Abstract
Smartphone indoor localization has attracted considerable attention over the past decade because of the considerable business potential in terms of indoor navigation and location-based services. In particular, Wi-Fi RSS (received signal strength) fingerprinting for indoor localization has received significant attention in the industry, for its advantage of freely using off-the-shelf APs (access points). However, RSS measured by heterogeneous mobile devices is generally biased due to the variety of embedded hardware, leading to a systematical mismatch between online measures and the pre-established radio maps. Additionally, the fingerprinting method based on a single RSS measurement usually suffers from signal fluctuations due to environmental changes or human body blockage, leading to possible large localization errors. In this context, this study proposes a space-constrained pairwise signal strength differences (PSSD) strategy to improve Wi-Fi fingerprinting reliability, and mitigate the effect of hardware bias of different smartphone devices on positioning accuracy without requiring a calibration process. With the efforts of these two aspects, the proposed solution enhances the usability of Wi-Fi fingerprint positioning. The PSSD approach consists of two critical operations in constructing particular fingerprints. First, we construct the signal strength difference (SSD) radio map of the area of interest, which uses the RSS differences between APs to minimize the device-dependent effect. Then, the pairwise RSS fingerprints are constructed by leveraging the time-series RSS measurements and potential spatial topology of pedestrian locations of these measurement epochs, and consequently reducing possible large positioning errors. To verify the proposed PSSD method, we carry out extensive experiments with various Android smartphones in a campus building. In the case of heterogeneous devices, the experimental results demonstrate that PSSD fingerprinting achieves a mean error ∼20% less than conventional RSS fingerprinting. In addition, PSSD fingerprinting achieves a 90-percentile accuracy of no greater than 5.5 m across the tested heterogeneous smartphones
Highlights
Because of the popularity of built-in global navigation satellite systems (GNSSs) with smartphones, smartphone navigation has been one of the most popular applications
We propose a pairwise signal strength difference (PSSD) indoor location system, which is extended from the traditional Wi-Fi-received signal strength (RSS) fingerprinting method
We proposed the pairwise signal strength differences (PSSD), a novel fingerprint-based smartphone indoor localization leveraging signals of opportunity of Wi-Fi RSS measurements
Summary
Because of the popularity of built-in global navigation satellite systems (GNSSs) with smartphones, smartphone navigation has been one of the most popular applications. Smartphone indoor localization has attracted considerable study efforts in the past decade to provide a smartphone with the capability of indoor localization, and a variety of solutions have been presented in the literature [4,5,6]. Signals of opportunity-based solutions, such as Wi-Fi fingerprinting, have been studied largely in the context of smartphone applications because of the advantages of low cost and the requirement of no additional infrastructure. Few of these reported solutions have been applied widely in real marketing due to several issues regarding the usability. Usability is important for user experience and applicability of the solution, and usability must be considered in particular in the algorithm design
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