Landmark Placement for Wireless Localization in Rectangular-Shaped Industrial Facilities

Wireless localization is an important application of emerging technologies, e.g., wireless sensor network and radio-frequency identification (RFID). In this paper, the effect of landmark placement on localization performance in rectangularshaped facilities is investigated. The localization performance is evaluated by multiple performance metrics based on the Cramer-Rao lower bound (CRLB), i.e., expected CRLB, probability of lower CRLB, minimum CRLB, and maximum CRLB. Analytical analysis shows that all rectangular landmark layouts have the same minimum CRLB. Numerical results show that the optimal layout in terms of expected CRLB changes with respect to the aspect ratio of facility geometry, which can be predicted by statistical models. The performance on maximum CRLB deteriorates as the aspect ratio of the facility increases. Moreover, the performance in terms of every metric becomes significantly poorer if one landmark fails. Localization experiment based on active RFID devices confirms the findings from both analytical and numerical results.