Date of Submission


Date of Award


Institute Name (Publisher)

Indian Statistical Institute

Document Type

Doctoral Thesis

Degree Name

Doctor of Philosophy

Subject Name

Computer Science


Applied Statistics Unit (ASU-Kolkata)


Roy, Bimal Kumar (ASU-Kolkata; ISI)

Abstract (Summary of the Work)

A Wireless Sensor Networks (WSNs), which are two or three dimensional systems, usually consist of a large number of small sensors equipped with some processing circuit, and a wireless transceiver. The sensors have small size, low battery capacity, non-renewable power supply, small processing power, limited buffer capacity and low-power radio. They may measure distance, direction, speed, humidity, wind speed, soil makeup, temperature, chemicals, light, and various other parameters. The sensors are autonomous devices with integrated sensing, processing, and communication capabilities.In this thesis, we consider ‘coverage problem’ and ‘detection problem’ in Wireless Sensor Networks (WSNs) in grid as well as in continuous domain. Sensor networks aim at monitoring their surroundings for event detection and object tracking. But, due to death of a sensor or due to obstructive, false detection may occur. Also false signal can be transmitted due to noise or faulty sensors. For detection of an event or events in a region, called Region Of Interest (ROI), coverage is essential in WSNs, i.e., every point of ROI should be in the sensing disc of at least one sensor. In case of grid, each vertex and in case of continuous ROI all the points of the ROI should be covered by at least one sensor. When sensors are deployed from air on some previously fixed points (vertices) in the Region of Interest (ROI), they may not fall on the target vertices. So, some part of the ROI may be uncovered by the sensors. In this thesis, we discuss optimal placement of sensors and coverage criteria in R2 and R3 and for cylindrical grid. We use graph theory and geometry to solve the problems.Optimal placement of sensors may not be possible due to random deployment. So there may be uncovered area in ROI. We also consider the problem, how one reduce the uncovered area in random deployment scenario. To reduce the uncovered area, extra sensors are usually deployed on some randomly chosen vertices. We develop a new strategy for deployment of extra sensors. Uncovered area i.e., sensing holes can also be repaired using actuators. We develop three strategies for actuator to minimize the travel of the actuator.Sensor could fail at runtime for various reasons such as power depletion, hardware defects etc. These sensors are known as faulty sensors. We consider the problem of distributed fault detection in wireless sensor network (WSN). In particular, we consider how to take decision regarding fault detection in a noisy environment as a result of false detection or false response of event by some sensors, where the sensors are placed at the center of regular hexagons or square and an event (or events) can occur at any number of hexagons. We propose fault detection schemes that explicitly introduce the error probabilities into the optimal event detection process. We introduce two types of detection probabilities, one for the center node, where the event occurs and the other one for the adjacent nodes. We also introduce probability for correct response and wrong response. We develop two schemes under the model selection and multiple model selection procedure and discuss two interesting special situations. We consider two different scenario: (i) at most one event can occur and (ii) any number of events can occur. We use classical Neyman Pearson hypothesis approach, decision theoretic approach, Bayesian approach, near optimal method and a new method to find solution of detection problem.


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Creative Commons License

Creative Commons Attribution 4.0 International License
This work is licensed under a Creative Commons Attribution 4.0 International License.


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