无线多跳网QoS性能统计性边界的研究

为保证无线多跳网的服务质量（QoS）,需要求解其性能边界。基于统计型流量包络建立了无线多跳网的数据流传输模型,在此模型的基础上利用统计网络演算理论推导了无线多跳网单节点的时延统计性边界、端到端的时延统计性边界以及端到端数据积压统计性边界。仿真实验结果表明,不同数据流的测量值都在数值计算的边界范围之内,表明基于统计网络演算理论的无线多跳网QoS边界模型具有较好的性能。     

Analysis of total average queue length in multi-hop wireless networks

In upcoming communication environments, multi-hop networking is expected to be pervasive in wireless access and backbone networks because it promises large coverage and increased capacity. Many studies have been devoted to the throughput of multi-hop wireless networks, but the delay performance is not clearly investigated yet. In this Letter, we analyze a multi-hop wireless network to obtain a lower bound of the total average queue length since it is closely related to the delay. We first consider a network with single hop sessions only, and its total average queue length is characterized as a solution of a linear program. Then we present a novel idea of translating a network with multi-hop sessions into a network with single hop sessions only, thereby the linear programming approach can be applied again. Simulation results show that the lower bound is very close to the achievable value of our reference link scheduler. Hence, our bound is tight.     

面向编码机会路由的无线Mesh 网络广播信道接入

编码机会路由是有损无线Mesh网络中提供高吞吐量和高可靠性传输的理想方案.该路由机制建立在无线广播的多用户分集优势和随机网络编码的纠删特性之上,为广播MAC的设计引入了新的机会和挑战.基于最优停止理论,研究面向编码机会路由的机会广播信道接入问题,提出一种在接入延迟和信道交付能力之间加以折衷,以获得最优的平均有效速率的方法,并在IEEE 802.11 DCF协议基础上设计实现面向NCOR的广播MAC协议O-BCast.仿真结果表明,该协议显著提高了编码机会路由的端到端吞吐量,具有网络负载自适应的良好特性.     

存在隐藏终端的IEEE 802.11e多跳无线网络模型分析*

首次将802.11e的接入机制放入多跳环境中进行仿真分析和定量研究。提出一种新的多跳环境下802.11e网络模型,结合M/G/1/K排队模型,定量分析在隐藏终端影响下802.11e网络的MAC层吞吐率、MAC时延和帧丢失率,研究802.11e在多跳环境下性能表现的内在原因。经过仿真实验结果与数值分析结果的对比,验证了分析模型的准确性;通过有（无）隐藏终端影响下MAC层性能的对比分析,指出了802.11e在多跳无线网络中支持QoS的局限性：受隐藏终端的影响,802.11e对不同接入等级的业务提供QoS区分的性能明显降级。因而有必要研究隐藏终端问题的解决方案,提高802.11e在多跳环境下的性能。     

存在隐藏终端的IEEE802.11e多跳无线网络模型分析

首次将802.11e的接入机制放入多跳环境中进行仿真分析和定量研究。提出一种新的多跳环境下802.11e网络模型,结合M/G/1/K排队模型,定量分析在隐藏终端影响下802.11e网络的MAC层吞吐率、MAC时延和帧丢失率,研究802.11e在多跳环境下性能表现的内在原因。经过仿真实验结果与数值分析结果的对比,验证了分析模型的准确性;通过有(无)隐藏终端影响下MAC层性能的对比分析,指出了802.11e在多跳无线网络中支持QoS的局限性:受隐藏终端的影响,802.11e对不同接入等级的业务提供QoS区分的性能明显降级。因而有必要研究隐藏终端问题的解决方案,提高802.11e在多跳环境下的性能。     

Dynamic end-to-end capacity in IEEE 802.16 wireless mesh networks

The IEEE 802.16 standard defines mesh mode as one of its two operational modes in medium access control (MAC). In the mesh mode, peer-to-peer communication between subscriber stations (SSs) is allowed, and transmissions can be routed via other SSs across multiple hops. In such an IEEE 802.16 mesh network, accurate and reliable determination of dynamic link capacity and end-to-end capacity of a given multi-hop route is crucial for robust network control and management. The dynamic capacities are difficult to determine in a distributed system due to decentralized packet scheduling and interference between communicating nodes caused by the broadcast nature of radio propagation. In this paper, we first propose a method for computing the dynamic link capacity between two mesh nodes, and extend that to determine the dynamic end-to-end capacity bounds of a multi-hop route based on the concept of Bottleneck Zone. The physical deployments of networks are also considered in the capacity estimation. We demonstrate the effectiveness and accuracy of our methods for computing dynamic link capacity and end-to-end capacity bounds through extensive simulations.     

