Purposeful mobility and capacity issues in sensor networks

by Rao, Rajesh N.

In this thesis methods to exploit “purposeful” mobility to improve the efficiency and performance of a sensor network are presented. For example a mobile node experiencing local deep fades and shadowing can move to a different location for better channel conditions. Transmission power required to transmit over a distance d is here on assumed to be given by Kd? where K is a constant and ? ? 2 is the transmission attenuation factor. Mobility can reduce transmission power by reducing the transmission distance d. The thesis presents an algorithm to move sensor nodes to reduce transmission distance and hence transmission energy, spending less energy for motion compared to the energy saved in transmission over time. In our sensor network, data generated by sensor nodes is aggregated at local sinks and forwarded to a central node. “Capacity” is defined as the number of sensor nodes that a sink can support. The number of data flows (each emanating from a sensor node) that a sensor node can relay is limited by a variety of factors such as channel conditions (including interference, attenuation, fading and ambient noise) and internal hardware and energy resources of the node. Assuming that the one-hop neighbors of a sink form the most significant communication relaying bottleneck, an analytical result for the fraction of sensor nodes that are unable to connect to their sink, i.e., the outage probability is presented. iii