Proportional bandwidth allocation with consideration of delay constraint over IEEE 802.11e-based wireless mesh networks

Wireless mesh networks (WMNs) extend the limited transmission coverage of wireless LANs by enabling users to connect to the Internet via a multi-hop relay service provided by wireless mesh routers. In such networks the quality of experience (QoE) depends on both the user location relative to the Internet gateway and the traffic load. Various channel access or queue management schemes have been proposed for achieving throughput fairness among WMN users. However, delay and bandwidth utilization efficiency of such schemes may be unacceptable for real-time applications. Accordingly, the present study proposes a proportional bandwidth allocation scheme with a delay constraint consideration for enhancing the QoE of users of WMNs based on the IEEE 802.11e standard. An analytical model of the proposed scheme is provided. Moreover, the performance of the proposed scheme is systematically compared with that of existing bandwidth allocation methods. The simulation results show that the proposed scheme outperforms previously proposed schemes in terms of both an improved throughput fairness among the WMN users and a smaller end-to-end transmission delay.     

Interference and traffic aware channel assignment in WiFi-based wireless mesh networks

Wireless mesh networks (WMN) typically employ mesh routers that are equipped with multiple radio interfaces to improve network capacity. The key aspect is to cleverly assign different channels (i.e., frequency bands) to each radio interface to form a WMN with minimum interference. The channel assignment must obey the constraints that the number of different channels assigned to a mesh router is at most the number of interfaces on the router, and the resultant mesh network is connected. This problem is known to be NP-hard. In this paper we propose a hybrid, interference and traffic aware channel assignment (ITACA) scheme that achieves good multi-hop path performance between every node and the designated gateway nodes in a multi-radio WMN network. ITACA addresses the scalability issue by routing traffic over low-interference, high-capacity links and by assigning operating channels in such a way to reduce both intra-flow and inter-flow interference. The proposed solution has been evaluated by means of both simulations and by implementing it over a real-world WMN testbed. Results demonstrate the validity of the proposed approach with performance increase as high as 111%.     

无线网格网中一种基于树的先验式路由协议

Wireless Mesh Network (WMN) is seen as an effective Internet access solution for dynamic wireless applications . For the low mobility of mesh routers in WMN, the backbone topography can be effectively maintained by proactive routing protocol. Preproposals like Tree Based Routing (TBR) protocol and Root Driven Routing (RDR) protocol are so centralized that they make the gateway become a bottleneck which severely restricts the network performance. We proposed an Optimized Tree-based Routing (OTR) protocol that logically separated the proactive tree into pieces. Route is partly computed by the branches instead of root. We also discussed the operation of multiple Internet gateways which is a main issue in WMN. The new proposal lightens the load in root, reduces the overhead and improves the throughput. Numerical analysis and simulation results confirm that the performance of WMN is improved and OTR is more suitable for large scale WMN.     

Cross-layer Scheduling Algorithms for IEEE 802.16 Based Wireless Mesh Networks

Wireless mesh network (WMN) is emerging as an important networking architecture for future wireless communications. The mesh mode supported in IEEE 802.16 protocol provides a TDMA solution for WMN, in which scheduling is an important issue. In this paper, we discuss the issues on how to satisfy a set of bandwidth requests in IEEE 802.16 WMNs using minimal radio resources (or solving minimal schedule length problem). In consideration of transmission overhead and adaptive modulation and coding (AMC), two cross-layer scheduling algorithms are proposed, namely max-transmission and priority-based algorithms. In particular, they are proposed based on a physical interference model, instead of a protocol interference model as suggested in the literature. For the priority-based algorithm, we study several priority criteria based on different cross-layer information. An iterative scheme for QoS traffic is introduced to guarantee fairness when traffic load exceeds the network capacity. Simulation results show that our algorithms outperform the existing schemes based on protocol model, and they also ensure better fairness among different nodes.     

多射频无线Mesh网中的接口分域信道分配

在多射频多信道无线Mesh网中,是无线宽带接入的重要候选技术之一.为了满足无线宽带接入的容量要求,Mesh路由器节点常需要配置多个无线接口并使用多个正交信道.已有的信道分配方法虽能减少干扰和碰撞,但不能完全避免.本文提出一种域内中心式调度的接口分域信道分配(ICCA)方案,旨在完全避免干扰与碰撞以提高网络吞吐量,尤其能...     

