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 optimization for CDMA/TDD wireless mesh networks

This paper proposes a new cross‐layer optimization algorithm for wireless mesh networks (WMNs). CDMA/TDD (code division multiple access/time division duplex) is utilized and a couple of TDD timeslot scheduling schemes are proposed for the mesh network backbone. Cross‐layer optimization involves simultaneous consideration of the signal to interference‐plus‐noise ratio (SINR) at the physical layer, traffic load estimation and allocation at medium access control (MAC) layer, and routing decision at the network layer. Adaptive antennas are utilized by the wireless mesh routers to take advantage of directional beamforming. The optimization formulation is subject to routing constraints and can be solved by general nonlinear optimization techniques. Comparisons are made with respect to the classic shortest‐path routing algorithm in the network layer. The results reveal that the average end‐to‐end successful packet rate (SPR) can be significantly improved by the cross‐layer approach. The corresponding optimized routing decisions are able to reduce the traffic congestion. Copyright © 2010 John Wiley & Sons, Ltd.     

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.     

Throughput-range tradeoff of wireless mesh backhaul networks

Wireless backhaul communication is expected to play a significant role in providing the necessary backhaul resources for future high-rate wireless networks. Mesh networking, in which information is routed from source to destination over multiple wireless links, has potential advantages over traditional single-hop networking, especially for backhaul communication. We develop a linear programming framework for determining optimum routing and scheduling of flows that maximizes throughput in a wireless mesh network and accounts for the effect of interference and variable-rate transmission. We then apply this framework to examine the throughput and range capabilities for providing wireless backhaul to a hexagonal grid of base stations, for both single-hop and multihop transmissions for various network scenarios. We then discuss the application of mesh networking for load balancing of wired backhaul traffic under unequal access traffic conditions. Numerical results show a significant benefit for mesh networking under unbalanced loading.     

Cross-Layer Optimization of Multichannel Multiantenna WMNs

Use of multiple channels can significantly improve the throughput of wireless mesh networks (WMNs). Additionally, recent advances in radio technology have made it possible to realize software-defined radio (SDR), which is capable of switching from one channel to another dynamically. On the other hand, equipping wireless nodes with multiple antennas creates great potential for throughput improvement via interference suppression, spatial multiplexing, and spatial division multiple access techniques. In this paper, we investigate the joint optimization of routing and scheduling in multichannel WMNs, where nodes are equipped with a single SDR and multiple antenna elements. We analyze achievable throughput of these networks under four different multiantenna modes: single user single stream, single user multi stream, multi user single stream, and multi user multi stream, each mode integrates different combinations of multiantenna techniques. We mathematically model scheduling and interference constraints and formulate joint routing and scheduling optimization problem with the objective of maximizing the throughput by minimizing network schedule time such that traffic demands for a set of sessions are satisfied. A column generation-based decomposition approach is proposed to solve the problem. Simulation results are presented to evaluate the impact of number of antennas, number of channels, and number of sessions on the schedule time for the four proposed modes.     

基于动态规划法的无线Mesh网络QoS路由算法和性能评价

该文针对时延敏感的多媒体业务吞吐率和传输可靠性的考虑,在无线Mesh网络中,引入动态规划和跨层设计方法设计QoS路由算法。在假设的网络模型上,提出了一个新的基于MAC层信息的综合凸规划路由准则,以及基于此实现的路由算法CPRMQS,详细给出了利用动态规划法解决路由优化问题的算法流程和样例分析。最后通过仿真验证了该算法的可行性,并给出了基于DSR扩展协议的性能评价,其中包括吞吐率和延时等性能。     

A Lagrangian-Relaxation Based Network Profit Optimization For Mesh SONET-Over-WDM Networks

