Cross-Layer Design for QoS Support in Multihop Wireless Networks

Due to such features as low cost, ease of deployment, increased coverage, and enhanced capacity, multihop wireless networks such as ad hoc networks, mesh networks, and sensor networks that form the network in a self-organized manner without relying on fixed infrastructure is touted as the new frontier of wireless networking. Providing efficient quality of service (QoS) support is essential for such networks, as they need to deliver real-time services like video, audio, and voice over IP besides the traditional data service. Various solutions have been proposed to provide soft QoS over multihop wireless networks from different layers in the network protocol stack. However, the layered concept was primarily created for wired networks, and multihop wireless networks oppose strict layered design because of their dynamic nature, infrastructureless architecture, and time-varying unstable links and topology. The concept of cross-layer design is based on architecture where different layers can exchange information in order to improve the overall network performance. Promising results achieved by cross-layer optimizations initiated significant research activity in this area. This paper aims to review the present study on the cross-layer paradigm for QoS support in multihop wireless networks. Several examples of evolutionary and revolutionary cross-layer approaches are presented in detail. Realizing the new trends for wireless networking, such as cooperative communication and networking, opportunistic transmission, real system performance evaluation, etc., several open issues related to cross-layer design for QoS support over multihop wireless networks are also discussed in the paper.     

基于跨层设计的无线网络QoS技术

随着多媒体业务的不断发展,如何保证无线网络上的QoS成为一个很重要的问题.基于传统的分层设计方法很难适应快速变化的无线通信环境.主要研究无线网络QoS的跨层设计技术,分析了无线网络的特点及其QoS需求,在此基础上阐述跨层设计的思想和方法,讨论了QoS跨层设计目前存在的问题,对QoS跨层设计技术进行了展望.     

认知无线Mesh网络跨层设计研究

传统网络的分层设计不能满足具有特殊QoS需求的无线宽带业务,无法应对动态频谱接入的无线通信环境。采用联合开放、架构灵活的跨层设计研究无线Mesh网络接入技术日渐成为热点。本文首先介绍了跨层设计的起源、分类,然后分析了认知无线Mesh网络跨层研究的挑战、难点及最新进展,并提出利用跨层设计实现路由及频谱管理的一种构想,最后展望了认知无线Mesh网络跨层研究的新方向。     

Cross-Layer Design of Wireless Mesh Networks with Network Coding

We investigate the optimal design of a multihop wireless mesh network equipped with multiple orthogonal wireless channels and multiple radios. Specifically, we focus on solutions that can efficiently utilize the limited resource to support multiple unicast applications by routing and network coding. We propose a cross-layer optimization framework where the broadcasting feature of the wireless environment, which plays an important role in realizing the achievable gain of network coding, is taken into account. Moreover, we propose a network code construction scheme based on linear programming, with which the possible achievable Coding+MAC gain could be significantly increased. Delay constraints are also included in the network code construction formulation so that the possible impact of the extra decoding delay to the TCP/IP performance can be reduced without changing the upper-layer protocols. The proposed network design based on cross-layer optimization results in significant increase in network throughput.     

无线Mesh网络跨层路由技术研究

无线Mesh网络(WMN:wireless mesh networks)作为一种新型的无线网络,成为近几年研究的热点。由于无线信道不稳定等特性,如何设计WMN的路由协议成为决定其性能的关键因素之一。近几年来的研究表明,通过跨层设计的方式综合其他层的重要参数来实现路由选择,能够很好地解决这一难题。介绍了几种先进的跨层路由设计方案,总结了现有的跨层路由协议的优缺点,并对如何设计并实现跨层路由协议进行了分析和总结。     

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.     

Cross-Layer Fair Bandwidth Sharing for Multi-Channel Wireless Mesh Networks

In a wireless mesh network (WMN) with a number of stationary wireless routers, the aggregate capacity can be increased when each router is equipped with multiple network interface cards (NICs) and each NIC is assigned to a distinct orthogonal frequency channel. In this paper, given the logical topology of the network, we mathematically formulate a crosslayer fair bandwidth sharing problem as a non-linear mixedinteger network utility maximization problem. An optimal joint design, based on exact binary linearization techniques, is proposed which leads to a global maximum. A near-optimal joint design, based on approximate dual decomposition techniques, is also proposed which is practical for deployment. Performance is assessed through several numerical examples in terms of network utility, aggregate network throughput, and fairness index. Results show that our proposed designs can lead to multi-channelWMNs which are more efficient and fair compared to their singlechannel counterparts. The performance gain on both efficiency and fairness increase as the number of available NICs per router or the number of available frequency channels increases.     

