Reliable and energy-efficient data collection in wireless sensor networks

In recent years, wireless sensor networks (WSNs) have attracted significant attentions from both academia and industry, and are widely proposed for a broad range of applications, where data collection is often a core service to facilitate sensed data being forwarded to a central base station for further processing. Powered by batteries and using wireless communications, a WSN is more flexible than its wired counterpart. However, wireless losses/collisions may be prevalent when nodes communicate with each other. Moreover, the lifetime of a WSN largely depends on that of individual nodes, which is further constrained by the generally non-replenishable batteries. Energy-efficiency thus becomes a critical concern that must be addressed. In practice, using WSNs for data collection can be broken into three major stages, namely, deployment, message dissemination and data delivery. The deployment stage focuses on best deploying the network in the sensing field. In the message dissemination stage, network setup/management and/or collection command messages are disseminated from the base station to all sensor nodes, where the challenges lie in how to disseminate messages with low transmission costs and latencies in the presence of error-prone wireless communications. The data delivery stage fulfills the main task of data collection. Based on the information indicated by the message dissemination stage, sensed data are gathered at different nodes and delivered to the base station, with application-specified Quality-of-Service requirements to be fulfilled. In this thesis, we tackle the design issues for each of these stages. For the deployment stage, we propose to use relay nodes for traffic relaying and suggest that the deployment should be aware of the data traffic to be collected by specific applications. We then discuss how to efficiently disseminate message in a low duty-cycle scenario, where nodes alternate between active and dormant states to conserve energy and thus extend the network lifetime. To address the traffic accumulation problem, particularly in the data delivery stage, we take a case study on high-rise structure monitoring application and propose to use elevators to facilitate data collection. Our analysis and experimental results offer systematic solutions toward reliable and energy-efficient data collection by WSNs.