Mobile location with bias tracking in non-line-of-sight

The main impairment for the location of terminals in a wireless communications system is the non-line-of-sight (NLOS) condition which is mainly due to blocking of the transmitted signal by obstacles. It is well known that NLOS biases time-of-arrival (TOA) and time-difference-of-arrival (TDOA) estimates, therefore providing a biased position. The paper analyzes the improvements in positioning accuracy by tracking the bias of the time measures with the Kalman filter proposed for location estimation. The evaluation of the approach has been carried out with measures taken in real scenarios, for positioning techniques based on TDOA and TOA+AOA (angle of arrival) measurements.