this paper, we propose and evaluate one of the first multi-channel multi-hop wireless ad-hoc network architectures that can be built using standard 802.11 hardware by equipping each node with multiple network interface cards (NICs) operating on different channels. We focus our attention on wireless mesh networks that serve as the backbone for relaying end-user traffic from wireless access points to the wired network. The idea of exploiting multiple channels is particularly appealing in wireless mesh networks because of their high capacity requirements to support backbone traffic

The widespread use of mobile and handheld devices is likely to popularize ad hoc networks, which do not require any wired infrastructure for intercommunication. The nodes of mobile ad hoc networks (MANETs) operate as end hosts as well as routers. They intercommunicate through single-hop and multi-hop paths in a peer-to-peer fashion. With the expanding range of applications of MANETs, the need for supporting Quality of Service (QoS) in these networks is becoming essential. This paper provides a survey of issues in supporting QoS in MANETs. We have considered a layered view of QoS provisioning in MANETs. In addition to the basic issues in QoS, the report describes the efforts on QoS support at each of the layers, starting from physical and going up to the application layer. A few proposals on the inter-layer approaches for QoS provisioning have also been addressed. The paper concludes with a discussion on the future directions and challenges in the areas of QoS support in MANETs.

Wireless LAN administrators are often called upon to deal with the problem of sporadic user congestion at certain popular spaces ("hot-spots") within the network. To address this problem, we describe and evaluate two new approaches, explicit channel switching and networkdirected roaming for providing hot-spot congestion relief while maintaining pre-negotiated user bandwidth agreements with the network. The goals of these algorithms are: (i) to accommodate more users by dynamically providing capacity where it is needed, when it is needed; (ii) to improve overall network utilization by making more efficient use of deployed resources; and (iii) to guarantee at least a minimum amount of bandwidth to users. We propose that both the network and its users should explicitly and cooperatively adapt themselves to changing load conditions depending on their geographic location within the network. We describe how these algorithms enable the network to transparently adapt to user demands and balance load across its access points (APs). We evaluate the effectiveness of these algorithms on improving user service rates and network utilization using simulations. Our algorithms improve the degree of load balance in the system by over 30%, and user bandwidth allocation by up to 52% in comparison to existing schemes that offer little or no load balancing. 1.

In this paper, we present a routing and channel assignment protocol for multi-channel multi-hop wireless net-works. We view a multi-hop network as an extension to infrastructure networks, where a mobile host may connect to an access point using multi-hop wireless routes, via other mobile hosts or wireless routers. The access points are configured to operate on one of multiple available channels. Mobile hosts and wireless routers can select its operating channel dynamically through channel switching. In this environment, we propose a routing protocol that finds routes and assigns channels to balance load among channels while maintaining connectivity. The protocol works with nodes equipped with a single network interface, which distinguishes our work with other multi-channel routing protocols that require multiple interfaces per node. Supporting nodes with single network interface is beneficial because having multiple interfaces can be costly for small and cheap devices. The protocol discovers multiple routes to multiple access points, possibly operating on different channels. Based on traffic load information, each node selects the “best ” route to an access point, and synchronizes its channel with the access point. With this behavior, the channel load is balanced, removing hot spots and improving channel utilization. The channel assignment assures every node has at least one route to an access point, where all intermediate nodes are operating on the same channel. Our simulation results show that the proposed protocol successfully adapts to changing traffic conditions and improves performance over a single-channel protocol and a protocol with random channel assignment.

IEEE 802.11 wireless LAN technology is mainly used as an access network within corporate enterprises. All the WLAN access points are eventually connected to a wired backbone to reach the Internet or enterprise computing resources. In this project, we aim to expand WLAN into an enterprisescale backbone network technology by developing a multichannel wireless mesh network architecture called Hyacinth. Hyacinth equips each node with multiple IEEE 802.11a/b NICs and supports distributed channel assignment/routing to increase the overall network throughput. In this paper, we present the results of a detailed performance evaluation study on the multichannel mesh networking aspect of Hyacinth, based on both NS2 simulations and empirical measurements collected from a 9node Hyacinth prototype testbed. A key result of this study is that equipping each node of a Hyacinth network with just 3 NICs can increase the total network bandwidth by a factor of 6 to 7, as compared with single-channel wireless mesh network architecture.