Extra back-off flow control in multi-hop wireless networks

CSMA is the predominant distributed access protocol for wireless mesh networks. Originally designed for single-hop settings, CSMA can exhibit severe performance problems in multi-hop networks in terms of stability and end-to-end throughput. To ensure a smoother flow of packets, we examine an enhancement referred to as Extra Back-off (EB) flow control. In this enhanced scheme a node remains silent for a certain extra back-off time (imposed on top of the usual back-off time that is part of CSMA) after it has transmitted a packet, to give both the downstream and upstream neighbors the opportunity to transmit. EB flow control entails only a small modification to CSMA, preserving its distributed character. In order to examine the performance of EB flow control, we analyze a novel class of Markov models at the interface between classical tandem queues and interacting particle systems. The results demonstrate that EB flow control provides an effective mechanism for improving the end-to-end throughput performance.     

基于探测的多信道无线网状网机会路由算法

多信道无线网状网的性能在很大程度上依赖于信道分配和路由选择.现有的多信道无线网状网路由大多没有考虑信道之间的干扰问题,从而导致通信性能下降.针对这一问题,提出一种基于探测的多信道无线网状网机会路由(POR)算法.首先,根据干扰能量,选出最佳通信信道集来降低信道间的传榆干扰.在此基础上,采用探测方式计算路径期望传输时延,确定候选链路集并运用机会路由机制进行数据传输以最小化端到端的传输时延.实验结果表明,POR可以显著地降低平均端到端时延,提高数据包投递率,为数据传输提供实时性和可靠性保证.     

Real-time video streaming over multipath in multi-hop wireless networks

Given the limited wireless link throughput, high loss rate, and varying end-to-end delay, supporting video applications in multi-hop wireless networks becomes a challenging task. Path diversity exploits multiple routes for each session simultaneously, which achieves higher aggregated bandwidth and potentially decreases delay and packet loss. Unfortunately, for TCP-based video streaming, naive load splitting often results in inaccurate estimation of round trip time (RTT) and packet reordering. As a result, it can suffer from significant instability or even throughput reduction, which is also validated by our analysis and simulation in multi-hop wireless networks. To make real-time TCP-based streaming viable over multi-hop wireless networks, we propose a novel cross-layer design with a smart traffic split scheme, namely, multiple path retransmission (MPR). MPR differentiates the original data packets and the retransmitted packets and works with a novel QoS-aware multi-path routing protocol, QAOMDV, to distribute them separately. MPR does not suffer from the RTT underestimation and extra packet reordering, which ensures stable throughput improvement over single-path routing. Through extensive simulations, we further demonstrate that, as compared with state-of-the-art multi-path protocols, our MPR with QAOMDV noticeably enhances the TCP streaming throughput and reduces bandwidth fluctuation, with no obvious impact to fairness.     

A quality based routing protocol for wireless mesh networks

Wireless mesh networks can provide low-cost solutions for extending the reach of wireless access points by using multi-hop routing over a set of stationary wireless routers. The routing protocol for these networks may need to address quality considerations to meet the requirements of the user. In this paper, we present a quality based routing protocol for wireless mesh networks that tries to maximize the probability of successful transmissions while minimizing the end-to-end delay. The proposed routing protocol uses reactive route discoveries to collect key parameters from candidate routes to estimate the probability of success and delay of data packets transmitted over them. To achieve accurate route quality assessments, a new route quality metric is proposed that uses performance models of data packet transmissions as opposed to estimating route quality from the transmission of control packets, which have different transmission characteristics. These models are developed after careful evaluations of multi-hop wireless transmissions and validated by computer simulations. Relevant parameters that can be used to assess the route quality metric using these models are explained. Extensive performance evaluations of the proposed quality based routing protocol are presented and its benefits in comparison to some other known routing protocols are discussed.     

