LOS and NLOS Classification for Underwater Acoustic Localization
The low sound speed in water makes Propagation Delay (PD) based range estimation attractive for UnderWater Acoustic Localization (UWAL). However, due to the long channel impulse response and the existence of reflecting objects, PD-based UWAL suffers from significant degradation when PD measurements of Non-Line-Of-Sight (NLOS) communication links are falsely identified as Line-Of-Sight (LOS) communication links. In this paper, the authors present an algorithm to classify PD measurements into LOS and NLOS links for a single transmitter-receiver pair. First, by comparing signal strength-based and PD-based range measurements, they identify Object-related NLOS (ONLOS) links, where signals are reflected from objects with high reflection loss, e.g., ship's hull, docks, rocks, etc.