Adding link quantity information to redundant RF signal strength estimates for improved indoor positioning

A common approach of range-based indoor positioning methods use the received signal strength (RSS) of RF packets from several anchor nodes to estimate their distances to a mobile emitter with unknown position. The range-based weighted centroid localization (WCL) approach with link quality information (LQI) is known to be more accurate than range-free centroid localization (CL) methods using only a binary radio link information according to the cell of origin (COO) principle. With the combining of redundant RF channels using spatial and frequency diversity the WCL position estimation is proved to be even more reliable, although the RSS-based distance estimations of a single RF channel are known to be error-prone in multipath indoor environments. A novel range-free approach using the exact number of available diversity channels - the link quantity information (LQnI) - is proposed. It needs no more infrastructural effort or processing power and can easily be applied to the range-based WCL estimation technique with redundant sensor information. Especially the combining of the redundant RSS-based distance estimations together with the LQnI approach leads to a more accurate position estimation. Experimental results in an office building and in a real-life tracking application for maintenance staff in the underground coal mining show the improvements of the additional range-free approach.