Robust indoor positioning using differential wi-fi access points

Location positioning systems using wireless area local network (WLAN) infrastructure are considered cost effective and practical solutions for indoor location tracking and estimation. However, accuracy deterioration due to environmental factors and the need for manual offline calibration limit the application of these systems. In this paper, a new method based on differential operation access points is proposed to eliminate the adverse effects of environmental factors on location estimation. The proposed method is developed based on the operation of conventional differential amplifiers where noise and interference are eliminated through a differential operation. A pair of properly positioned access points is used as a differential node to eliminate the undesired effects of environmental factors. As a result the strength of received signals, which is used to determine the location of a user, remains relatively stable and supports accurate positioning. To estimate wave propagation in indoor environments, log-distance path loss model has been employed at the system level. Experimental results indicate that the proposed method can effectively reduce the location estimation error and provide accuracy improvement over existing methods.