A genetic approach to joint routing and link scheduling for wireless mesh networks

Wireless mesh networks are an attractive technology for providing broadband connectivity to mobile clients who are just on the edge of wired networks, and also for building self-organized networks in places where wired infrastructures are not available or not deemed to be worth deploying. This paper investigates the joint link scheduling and routing issues involved in the delivery of a given backlog from any node of a wireless mesh network towards a specific node (which acts as a gateway), within a given deadline. Scheduling and routing are assumed to be aware of the physical interference among nodes, which is modeled in the paper by means of a signal-to-interference ratio. Firstly, we present a theoretical model which allows us to formulate the task of deriving joint routing and scheduling as an integer linear programming problem. Secondly, since the problem cannot be dealt with using exact methods, we propose and use a technique based on genetic algorithms. To the best of our knowledge, these algorithms have never been used before for working out these kinds of optimization problems in a wireless mesh environment. We show that our technique is suitable for this purpose as it provides a good trade-off between fast computation and the overall goodness of the solution found. Our experience has in fact shown that genetic algorithms would seem to be quite promising for solving more complex models than the one dealt with in this paper, such as those including multiple flows and multi-radio multi-channels.     

无线Mesh网络中基于链路负载估算的拥塞控制策略

针对无线Mesh网络的网络特性,提出了一种基于链路负载估算的拥塞控制策略LLECC。LLECC算法计算有效链路带宽和链路负载估算确定RED算法中的调整因子,通过调整因子调整RED算法中的参数从而实现动态的对无线网络拥塞控制。详细讨论了LLECC算法的实现过程和相关参数的计算方法,通过仿真分析验证了该算法对无线Mesh网络性能的提高。     

Call admission control with active link protection for opportunistic wireless networks

In this paper we suggest a call admission control (CAC) algorithm for high speed downlink packet access HSDPA UMTS systems. In this algorithm the user requesting admission is gradually admitted into the system. This is done by setting a back-off factor limiting the new user’s throughput. The back-off factor is gradually decreased leading to a gradual increase in the new user’s throughput until it is fully integrated into the system. The back-off factor works on protecting the active links in a way that their rates do not drop below a guaranteed quality of service (QoS) level.     

Delay minimization and priority scheduling in wireless mesh networks

Wireless mesh networks (WMNs) have emerged as a significant technology for applications because of its advantage of multi-radio and multi-channel which makes it perform better than wireless LANs. Furthermore, quality-of-service (QoS) support can be achieved by some distinguished ways in WMN. In this paper, QoS requirements are recorded by traffic profile, QoS constraints are formulated as delay time of transmitting all the requested data flows in the network. Multi-commodity flow technologies are applied for handling this issue. After minimizing the delay of the network by the assistance of multi-commodity-flow techniques and resource contention graph, we use effective channel assignment algorithm to schedule the data flows under the QoS constraints. Our evaluation indicates that our technologies successfully route flows under their special QoS requirements with different priority.     

Towards benchmarking routing protocols in wireless mesh networks

Wireless mesh networks (WMNs) establish a new, quick and low-cost alternative to provide communications when deploying a fixed infrastructure that could result prohibitive in terms of either time or money. During last years, the specification of multi-hop routing protocols for WMNs has been promoted, leading to their recent exploitation in commercial solutions. The selection of routing protocols for integration in WMNs requires the evaluation, comparison and ranking of eligible candidates according to a representative set of meaningful measures. In this context, the development of suitable experimental techniques to balance different features of each protocol is an essential requirement. This paper copes with this challenging task by proposing a benchmarking methodology to experimentally evaluate and compare the behaviour of these protocols. The feasibility of the proposed approach is illustrated through a simple but real (non-simulated) case study and reflects to what extent this methodology can be useful in increasing our knowledge on how real WMNs behave in practice.     

