Data collection in sensor networks with data mules: An integrated simulation analysis

Wireless sensor networks (WSNs) have emerged as the enabling technology for a wide range of applications. In the context of environmental monitoring, especially in urban scenarios, a mobile data collector (data mule) can be exploited to get data sensed by a number of nodes sparsely deployed in the sensing field. In this paper we describe and analyze protocols for reliable and energy-efficient data collection in WSNs with data mules. Our main contribution is the joint performance analysis of the discovery and the data transfer phases of the data collection process. Our results show that a low duty cycle (i.e. in the order of 1%) is actually feasible for most common environmental monitoring applications. We also found that, depending on the mobility pattern of the data mule, a lower duty cycle may not be always a more convenient option for energy efficiency. Based on these results, we outline in the paper possible directions for improving the energy efficiency of data collection in sparse WSNs with data mules.