Measurements and characterizations of spatial and temporal TOA based ranging for indoor WLAN channels

Indoor localization has gained considerable attention in the last decade. Different approaches and techniques have been proposed to solve the indoor location problem from received signal strength (RSS) fingerprinting to time of arrival (TOA) based ultra wideband (UWB) systems. However it is highly desirable for the solution to take advantage of existing network infrastructure such as WLAN. RSS based localization for WLAN cannot provide the required accuracy and recently TOA based ranging approaches have been proposed in IEEE 802.11v. The performance of TOA ranging in WLAN channels has not been investigated and characterized in the literature. In this paper, to the best of the authors´ knowledge, the first experimental measurement and analysis to characterize and model the TOA ranging in indoor environment is introduced. Using the well-known frequency domain measurement system, the ranging error performance in line of sight (LOS) and non-line of sight (NLOS) environments is investigated. In addition the performance in time-varying channels is analyzed, where the impact of human induced motion (small-scale fading) on the accuracy of TOA estimation is investigated. The results indicate that for a given location the time-varying error can be modeled as a normal distribution. The mean and the variance vary spatially and are directly related to the movements and the multipath structure (open space, cluttered environment, etc.).