proposed mechanism outperforms other approaches in terms of network throughput, bandwidth utilization, fairness, end-to-end delay, packet loss rate, and robustness.     

WDM网络中的光层组播技术

组播应用主要是一些带宽密集型的业务,而光网络又能够提供巨大的带宽。随着光通信技术的发展,如何在光层实现组播已经成为光网络研究的热点之一。主要介绍了组播的应用以及在光层实现组播的关键技术;分析了实现光层组播的节点结构、光树的概念以及针对组播的波长路由算法。     

Efficient Cache Placement in Multi-Hop Wireless Networks

In this paper, we address the problem of efficient cache placement in multi-hop wireless networks. We consider a network comprising a server with an interface to the wired network, and other nodes requiring access to the information stored at the server. In order to reduce access latency in such a communication environment, an effective strategy is caching the server information at some of the nodes distributed across the network. Caching, however, can imply a considerable overhead cost; for instance, disseminating information incurs additional energy as well as bandwidth burden. Since wireless systems are plagued by scarcity of available energy and bandwidth, we need to design caching strategies that optimally trade-off between overhead cost and access latency. We pose our problem as an integer linear program. We show that this problem is the same as a special case of the connected facility location problem, which is known to be NP-hard. We devise a polynomial time algorithm which provides a suboptimal solution. The proposed algorithm applies to any arbitrary network topology and can be implemented in a distributed and asynchronous manner. In the case of a tree topology, our algorithm gives the optimal solution. In the case of an arbitrary topology, it finds a feasible solution with an objective function value within a factor of 6 of the optimal value. This performance is very close to the best approximate solution known today, which is obtained in a centralized manner. We compare the performance of our algorithm against three candidate cache placement schemes, and show via extensive simulation that our algorithm consistently outperforms these alternative schemes.