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This paper deals with the problem of nonline-of-sight (NLOS) in wireless communications systems devoted to location purposes. It is well known that NLOS biases time of arrival (TOA) and time difference of arrival (TDOA) estimates thus reducing accuracy of positioning algorithms. In order to achieve positioning error reduction the Kalman filter proposed for location estimation includes the time measurement bias for each base station (BS) as additional parameters to be estimated. The use of the Kalman filter allows then tracking, not only the position and speed of the mobile, but also the bias due to NLOS, yielding an accurate location prediction algorithm.