Query processing and link layer qos provisioning mechanisms for wireless sensor networks

Recent advances in MEMS (micro-electro-mechanical systems) and radio technology has enabled development of low-cost wireless sensor networks (WSNs). Due to their ease of deployment and ad hoc connectivity, WSNs are emerging as a promising tool for a wide range of applications. Each sensor node is equipped with programmable computing, multiple-parameter sensing and wireless communication capability. Sensor nodes are however, constrained in terms of available resources such as energy, storage and computation. Such limitations make it really challenging to realize a reliable WSN infrastructure that can efficiently process different types of user queries. The objective of this dissertation is to develop energy-efficient mechanisms for enabling query processing in WSNs, despite unreliable nature of the wireless medium. The first part of this dissertation focuses on designing energy-efficient architectures for processing different kinds of user queries. Queries in WSNs can be broadly classified as location-based queries and attribute-based queries. To enable processing of long-running location-based queries, the recent trend is to evaluate queries within the WSN, so as to reduce the overall communication and energy consumption of the WSN. The in-network query processing architecture proposed in this dissertation determines optimal placement of query operators within a WSN in a decentralized manner and also adapts to continual changes in network and data properties. On the other hand, the recent trend in processing attribute-based queries is employing data-centric storage schemes that eliminate the need for flooding the WSN. In this dissertation, a novel data-centric storage scheme has been developed to determine rendezvous points for storing individual attributes depending on their correlation with other attributes. Both analytical and simulation studies have been performed to identify the conditions under which the proposed architecture is useful. The second part of this dissertation focuses on designing mechanisms for ensuring reliable and timely delivery of the sensed data. WSNs are generally deployed in inhospitable terrains and consist of a dense deployment of sensor nodes. Furthermore, wireless communication is inherently unpredictable and error-prone. Hence, it is imperative to design an efficient medium access control (MAC) protocol that facilitates guaranteed delivery of data over unreliable wireless links. In this dissertation, such an on-demand reliable MAC protocol has been proposed and its superior performance in terms of reliability, latency and scalability has been demonstrated. Furthermore, we have also proposed another MAC protocol that is both energy-efficient and reliable. The energy-efficiency of the proposed MAC protocol has been achieved by switching the sensor nodes to sleep mode when they are not involved in data communication. However in doing so, measures have been taken to avoid problems like overemitting, excessive latency and frequent changes of the radio state. Thus, our proposed MAC protocol reliably delivers sensed data with minimum power consumption, thereby attempting to reach the desirable objectives of WSNs.