Energy-efficient distributed query processing in heterogeneous sensor networks

Abstract

A sensor network is an ad hoc network composed of tiny sensor nodes having restricted battery, communication, and computation capabilities. These restrictions have made a sensor network system managed differently, compared with traditional mobile or distributed systems. A database community has viewed a sensor network as a virtual database system and has proposed various energy-efficient query processing algorithms. Recently, there has been much interest in the spatial query processing algorithms based on the locations of sensor nodes. The spatial query acquires sensor readings from sensor nodes inside specified geographical area of interests. The centralized approach which performs the spatial query at a server after acquiring all sensor readings, though simple, it incurs high wireless transmission cost in accessing all sensor nodes. Therefore, various in-network spatial query processing approaches have been proposed. They have focused on reducing wireless transmission cost in a sensor network. However, the existing in-network processing approaches may incur unnecessary wireless transmissions because of the dead space which is spatially indexed but does not contain real sensor nodes. In the first part of this dissertation, we propose a hybrid spatial query processing algorithm which can remove the unnecessary wireless transmissions. The main idea of the hybrid algorithm is to find intermediate results of a spatial query at a server in advance, and use the intermediate results when removing the unnecessary wireless transmissions at in-network query processing. Here, we assume that sensor nodes are placed at fixed locations and the server maintains the same index as the distributed spatial index built in a sensor network. We compare the existing in-network approach through extensive performance experiments and clarify our algorithm’s distinguished features. Spatial join query as well as the in-network spatial search query has been studied in works of energy-ef...