Showing papers by "J.M. Villadangos published in 2005"

Iimprovement of ultrasonic beacon-based local position system using multi-access techniques

Abstract: The present work shows a local positioning system (LPS) for mobile robots (MR) using simultaneous emissions in the ultrasonic beacons. In order to solve the problem of the simultaneous emission of the ultrasonic beacons, the well-known technique called direct sequence code division multiple access (DS-CDMA) is used. This technique modulates the ultrasonic signal (50 kHz) with a 127-bit Gold code for even beacon. In this way, it is possible to detect the arrival time of the code, by earning out the simultaneous correlations with the assigned codes to each beacon. For determining the absolute position, the triangulation technique uses the time difference-of-arrival (TDOA) obtained between a reference beacon and the others. Using this method, certain errors, derived from the delay in the firing of the beacons and the response times of the ultrasonic transducers, are avoided. The existence of a synchronism in the emission of the beacons, that guarantees a periodic and simultaneous emission in all of them, is required, not being necessary to know the emission instant in the mobile robot. This is particularly useful in environments where several robots can coexist

Simultaneous measurement of times-of-flight and communications in acoustic sensor networks

Abstract: This article presents a process for the simultaneous determination of distances among objects in an indoor localization system using an acoustic sensor network. The proposed technique is based on a simultaneous time-of-flight measurement for the emitted acoustic signals from every object, without needing any additional signal to be used for synchronization. This is possible thanks to the properties of the used emission codification, which consists of complementary sets of sequences. According to the requirements of the positioning algorithm, a communication protocol is designed in order to transmit the collected information among nodes, so, locally, the distances and positions can be computed at each node.

A comparison of computing architectures for ultrasonic signal processing

Abstract: The design of advanced sonar modules implies the use of more and more complex processing algorithms, in order to obtain as much information as possible from the environment. The use of simultaneous emission and reception techniques in certain transducers, that form an ultrasonic sensorial module, allows to increase the benefits and the performance of this type of systems. These developments make possible to obtain more information for every ultrasonic emission, diminishing the scanning time and improving the interpretation and usefulness of the obtained results. These techniques are usually based on the encoding of the ultrasonic emission, so the received signals can be correlated in order to search For possible echoes. As a consequence, the computational complexity necessary to carry out the implementation of the new algorithms increases considerably. The analysis of possible computing platforms for the real-time processing of the new algorithms becomes a task of great importance. In this work, some computing architectures are analysed and compared, in order to determine which scheme is most suitable for the ultrasonic signal processing.

Sensor codification with mutually orthogonal complementary set of sequences

Abstract: This work deals with the use of sets to code multi-mode seasonal system, similar to code-division multiple-access (CDMA) communication ones. In multi-sensorial systems, as multi-user ones, it is necessary to avoid the multiple-access interference (MAI). We propose the use of mutually orthogonal complementary sets of sequences (MO-CSS) to avoid MAI among the sensors that are working simultaneously. This proposal sometimes involves complex emission and reception stages. In order to simplify them, and taking advantage of the properties from MO-CSS, a new code technique is presented. This can be used in smart spaces, or in a multi-sensorial robotic system, in order to improve processing times and to achieve simple computing modules.

Uusing complementary sets of sequences for direct channel estimation in asynchronous systems

Abstract: In this paper the estimation of a channel impulse response using complementary sets of sequences is considered. A direct (non-iterative) technique is presented and applied to an asynchronous system where the signals are recovered by matched filtering. The robustness of this technique is quantified in terms of the signal-to-noise ratio (SNR) obtained at the process output and the relative root mean square error (RRMSE) committed in the estimation of the channel coefficients