Design and implementation of a time synchronization-free distributed localization scheme for underwater acoustic sensor network

Underwater acoustic sensor network (UASN), which is a network of wireless sensor nodes distributed over a certain area within the underwater environment and communicating via acoustic signal, can act as an assisting technology for a variety of underwater applications including earthquake and tsunami forewarning, naval surveillance, marine biology etc. As the GPS signal is highly absorbed within the water, whereas radio signal attenuates more and optical signal scatters while they try to propagate within the underwater environment, acoustic signal is preferred for communication between the underwater sensor nodes. In spite of the data centric nature of the UASN, sometimes the collected data without its location of occurrence become meaningless. Thus, localization for UASNs has become a very interesting topic of research. However, several limitations of acoustic channel like low bandwidth, high bit error rate etc. along with long propagation delay of the sound wave and limited battery power of the sensor nodes within the water make the localization of underwater nodes very challenging. This paper proposes an event-driven time-synchronization free distributed localization scheme for large scale three dimensional UASN. Our proposed scheme employs a recursive localization process in which successfully localized nodes can act as reference node to aid in localization of the other ordinary sensor nodes and two-way ToA technique for distance measurement in order to avoid the requirement of time synchronization.