In Wavelength Division Multiplexing (WDM) networks, the huge capacity of wavelength channels is generally much larger than the bandwidth requirement of individual traffic streams from network users. Traffic grooming techniques aggregate low-bandwidth traffic streams onto high-bandwidth wavelength channels. In this paper, we study the optimization problem of grooming the static traffic in mesh Synchronous Optical Network (SONET) over WDM networks. The problem is formulated as a constrained integer linear programming problem and an innovative optimization objective is developed as network profit optimization. The routing cost in the SONET and WDM layers as well as the revenue generated by accepting SONET traffic demands are modelled. Through the optimization process, SONET traffic demands will be selectively accepted based on the profit (i.e., the excess of revenue over network cost) they generate. Consiering the complexity of the network optimization problem, a decomposition approach using Lagrangian relaxation is proposed. The overall relaxed dual problem is decomposed into routing and wavelength assignment and SONET traffic routing sub-problems. The subgradient approach is used to optimize the derived dual function by updating the Lagrange multipliers. To generate a feasible network routing scheme, a heuristic algorithm is proposed based on the dual solution. A systematic approach to obtain theoretical performance bounds is presented for an arbitrary topology mesh network. This is the first time that such theoretical performance bounds are obtained for SONET traffic grooming in mesh topology networks. The optimization results of sample networks indicate that the roposed algorithm achieves good sub-optimal solutions. Finally, the influence of various network parameters is studied.     

Topology control for multi-channel multi-radio wireless mesh networks using directional antennas

Directional antennas are widely used technologies for reducing signal interference and increasing spatial reuse. In this paper, we propose a topology control method for multi-channel multi-radio wireless mesh networks that use directional antennas. We are given a set of mesh routers installed in a region and some of them are gateway nodes that are connected to the Internet via wired lines. Each router has a traffic demand (Internet access traffic) generated from the end-users. The problem is how to adjust antenna orientations of radios and assign channels to them to construct a logical network topology, such that the minimum delivery ratio of traffic demands of routers is maximized. We first formulate the problem to an equivalent optimization problem with a clearer measurable metric, which is to minimize the largest interfering traffic of links in the network. We then propose a three-step solution to solve the problem. Firstly, we construct a set of routing trees, with the objective to balance the traffic among tree links. Secondly, we assign the radios of a node to the links it needs to serve, such that the total traffic load of the links that each radio serves is as balanced as possible. Thirdly, we do a fine-grained adjustment of antenna orientations and assign channels to them, such that the transmission area of each antenna will cover all the links it serves and the largest interfering traffic of links is minimized.     

Adaptive Optimization-based Routing in Wireless Mesh Networks

Routing is a critical component in wireless mesh networks. The inherent shared-medium nature of the wireless mesh networks, however, poses fundamental challenges to the design of effective routing policies that are optimal with respect to the resource utilization. Node churns and traffic fluctuations exacerbate such a problem. In this paper, we propose a novel adaptive routing algorithm for multiple subscribers in wireless mesh networks. We view a mesh network with multiple nodes as an entity that optimizes some global utility function constrained by the underlying MAC layer interference. By solving the optimization problem, the network is driven to an efficient operating point with a certain routing policies for each node. We then use this operating point information to adaptively find better paths, which is able to gear the network towards optimal routing. Further, we take the fluctuations of the network into consideration and thus render our algorithm more robust for a variety of network situations. Simulations demonstrate the efficiency and efficacy of our algorithm.     

Incremental demand rerouting: optimization models and algorithms

This investigation addresses an important and difficult combinatorial optimization problem in the design and management of telecommunication systems known as the path assignment problem. The path assignment problem is specified by a set of demands on a network with given link capacities. Each demand must be assigned to exactly one routing path in such a way that the total amount of traffic routed over any link does not exceed that link’s capacity. Given a network and a path assignment, the problem of interest is to maximize the available bandwidth (throughput) for a new demand. Network managers are concerned with the quality of service provided by their networks, and so they are reluctant to make major changes to an operating network that may inadvertently result in service disruptions for numerous clients simultaneously. Therefore, the objective of this investigation is to develop and test optimization models and algorithms that produce a series of throughput-improving modifications to the original path assignment. This allows network managers to implement the improved routing in stages with minimal changes to the overall routing plan between any two consecutive stages. Although the procedure may only reroute a few demands at each stage, the routing after the last stage should be as close as possible to an optimal routing. That is, it must maximize the throughput for the new demand. We present integer programming models and associated solution algorithms to maximize the throughput with a sequence of incremental path modifications. The algorithms were implemented with the AMPL modeling language and the CPLEX ILP solver, and tested on a family of five different data sets based on a European network widely studied in the literature. Empirical results show that the incremental approach finds near-optimal results within reasonable limits on CPU time.     