Transmission scheduling for wireless mesh network systems equipped with multiple directional antennas

All existing broadcast scheduling algorithms (BSAs) were designed for omnidirectional antenna (OA) packet radio (PR) nodes of a wireless mesh network (WMN). However, when WMN nodes are equipped with multiple directional antennas (DAs), a signal sent from a neighboring node may be received by more than one DA of the receiving node, and some nodes may receive signals from multiple DAs sent from the same node. When existing OA BSAs are used for scheduling transmission time-slots in time division multiple access (TDMA), due to the multiple DA signal detection phenomenon a weak performance in average time delay and channel utilization is obtained. Therefore, a novel transmission scheduling algorithm (TSA) for WMN nodes equipped with multiple DAs is proposed. Simulation results demonstrate that a significant performance gain can be obtained from using the proposed DA-TSA scheme.     

拓展宽带接入的无线Mesh网技术

无线Mesh网(wireless mesh network,WMN)作为一种新的网络结构,正在成为下一代无线接入研究中的一个热点.本文首先介绍了无线Mesh网的一些基本概念,然后讨论了无线Mesh网中的关键技术,并在此基础上分析了其应用前景,最后介绍了当前的主要商用无线Mesh系统和该技术的标准化进展.     

新型宽带无线网络技术——无线网状网

无线网状网技术是一种具有良好市场应用前景的新型宽带无线网络技术.本文首先简要介绍了无线网状网的产生和发展,然后针对无线网状网的定义、特点、应用以及影响网络性能的关键因素等最核心的几个问题,进行了初步的探讨和总结.     

基于WMN变节节点多径检测的Petri网模型分析

针对WMN中出现的安全问题,提出了利用WMN多径特性的密钥协商模型,可以在防止中间人攻击的同时发现网络中的变节节点。采用Petri网理论对模型结构特性及安全性进行形式化分析,对发现的漏洞给出解决方案。通过引入新的变节节点的检测安全模型和算法,使WMN的安全性得到增强。     

Oblivious routing in wireless mesh networks

As new network applications have arisen rapidly in recent years, it is becoming more difficult to predict the exact traffic pattern of a network. In consequence, a routing scheme based on a single traffic demand matrix often leads to a poor performance. Oblivious routing (Racke in Proceedings of the 43rd annual IEEE symposium on foundations of computer science 43–52, 2002) is a technique for tackling the traffic demand uncertainty problem. A routing scheme derived from this principle intends to achieve a predicable performance for a set of traffic matrixes. Oblivious routing can certainly be an effective tool to handle traffic demand uncertainty in a wireless mesh network (WMN). However, a WMN has an additional tool that a wireline network does not have: dynamic bandwidth allocation. A router in a WMN can dynamically assign bandwidth to its attached links. This capability has never been exploited previously in works on oblivious routing for a spatial time division multiple access (STDMA) based WMN. Another useful insight is that although it is impossible to know the exact traffic matrix, it is relatively easy to estimate the amount of the traffic routed through a link when the routing scheme is given. Based on these two insights, we propose a new oblivious routing framework for STDMA WMNs. Both analytical models and simulation results are presented in this paper to prove that the performance—in terms of throughput, queue lengths, and fairness—of the proposed scheme can achieve significant gains over conventional oblivious routing schemes for STDMA based WMNs.     

Capacity and QoS for a Scalable Ring-Based Wireless Mesh Network

The wireless mesh network (WMN) is an economical solution to support ubiquitous broadband services. This paper investigates the tradeoffs among quality-of-service (QoS), capacity, and coverage in a scalable multichannel ring-based WMN. We suggest a simple frequency planning in the proposed ring-based WMN to improve the capacity with QoS support, and to make the system more scalable in terms of coverage. We develop a physical (PHY)/medium access control (MAC) cross-layer analytical model to evaluate the delay, jitter, and throughput of the proposed WMN, by taking account of the carrier sense multiple-access (CSMA) MAC protocol, and the impact of hop distance on transmission rate in the physical layer. Furthermore, the mixed-integer nonlinear programming optimization approach is applied to determine the optimal number of rings and the associated ring widths, aiming at maximizing the capacity and coverage of a mesh cell subject to the delay requirement     

