A Survey of Indoor Localization Systems for Multi-Floor Environments

Most indoor localization systems determine only the 2D location of a user on a single floor, often overlooking multi-floor environments. This limitation reduces their effectiveness in scenarios such as emergency response in multi-floor buildings. As a result, multi-floor localization systems capable of identifying the user’s floor as well have recently gained significant attention. However, designing and deploying accurate multi-floor localization systems presents unique challenges due to the increased scale and complexity of the environment. These challenges include ensuring sensor reliability, addressing signal space ambiguity caused by complex environmental structures and infrastructure configurations, and managing deployment overhead and resource requirements. Despite growing interest in this area, a comprehensive, up-to-date survey on the challenges and recent advances in multi-floor localization remains lacking. In this paper, we present the first exhaustive survey of indoor localization systems designed for multi-floor environments. We begin by highlighting the importance of floor identification through various applications and provide background on extending localization techniques from 2D to multi-floor scenarios. We then categorize and analyze the key challenges unique to multi-floor localization, including both input-level and system-level challenges. Next, we review existing solutions aimed at mitigating these challenges, with a focus on recent advancements. Finally, we discuss open problems and outline future research directions. Although significant progress has been made in indoor localization, multi-floor localization remains an active and evolving research area with numerous opportunities to bridge existing gaps and drive further innovation.