Abstract

Routing protocols for wireless ad-hoc networks have traditionally focused on finding paths with the least number of intermediate hops. However, such paths can include slow or lossy links, leading to poor throughput. A routing algorithm can select better paths by explicitly taking into account the quality of the wireless links. Metrics to measure wireless link quality have been proposed, but their relative performance has not been studied. In this paper, we conduct a detailed, empirical evaluation of the performance of three link-quality metrics—ETX, per-hop RTT, and per-hop packet pair—and compare them against minimum hop count. We study these metrics using a DSR-based routing protocol running over a wireless testbed consisting of 23 nodes with 802.11a cards. We find that the ETX metric has the best performance when all nodes are stationary. We also find that the per-hop RTT and per-hop packet-pair metrics perform poorly due to self-interference. Interestingly, the hop-count metric outperforms all of the link-quality metrics in a scenario where the sender is mobile.