Belief Propagation-based Cooperative Localization for Quasi-Synchronous UWSNs with Sound Propagation Speed Uncertainty

Underwater wireless sensor networks (UWSNs) provide a promising approach for ocean monitoring. Locating the sensor nodes (SNs) in UWSNs is critical 14 annotating data samples. However, the global positioning system (CPS) is not available underwater. The locations of SNs are usually interpreted from anchor nodes which are deployed at known locations on the seafloor or sea surface. Due to the characteristics of UWSNs such as node sparsity, network asynchrony, energy restriction and sound propagation speed uncertainty, to locate the SN accurately is challenging. In this paper, we propose a factor graph framework and a Gaussian message-based belief propagation algorithm for the joint localization and synchronization problem. Particularly, the proposed algorithm jointly estimates the SN's position and clock offset as well as the sound propagation speed in a fully distributed fashion. Simulation results show that the proposed algorithm converges in a few iterations and achieves good performance.