Quality of service enhancement in multi-hop wireless networks

Abstract

IEEE 802.11 is a successful technology for wireless networks. Wireless LANs (WLANs) based on it have successfully replaced wired access links in recent years. Currently, it is attempted to extend it for multi-hop wireless networks such as ad-hoc networks and mesh networks. As more traffic is delivered over wireless networks, QoS (Quality of Service) support for them becomes an important issue. In single hop WLANs, IEEE 802.11e is a key technique to provide QoS, but there are still arguments for how to apply it for multi-hop wireless networks. In this dissertation, we propose techniques to provide QoS in multi-hop wireless networks. In wireless networks, AIMD (Additive Increase Multiplicative Decrease) based rate control schemes are used to fairly allocate resources to nodes. Most of these schemes assume that all nodes observe the same channel condition. In most of wireless network topologies, however, nodes may have different channel condition, and consequently channel resources can be allocated to nodes unfairly. To allocate resources to nodes fairly using AIMD based rate control schemes, nodes should be able to reduce their rate synchronously when congestion is occurred. In this dissertation, we propose a contending region based rate control scheme to allocate channel resources to nodes fairly in multi-hop wireless networks. The objective of the proposed scheme is to achieve fairness while maintaining the spatial reuse characteristic of multi-hop wireless networks. Moreover, the proposed scheme narrows the range of contending nodes based on the cause of congestion to improve channel utilization. The proposed scheme is evaluated through extensive ns-2 simulations. It is shown that the proposed scheme allocates resources to contending nodes fairly under asymmetric channel condition and improves the channel utilization. The Assured Forwarding (AF) service in a differentiated services network offers different levels of forwarding assurance for IP packets. In ...