Data rate,path length and network contention trade-off in IEEE 802.11s mesh networks: A dynamic data rate selection approach

Most of the commercially available wireless routers are equipped with multi-rate support to adopt physical data rates based on the channel condition fluctuations. The recent studies in multi-rate support have shown that low data rates are more effective when the channel error rate is high. Because of the physical layer modulation and signal decoding issues, low data rates are sustainable for long transmission ranges. Therefore, for multi-hop mesh networks, low data rates may scale down the end-to-end path length towards the destination in terms of number of hops, resulting in less end-to-end forwarding delay. However, for a network with high traffic load, long transmission ranges may increase contention for channel access among the contending neighbors. This paper uses the diffusion approximation method of queuing analysis to study the trade-off among data rate, end-to-end path length and network contention in a multi-rate mesh network built over the IEEE 802.11s specifications. From the observations of the theoretical analysis, a distributed and localized rate adaptation scheme is proposed for IEEE 802.11s mesh networks, by augmenting the standard peer selection, channel access and forwarding protocols. The performance of the proposed rate adaptation protocol is evaluated and compared with existing rate adaptation protocols using simulation results.     

无线多跳网络的延迟性能分析

多跳无线网络技术具有广阔的应用前景。研究如何精确地分析、预知和保证多跳无线通信路线的端到端延迟性能非常重要。通过引入一个延迟违约概率的下限,扩展链路层等效带宽模型,并在不同的信道服务速率和无线信道条件下进行模拟。分析和仿真发现,与信道服务速率相比,最大多普勒频移对多跳延迟性能的影响更大。     

Stability–throughput tradeoff and routing in multi-hop wireless ad hoc networks

We study the throughput of multi-hop routes and stability of forwarding queues in a wireless ad-hoc network with random access channel. We focus on a wireless network with static nodes, such as community wireless networks. Our main result is characterization of stability condition and the end-to-end throughput using the balance rate. We also investigate the impact of routing on end-to-end throughput and stability of intermediate nodes. We show that (i) as long as the intermediate queues in the network are stable, the end-to-end throughput of a connection does not depend on the load on the intermediate nodes, (ii) we show that if the weight of a link originating from a node is set to the number of neighbors of this node, then shortest-path routing maximizes the minimum probability of end-to-end packet delivery in a network of weighted fair queues. Numerical results are given and support the results of the analysis. Finally, we perform extensive simulation and verify that the analytical results closely match the results obtained from simulations.     

Packet delay analysis on IEEE 802.11 DCF under finite load traffic in multi-hop ad hoc networks

In this paper, the average packet delay on IEEE 802.11 DCF under finite load traffic in multi-hop ad hoc networks is analyzed. We employ a Markov chain model to analyze the probability of transmission at each node in an arbitrary slot and derive the channel access delay. We model each node using an M/G/1 queue and derive the queueing delay. The model is extended from analyzing the single-hop average packet delay to evaluating the end-to-end packet delay in multi-hop ad hoc networks without assuming the traffic to be in a saturation state. To validate our analytic results, we have done extensive simulation. The analytic and the simulation results match very well.     

基于跨层竞争的同步MAC协议研究

在无线传感器网络(WSNs)中,基于跨层竞争的同步媒体接入控制(MAC)在一周期内可安排多个数据包的多跳传输,传统的协议在同一个数据窗口传输请求数据包和确认数据包,降低了数据窗口的多跳流量的建立,也降低了在多跳场景中的数据包传输率和传输时延性能.本文提出了基于新的基于跨层竞争的同步MAC(CLC-MAC)协议,CLC-MAC协议引用新的周期结构,且其包含两个独立窗口,并由该窗口分别传输数据请求包和确认包,即请求包在数据窗口传输,而确认包在休眠窗口传输.实验数据表明:与先锋路由帧MAC(PRMAC)协议相比,CLC-MAC协议的端到端传输时延和数据包传输率的性能均得到了提高.     

