Multipath mitigation for a phase-based infrared ranging system applied to indoor positioning

A new measuring architecture for phase-based infrared ranging applied to indoor positioning is presented. The motivation to develop this proposal was to reduce the critical effect of multipath interferences on the differential distances estimated by the ranging system. The multipath mitigation feature of the proposed system is based on applying a spread spectrum modulation on the emitted signal so that the line-of-sight component reaching the receivers can be discriminated from the non-line-of-sight components by applying a selective coherent demodulation. An overview of the system architecture is provided, together with the first approach to the model of the demodulation process and its validation. The conclusions obtained from the study of the proposal are used to provide preliminary results of the mitigation capabilities of the system, and to analyze the key issues involved in its implementation. The results show that the effectiveness of the proposal is strongly related with the infrared link bandwidth. Mitigation levels above 50% for multipath 4.5 meters longer than the direct path are reached if the infrared link bandwidth is higher than 200 MHz.