Indoor acoustic localization: a survey
Human-Centric Computing and Information Sciences
Introduction Indoor localization is essential to enable location based services (LBS) such as indoor navigation [27, 35, 37, 84] , health rehabilitation [14, 45, 49, 54] and human-computer interaction (HCI) devices [47, 70, 83, 85] . Aiming at higher accuracy, shorter time latency and lower infrastructure requirement, many localization systems have been designed for various scenarios. Generally, localization algorithms can be described as a two-stage procedure  . In the first step,
... c information such as distances and angles are measured. In the second step, the target is located using those data. Physical phenomena such as Time of Flight (ToF) [9, 40, 50, 51], Doppler Effect [20, 42, 76, 85] and phase shift [64, 70, 77, 81] assist in the first step. Geometric knowledge [9, 76, 81] and optimization methods [24, 40, 42] are common choices for the second step. In addition to the acoustic signal on which we will concentrate in this survey, other ways have also been exploited for localization systems in many scenarios. Inertial sensors [49, 62, 87] are frequently utilized due to their highly accessible equipments and straightforward principles. An intuitive idea is using the double integration of the acceleration to estimate the displacement and applying the gyroscope to predict the direction, which however leads to significant location error with even a small measurement error  . Although it is challenging to achieve high accuracy with inertial sensors, we can still leverage them as an auxiliary tool in acoustic localization. For example, Abstract Applications of localization range from body tracking, gesture capturing, indoor plan construction to mobile health sensing. Technologies such as inertial sensors, radio frequency signals and cameras have been deeply excavated to locate targets. Among all the technologies, the acoustic signal gains enormous favor considering its comparatively high accuracy with common infrastructure and low time latency. Rangebased localization falls into two categories: absolute range and relative range. Different mechanisms, such as Time of Flight, Doppler effect and phase shift, are widely studied to achieve the two genres of localization. The subcategories show distinguishing features but also face diverse challenges. In this survey, we present a comprehensive overview on various indoor localization systems derived from the various mechanisms. We also discuss the remaining issues and the future work.