On the Precision of Common Individual or Hybrid Positioning Systems

Nowadays, there are a variety of different indoor positioning systems employing diverse techniques. Often, developers and users only have a rough idea about the essential figure of merits of these systems, first and foremost of the precision, accuracy and costs. In this paper, we analyse the former parameter and establish bounds for any unbiased estimator. In particular, we derive the Cramer-Rao Lower Bound (CRLB). This enables us to compare common approaches and to evaluate their combination with regard to hybrid techniques. As an example, it is shown that even though techniques employing the Received Signal Strength (RSS) are inferior to Time of Arrival (ToA) or Time Difference of Arrival (TDoA), the inclusion of RSS provides a means to significantly improve these systems. Our investigations additionally reveal that not all locations in a scenario exhibit the same errors. We validate our findings by means of simulations and experiments. For the latter we employ Wireless Local Area Networks (WLAN), Ultra-Wideband (UWB) radar and ZigBee.