-Data sensing and retrieval in wireless sensor systems have a widespread application in areas such as security and surveillance monitoring, and command and control in battlefields. In query-based wireless sensor systems, a user would issue a query and expect a response to be returned within the deadline. While the use of fault tolerance mechanisms through redundancy improves query reliability in the presence of unreliable wireless communication and sensor faults, it could cause the energy of the system to be quickly depleted. Therefore, there is an inherent tradeoff between query reliability vs.energy consumption in query-based wireless sensor systems. In this paper, we develop adaptive fault tolerant quality of service (QoS) control algorithms based on hop-by-hop data delivery utilizing "source" and "path" redundancy, with the goal to satisfy application QoS requirements while prolonging the lifetime of the sensor system. We develop a mathematical model for the lifetime of the sensor system as a function of system parameters including the "source" and "path" redundancy levels utilized. We discover that there exists optimal "source" and "path" redundancy under which the lifetime of the system is maximized while satisfying application QoS requirements. Numerical data are presented and validated through extensive simulation, with physical interpretations given, to demonstrate the feasibility of our algorithm design.

Recently, wireless sensor networks (WSNs) have gained a great attention due to their ability to monitor various environments, such as temperature, pressure sound, etc. They are constructed from a large number of sensor nodes with computation and communication abilities. Most probably, sensors are deployed in an uncontrolled environment and hence their failures are inevitable all times of work. Faulty sensor nodes may cause incorrect sensing data, wrong data computation or even incorrect communication. Achieving a reliable wireless sensor networks is a most needed goal to ensure quality of service whether at deployment time or during normal operation. While Nodes redundancy is considered as an effective solution to overcome nodes failures, it may negatively affect the WSN lifetime. Redundancy may lead to more energy drains of the whole system. In this paper, the impact of redundancy level on the Mean Time to Failure (MTTF) of a clustered based wireless Sensor Networks (WSNs) is investigated. An expression that can be used to determine the most suitable redundancy level that maximizes the network MTTF is derived and evaluated.

Data sensing and retrieval in wireless sensor systems have a widespread application in areas such as security and surveillance monitoring, as well as command and control in battlefield situations. In query-based sensor systems, a user would issue a query with quality of service (QoS) requirements in terms of reliability and timeliness, and expect a response to be returned within the deadline. Satisfying these QoS requirements implies that fault tolerance mechanisms through redundancy will be used, which may cause the energy of the system to be quickly depleted. We develop a hop-by-hop data delivery mechanism in which we utilize "source" and "path" redundancy with the goal to satisfy application QoS requirements while maximizing the lifetime of the sensor system. When given QoS requirements of a query, we identify optimal "source" and "path" redundancy such that not only QoS requirements are satisfied, but also the lifetime of the system is prolonged. Numerical data are presented with physical interpretations given to demonstrate the feasibility of our approach.

In query-based wireless sensor networks (WSNs)

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