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     

Estimating the channel capacity of multi-hop IEEE 802.11 wireless networks

In IEEE 802.11 wireless networks, the residual capacity of the wireless links should be accurately estimated to realize advanced network services such as flow admission control or load balancing. In this paper, we propose an algorithm that estimates the packet delivery failure probability by collecting transmission statistics from nearby nodes, and by using a basic collision detection mechanism. This probability is then used in an analytical model to calculate the maximum allowable traffic needed to reach the saturation condition. We show by simulations that estimation error is within 0.5–5.0%, which is significantly lower than the best performance of prior estimation methods. We also demonstrate that the flow admission control is successfully achieved in a realistic wireless network scenario by the help of accurate link residual bandwidth estimation, where the unsatisfied traffic demand remain bounded at a negligibly low level. A routing algorithm that finds max–min residual bandwidth path between source and destination nodes is also implemented, and simulation results show that the network throughput achieved by this algorithm significantly exceeds that of other popular mesh routing protocols. Finally, we provide test results from the real implementation of our algorithm on 802.11 wireless equipment, which are consistent with the simulations.     

Modeling throughput gain of network coding in multi-channel multi-radio wireless ad hoc networks

In this paper, we model the network throughput gains of two types of wireless network coding (NC) schemes, including the conventional NC and the analog NC schemes, over the traditional non-NC transmission scheduling schemes in multihop, multi-channel, and multi-radio wireless ad hoc networks. In particular, we first show that the network throughput gains of the conventional NC and analog NC are (2n)/(2n-1) and n/(n-1), respectively, for the n-way relay networks where n ges 2. Second, we propose an analytical framework for deriving the network throughput gain of the wireless NC schemes over general wireless network topologies. By solving the problem of maximizing the network throughput subject to the fairness requirements under our proposed framework, we quantitatively analyze the network throughput gains of these two types of wireless NC schemes for a variety of wireless ad hoc network topologies with different routing strategies. Finally, we develop a heuristic joint link scheduling, channel assignment, and routing algorithm that aims at approaching the optimal solution to the optimization problem under our proposed framework.     

分布式多网关无线mesh网公平协作路由算法

现有的协作路由协议不能公平地分配无线网络资源,无法满足网络最小流的吞吐量需求。将多并发流的协作路由问题形式化成一个最大化网络整体效用的凸优化问题,并基于对偶分解和子梯度,提出一种分布式的多网关无线mesh网公平协作路由算法FCRMG。实验结果表明,与基于期望传输时间的非协作路由和基于竞争感知的协作路由相比,FCRMG算法在保证网络吞吐量的前提下,能显著提高最小业务流的吞吐量。     

Evaluating a cross-layer approach for routing in Wireless Mesh Networks

Routing in Wireless Mesh Networks is challenging due to the unreliable characteristics of the wireless medium. Traditional routing paradigms are not able to propose an efficient solution to this problem. Further, Gupta et al. demonstrated that the average throughput capacity per node of a wireless multi-hop network decreases as 1/n, where n is the number of nodes in the network. Recent studies have shown that a cross-layer approach is a promising solution to get closer to the theoretic throughput capacity bound. Cross-layer solutions have been already proposed either for specific TDMA/CDMA networks or for power-efficient routing protocols. These proposals are strongly MAC dependent, or suffer from targeting a steady state offering the best trade-off performance. In this paper, the problem we tackle in a more general context, disregarding the specific MAC and Physical layers technologies, can be formulated as follows: How to design a routing algorithm able to increase the average throughput capacity experienced by Wireless Mesh Networks? Starting from a theoretic result, we analyze the gain that a cross-layer approach can deliver, the metrics suitable to improve throughput capacity, and the power control policy that reduces interference. We take a MAC independent approach, focusing on the general characteristics of wireless links, targeting the improvement of throughput capacity in Wireless Mesh Networks. Our proposal performs path selection and power optimization based on three metrics, namely physical transmission rate, interference, and packet error rate. Performances are thoroughly analyzed and evaluated by extensive simulations, with both TCP and UDP traffic, and compared to other multi-hop routing protocols. For both kind of traffic, the simple heuristic we propose here allows to double the average throughput the network is able to route.     