Characterizing the capacity gain of stream control scheduling in MIMO wireless mesh networks

Stream control (SC) has recently attracted attentions in the research of multiple input multiple output (MIMO) wireless networks as a potential way to improve network capacity. However, inappropriate use of SC may significantly degrade network capacity as well. In this paper, we provide the first formal study on SC scheduling in MIMO wireless mesh networks (WMNs). We derive the theoretical upper bound on network capacity gain of SC scheduling. We also provide an efficient scheduling algorithm and show that its achieved network capacity gain is close to its theoretical upper bound. Moreover, we point out the poor performance of a previous SC scheduling algorithm SCMA under the general settings of WMNs. This formal characterization provides a deeper understanding of steam control scheduling in MIMO WMNs. Copyright © 2008 John Wiley & Sons, Ltd.     

MrFair: Misbehavior-resistant fair scheduling in wireless mesh networks

It is a critical issue to ensure that nodes and/or flows have fair access to the network bandwidth in wireless mesh networks (WMNs). However, current WMNs based on IEEE 802.11 exhibit severe unfairness. Several scheduling schemes have been proposed to ensure fairness in WMNs. Unfortunately, all of them implicitly trust nodes in the network, and thus are vulnerable to the misbehavior of nodes participating in scheduling. In this paper, we address the threats to fair scheduling in WMNs resulting from node misbehavior and present a generic verification framework to detect such misbehavior. Moreover, we develop two verification schemes based on this framework for distributed and centralized authentication environments, respectively. We validate our approach by extending an existing fair scheduling scheme and evaluating it through simulation. The results show that our approach improves misbehavior detection with light performance overhead.     

Combined admission control and scheduling in multi-service networks

Providing the required metrics for different service respectively is a basic characteristic in multi-service networks. The different service can be accessed and forwarded differently to provide the different transmission performance. The state information between admission control and scheduling can be exchanged each other by the defined correlation coefficient to adjust the flow distribution in progress. The priority queue length measured by scheduler implicitly can describe the priority flows load. And the fair rate can describe the non-priority flows load. Different admission decision will be made according to the state of scheduler to assure the time-delay upper threshold for the priority flows under heavy load and the fairness for elastic flows in light load, respectively. The stability condition was conduced and proved. Simulation results show the policy can ensure both the delay for the priority flows and the minimal throughput for non-priority flows.     

Call admission control in wireless multimedia networks

Call admission control (CAC) is a mechanism used in networks to administer quality of service (QoS). Whereas the CAC problem in time-division multiple access (TDMA)-based cellular networks is simply related to the number of physical channels available in the network, it is strongly related to the physical layer performance in code-division multiple access (CDMA) networks since the multi-access interference in them is a function of the number of users and is a limiting factor in ensuring QoS. In this article, the CAC issues in multimedia DS-CDMA systems are reviewed by illustrating the basic principles underlying various schemes that have been proposed progressively from the simplest to the complex. The article also introduces SIR as a measure of QoS and describes the relatively simple schemes to administer CAC. The expression for SIR resulting from linear minimum mean-squared error processing is also presented. This article illustrates how CAC for multiple class service can be casted into an optimality framework and then discuss the recent work addressing self-similar multiple access interference.     

Stability and sensitivity for congestion control in wireless mesh networks with time varying link capacities

A critical challenge for wireless mesh networks is the design of efficient transport protocols that provide high bandwidth utilization and desired fairness in the multi-hop, wireless environment. While extensive efforts have been devoted to providing optimization based, distributed congestion control schemes for efficient bandwidth utilization and fair allocation in both wireline and wireless networks, a common assumption therein is fixed link capacities. This unfortunately will limit the application scope in wireless mesh networks where channels are ever changing. In this paper, we explicitly model link capacities to be time varying and investigate congestion control problems in multi-hop wireless networks. In particular we propose a primal–dual congestion control algorithm which is proved to be trajectory stable in the absence of feedback delay. Different from system stability around a single equilibrium point, trajectory stability guarantees the system is stable around a time varying reference trajectory. Moreover, we obtain sufficient conditions for the scheme to be locally stable in the presence of delay. Our key technique is to model time variations of capacities as perturbations to a constant link. Furthermore, to study the robustness of the algorithm against capacity variations, we investigate the sensitivity of the control scheme and through simulations to study the tradeoff between stability and sensitivity.     

