Online Estimation of Effective Delivery Capability in Delay-Tolerant Mobile Sensor Networks

The delay-tolerant mobile sensor network (DTMSN) distinguishes itself from conventional sensor networks by several unique characteristics, such as nodal mobility, sparse connectivity, delay tolerability, and fault tolerability. Being an opportunistic network where the communication links exist with certain probabilities only and thus become the scarcest resource, the routing metrics that have been commonly adopted in conventional networks do not reflect this unique network resource of DTMSN. Therefore, they may lead to poor network performance or even failure if used for routing in DTMSN. In this work, we investigate a simple and effective online estimation approach to obtain a converged and accurate parameter that reflects the node's effective delivery capability. Specifically, we devise an exponentially weighted moving average (EWMA) approach to effectively maintain and update the routing metrics. We prove that the expectation of the EWMA parameter converges to a constant when the nodes are under statically distributed mobility and the system becomes stable as time t rarr infin, and the converged value is the average data delivery rate of the node. To further validate our discussion in a close-to-realistic mobility, we conduct simulations under the CRAWDAD mobility traces. The simulation results show that EWMA closely follows the variation of the actual delivery rate and thus serves as an effective metrics for efficient routing.