Recent developments in the area of ubiquitous and pervasive computing emphasize the interest in context-aware applications. Location is probably the most important context. Indoor location estimation and tracking remains challenging due to the lack of usable and cost-effective technologies. GPS has proved itself for outdoor usage, but it is not suitable for indoor applications due to poor coverage. Assuming that multiple wireless sensors will be attached to ubiquitous environments, they could also support location estimation and tracking.