Joaquín Aparicio

Simultaneous Round-Trip Time-of-Flight Measurements With Encoded Acoustic Signals

In relative positioning systems, with the aim of estimating object positions, distances among them are computed in a cooperative way, usually by measuring times-of-flight from the signals that they emit. These emissions are often synchronized with additional signals or suitable hardware that acts as a temporal reference. In this paper, a ranging system is presented where only acoustic emissions are used to compute the distances between objects or nodes. Thus, an organization and operation algorithm is proposed, which provides a temporal reference to the acoustic emissions carried out by every node. In this way, distances are computed by determining the temporal relation between a request of emission from a coordinator node and the corresponding answers emitted by the other nodes. In order to simultaneously detect the acoustic emissions, the signals are encoded with complementary set of sequences allowing multisensory operation and accepting low signal-to-noise conditions. With this measurement scheme, additional signals and high accuracy clocks often used for synchronization can be eliminated, thus reducing hardware complexity, power consumptions, and possible interferences with other systems (i.e., if radio frequency signals are used). The simulation and experimental results show that sub-centimeter accuracy can be obtained with the proposed ranging scheme.

Ultrasonic Array for Obstacle Detection Based on CDMA with Kasami Codes

This paper raises the design of an ultrasonic array for obstacle detection based on Phased Array (PA) techniques, which steers the acoustic beam through the environment by electronics rather than mechanical means. The transmission of every element in the array has been encoded, according to Code Division for Multiple Access (CDMA), which allows multiple beams to be transmitted simultaneously. All these features together enable a parallel scanning system which does not only improve the image rate but also achieves longer inspection distances in comparison with conventional PA techniques.

Simultaneous mobile robot positioning and LPS self-calibration in a smart space

This paper presents a new algorithm that allows the simultaneous positioning of a mobile robot and the self-calibration of an ultrasonic-based LPS (Local Positioning System). The system integrates the data obtained by the on-board dead reckoning (relative positioning) and the measurements from the beacons that constitute the LPS (absolute positioning), using an H−∞ filter. At the beginning of the process the dead reckoning is used for both, robot localization and LPS auto-calibration and after a predetermined time the system uses the LPS information to correct the positioning obtained with the dead reckoning (that is affected by a cumulative error as the position is calculated integrating the axis velocities in the robot). The formulation of the algorithm and the results obtained with some particular trajectories of the mobile robot in the coverage area of the LPS are presented.

Modeling the Behavior of an Underwater Acoustic Relative Positioning System Based on Complementary Set of Sequences

The great variability usually found in underwater media makes modeling a challenging task, but helpful for better understanding or predicting the performance of future deployed systems. In this work, an underwater acoustic propagation model is presented. This model obtains the multipath structure by means of the ray tracing technique. Using this model, the behavior of a relative positioning system is presented. One of the main advantages of relative positioning systems is that only the distances between all the buoys are needed to obtain their positions. In order to obtain the distances, the propagation times of acoustic signals coded by Complementary Set of Sequences (CSS) are used. In this case, the arrival instants are obtained by means of correlation processes. The distances are then used to obtain the position of the buoys by means of the Multidimensional Scaling Technique (MDS). As an early example of an application using this relative positioning system, a tracking of the position of the buoys at different times is performed. With this tracking, the surface current of a particular region could be studied. The performance of the system is evaluated in terms of the distance from the real position to the estimated one.

Multilevel LS sequences with flexible ZCZ length and their application to local positioning systems

In this paper multilevel complementary pairs of sequences without limitation in length and the generation of multilevel Loosely Synchronized (LS) sequences with flexible Zero Correlation Zones (ZCZ) length are proposed. The existence of efficient correlators and the fewer restrictions on the length of the multilevel LS sequences compared to binary LS ones, makes them worthwhile for their application to Local Positioning Systems (LPS).

Code detection based on generalized Cross-Correlation in DS-CDMA underwater aplications

Underwater Wireless Sensor Network applications require the design of efficient communications links due to the rough environment. Acoustic signals make feasible the data transmission based on Direct Sequence Code Division Multiple Access (DS-CDMA) techniques, because compensates the multipath effect and allow receivers to simultaneously distinguish among multiple independent emitters. For that purpose, cross-correlation techniques based on matched filtering are often used, by detecting at what e instant arrives maximum correlation value is provided. Inter-Symbol Interference (ISI) caused by the Auto-Correlation (AC) function of the used sequences, and the Cross-Correlation (CC) between them, is not null around maximum matching value. This implies that it is sometimes difficult to detect the accurate position of correlation maxima. In order to improve the detection process without applying common communications algorithms for interference compensation, that usually involve a high computational load, the use of Generalized Cross-Correlation (GCC) is here analyzed.

Effect of CDMA techniques with Kasami codes on ultrasound-image quality parameters

This works presents an analysis of the benefits of CDMA (Code Division for Multiple Access) excitation techniques on the quality parameters of ultrasonic phased array images such as gratinglobes, sidelobes, dynamic range, lateral resolution and range resolution. In order to consolidate these benefits, a comparison between phased array excitation and CDMA techniques in airborne transmission is performed. Furthermore it is shown how not only image rate, but also range resolution and SNR (Signal to Noise Ratio) are improved with CDMA excitation techniques. A disadvantage of the proposal is a decreased dynamic range in the B-Scan image, therefore a different emission schema is proposed.

Bearing estimation algorithm based on spectral analysis of the ultrasonic received echoes

A method to locate reflectors, based on the spectral analysis of ultrasonic received echoes, is provided in this study. The main contribution of this work lies in the spectral analysis for bearing estimation. A single ultrasonic transducer, acting as emitter and receiver, is used. The transmitted signal is a 1023-bits Kasami code BPSK modulated by a carrier that ranges from 30 kHz to 55 kHz, implying a 6-component transmitted pulse. Since the ultrasonic transducer works as an angle-dependent filter, it is possible to estimate the bearing angle of the reflector based on the received spectrum. It is shown how the amplitude of each frequency contains information about the environment, particularly about the bearing angle of the reflector. Finally, a set of experimental results is included to validate the sensory system, showing how it can deal with realistic reflectors.

Comparative analysis of an underwater acoustic relative positioning system using coded signals

Positioning systems in underwater environments constitute a relatively new field of research that is gaining increasing interest in recent days. These systems are useful to locate buoys that are monitoring the environment, as well as Remotely Operated Vehicles (ROVs) or Autonomous Underwater Vehicles (AUVs). An acoustic relative positioning system is presented in this work, based solely on pseudorandom coded acoustic signals emitted underwater and detected by matched filtering processes. One of the buoys acts as the master node, emitting its code through a hydrophone, which will be received by the other buoys. These buoys will after reply with their own code, obtaining the round-trip times of flight (RTOF) for each pair of buoys. Once the RTOFs are obtained, the distances between them can be computed knowing the sound speed value, and from them the positions are calculated by means of the Multidimensional Scaling technique (MDS). Different codes are studied, being the performance criteria the average erro...

Accurate 3D localization of reflectors with an EMFi sensor array

A new sensor array based on the EMFi material is presented in this work to perform 3D localization of reflectors. This operation is accomplished by means of an algorithm that performs spherical trilateration using the Time-Of-Flight (TOF) of the emissions from every sensor. An accurate measurement of these TOFs is obtained by encoding the emissions with Kasami binary sequences and applying pulse compression to detect the corresponding echoes. Experimental results show a high level of agreement with the behavior of the simulated model.