Advanced sensorial system for an acoustic LPS

This work presents the development and implementation of a Local Positioning System (LPS) based on the transmission of ultrasonic signals, proposed for indoor positioning of mobile robots. The LPS consists of several ultrasonic beacons located in the environment, all of them emitting periodically and simultaneously. A portable receiver collects all the transmissions and autonomously computes its position. Neither infrared nor radiofrequency are required for synchronization in the localization process, compared to other related works. Direct Sequence Code Division Multiple Access (DS-CDMA) techniques are used to allow simultaneous emission from several beacons; each one transmitting a different 255-bit Kasami code. The portable receiver can detect the time of arrival for the different signals coming from the beacons, by carrying out all the correlations with the emitted codes. Absolute position of the receiver is determined by hyperbolic trilateration, using the Differences in Times-of-Arrival (DTOA) between a reference beacon and the other ones. The main advantage of this proposal is to permit the coexistence of an unlimited number of portable receivers, what is useful in applications like multirobot cooperation.