Routing Metrics for Multi-Hop Wireless Mesh Networks

Abstract

Wireless Mesh Networks (WMNs) have gained considerable popularity recently. Most research on WMNs focuses on improving network capacity, because WMNs suffer from severe throughput degradation due to interferences. Among them, routing has been an active area of research for a long time, and it is also the focus of this dissertation. Routing metrics are critical for selection of a path with a maximum throughput in multi-hop wireless networks. Due to the nature of wireless losses and multi-rate support, wireless links in one single network may have a broad range of characteristics such as loss rates and data transmission rates. In addition, wireless nodes may be equipped with multiple radios tuned to non-overlapping channels in order to improve network performance. All these technologies bring new challenges to route selection in wireless multi-hop networks, and the traditional minimum hop count metric does not suffice in such a complicated environment, since it does not take any aforementioned characteristics into account. To design an effective routing metric, it is necessary to accurately acquire the link properties that might affect path performance, most importantly, the loss rate. To better assess individual link loss rate, this study proposes several modifications to existing broadcast based probe method that leads to a more accurate link loss rate measurement. In recent years, although many link qualitybased routing metrics have been explored, none of the current routing metrics is capable of capturing the necessary link properties, which is critical for a comprehensive evaluation of routing path performances and the selection of the best route. In this study, we explore the drawbacks of current routing metrics and propose two improved strategies, improved Expected Time Transmission (iETT) and improved Bottleneck Aware Transmission Delay (iBATD), respectively, to address the challenges for single-radio and multi-radio wireless mesh networks. The proposed routing metrics will be explored in various wireless network scenarios through ns-2 simulations and their performances will be compared to current routing metrics, such as minimum hop count metric (HOP), Expected Transmission Count (ETX), Expected Transmission Time (ETT) and Weighted Cumulative ETT (WCETT) metrics. Additionally, an extended Dynamic Source Routing (DSR)-based routing protocol (eDSR), which works effectively in multi-radio scenarios and performs seamlessly with any quality aware routing metrics, has also been designed to aid the performance comparisons. Moreover, we develop iETT routing metric and three other selected representative routing metrics on a Linux based test bed and assess their performances with extensive experiments.