Estimating position of mobile terminals from delay measurements with survey data

An accurate method to locate mobile terminals is to measure the radio propagation time from the base stations to the mobile terminal. From these measurements, the distance from the base stations to the mobile terminal are estimated and an estimate of the location for the mobile terminal can be calculated. This method is highly accurate when the shortest distance propagation paths between the mobile terminal and base stations are not blocked. Unfortunately, when these paths are blocked the propagation delays are non-linear functions of the mobile terminal location and the accuracy of the standard location solution is reduced. This paper demonstrates how the conditional density of the location given measured propagation delays can be approximated as a sum of kernel density functions based on data collected during propagation surveys. These approximate density functions allow an accurate location estimate for the mobile terminal to be calculated from propagation delay measurements even with obstructed radio propagation