Cross-Layer Optimization of MAC and Network Coding in Wireless Queueing Tandem Networks

In wireless networks, throughput optimization is an essential performance objective that cannot be adequately characterized by a single criterion (such as the minimum transmitted or sum-delivered throughput) and should be specified over all source-destination pairs as a rate region. For a simple and yet fundamental model of tandem networks, a cross-layer optimization framework is formulated to derive the maximum throughput region for saturated multicast traffic. The contents of network flows are specified through network coding (or plain routing) in network layer and the throughput rates are jointly optimized in medium access control layer over fixed set of conflict-free transmission schedules (or optimized over transmission probabilities in random access). If the network model incorporates bursty sources and allows packet queues to empty, the objective is to specify the stability region as the set of maximum throughput rates that can be sustained with finite packet delay. Dynamic queue management strategies are used to expand the stability region toward the maximum throughput region. Network coding improves throughput rates over plain routing and achieves the largest gains for broadcast communication and intermediate network sizes. Throughput optimization imposes fundamental tradeoffs with transmission and processing energy costs such that the throughput-optimal operation is not necessarily energy efficient.     

A QoS aware joint design for wireless mesh networks

Wireless mesh networks (WMNs) provide Internet access to remote areas and wireless connections on a metropolitan scale. In this paper, we focus on the problem of improving the gateway throughput in WMNs while achieving fairness and supporting quality-of-service (QoS) differentiation for end-users. To address this problem, we propose a new distributed dynamic traffic scheduling algorithm that supports different QoS requirements from different users. We also develop a joint weight-aware channel assignment and minimum expected delay routing mechanism. Simulation results demonstrate the performance of the proposed work in terms of the achieved throughput and minimized packet loss ratio and delay.     

Channel Assignment and Link Scheduling in Multi-Radio Multi-Channel Wireless Mesh Networks

Capacity limitation is one of the fundamental issues in wireless mesh networks. This paper addresses capacity improvement issues in multi-radio multi-channel wireless mesh networks. Our objective is to find both dynamic and static channel assignments and corresponding link schedules that maximize the network capacity. We focus on determining the highest gain we can achieve from increasing the number of radios and channels under certain traffic demands. We consider two different types of traffic demands. One is expressed in the form of data size vector, and the other is in the form of data rate vector. For the first type of traffic demand, our objective is to minimize the number of time slots to transport all the data. For the second type of traffic demand, our objective is to satisfy the bandwidth requirement as much as possible. We perform a trade-off analysis between network performance and hardware cost based on the number of radios and channels in different topologies. This work provides valuable insights for wireless mesh network designers during network planning and deployment.     

Gateway Placement for Throughput Optimization in Wireless Mesh Networks

In this paper, we address the problem of gateway placement for throughput optimization in multi-hop wireless mesh networks. Assume that each mesh node in the mesh network has a traffic demand. Given the number of gateways to be deployed (denoted by k) and the interference model in the network, we study where to place exactly k gateways in the mesh network such that the total throughput is maximized while it also ensures a certain fairness among all mesh nodes. We propose a novel grid-based gateway deployment method using a cross-layer throughput optimization, and prove that the achieved throughput by our method is a constant times of the optimal. Simulation results demonstrate that our method can effectively exploit the available resources and perform much better than random and fixed deployment methods. In addition, the proposed method can also be extended to work with multi-channel and multi-radio mesh networks under different interference models.     

Network-coding-based scheduling and routing schemes for service-oriented wireless mesh networks - [Service-oriented broadband wireless network architecture]

Service-oriented wireless mesh networks have recently been receiving intensive attention as a pivotal component to implement the concept of ubiquitous computing due to their easy and cost-effective deployment. To deliver a variety of services to subscriber stations, a large volume of traffic is exchanged via mesh routers in the mesh backbone network. One of the critical problems in service-oriented wireless mesh networks is to improve the network throughput. Wireless network coding is a key technology to improve network throughput in multihop wireless networks since it can exploit not only the broadcast nature of the wireless channel, but also the native physical-layer coding ability by mixing simultaneously arriving radio waves at relay nodes. We first analyze the throughput improvement obtained by wireless network coding schemes in wireless mesh networks. Then we develop a heuristic joint link scheduling, channel assignment, and routing algorithm that can improve the network throughput for service-oriented wireless mesh networks. Our extensive simulations show that wireless network coding schemes can improve network throughput by 34 percent.