Non-Line of Sight Mitigation using a Measurement and Positioning Filtering Algorithm

In recent years, research interest in location systems has increased due to the emergence of mobile computing devices and the promise of Ubiquitous Computing. This paper considers the problem arising in ultrasonic location systems of Non-Line of Sight (NLOS) between Base Stations and Mobile Devices, which can give significant location errors. Herein, a Dual Kalman Filtering method is proposed to mitigate NLOS effects, using an a-priori partial knowledge of the ultrasonic signals. The main advantage of this method is that the first filter provides a set of filtered ranges that mitigates the NLOS ranging error, while the second filter, by taking these measurements, provides a second positioning filtering that mitigates the overall positioning error. The method is shown to reduce location errors providing a maximum error in location of 9cm.