In-network querying on federated sensor networks
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Querying and tracking are two major in-network data processing services for Wireless Sensor Networks (WSNs). Although there are several in-network querying and tracking protocols in the WSNs literature, those protocols are not directly applicable for large-scale federated/partitioned WSN deployments where loss of connectivity and network partitioning is a norm rather than an exception. Due to large-scale federated/partitioned deployment characteristics, a so-called Federated Sensor Network (FSN) needs to cope with the distribution and sparse-connectivity of distinct WSN islands via interspace network of either mobile or static relay nodes. This dissertation investigates the characteristics of FSNs for designing resilient querying and tracking services. The federated and sparsely/intermittently connected nature of FSNs introduces several challenges for deploying middleware services such as routing, querying, and tracking. In this dissertation, effective information querying from FSN islands using in-network data processing and indexing techniques is explained by static and mobile federation of FSN islands. For static federation, the challenges for deploying a querying service on both flat and layered FSN models are investigated. Several querying protocols proposed in the WSNs literature are applied and reviewed, and the shortcomings of these protocols are identified for the flat FSN management by several simulation results. The layered federation of islands by the L-FSN protocol is found to be alleviating the shortcomings of flat federation and increasing the querying performance compared to flat federation. L-FSN allows islands to be managed autonomously by a degree of privacy. Inter-island querying of L-FSN is based on the path selection policies while intra-island querying protocols of L-FSN can be selected according to the size of islands to gain benefit on energy-efficiency and query resolving latency. In order to suggest directions for future intra-island querying protocols, this dissertation presents a review of in-network querying and tracking protocols in static and mobile WSNs under the categorizations of geometrical, hierarchical cluster-based, hash-based, and tree-based. For mobile federation, a mobility dataset is analyzed to understand and highlight the characteristics of the federation of FSN islands by smartphones as mobile relay nodes. The analysis of this mobility dataset revealed the existence of island regions in an urban area which lack regular visitors. Since these islands are found to be adjacent to city roads, multi-hop data collection is feasible from island nodes by smartphone users traveling on city roads. This analysis discusses the spatial and energy-related opportunities of mobile federation by smartphones. In the light of this analysis, the duty cycling PLMAC protocol is proposed to conserve energy on islands for smartphone-based data collection applications.