Distributed positioning algorithms in underwater acoustic networks

Underwater acoustic networks are gaining rapidly increasing interest driven by their ability to support applications such as real time remote ocean sensing and monitoring tasks of coastal areas. Generally military applications such as detection, classification and tracking of sea and underwater targets, or civilian applications such as habitat monitoring, natural disaster prevention and sea life tracking in observing systems may be assisted by underwater acoustic networks. For that a good estimation of the position of the sensor nodes that form the underwater acoustic network is required to accurately report the origin or remote area of the desired sensed phenomenon and take the response actions. An accurate estimation of the position of the nodes is difficult in underwater acoustic networks for various reasons. In the underwater acoustic environment the signal propagation is affected by a large variety of factors including sensitivity to water temperature, water salinity, and water pressure which define the sound speed profile of a determined ocean area or region, surface roughness, seafloor geology, area latitude, and others. Typical acoustic underwater positioning systems rely on the existence of an external communications infrastructure providing position references to the single network elements to be positioned. However in situations where the position references cannot be delivered to all the network nodes and their position is initially unknown after deployment a collaborative distributed positioning algorithm among the network nodes is required to estimate their position. This thesis proposes a distributed positioning algorithm for estimating the position of network nodes in underwater acoustic networks and compares its performance to selected distributed positioning algorithms. Water temperature, water salinity and water pressure are included in the algorithmic calculations for a better position estimation. A simulation software system tool has been developed and implemented integrating an underwater acoustic propagation model which has been validated by comparing the simulated results with those from real measurements recorded experimental data. A number of communications and algorithm parameters are defined to quantitatively estimate and compare the performance of the different positioning algorithms. The performance evaluation of the different positioning algorithms has been conducted according to the simulation results obtained with the deployed simulation software system. Within this general simulation software tool we have investigated the influence of variations in the water properties and algorithm parameters in the performance of the positioning algorithms under similar environment conditions. The simulation results obtained show the performance improvement of the presented distributed positioning algorithm developed and adapted to underwater acoustic networks within this thesis.