NETS-NOSS: Routing and Topology Design of Hierarchical Sensor Networks

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A hierarchical sensor network is a sensor network that contains relay nodes appropriately distributed throughout the network. The relays are advantaged nodes that are connected by wireless transmission to form a backbone. Transmission in the backbone may use a different frequency and have longer range than the transmissions between sensor nodes. The backbone nodes may also have larger energy supplies than the sensor nodes. A message travels through one or more sensor nodes until it reaches a relay. Then it is transmitted in the backbone until it reaches a sink (destination) node. The presence of the backbone limits traffic among the sensor nodes thereby reducing interference and prolonging battery life.In order to design hierarchical sensor networks, it is necessary to determine how many relays are required, where they should be located, to which relay a sensor message should be directed, and what route the message should follow. This project pursues two lines of investigation to address these issues. The first develops analogies between sensor networks and the theory of electrostatics. It is applicable to networks with high sensor density. The discrete problem of routing is replaced by the continuous problem of finding a forwarding direction (vector field) at each point in the plane in such a way that a performance index (e.g., energy efficiency) is optimized. The optimal vector field can be obtained by solving a pair of partial differential equations that are analogous to Maxwell's equations in electrostatics. Making this approach distributed and applicable to hierarchical networks are important problems to be solved. The second line of investigation is concerned with the development of theory and algorithms for obtaining hierarchical sensor networks that have desirable topological properties such as k-connectivity and d-hop dominant backbones. Graph theory techniques are applied here.The project is expected to result in algorithms for the design and operation of sensor networks that have high throughput, are energy efficient, and avoid passing messages through regions in which communication may be unreliable due to environmental conditions. Potential applications include sensing of forest fires.