On the Efficacy of Opportunistic Routing

Traditional routing schemes select the best path for each destination and forward a packet to the corresponding next hop. While such best-path routing schemes are considered well-suited for networks with reliable point-to-point links, they are not necessarily ideal for wireless networks with lossy broadcast links. Consequently, opportunistic routing schemes that exploit the broadcast nature of wireless transmissions and dynamically select a next-hop per-packet based on loss conditions at that instant are being actively explored. It is generally accepted that opportunistic routing performs substantially better than best-path routing for wireless mesh networks. In this paper, we analyze the efficacy of opportunistic routing. We define a new metric EAX that captures the expected number of any-path transmissions needed to successfully deliver a packet between two nodes under opportunistic routing. Based on EAX, we develop a candidate selection and prioritization method corresponding to an ideal opportunistic routing scheme. We then conduct an off-line comparison of best-path routing and opportunistic routing using our EAX metric and MIT Roofnet trace. We observe that while opportunistic routing offers better performance than best-path routing, the gain is not as high as commonly believed.