J.M. Villadangos

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

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

Ultrasonic Local Positioning System with Large Covered Area

This work describes the design of a ultrasonic local positioning system (ULPS) with large covered area. The beacons have been designed with a cylindrical PVDF transducer (piezofilm transducer) to which a conical reflector has been connected to enlarge the covered area and to guarantee 3D indoor positioning. The proposed ULPS for mobile robots (MR) uses simultaneous emissions from ultrasonic beacons. In order to solve the problem of simultaneous emissions from ultrasonic beacons, the well-known technique, direct sequence code multiple division access (DS-CDMA), is used. This technique encodes the ultrasonic signal with a 255-bit Kasami code for every beacon. It implies the emitted signal by every beacon to have a wide bandwidth. PVDF-based transducers suitably guarantee this requirement. Their cylindrical or semi-cylindrical shape makes the emission pattern not suitable when using them as ultrasonic beacons, often located in the ceiling of an indoor room. To adapt the emission pattern and to increase the covered area in the ground, the design process of a conical reflector is described.

Acoustic Sensor Network for Relative Positioning of Nodes

In this work, an acoustic sensor network for a relative localization system is analyzed by reporting the accuracy achieved in the position estimation. The proposed system has been designed for those applications where objects are not restricted to a particular environment and thus one cannot depend on any external infrastructure to compute their positions. The objects are capable of computing spatial relations among themselves using only acoustic emissions as a ranging mechanism. The object positions are computed by a multidimensional scaling (MDS) technique and, afterwards, a least-square algorithm, based on the Levenberg-Marquardt algorithm (LMA), is applied to refine results. Regarding the position estimation, all the parameters involved in the computation of the temporary relations with the proposed ranging mechanism have been considered. The obtained results show that a fine-grained localization can be achieved considering a Gaussian distribution error in the proposed ranging mechanism. Furthermore, since acoustic sensors require a line-of-sight to properly work, the system has been tested by modeling the lost of this line-of-sight as a non-Gaussian error. A suitable position estimation has been achieved even if it is considered a bias of up to 25 of the line-of-sight measurements among a set of nodes.

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

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.

Improvement of Cover Area in Ultrasonic Local Positioning System Using Cylindrical PVDF Transducer

This work describes the design of a reflector for a PVDF-based ultrasonic transducer (Piezofilm transducer) to carry out a ultrasonic beacon system, where the covered area be improved and a 3D indoor positioning be guaranteed. The proposed Local Positioning System (LPS) for Mobile Robots (MR) uses simultaneous emissions from ultrasonic beacons. In order to solve the problem of simultaneous emissions from ultrasonic beacons, the well-known technique Direct Sequence Code Multiple Division Access (DS-CDMA) is used. This technique encodes the ultrasonic signal with a 127-bit Gold code for every beacon. It implies the emitted signal by every beacon to have a wide bandwidth. PVDF-based transducers suitably guarantee this requirement. Their cylindrical or semi-cylindrical shape makes the emission pattern not suitable when using them as ultrasonic beacons, often located in the ceiling of an indoor room. To adapt the emission pattern and to increase the covered area in the ground, the design process of a conical reflector is described.

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.

FPGA-based Implementation of an Ultrasonic Beacon for a Local Positioning System

Ultrasonic transducers have been often used to develop local positioning systems (LPS) in the field of intelligent spaces. In these systems, it is necessary to design an ultrasonic beacon, which is distributed in the environment to cover a determined area where mobile robots or people can be located. This work describes the design and the implementation of an ultrasonic beacon in an FPGA-based platform. The design is flexible enough to allow the real-time configuration of the ultrasonic emission, according to parameters as efficient encoding or suitable modulation schemes. Furthermore, the beacons have available a 12C link, so they are in permanent communication for exchanging configuration parameters and synchronization, not only among them, but also with a central configuration module

Android application for indoor positioning of mobile devices using ultrasonic signals

In this paper we present an Android application, called LOCATE-US, that allows accurate indoor positioning of mobile devices by processing the ultrasonic signals coming from a local positioning system (LPS). The LPS operates around 41KHz, and an external hardware based on an ultrasonic microphone digitizes the incoming signals and send them to the mobile device, where they are processed by means of the proposed application. This allows the use of CDMA techniques and overcomes most of the problems to be faced at the 20-22kHz range available in current smartphones, which include audible artifacts and poor resolution. The proposed software allows each mobile device in the environment to compute its own position by means of hyperbolic trilateration and represents the trajectory in the device screen, for future Location Based Services applications. Experimental results show that the proposed application achieves centimeter accuracy and can execute all the data processing for the position estimation in a time less than 0.5s.

New iterative algorithm for hyperbolic positioning used in an Ultrasonic Local Positioning System

Ultrasonic local positioning systems (US-LPS) utilize hyperbolic trilateration to avoid the necessity of synchronizing the beacons and the tag. In actual systems the beacons emit coded signals which are processed in the tag to obtain the time-differences of arrival, with one of the beacons as reference. The absolute position is computed using an iterative method to solve the non-linear equation system as the Newton-Gauss algorithm: it is time-consuming and need a good initialization of the estimated position. In this work, a new and simpler iterative algorithm is presented to be used in hyperbolic trilateration derived using the Cayley-Menger bideterminant. Instead of use the iterative algorithm to compute the coordinates of the tag position (three unknowns in 3D), here is used to calculate the distance from the tag to the reference beacon (only one unknown).

A comparison of computing architectures for ultrasonic signal processing

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.