基于MANET的无线自组织网按需路由协议DSR的优化研究与实现

无线自组织网络由不需要任何基础设施的一组具有动态组网能力的节点组成,因此网络可以通过节点路由发现机制转发分组,并进行路由维护。这种网络适应了军事和商用中对网络和设备移动性的要求,而引起了人们的关注,并在20世纪90年代以后获得了广泛的研究和发展。文章对DSR(动态源路由协议)的路由发现过程进行了优化,并采用OPNET仿真软件对基于DSR协议的Ad Hoc网络的路由开销和时延等关键参数进行了仿真统计,分析了改进后的路由协议对网络质量的影响。     

Performance analysis of ad-hoc routing in heterogeneous clustered multi-hop wireless networks

This paper analyzes the performance of clustered decode-and-forward multi-hop relaying (CDFMR) wireless Rayleigh fading networks, and sheds light on their design principles for energy and spectral efficiency. The focus is on a general performance analysis (over all SNR range) of heterogeneous wireless networks with possibly different numbers of relays in clusters of various separations. For clustered multi-hop relaying systems, hop-by-hop routing is known as an efficient decentralized routing algorithm which selects the best relay node in each hop using local channel state information. In this article, we combine hop-by-hop routing and cooperative diversity in CDFMR systems, and we derive (i) a closed-form expression for the probability distribution of the end-to-end SNR at the destination node; (ii) the system symbol error rate (SER) performance for a wide class of modulation schemes; and (iii) exact analytical expressions for the system ergodic capacity, the outage probability and the achievable probability of the SNR (power) gain. We also provide simple analytical asymptotic expressions for SER and the outage probability in high SNR regime. Numerical results are provided to validate the correctness of the presented analyses.     

时延受限且能量高效的无线传感网络跨层路由

如何通过网络的多跳中继把传感器节点收集的信息快速、高效地传输至基站,是无线传感器网络的基本问题.研究发现,MAC(media access control)层的睡眠调度和无线信道的不规则性均会对路由协议的效率产生较大影响.虽然传统分层设计的网络协议有着模块化的优点,但各层之间的相互独立却导致网络的整体性能不能达到最优.此外,已有协议通常采用牺牲时延以提高能量效率的方法,会给时延敏感系统带来不能容忍的端到端时延.提出一种时延受限且能量高效的跨层路由协议(delay-constrained and energy-efficient cross-layer routing,简称DECR),该协议在做出路由决定时考虑MAC层以及链路层的相关信息,其目标是在将端到端时延控制到低于预定上界的前提下最优化节点的能量效率.理论分析和实验结果表明,所提出的跨层路由协议具有较好的性能.     

Modelling and performance analysis of multi-hop ad hoc networks

Mobile ad hoc networks are becoming very attractive and useful in many kinds of communication and networking applications. Due to the advantage of numerical analysis, analytical modelling formalisms, such as stochastic Petri nets, queuing networks and stochastic process algebra have been widely used for performance analysis of communication systems. To the best of our knowledge, there is no previous analytical study that analyses the performance of multi-hop ad hoc networks, where mobile nodes move according to a random mobility model in terms of the end-to-end delay and throughput. This work presents a novel analytical framework developed using stochastic reward nets for modelling and analysis of multi-hop ad hoc networks, based on the IEEE 802.11 DCF MAC protocol, where mobile nodes move according to the random waypoint mobility model. The proposed framework is used to analyse the performance of multi-hop ad hoc networks as a function of network parameters such as the transmission range, carrier sensing range, interference range, number of nodes, network area size, packet size, and packet generation rate. The proposed framework is organized into several models to break up the complexity of modelling the complete network, and make it easier to analyse each model as required. The framework is based on the idea of decomposition and fixed point iteration of stochastic reward nets. The proposed models are validated using extensive simulations.     

Load-balanced AP association in multi-hop wireless mesh networks

Wireless mesh networks (WMNs) provide high-bandwidth wireless access, which makes it capable for multimedia services. A user in a WMN may be covered by multiple APs, while it should be associated with only one to access the Internet. Conventional IEEE 802.11 user-AP association mechanism for WLANs employs signal strength as the sole metric. However, this may lead to network congestion and performance degradation in multi-hop networks such as WMNs, especially for multimedia services that require a large bandwidth and a low latency. Thus AP association in WMNs becomes an important research issue. In this paper we propose a novel AP association approach LBAA, taking AP’s load-balancing, WMN’s multi-hop characteristic, and user’s RSSI into consideration. We first propose a centralized algorithm and then extend it to a distributed one, with the latter one more practical and convenient for deployment. Network throughput and max–min user fairness are improved by LBAA. Performance evaluation demonstrating the benefits of our approach is given through a series of experiments in terms of collision probability, access bandwidth, end-to-end throughput, and average RSSI.