TDOA Measurement Processing for Positioning in Non-Line-of-Sight Conditions

In this paper three-stage time difference of arrival (TDOA) measurements processing algorithm is presented for positioning a transmitter in non-line-of-sight (NLOS) conditions when there are up to two receivers with NLOS measurements. The method used for NLOS identification and mitigation exploits the comparison of variance for intermediate location estimates calculated from different combinations of TDOA receivers with thresholds and does not require a priori knowledge. Contribution of proposed algorithm lies in accounting of calculated variances for different combinations within individual set of receivers and among all possible sets of receivers for the case when there up to two NLOS measurement sources. Proposed algorithm was realized in simulation model including TDOA system and link level model subsystems. TDOA system level model represents positioning layout with spatially distributed transmitter, receivers, obstacles and NLOS reflectors. TDOA link level model represents radio links between transmitter, receivers, and NLOS reflectors taking into account actual pathloss, signal modulation, sampling rate, additive noise and cross-correlation calculation. Resulting estimates refine known results for the case of actual pathloss and reveal possibility to reliably identify and exclude up to two NLOS receivers from measurement processing.