Joint channel assignment and routing in multiradio multichannel wireless mesh networks with directional antennas

The aggregate capacity of a wireless mesh network (WMN) is severely affected by interflow interference. In this paper, we propose a network architecture that incorporates directional antennas with multiple orthogonal channels to effectively enhance the performance of WMNs. First, a sectored connectivity graph is introduced to model multiradio multichannel WMNs with directional antennas. Next we formulate the topology design, directional interface assignment, channel allocation, and routing mathematically as a mixed integer linear programming problem. This problem is solved using an iterated local search algorithm to obtain optimized network resource allocation. Simulation results indicate that the proposed architecture can achieve higher packet delivery ratio while providing better network fairness. Copyright © 2014 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.     

Asymptotic Capacity of Infrastructure Wireless Mesh Networks

An infrastructure wireless mesh network (WMN) is a hierarchical network consisting of mesh clients, mesh routers and gateways. Mesh routers constitute a wireless mesh backbone, to which mesh clients are connected as a star topology, and gateways are chosen among mesh routers providing Internet access. In this paper, the throughput capacity of infrastructure WMNs is studied. For such a network with Nc randomly distributed mesh clients, Nr regularly placed mesh routers and Ng gateways, assuming that each mesh router can transmit at W bits/s, the per-client throughput capacity has been derived as a function of Nc , Nr , Ng and W . The result illustrates that, in order to achieve high capacity performance, the number of mesh routers and the number of gateways must be properly chosen. It also reveals that an infrastructure WMN can achieve the same asymptotic throughput capacity as that of a hybrid ad hoc network by choosing only a small number of mesh routers as gateways. This property makes WMNs a very promising solution for future wireless networking.     

Angular MAC: a framework for directional antennas in wireless mesh networks

Capacity of wireless mesh networks can be enhanced through the use of smart directional antennas, which not only enable nodes to have high quality links but also increase network throughput by allowing spatial reuse. This paper proposes a new MAC protocol and framework, called Angular MAC (ANMAC) that enables directional antennas in wireless mesh networks. The protocols and algorithms of the ANMAC framework fit well with the requirements of mesh networks such as neighbor discovery and self-configuration, while providing significant throughput enhancements. The throughput enhancements are proven by comprehensive simulations with realistic antenna patterns, including performance comparisons of ANMAC with directional schemes using a similar node architecture and omni 802.11. Also, the effect of contention window size is analyzed and a dynamic contention window adaptation algorithm is proposed to maximize the throughput of the self-configuring mesh network, by taking instantaneous traffic conditions into account.     

Mitigating the gateway bottleneck via transparent cooperative caching in wireless mesh networks

Wireless mesh networks (WMNs) have been proposed to provide cheap, easily deployable and robust Internet access. The dominant Internet-access traffic from clients causes a congestion bottleneck around the gateway, which can significantly limit the throughput of the WMN clients in accessing the Internet. In this paper, we present MeshCache, a transparent caching system for WMNs that exploits the locality in client Internet-access traffic to mitigate the bottleneck effect at the gateway, thereby improving client-perceived performance. MeshCache leverages the fact that a WMN typically spans a small geographic area and hence mesh routers are easily over-provisioned with CPU, memory, and disk storage, and extends the individual wireless mesh routers in a WMN with built-in content caching functionality. It then performs cooperative caching among the wireless mesh routers.We explore two architecture designs for MeshCache: (1) caching at every client access mesh router upon file download, and (2) caching at each mesh router along the route the Internet-access traffic travels, which requires breaking a single end-to-end transport connection into multiple single-hop transport connections along the route. We also leverage the abundant research results from cooperative web caching in the Internet in designing cache selection protocols for efficiently locating caches containing data objects for these two architectures. We further compare these two MeshCache designs with caching at the gateway router only.Through extensive simulations and evaluations using a prototype implementation on a testbed, we find that MeshCache can significantly improve the performance of client nodes in WMNs. In particular, our experiments with a Squid-based MeshCache implementation deployed on the MAP mesh network testbed with 15 routers show that compared to caching at the gateway only, the MeshCache architecture with hop-by-hop caching reduces the load at the gateway by 38%, improves the average client throughput by 170%, and increases the number of transfers that achieve a throughput greater than 1 Mbps by a factor of 3.     

Path diversified multi-QoS optimization in multi-channel wireless mesh networks

Wireless mesh networks (WMNs) have become a promising solution for quick and low-cost spreading of Internet accesses and other network services. Given the mesh topology, multiple paths are often available between node pairs, which thus naturally endorse path-diversified transmission. Unfortunately, like in wired networks, discovering completely disjoint paths in a WMN remains an intractable problem. It indeed becomes more challenging given the interferences across wireless channels in a WMN, not to mention that applications may demand heterogeneous QoS optimizations across different paths. The availability of multiple channels in advanced WMNs however sheds new lights into this problem. In this paper, we show that, as long as the best channels with different QoS metrics are not overlapped between neighboring node pairs, complete disjoint paths with heterogeneous QoS targets are available in a multi-channel WMN. We present efficient solutions to discover such paths, particularly for bandwidth- and delay-optimization. We also develop novel algorithms for accurately estimating path bandwidth and delay in the multi-channel environment. These lead to the design of a practical protocol that extends the classical Ad hoc On-demand Multi-path Distance Vector (AOMDV). Through extensive simulations, we show that our protocol yields significant improvement over state-of-the-art multi-path protocols in terms of both end-to-end throughput and delay.     

