Repairing wireless sensor network connectivity in damaged environments

A wireless sensor network can become partitioned due to node failure, requiring the deployment of additional relay nodes in order to restore network connectivity. This introduces an optimisation problem involving a tradeoff between the number of additional nodes that are required and the costs of moving through the sensor field for the purpose of node placement. This tradeoff is application-dependent, influenced for example by the relative urgency of network restoration. In addition, minimising the number of relay nodes might lead to long routing paths to the sink, which may cause problems of data latency. This data latency is extremely important in wireless sensor network applications such as battlefield surveillance, intrusion detection, disaster rescue, highway traffic coordination, etc. where they must not violate the real-time constraints. Therefore, we also consider the problem of deploying multiple sinks in order to improve the network performance. Previous research has only parts of this problem in isolation, and has not properly considered the problems of moving through a constrained environment or discovering changes to that environment during the repair or network quality after the restoration. In this thesis, we firstly consider a base problem in which we assume the exploration tasks have already been completed, and so our aim is to optimise our use of resources in the static fully observed problem. In the real world, we would not know the radio and physical environments after damage, and this creates a dynamic problem where damage must be discovered. Therefore, we extend to the dynamic problem in which the network repair problem considers both exploration and restoration. We then add a hop-count constraint for network quality in which the desired locations can talk to a sink within a hop count limit after the network is restored. For each new problem of the network repair, we have proposed different solutions (heuristics and/or complete algorithms) which prioritise different objectives. We evaluate our solutions based on simulation, assessing the quality of solutions (node cost, movement cost, computation time, and total restoration time) by varying the problem types and the capability of the agent that makes the repair. We show that the relative importance of the objectives influences the choice of algorithm, and different speeds of movement for the repairing agent have a significant impact on performance, and must be taken into account when selecting the algorithm. In particular, the node-based approaches are the best in the node cost, and the path-based approaches are the best in the mobility cost. For the total restoration time, the node-based approaches are the best with a fast moving agent while the path-based approaches are the best with a slow moving agent. For a medium speed moving agent, the total restoration time of the node-based approaches and that of the path-based approaches are almost balanced.

Migration: A Heideggerian analysis

The phenomenon of migration has been widely researched by the social sciences. Theories regarding the migrant have been developed in terms of the oppressive social context that is often encountered, proposing different alternatives to understand and overcome such oppression. Through the current project, an alternative view is presented that first, questions the accuracy of the social theories of migration and second, proposes an alternative understanding of this experience. Martin Heidegger’s phenomenology of Being offers a contextualized view of existence that nonetheless includes elements of our experience that are shared due to a common mode of being. I use Heidegger’s philosophy in order to broaden the understanding of the migrant’s experience analyzing those elements that he identifies as shared (for instance: human sociability, a desire for a home, the uncanny, etc.) and comparing them with common issues raised by migrants (identity, homesickness, belonging, etc.). In this way, I intend to present a more complete picture of the experience of migration that considers both empirical evidence of individual migrants and an existential analysis that incorporates the defining elements of our world and our existence as crucial means to understand any experience, including that of migration.