Design and Analysis of Adaptive Fault Tolerant QoS Control Algorithms for Query Processing in Wireless Sensor Networks

Wireless sensor networks (WSNs) present several unique characteristics such as resource-constrained sensors, random deployment, and data-centric communication protocols. These characteristics pose unprecedented challenges in the area of query processing in WSNs. This dissertation presents the design and validation of adaptive fault tolerant QoS control algorithms with the objective to achieve the desired quality of service (QoS) requirements and maximize the system lifetime in query-based WSNs. Data sensing and retrieval in WSNs have a great applicability in military, environmental, medical, home and commercial applications. In query-based WSNs, a user would issue a query with QoS requirements in terms of reliability and timeliness, and expect a correct response to be returned within the deadline. Satisfying these QoS requirements requires that fault tolerance mechanisms through redundancy be used, which may cause the energy of the system to deplete quickly. We analyze the effect of redundancy on the mean time to failure (MTTF) of querybased cluster-structured WSNs, defined as the mean number of queries that a WSN is able to answer correctly until it fails due to channel faults, sensor faults, or sensor energy depletion. We show that a tradeoff exists between redundancy and MTTF. Furthermore, an optimal redundancy level exists such that the MTTF of the system is maximized. We develop a hop-by-hop data delivery (HHDD) mechanism and an Adaptive Fault Tolerant Quality of Service Control (AFTQC) algorithm in which we utilize “source” and “path” redundancies with the goal to satisfy application QoS requirements while maximizing the lifetime of WSNs. We also compare and contrast AFTQC without acknowledgment vs. AFTQC with acknowledgement and identify conditions under which AFTQC should couple with acknowledgement to maximize the system MTTF.