Error characteristics and calibration-free techniques for wireless LAN-based location estimation

Using wireless LAN technology for location estimation provides alternate means to enable location-based applications without investment in sensor network infrastructure and special hardware. However, the main drawback of wireless LAN-based location systems is calibration of signal strength as a function of location in spatially high-density, which consumes manual labor and needs to be carried out repeatedly. In this paper, we analyze empirical error characteristics of calibration-based location algorithms such as triangulation in various spatial densities of calibration, using commercially available wireless LAN products. Then, we propose Triangular Interpolation and eXtrapolation (TIX), a calibrationfree location algorithm, and present empirical performance evaluation. TIX can achieve mean distance error within 5.4 m, which is comparable to within 4.7 m errors of the calibrationbased algorithms. We also present theoretical analysis on error characteristics of the location algorithms deriving accuracy limits and quantifying the effect of RF measurement and calibration.