Cross-Layer Design Based Optimized Link State Routing Protocol for Wireless Mesh Networks

A proactive routing protocol CL-OLSR (cross-layer based optimized link state routing) by using a brand-new routing metric CLM (cross-layer metric) is proposed. CL-OLSR takes into account four link quality impact factors in route calculation through the cross-layer operation mechanism: the node available bandwidth, the node load, the link delivery rate, and the link interference, and thus the effect of route selection is optimized greatly. The simulation results show that the proposed CL-OLSR protocol can not only improve the network throughput to a large extent, but also reduce the end-to-end delay, while achieving load balance route results.     

Cross-Layer Design for End-to-End Throughput and Fairness Enhancement in Multi-Channel Wireless Mesh Networks

In this paper, we study joint rate control, routing and scheduling in multi-channel wireless mesh networks (WMNs), which are traditionally known as transport layer, network layer and MAC layer issues respectively. Our objective is to find a rate allocation along with a flow allocation and a transmission schedule for a set of end-to-end communication sessions such that the network throughput is maximized, which is formally defined as the maximum throughput rate allocation (MRA) problem. As simple throughput maximization may result in a severe bias on rate allocation, we take account of fairness based on a simplified max-min fairness model and the proportional fairness models. We define the max-min guaranteed maximum throughput rate allocation (MMRA) problem and proportional fair rate allocation (PRA) problem. We present efficient linear programming (LP) and convex programming (CP) based schemes to solve these problems. Numerical results show that proportional fair rate allocation schemes achieves a good tradeoff between throughput and fairness.     

A Cross-Layer Framework for Association Control in Wireless Mesh Networks

The user association mechanism specified by the IEEE 802.11 standard does not consider the channel conditions and the AP load in the association process. Employing the mechanism in its plain form in wireless mesh networks we may only achieve low throughput and low user transmission rates. In this paper we design a new association framework in order to provide optimal association and network performance. In this framework we propose a new channel-quality based user association mechanism inspired by the operation of the infrastructure-based WLANs. Besides, we enforce our framework by proposing an airtime-metric based association mechanism that is aware of the uplink and downlink channel conditions as well as the communication load. We then extend the functionality of this mechanism in a cross-layer manner taking into account information from the routing layer, in order to fit it in the operation of wireless mesh networks. Lastly, we design a hybrid association scheme that can be efficiently applied in real deployments to improve the network performance. We evaluate the performance of our system through simulations and we show that wireless mesh networks that use the proposed association mechanisms are more capable in meeting the needs of QoS-sensitive applications.     

多媒体异构Mesh网络体系设计及跨层QoS路由算法研究

 针对无线Mesh网络的异构特性和多媒体业务的QoS要求,研究了一种跨域、跨层、跨节点的无线Mesh网络QoS自适应体系架构.在此基础上,利用双层规划数学模型描述之,并利用改进的蚁群算法来求解该双层规划模型,从而提出了基于双层规划模型的蚁群优化路由算法.仿真结果表明双层规划数学模型充分地考虑并优化了路径的各QoS指标,提出的蚁群优化路由算法能够很好地收敛于双层规划模型的最优解,且具有复杂度低、收敛速度快的特点.     

Cross-Layer QoS Scheduling for Layered Multicast Streaming in OFDMA Wireless Networks

The conventional multicast scheme of wireless networks, though establishing a bandwidth-saving means for point-to-multipoint transmission, is very conservative by limiting the throughput of short-range communications. The multicast performance can be significantly improved if some low-rate users are pruned. In this paper, we investigate the subchannel assignment mechanism of multicast streaming services in the emerging WiMax/802.16e systems, where each multimedia stream is composed of a basic layer and an enhancement layer. The former affords a low-resolution video image to all the subscribers, while the latter only serves those with preferable channel states. Optimization frameworks are formulated to characterize the QoS requirements of multicast flows: pruned proportional rate ratio (PPRR), pruned stream rate guarantee (PSRG) and pruned user proportional fairness (PUPF). Three cross-layer algorithms are presented to perform channel assignment for different QoS requirements. Analytical study shows that the proposed algorithms have polynomial-time computational complexity. Numerical experiments validate that our proposals significantly outperform the conventional peer schedulers in terms of system throughput.     

