US Patent 7791538 Location estimation method and system, and wireless device

A location estimation system in which the location of a target device is estimated from the known locations of a set of anchor devices and information obtained from wireless signals transmitted between the target device and the anchor devices. The estimation process makes use of parameters indicating propagation characteristics of the wireless signals. When the location of the target device has been estimated, new values are estimated for the parameters, based on the estimated location of the target device. The new parameter values are then used to estimate the location of the target device again. The location estimation and parameter estimation process is iterated until a predetermined condition is satisfied.