Efficient link-heterogeneous multicast for wireless mesh networks

A wireless mesh network (WMN) is a type of communication network made up of wireless devices and organized in a mesh topology. Multicast is a fundamental service in WMNs because it efficiently distributes data among a group of nodes. Multicast algorithms in WMNs are designed to maximize system throughput and minimize delay in order to satisfy the end users?? requirement. Previous work has unrealistically assumed that the underlying WMN is link-homogeneous. We consider one important form of link heterogeneity: different link loss ratios, or equivalently different ETX. Different from other work addressing multicast in wireless networks, we point out that the local broadcast quality relies on the worst involved link. We model different link loss ratios by defining a new graph theory problem, Heterogeneous Weighted Steiner Connected Dominating Set (HW-SCDS), on an edge-weighted directed graph, where the edge weights model ETX, the reciprocal of link loss ratios. We minimize the number of transmissions in a multicast by computing a minimum HW-SCDS in the edge-weighted graph. We prove that HW-SCDS is NP-hard and devise a greedy algorithm for it. To improve the effectiveness of our algorithm, we design a dedicated channel assignment algorithm. Simulations show that our algorithm significantly outperforms the current best WMN multicast algorithm by both increasing throughput and reducing delay.     

On Efficient Traffic Distribution for Disaster Area Communication Using Wireless Mesh Networks

In recent time, a great deal of research effort has been directed toward promptly facilitating post-disaster communication by using wireless mesh networks (WMNs). WMN technology has been considered to be effectively exploited for this purpose as it provides multi-hop communication through an access network comprising wireless mesh routers, which are connected to the Internet through gateways (GWs). One of the critical challenges in using WMNs for establishing disaster-recovery networks is the issue of distributing traffic among the users in a balanced manner in order to avoid congestion at the GWs. To overcome this issue, we envision a disaster zone WMN comprising a network management center. First, we thoroughly investigate the problem of traffic load balancing amongst the GWs in our considered disaster zone WMN. Then, we develop traffic load distribution techniques from two perspectives. Our proposal from the first perspective hinges upon a balanced distribution of the bandwidth to be allocated per user. On the other hand, our second perspective considers the dynamic (i.e., varying) bandwidth demands from the disaster zone users that requires a more practical and refined distribution of the available bandwidth by following an intelligent forecasting method. The effectiveness of our proposals is evaluated through computer-based simulations.     

Throughput Gateways-Congestion Trade-Off in Designing Multi-Radio Wireless Networks

In Wireless Mesh Networks (WMNs), traffic is mainly routed by WMN Backbone (WMNB) between the mesh clients and the Internet and goes through mesh gateways. Since almost all traffic has to pass through one of the MGs, the network may be unexpectedly congested at one or more of them, even if every mesh router provides enough throughput capacity. In this paper, we address the problem of congestion of gateways while designing WMNs. We propose a simultaneous optimization of three competing objectives, namely network deployment cost, interference between network channels and congestion of gateways while guaranteeing full coverage for mesh clients. We tailor a nature inspired meta-heuristic algorithm to solve the model whereby, several trade-off solutions are provided to the network planner to choose from. A comparative experimental study with different key parameter settings is conducted to evaluate the performance of the model.     

ARSA: An Attack-Resilient Security Architecture for Multihop Wireless Mesh Networks

Multihop wireless mesh networks (WMNs) are finding ever-growing acceptance as a viable and effective solution to ubiquitous broadband Internet access. This paper addresses the security of WMNs, which is a key impediment to wide-scale deployment of WMNs, but thus far receives little attention. We first thoroughly identify the unique security requirements of WMNs for the first time in the literature. We then propose ARSA, an attack-resilient security architecture for WMNs. In contrast to a conventional cellular-like solution, ARSA eliminates the need for establishing bilateral roaming agreements and having real-time interactions between potentially numerous WMN operators. With ARSA in place, each user is no longer bound to any specific network operator, as he or she ought to do in current cellular networks. Instead, he or she acquires a universal pass from a third-party broker whereby to realize seamless roaming across WMN domains administrated by different operators. ARSA supports efficient mutual authentication and key agreement both between a user and a serving WMN domain and between users served by the same WMN domain. In addition, ARSA is designed to be resilient to a wide range of attacks. We also discuss other important issues such as incontestable billing.     

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.     

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.     

