Indoor Localization With a Single Wi-Fi Access Point Based on OFDM-MIMO

In this paper, we propose S-Phaser, an indoor localization system that uses a singleWi-Fi access point (AP) to locate terminals. Compared to traditional indoor localization systems based on the fingerprint positioning technology, S-Phaser does not need to deploy a large number of APs and has better localization accuracy. S-Phaser utilizes channel state information (CSI) to compute the direct path length between a single AP and terminals, thereby efficiently improving the accuracy in the line-of-sight (LOS) scenario. S-Phaser is still able to get satisfied accuracy in the non-LOS scenario even not as good as in the LOS scenario. Using the feature of multiple channels in 802.11n, we design an interpolation-based algorithm, named as the interpolation elimination method to calibrate signal phases from CSI, and then we use two different algorithms, the Chinese residue theoremand broadband angle ranging, to compute the real distance of the direct path from the calibrated phases. Then, S-Phaser uses a geometric positioning algorithm to determine the user's location. To verify the practicability of the proposed S-Phaser, we set up a localization system in an actual environment. S-Phaser can improve the median localization error to 1.5 m with a singleWi-Fi AP.