Advances in ubiquitous mobile computing and rapid spread of information
systems have fostered a growing interest in indoor location-aware or location-based
technologies. In this paper we will introduce the primary technologies used in indoor
localization systems by classifying them in three categories: Non-RF technologies,
Active-RF technologies and Passive-RF technologies. Both commercialized products and
research prototypes in all categories are involved in our discussion. The Passive-RF
technologies are further divided into “Mobile tag” and “Mobile reader” systems. We
expect such classification can cover most of the indoor localization systems. Features of
these systems are briefly compared at the end of this paper
