Certain indoor applications, mainly related to unmanned mobile vehicles or accurate monitoring of targets, robots or people, require positioning systems with centimeter accuracy. Although some RFbased systems, such as UWB, have recently provided commercially available solutions for that purpose, ultrasound-or infrared-based systems still represent a feasible approach, due to their particular features and advantages. Whether having a direct line of sight between the emitting beacons and the

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... vers, these systems provide signal confinement in a reduced environment (typically room level), thus providing high robustness against external interference. Furthermore, their combination in mixed solutions may also achieve better performances, by mitigating the complementary drawbacks from each other, covering larger areas while minimizing interferences between beacons (alternating technologies), or increasing the availability of measurements. In this context, this work describes the experimental evaluation of a loosely-coupled fusion method that merges two positioning systems, one based on ultrasounds and the other on infrareds. Both systems are described hereinafter, and the range and accuracy performance individually obtained are presented as well. Experimental results for both systems are similar in terms of accuracy (below 15 cm between 80 and 95% of cases) in the common coverage area. These figures are similar when measurements are merged by means of a Kalman Filter (KF) into a single position estimate, while increasing the availability of the final system and discarding the effect from possible outliers in the original independent estimates.