无线网格网的跨层安全架构研究

概要介绍了无线网格网(WMN:wireless mesh networks)的发展状况、网络结构及主要优缺点,指出其是构建大规模无线宽带接入网络的一种经济、可行的理想方案;探讨了其安全服务的需求,在重点分析当前链路层和网络层安全协议的基础上,提出基于多信任域的跨层安全架构,来确保无线网格网中灵活高效的安全无线通信。     

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     

Cross-Layer Optimized Video Streaming Over Wireless Multihop Mesh Networks

The proliferation of wireless multihop communication infrastructures in office or residential environments depends on their ability to support a variety of emerging applications requiring real-time video transmission between stations located across the network. We propose an integrated cross-layer optimization algorithm aimed at maximizing the decoded video quality of delay-constrained streaming in a multihop wireless mesh network that supports quality-of-service. The key principle of our algorithm lays in the synergistic optimization of different control parameters at each node of the multihop network, across the protocol layers-application, network, medium access control, and physical layers, as well as end-to-end, across the various nodes. To drive this optimization, we assume an overlay network infrastructure, which is able to convey information on the conditions of each link. Various scenarios that perform the integrated optimization using different levels ("horizons") of information about the network status are examined. The differences between several optimization scenarios in terms of decoded video quality and required streaming complexity are quantified. Our results demonstrate the merits and the need for cross-layer optimization in order to provide an efficient solution for real-time video transmission using existing protocols and infrastructures. In addition, they provide important insights for future protocol and system design targeted at enhanced video streaming support across wireless mesh networks     

An Effective QoS Differentiation Scheme for Wireless Mesh Networks

Wireless mesh networking is emerging as an important architecture for future-generation wireless communications systems. Quality of service provisioning is a challenging issue in WMNs. In this article we study an effective QoS differentiation scheme for IEEE 802.16 WiMAX mesh networks. Both collocated and general topologies are exploited. Illustrative numerical examples are presented to demonstrate the effectiveness of the proposed strategy. The impact of key parameters on performance is discussed for differentiating various services. Moreover, with the proposed scheme, WMN scalability can be greatly improved. The challenges with respect to the integration of WMN and cooperative transmission are discussed, and the fairness problem is addressed with potential solutions.     

无线Mesh网络QoS保障技术综述

首先,简要回顾了无线Mesh网络的基本概况,分析了在无线Mesh网络中提供QoS保障的必要性和重要意义。然后,系统地介绍了无线Mesh网络的物理层、MAC层和路由层QoS保障技术以及跨层QoS设计技术的国内外研究现状,对其进行了细致而科学的分类。最后,给出了它们的研究难点和研究方向。     

能量受限无线Ad Hoc网络跨层设计

介绍了无线Ad Hoc网络的特点和应用,讨论了分层设计与跨层设计模式,并讨论了对有限能量的无线Ad Hoc网络跨层设计时链路层、MAC层、网络层以及应用层协议设计应考虑的因素,以及它们的交互操作。     

Cross-Layer Optimized Conditions for QoS Support in Multi-Hop Wireless Networks with MIMO Links

Recent advances in antenna technology made it possible to build wireless devices with more than one antenna at affordable costs. Because multiple antennas offer wireless networks a potential capacity increase, they are expected to be a key part of next-generation wireless networks to support the rapidly emerging multimedia applications characterized by their high and diverse QoS requirements. This paper developed methods that exploit the benefits of multiple antennas to enable multi-hop wireless networks with flow-level QoS capabilities. The authors first propose a cross-layer table-driven statistical approach that allows each node to determine the amount of spatial reuse and/or multiplexing, offered by the multiple antennas that are available to it. The authors then use the developed statistical approach to derive sufficient conditions under which flow rates are guaranteed to be feasible. The derived conditions are multi-layer aware in the sense that they account for cross-layer effects between the PHY and the MAC layers to support QoS at higher layers. The authors evaluate and compare the derived sufficient conditions via extensive simulations. The authors show that the conditions result in high flow acceptance rates when used in multi-hop wireless networking problems such as QoS routing and multicommodity flow problems. The authors also demonstrate the importance and the effect of considering cross-layer couplings into the development of flow acceptance methods.