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.     

Probabilistic call admission control in wireless multiservice networks

A new probabilistic call admission control scheme is proposed for multiservice wireless networks. The new scheme gradually suppresses the admission rate of the new calls and of the calls of each service class (SC) supported considering their priorities independently. The scheme is examined both for a single SC and for multiple SCs under general conditions. The analysis employs Markov chain theory and yields analytical expressions for the call blocking probabilities. The proposed analytical method was validated via simulations employing different distributions for the channel holding time; the simulations demonstrated the accuracy of the proposed framework.     

无线网络链路传输调度策略研究综述

无线网络链路传输调度策略确定各个时间槽内进行传输的链路集合,这些链路互不冲突,能够同时进行传输.对于当前的无线网络链路传输调度策略建立一个全面的了解有助于对无线网络的性能做出客观评估,并且成为网络设计的基本依据之一.文章总结了当前主流的无线网络链路传输调度策略,并且给出了这一领域的后续发展趋势和主要挑战.在具体的介绍过程中,本文重点介绍了基于吞吐量的调度策略、基于链路服务质量的调度策略、基于应用的服务策略,以及应对于在线视频传输的策略.在后续挑战的介绍中,文章主要归纳了基于应用的调度策略的实施前提要求和挑战.     

Cross-layer adaptive control for wireless mesh networks

This paper investigates optimal routing and adaptive scheduling in a wireless mesh network composed of mesh clients and mesh routers. The mesh clients are power constrained mobile nodes with relatively little knowledge of the overall network topology. The mesh routers are stationary wireless nodes with higher transmission rates and more capabilities. We develop a notion of instantaneous capacity regions, and construct algorithms for multi-hop routing and transmission scheduling that achieve network stability and fairness with respect to these regions. The algorithms are shown to operate under arbitrary client mobility models (including non-ergodic models with non-repeatable events), and provide analytical delay guarantees that are independent of the timescales of the mobility process. Our control strategies apply techniques of backpressure, shortest path routing, and Lyapunov optimization.     

Buffer occupancy and link state opportunistic routing for wireless mesh networks

Wireless Networks - Providing a high level of Quality of Service is essential for future wireless networks. This article presents a new multihop wireless routing protocol that opportunistically...     

Iterative power control based admission control for wireless networks

This paper studies transmission power control algorithms for cellular networks. One of the challenges in commonly used iterative mechanisms to achieve this is to identify if the iteration will converge since convergence indicates feasibility of transmit power allocation under prevailing network conditions. The convergence criterion should also be simple to calculate given the time constraints in a real-time wireless network. Towards this goal, this paper derives simple sufficient conditions for convergence of an iterative power control algorithm using existing bounds from matrix theory. With the help of suitable numerical examples, it is shown that the allocated transmit powers of the nodes converge when sufficient conditions are satisfied, and diverge when they are not satisfied. This forms the basis for an efficient link data-rate based admission control mechanism for wireless networks. The mechanism considers parameters such as signal strength requirement, link datarate requirement, and number of nodes in the system. Simulation based analysis shows that existing links are able to maintain their desired datarates despite the addition of new wireless links.     

Congestion-aware fair rate control in wireless mesh networks

This paper presents a fair and efficient rate control mechanism, referred to as congestion-aware fair rate control (CFRC), for IEEE 802.11s-based wireless mesh networks. Existing mechanisms usually concentrate on achieving fairness and achieve a poor throughput. This mainly happens due to the synchronous rate reduction of neighboring links or nodes of a congested node without considering whether they actually share the same bottleneck or not. Furthermore, the achievable throughput depends on the network load, and an efficient fair rate is achievable when the network load is balanced. Therefore, existing mechanisms usually achieve a fair rate determined by the mostly loaded network region. CFRC uses an AIMD-based rate control mechanism which enforces a rate-bound to the links that use the same bottleneck. To achieve the maximum achievable rate, it balances the network load in conjunction with the routing mechanism. Furthermore, it allows the intra-mesh flows to utilize the network capacity, and the intra-mesh flows achieve a high throughput. Finally, we investigate the performance of CFRC using simulation in ns-2, and the results demonstrate that CFRC increases the throughput with the desired fairness.     