Abstract-We propose an efficient centralized scheduling algorithm in IEEE 802.16 based Wireless Mesh Networks (WMN) to provide high qualified wireless multimedia services. Our algorithm takes special attention on the relay function of the mesh nodes in a transmission tree which is seldom studied in previous research. Some important design metrics, such as fairness, channel utilization and transmission delay are considered in this scheduling algorithm. IEEE 802.16 employs TDMA and the selection policy for scheduled links in a time slot will definitely impact the system performance. We evaluated the proposed algorithm with four selection criteria through extensive simulations and the results are instrumental for improving the performance of IEEE 802.16 based WMNs in terms of link scheduling. I.

Abstract — In this paper, we consider a mobile ad-hoc wireless access network in which mobile nodes can access the Internet via a stationary gateway node or access point. Mobile nodes that are outside the transmission range of the gateway can continue to communicate with the gateway via a multi-hop connection with their neighboring nodes. The Ad-hoc On-demand Distance Vector (AODV) routing protocol is extended by incorporating the concept of load-balancing (LB). We call this the LB-AODV routing protocol. Simulation results show that in a congested network environment, our proposed LB-AODV has a higher packet delivery fraction, a lower end-to-end delay and control overhead when compared with both AODV and gossip-based routing protocols.

Wireless networks have been widely deployed in the past few years. With rapidly increasing number of users, it is important to maximize utilization of given resources to achieve high perfor-mance. Among many approaches, the aim of this dissertation is in utilizing available frequency spectrum, which may be divided into multiple non-overlapping channels. Particularly, we focus on the case where wireless nodes are equipped with a single network interface, which can operate on any one channel at a given time. Wireless network standards such as IEEE 802.11 provide multiple non-interfering frequency channels, where multiple communications can take place simultaneously. However, current proto-cols cannot exploit this availability to achieve high performance. The main challenge in utilizing multiple channels is the fact that a node equipped with a single network interface can only operate on a single channel, although it is capable of switching its operating channel. When two nodes want to communicate, they must be operating on the same channel. Thus, to support multiple channels, protocols need to properly assign and coordinate channels among nodes. Without careful design, multi-channel protocols may not be able to achieve higher performance than single-channel protocols.

In this paper, we study the problem of providing fairness in multi-hop wireless infrastructure access. In such networks, it is well known that the use of current media access and transport protocols can result in severe unfairness and even starvation for flows originated from different numbers of hops away from a wired infrastructure point or gateway. In this paper, we study a different type of fairness that exists in such networks – flows initiated by nodes that are similar numbers of hops away from the gateway can experience significant unfairness, and such unfairness exists even for perfectly symmetrical node distribution and channel conditions. We denote such fairness as symmetrical fairness. We first provide a framework to characterize and measure symmetrical fairness. We then perform an extensive set of simulation experiments to quantify the causes of symmetrical unfairness. Finally, we develop and study a distributed routing algorithm that significantly improves the symmetrical fairness. 1

Abstract—Wireless Mesh Networks (WMNs) provide a costeffective way of deploying a network and providing broadband Internet access. In WMNs a subset of nodes called gateways provide connectivity to the wired infrastructure (typically the Internet). Because traffic volume of WMNs is expected to be high, and due to limited wireless link capacity, gateways are likely to become a potential bottleneck. In this paper, we propose a distributed load-balancing protocol where gateways coordinate to reroute flows from congested gateways to underutilized gateways. Unlike other approaches, our scheme takes into account the effects of interference. This makes it suitable for implementation in practical scenarios, achieving good results, and improving on shortest path routing. Also, it is load-sensitive and can improve network utilization in both balanced and skewed topologies. Simulation results prove the effectiveness of our approach, which outperforms all schemes tested. We have observed throughput gains of up to 80 % over the shortest path algorithm. I.