Location of mobile terminals using time measurements and survey points

The location of mobile terminals has recently become a topic of much research. One of the more popular methods of radio location is the time difference of arrival (TDoA) method where the location of the mobile terminal is estimated using measurements of the differences in propagation times from the mobile terminal to three or more base stations. The traditional approach used to perform the location estimation is the least squares algorithm assuming zero mean Gaussian measurement error distributions. In the urban microcell radio propagation environment with non line of sight (NLOS) propagation, this assumption is often violated causing large location estimation errors. This paper demonstrates an estimation algorithm based on non-parametric density approximation of the measurements using a survey of time difference measurements. This method gives high accuracy location estimates even in the presence of NLOS propagation.