Real-time CBR traffic scheduling in IEEE 802.16-based wireless mesh networks

This paper studies packet transmission scheduling for real-time constant-bit-rate (CBR) traffic in IEEE 802.16-based wireless mesh networks. We first formulate and solve the scheduling problem as a binary linear programming problem. The computational complexity of the optimum scheduling solution may prevent it from being implemented in practice. We then propose a heuristic scheme, namely bottleneck first scheduling scheme, where scheduling decisions at stations (base station or subscriber stations) with higher traffic loads are done before those at stations with lower traffic loads. At each station, scheduling decisions for CBR packets with more hops to their destinations are done first. Numerical results show that the proposed scheduling scheme achieves the same capacity as the optimal one while obtaining satisfactory delay performance. Dongmei Zhao received the Ph.D. degree in Electrical and Computer Engineering from the University of Waterloo, Waterloo, Ontario, Canada in June 2002. Since July 2002 she has been with the Department of Electrical and Computer Engineering, McMaster University, Hamilton, Ontario, Canada where she is an assistant professor. Dr. Zhao’s research interests include modeling and performance analysis, quality-of-service provisioning, access control and admission control in wireless networks. Dr. Zhao is a member of the IEEE and a registered Professional Engineer of Ontario. Jun Zou received the B.S. and M. Eng. Degrees from Tianjin University, China in 1999 and 2002, respectively. He worked at Siemens Communication Networks Ltd., Beijing from 2002 to 2004. Currently, he is a Ph.D. student at McMaster University, Canada. His research interests include wireless networking, routing protocols, architecture of next generation networks, network security and their applications in telecommunication industry.     

Heuristic approach for broadcast scheduling,problem in wireless mesh networks

Disasters can be natural and human-initiated events that interrupt the usual functioning of people on a large scale. Region where disasters have occurred causes hazards to the public of that area and to the rescue teams. Disaster causes the damage to the communication network infrastructure also. Once the communication infrastructure is damaged, it is very difficult to the rescue teams to actively involve in relief operation. To handle these hazards, different wireless technologies can be initiated in the area of disaster. This paper discusses the innovative wireless technology for disaster management. Specifically, issues related to the broadcast scheduling problem in wireless mesh network is deployed efficiently during disaster relief are discussed. A domain specific memetic algorithm is proposed for solving the optimum time division multiple access broadcast scheduling problem in wireless mesh networks. The aim is to increase the total number of transmissions in optimized time slot with high channel utilization in a less computation time. Simulation results showed that our memetic algorithm approach to this problem achieves 100% convergence to solutions within reduced computation time while compared to recent efficient algorithms. The results were compared with several heuristic and non-heuristic algorithms for broadcast scheduling problem.     

Efficient delay based scheduling with fairness in multi-hop wireless mesh networks

Some scheduling algorithms have been designed to improve the performance of multi-hop wireless mesh networks (WMNs) recently. However the end-to-end delay is seldom considered as the complexity of multi-hop topology and open wireless shared channel. This article proposes an efficient delay based scheduling algorithm with the concept of buffer-data- hops. Considering the demand satisfaction factor (DSF), the proposed algorithm can also achieve a good fairness performance. Moreover, with the interference-based network model, the scheduling algorithm can maximize the spatial reuse, compared to those graph-based scheduling algorithms. Detailed theoretical analysis shows that the algorithm can minimize the end-to-end delay and make a fair scheduling to all the links.