Ultrasonic beacon-based Local Positioning System using Loosely Synchronous codes

This work presents the development of a local positioning system (LPS), based on the transmission of ultrasonic signals, which have been previously encoded by loosely synchronous (LS) codes. The LPS consists of several ultrasonic emitters located at known positions in the environment, and of a portable receiver that computes its position by measuring the differences in times of arrival (DTOA) between a reference emitter and the others. LS codes exhibit an interference free window (IFW) in the auto-correlation and cross-correlation functions. Therefore, if the relative time-offset of the codes are within the IFW, it is possible to have simultaneous emissions without interference, as well as to reduce the multipath effect.