Connection-based scheduling for supporting real-time traffic in wireless mesh networks

Packet transmission scheduling for supporting real-time traffic in a WMN is difficult, and one of the main challenges is to coordinate temporal operations of the mesh access points (APs) in order to provide strict latency guarantee while efficiently utilizing the radio resources. In this paper a connection-based scheduling (CBS) scheme is proposed. Connections with more hops are given a higher priority, and connections with a lower priority can only use resources remaining from serving all higher priority ones. For each multihop connection, the scheduling minimizes latency between successive hops. A connection-based optimization problem is formulated with an objective to minimize the amount of required AP resources, subject to the latency requirement of the connections. Numerical results show that the proposed scheduling scheme achieves close-to-optimum performance at both the connection and packet levels.     

基于统计网络演算的无线mesh网络流量模型

基于无线mesh网络的基本特征,利用统计网络演算理论,构造了新型的无线mesh网络单节点和多节点的流量模型,该模型充分体现了无线mesh网的随机特性.该流量模型的特征是其求和函数及其输入输出函数的边界函数均受限于一个最小加卷积函数.理论分析证明构造的流量模型能正确描述无线mesh网络的实际情况.     

A weighted interference estimation scheme for interface‐switching wireless mesh networks

The co‐channel interference problem in wireless mesh networks (WMN) is extremely serious due to the heavy aggregated traffic loads and limited available channels. It is preferable for mesh routers to dynamically switch channels according to the accurate estimation of co‐channel interference level in the neighborhood. Most developed interference estimation schemes, however, do not consider the impact of interface switching. Furthermore, the interference in wireless networks has been extensively considered as an all‐or‐nothing event. In this paper, we develop a weighted interference estimation scheme (WIES) for interface‐switching WMN. WIES takes a new version of multi‐interface conflict graph that considers the impacts of frequent interface switching as the interference relationship estimation scheme. Besides, WIES uses a weight to estimate the interference level between links. The weight utilizes two empirical functions to denote the impacts of the relative distance and characteristics of traffic loads in WMN. Extensive NS2 simulations show that WIES achieves significant performance improvements, especially when the interference level of the network is high. We also validate that the interference level of networks is affected by several system parameters such as the number of available channels and the ratio between interference range and transmission range. Copyright © 2008 John Wiley & Sons, Ltd.     

无线Mesh网络流量自相似性研究

近年来,无线Mesh网络已成为一个倍受关注的研究领域.对无线Mesh网络流量特性的研究将有助于网络协议的研究、评估,以及网络结构的规划和建设.本文通过对无线Mesh测试网上采集的数据包进行统计分析,揭示了网络流量具有自相似的特性.同时,解释了无线Mesh网络流量自相似性是由网络中具有重尾分布特性的多个流叠加形成的,并通过仿真进一步分析了节点移动性对流量自相似性的影响.     

Proportional fairness in MAC layer channel access of IEEE 802.11s EDCA based wireless mesh networks

Fairness provisioning in IEEE 802.11s EDCA based Wireless Mesh Networks (WMNs) is a very challenging task due to relayed traffic and traffic load variation among mesh routers. Because of bursty traffic in general purpose community wireless mesh networks, proportional fairness is more suited than max–min fairness, where mesh routers and clients should get channel access proportional to their traffic load. However, proportional fairness is hard to achieve by solving optimization function because of non-linearity and non-concave property of the objective function. In this paper, a probabilistic approach is proposed to provide proportional fairness without solving global non-linear and non-concave optimization. Every mesh node use a load estimation strategy to estimate total traffic load that it needs to forward. The required channel share of a mesh node should be proportional to its traffic load, whereas, the total normalized channel share for all the contending mesh nodes should be kept less than unity to satisfy the clique constraint. The network architecture and contention property in WMN are explored to deduce the required channel share of mesh nodes. A probabilistic approach is used to tune the contention window based on the difference between actual channel share and required channel share, so that the node with more traffic load gets more channel share. A discrete time Markov Chain based modeling is used to deduce the overall network throughput for the proposed scheme. Simulation result shows that the proposed scheme works better than the standard IEEE 802.11s based EDCA MAC in terms of fairness and throughput.     

