Mobile robotic navigation and control for large-scale wireless sensor network repair

Wireless Sensor Networks (WSNs) have the potential to provide a wealth of high resolution sensory data, both temporally and spatially, over large areas and for long periods of time, but can be limited in effectiveness when a sensor node loses power or becomes damaged. The quality of the sensor network data is also reliant on the underlying network connectivity and can be degraded by imprecise deployments, and unforeseen changes in the network structure over time such as changes in weather conditions. The ability to use autonomous mobile robotic platforms to repair or replace bad sensor nodes, or to map out WSNs to identify weak nodes, has potential to enhance the performance of WSNs and improve their robustness. This dissertation investigates: (1) WSN connectivity issues over the lifetime of a network, and (2) identifying and repairing disconnects within a WSN using an autonomous robot.;The effects of asymmetric links between WSN nodes and the best methods to model networks composed of asymmetric nodes were studied in depth. It was found that for networks requiring bidirectional links that the use of a disk model was optimal; however, for networks with asymmetric links, elliptical or irregular models were preferred. Thus in situations where asymmetries are permitted, more efficient network connectivity is obtained using elliptical or irregular models.;Modeling, simulation, experimentation, and analysis, show that when a deployed WSN reaches a high nodal density, the network disconnects can be repaired by strategic placement of only a few nodes. The autonomous placement and repair of network disconnects was studied using the received signal strength (RSS) of messages within the WSN to navigate and control a robotic platform. This approach allows the control hardware of the mobile robot to use the same technology as that used by the WSN nodes. It is further shown by physical experiments that when the autonomous mobile robotic platform interacts directly with the RF signal transmitted from a single WSN node, that that mobile robot can carry out collision detection and obstacle avoidance tasks commonly found in mobile robotics research. Lastly, RSS has been shown to be useful for navigating around the perimeter of a deployed WSN. Using RSS for navigation and to provide a mobile node is shown to extend the range of the WSN, and to allow single-hop disconnects to be identified and repaired. Experiments were conducted both in simulation and in the physical world using a six-node WSN to prove that navigation based on RSS could repair a WSN.;The speed of RSS based repair of WSNs is improved if the nodes on the perimeter of the WSN are first identified by the WSN and this information is provided to the robot. An algorithm was developed that uses local neighborhood computation, one based on the convex hull, to determine whether or not a node lies on the perimeter of the WSN. The developed algorithm performed equally as well as, or better than, the distributed and centralized detection algorithms of others, and was implemented on a twenty-five node WSN.