An efficient communication relay placement algorithm for content‐centric wireless mesh networks

In this paper, we investigate a communication relay placement problem to optimize the network throughput in a content‐centric wireless mesh networks (WMN), in which the WMN is enhanced by including a small set of communication relays and a subset of wireless mesh routers serving as storage nodes. Specifically, we first define the communication relay placement problem in content‐centric WMNs. We then model the problem as a mathematical programming and propose a linear programming approach for calculating the achievable network throughput when the positions of communication relays are fixed. Next, to optimally placing the communication relays, we formulate an integer linear programming problem and we develop an efficient near‐optimal approximation algorithm based on linear programming relaxation. Finally, extensive simulation experiments have been conducted, and the results demonstrate the effectiveness of the proposed algorithms. Copyright © 2013 John Wiley & Sons, Ltd.     

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.     

The nominal capacity of wireless mesh networks

Wireless mesh networks are an alternative technology for last-mile broadband Internet access. In WMNs, similar to ad hoc networks, each user node operates not only as a host but also as a router; user packets are forwarded to and from an Internet-connected gateway in multihop fashion. The meshed topology provides good reliability, market coverage, and scalability, as well as low upfront investments. Despite the recent startup surge in WMNs, much research remains to be done before WMNs realize their full potential. This article tackles the problem of determining the exact capacity of a WMN. The key concept we introduce to enable this calculation is the bottleneck collision domain, defined as the geographical area of the network that bounds from above the amount of data that can be transmitted in the network. We show that for WMNs the throughput of each node decreases as O(1/n), where n is the total number of nodes in the network. In contrast with most existing work on ad hoc network capacity, we do not limit our study to the asymptotic case. In particular, for a given topology and the set of active nodes, we provide exact upper bounds on the throughput of any node. The calculation can be used to provision the network, to ensure quality of service and fairness. The theoretical results are validated by detailed simulations.     

Characterization of the impact of network topology on the performance of single-radio wireless mesh networks

Stub Wireless Mesh Networks (WMNs) are used to extend Internet access. The use of multiple channels improves the capacity of WMN but significant challenges arise when nodes are limited to a single-radio interface to form the WMN. In particular, the assignment of mesh nodes to channels results on the creation of multiple sub-networks, one per channel, where individual capacity may depend on the sub-network topologies This paper identifies the relevant topological characteristics of the sub-networks resultant from the channel assignment process and studies, through simulation, the impact and relative importance of those characteristics on the maximal throughput enabled by the stub WMN. The number of nodes in the gateways neighborhood and the hidden node problem in the gateways neighborhood were identified as the characteristics having the highest impact on the WMN throughput.     

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.     

GI/Geom/1 queue based on communication model for mesh networks

In mesh networks architecture, it should be permitted to visit the mobile client points. Whereas in mesh networks environment, the main throughput flows usually communicate with the conventional wired network. The so‐called gateway nodes can link directly to traditional Ethernet, depending on these mesh nodes, and can obtain access to data sources that are related to the Ethernet. In wireless mesh networks (WMNs), the quantities of gateways are limited. The packet‐processing ability of settled wireless nodes is limited. Consequently, throughput loads of mesh nodes highly affect the network performance. In this paper, we propose a queuing system that relied on traffic model for WMNs. On the basis of the intelligent adaptivenes, the model considers the influences of interference. Using this intelligent model, service stations with boundless capacity are defined as between gateway and common nodes based on the largest hop count from the gateways, whereas the other nodes are modeled as service stations with certain capacity. Afterwards, we analyze the network throughput, mean packet loss ratio, and packet delay on each hop node with the adaptive model proposed. Simulations show that the intelligent and adaptive model presented is precise in modeling the features of traffic loads in WMNs. Copyright © 2013 John Wiley & Sons, Ltd.     

Measurement‐based link scheduling for maritime mesh networks with directional antennas

The proliferation of wireless transceivers and the availability of the unlicensed band has given a boost to the deployment of wireless networks, with IEEE802.11/WiFi being the major driver in this arena. In this research, we consider a wireless mesh network designed for long‐distance communication with a typical deployment scenario of a maritime mesh network. This network uses an antenna system made up of multiple fixed‐beamwidth antennas. Compared to most other directional antenna schemes which use directional antenna for transmission and omni‐directional antenna for reception, our system uses directional antennas for both transmission and reception where a pair of transmitter–receiver antennas needs to be aligned and have an acceptable channel quality before transmission can take place. Through efficient use of directional antennas for both transmission and reception, and spatial reuse in transmission, we are able to realize a high‐capacity mesh network. In this paper, we present a practical approach to achieve contention‐free medium access, namely, a measurement‐based link‐scheduling algorithm. We evaluate the performance of the link‐scheduling algorithm using simulations and show that it is able to exploit the spatial diversity provided by the directional antennas to outperform comparable schemes for wireless mesh networks. We also briefly discuss implementation issues to demonstrate the viability of the approach. Copyright © 2010 John Wiley & Sons, Ltd.