Improving Delay and Jitter Performance in Wireless Mesh Networks for Mobile IPTV Services

Wireless mesh networking has recently emerged as a promising technology for the next-generation wireless networks. In wireless mesh networks (WMNs), it is practically attractive to support the low-cost quality-of-service (QoS) guaranteed mobile TV service. To meet this need, our study addresses how to improve the delay and jitter performance of mobile IPTV services over IEEE 802.11 based WMN. Particularly, we first discuss the adaptation of IEEE 802.11 MAC layer to construct a WMN with emphasis on mobile IPTV service; we then develop an enhanced version of Guaranteed-Rate (GR) packet scheduling algorithm, namely virtual reserved rate GR (VRR-GR), to further reduce the delay and suppress the jitter in multiservice network environment. Simulation results show that our proposed approach can satisfyingly prioritize mobile IPTV services in WMN, while providing non-IPTV services with what they need as well.      

Efficient routing for wireless mesh networks using a backup path

Wireless mesh networks (WMNs) have a proven record in providing viable solutions for some of the fundamental issues in wireless networks such as capacity and range limitations. WMN infrastructure includes clusters of mobile ad‐hoc networks connected through a fixed backbone of mesh routers. The mesh network can be constrained severely because of various reasons, which could result in performance degradation such as a drop in throughput or long delays. Solutions to this problem often focus on multipath or multichannel extensions to the existing ad‐hoc routing protocols. In this paper, we propose a novel solution by introducing an alternative path to the mesh backbone that traverses the mobile ad‐hoc networks part of the WMN. The new routing solution allows the mobile nodes (MNs) to establish direct communication among peers without going through the backbone. The proposed alternative ad‐hoc path is used only when the mesh backbone is severely constrained. We also propose, for the first time in WMNs, using MNs with two interfaces, one used in the mesh backbone communication and the other engaged in the ad‐hoc network. A scheme is presented for making the MN aware of link quality measures by providing throughput values to the ad‐hoc on‐demand distance vector protocol. We use piggybacking on route reply messages in ad‐hoc on‐demand distance vector to avoid incurring additional costs. We implemented our solution in an OPNET simulator and evaluated its performance under a variety of conditions. Simulation results show that the alternative ad‐hoc path provides higher throughput and lower delays. Delay analysis show that the throughput improvement does not impose additional costs. Copyright © 2012 John Wiley & Sons, Ltd.     

Channel‐switching and power control mechanisms for improving network connectivity in wireless mesh networks

A Wireless Mesh Network (WMN) consists of fixed wireless routers, each of which provides service for mobile clients within its coverage area and inter‐connects mesh routers to form a connected mesh backbone. Wireless mesh routers are assigned with a channel or a code to prevent collisions in transmission. With a power control mechanism, each router could be assigned with a power level to control connectivity, interference, spectrum spatial reuse, and topology. Assigning high transmitting power level to a router can enhance the network connectivity but may increase the number of neighbors and worsen the collision problem. How to assign an appropriate power level to each router to improve the network connectivity with a constraint of limited channels is one of the most important issues in WMNs. Given a network topology and a set of channels that has been assigned to mesh routers, the proposed channel‐switching mechanism further reassigns each router with a power level and switches channels of routers to optimize both power efficiency and connectivity. A matrix‐based presentation and operations are proposed to respectively identify and resolve the channel switching problems. Simulation study reveals that the proposed mechanisms increase network throughput and provides a variety of route selection, and thus improves the performance of a given WMN. Copyright © 2009 John Wiley & Sons, Ltd.     

Call admission control for wireless mesh network based on power interference modeling using directional antenna

Interference is a fundamental issue in wireless mesh networks (WMNs) and it seriously affects the network performance. In this paper we characterize the power interference in IEEE 802.11 CSMA/CA based wireless mesh networks using directional antennas. A model based centralized call admission control (CAC) scheme is proposed which uses physical collision constraints, and transmitter-side, receiver-side and when-idle protocol collision prevention constraints. The CAC assists to manage requests from users depending on the available bandwidth in the network: when a new virtual link establishment request from a user is accepted into the network, resources such as interface, bandwidth, transmission power and channel are allocated in the participating nodes and released once the session is completed. The proposed CAC is also able to contain the interference in the WMN by managing the transmission power of nodes.