Abstract
Indoor positioning poses a number of challenges, especially in large and complex buildings. Several effects, such as signal attenuation, signal fluctuations, interference, and multipath play a decisive role in signal propagation. The severity of each challenge depends on the method and technology adopted to perform user localization. Wi-Fi is a popular method because of its ubiquity with already available public and private infrastructure in many environments and the ability for mobile clients, such as smartphones, to receive these signals. In this contribution, the fundamental concepts and basics and the evolution of Wi-Fi as the most widely used indoor positioning technology are reviewed and demonstrated using four different conducted case studies. Starting from an analysis of the properties of Wi-Fi signals and their propagation, suitable techniques are identified. The mathematical models of location fingerprinting and lateration are consolidated and assessed as well as new technology directions and developments highlighted. Results of the case studies demonstrate the capability of Wi-Fi for continuous user localization also in dynamic environments and kinematic mode where the user walks with a usual step speed. However, to achieve acceptable localization accuracy, calibration of the devices is required to mitigate the variance problems due to the device heterogeneity.
Highlights
Location is one of the most important contexts for computing devices, especially mobile devices such as smartphones
It can happen that the number of received signal strengths for each scan is different, e.g., because an Access Points (APs) is temporarily unavailable or the signal is too weak. This fact can lead to problems in localization, certainly in the case if Received Signal Strengths (RSS) values of different APs occur in the currently observed fingerprint in the positioning phase and they are differing from the fingerprint in the radio map obtained from the training phase
As a novel approach that benefits from all advantages of the different techniques, the fusion of location fingerprinting and lateration was proposed by the author [71] to combine the advantages of both methods
Summary
Location is one of the most important contexts for computing devices, especially mobile devices such as smartphones. Thereby, the RSS-based fingerprinting approach has the advantage that no direct line-of-sight (LoS) is required and it does not need any prior knowledge of the APs deployment and their location [12]. It works well in environments with high multipath. The way to go in the future is a combination of different techniques to be able to use the advantages of all individual localization approaches This contribution reviews the major developments in the field of Wi-Fi user localization verified by investigations and results from different case studies.
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