Vehicle indoor positioning: A survey

Positioning systems play an ever increasing key role in vehicular applications. GNSS-based systems such as GPS represent the predominant primary technology for positioning in this context. However, in densely built-up urban areas, the positional accuracy of GNSS-based systems decreases significantly, and ceases operation indoors due to the lack of line- of-sight to the satellites. In these scenarios and for use cases in which GNSS-based systems do not meet the requirements, the need for alternative localization systems arises. There is a wide range of vehicle indoor positioning approaches ranging from optical systems over IMU-based systems to LiDAR SLAM. In general, all systems can usually be classified by their perspective (internal or external) and their order (absolute or relative). Furthermore, all considered systems are very application-specific, and additionally either require a comprehensive extension of the existing infrastructure or modification of the vehicle