Providing quality of service in wireless ad hoc networks
Date of Issue2008
School of Computer Engineering
Unlike conventional wireless networks where the mobile users can only connect to the access points (APs) or routers that are within their transmission range, wireless ad hoc networks do not rely on any existing infrastructure and can be formed dynamically. With its unique characteristics such as the self-forming, self-healing and self-organization, wireless ad hoc networks have recently received a lot of interest for commercial deployment. In this thesis, we study the provision of Quality of Service (QoS) in wireless ad hoc networks. We first consider a high mobility scenario which is common in Mobile Ad Hoc Networks (MANETs). A QoS framework is proposed to enhance QoS for real-time traffic in MANETs which consists of two components, a QoS routing protocol and a local scheduling algorithm. To reduce QoS violation like large delay and low delivery ratio, which can be caused by link breakage as well as excessive contention, a QoS routing algorithm is first proposed to discover multiple node-disjoint paths that also satisfy the QoS requirement of real-time traffic. Re-route discovery latency due to frequent link failures is minimized with the alternate path maintained at the sources. With passive acknowledgement, QoS violation due to link failure or excessive contention can be detected if a sent packet is not acknowledged for a certain time. To further enhance the QoS of admitted real-time traffic, a packet scheduling algorithm is implemented locally at each node which gives higher priority to real-time traffic over best-effort traffic. The simulation results show that our proposal can enhance the QoS of real-time traffic in terms of both low end-to-end transmission delay and high delivery ratio, even under high mobility scenario. We then consider a wireless network with infrastructure support (MWNI) that can be constructed from an existing IEEE 802.11 based WLAN with multihop extension. Assuming that only a single network interface card operating on a single channel MAC is equipped in each mobile host, the channel assignment is incorporated in the routing algorithm to maximally utilize all the available channels. A new load metric is first proposed which is more accurate than other existing methods by considering possible spatial reuse. Based on that metric, a QoS-aware routing protocol is then proposed which can enhance the QoS of end users by exploring the channel diversity in the face of dynamic traffic and unreliable wireless channels. A distributed channel switch algorithm is proposed that avoids switching oscillation and with little overhead incurred. Through simulation evaluation, our routing algorithm is shown to be able to achieve more stable performance comparing with existing routing algorithms in such networks, while achieving a better resource utilization. Finally, to support integrated services in MWNIs, a QoS framework is proposed to achieve the following objectives: (1) allow more real-time flows to be admitted into the network, (2) optimize the performance of best-effort traffic without losing fairness and (3) enhance QoS performance of admitted real-time traffic. There are three main components in our framework to provide corresponding solutions. First, a new QoS routing protocol is proposed that discovers global optimized topology based on the network interference modeled by flow contention graph. Second, admission control is performed at the AP so that a flow will be admitted only if the network has enough bandwidth to support its minimum bandwidth requirement. Third, a two-level hierarchical scheduling algorithm based on weighted fair queueing is implemented at the APs. On the first level, the available link bandwidth is divided between two virtual servers and each of them will schedule packets from the same type. On the second level, each virtual server performs weighted fair queueing algorithm so that the fairness among all backlogged flows of the same type is optimized. The efficiency of individual components, as well as the whole QoS framework is evaluated through simulation studies, and the results show our proposed QoS framework is able to achieve all the objectives.
DRNTU::Engineering::Computer science and engineering::Computer systems organization::Performance of systems