Contribución al diseño de un LPS ultrasónico de amplia cobertura empleando técnicas de codificación

Zusammenfassung

This thesis presents the contribution to the design of an Ultrasonic Local Positioning System (ULPS) for expanded coverage employing encoding techniques. One of the main objectives of the thesis is the design of an ultrasonic beacon to be placed on the ceiling of an indoor space, by means of a selected commercial transducer, in order to improve its radiation pattern to increase the area of coverage on the floor. Another objective is the development of a complete ULPS with encoding and detection signal based on Time Code Division Multiple Access, which improves the detection capability of the emitted ultrasonic signal by the beacons, without using an external synchronism between the mobile and the beacons. An important feature in any LPS is its coverage. The choice of an optimal transducer is not an easy task, and more difficult when it has to meet special requirements, such as in this case a large bandwidth, in order to use spread spectrum techniques. Once a commercial transducer is selected, it is proposed the design of a conical reflector in order to improve its emission pattern and to have a larger coverage area. This permits to keep a certain consistency in the received signal level, so a lower number of beacons can be used for implementing the positioning system. The behavior of the ULPS has been theoretically analyzed, and then, it has been simulated from the mobile standpoint (it has to detect the signals transmitted by the beacons), considering that ultrasonic beacons transmit continuously at regular intervals. For the study, several types of noise and different effects introduced by the transmitter, channel, and receiver have been taken into account. Several time and frequency domain techniques have been proposed, analyzing their more outstanding features. In addition, a MAI and ISI interference analysis has been carried out, including usual mitigation techniques. In order to improve the performance of the system against these interferences, a new emission technique has been proposed. For comparing simulated results with real data, a real-ULPS has been developed based on the mentioned proposals. All the algorithms have been validated by means of measurements carried out in fixed environment positions and on a moving robot.