Fernando J. Álvarez

Modular Architecture for Efficient Generation and Correlation of Complementary Set of Sequences

Golay sequences and complementary sets of sequences have been long studied for their application in multisensor and communication systems. The feasibility of these systems strongly depends on the design of an efficient generator and correlator with the aim of reducing the computational load and hardware complexity. Recursive algorithms, which allow efficient architectures, are available in the case of complementary pairs of sequences and complementary sets of four sequences. This work presents a generalization of these algorithms with the purpose of obtaining complementary sets of M sequences with length L, the number of sequences M being a power of two (M=2m), and the length L a power of M (L=2mN) with m,Nisin N-{0}. This fact allows an ideal Kroumlnecker delta function of weight MmiddotL in the addition of the autocorrelation functions of the M sequences of the set. Furthermore, the generation of M different mutually orthogonal sets can be obtained. This fact makes their application suitable in simultaneous multiemission systems. With the proposed algorithm, an effective reduction in the number of operations necessary to implement the correlator can be obtained, if it is compared with the straightforward implementation. Also, a regular structure is provided that allows implementation of the generator and/or the correlator for complementary sets of M sequences, based on the structure for complementary sets of M/2 sequences The sequence length can also be easily extended to any multiple of M. Finally, the generation and correlation of M different mutually orthogonal complementary sets of M sequences can be immediately derived

Using PCA in time-of-flight vectors for reflector recognition and 3-D localization

This paper presents a reflector recognition and localization technique in three-dimensional (3-D) environments, using only times-of-flight (TOFs) data obtained from ultrasonic transducers. The recognition and localization technique is based on the principal component analysis applied to the TOF vectors originating from a sensor that contains two emitting transducers and several receivers. The two emitters simultaneously transmit two coded pulses that are detected later on and discriminated by the receivers, after being reflected in the environment. The proposed technique allows for the possibility of not only recognizing the reflectors, but also estimating approximately its localization referred to the sensor. This technique has been tested with three types of reflectors in 3-D environments: planes, edges, and corners. The achieved results are very satisfactory for reflectors located in the range 50-350 cm.

Performance comparison of different codes in an ultrasonic positioning system using DS-CDMA

In this work, several Code Division Multiple Access encoding schemes are evaluated for their application in ultrasonic sensory systems based on the determination of times-of-flight. Proper encoding improves the performance of such systems in terms of noise immunity, capability of simultaneous measurements and precision in the distance measurements. Important applications that include encoded ultrasonic signals are obstacle detection, local positioning in ubiquitous computing or non-destructive testing. Here, Kasami, Golay and Loosey Synchronous codes are experimentally tested in a privacy-oriented ultrasonic Local Positioning System based on hyperbolic trilateration.

High reliability outdoor sonar prototype based on efficient signal coding

Many mobile robots and autonomous vehicles designed for outdoor operation have incorporated ultrasonic sensors in their navigation systems, whose function is mainly to avoid possible collisions with very close obstacles. The use of these systems in more precise tasks requires signal encoding and the incorporation of pulse compression techniques that have already been used with success in the design of high-performance indoor sonars. However, the transmission of ultrasonic encoded signals outdoors entails a new challenge because of the effects of atmospheric turbulence. This phenomenon causes random fluctuations in the phase and amplitude of traveling acoustic waves, a fact that can make the encoded signal completely unrecognizable by its matched receiver. Atmospheric turbulence is investigated in this work, with the aim of determining the conditions under which it is possible to assure the reliable outdoor operation of an ultrasonic pulse compression system. As a result of this analysis, a novel sonar prototype based on complementary sequences coding is developed and experimentally tested. This encoding scheme provides the system with very useful additional features, namely, high robustness to noise, multi-mode operation capability (simultaneous emissions with minimum cross talk interference), and the possibility of applying an efficient detection algorithm that notably decreases the hardware resource requirements

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

Application of HFCT and UHF Sensors in On-Line Partial Discharge Measurements for Insulation Diagnosis of High Voltage Equipment

Partial discharge (PD) measurements provide valuable information for assessing the condition of high voltage (HV) insulation systems, contributing to their quality assurance. Different PD measuring techniques have been developed in the last years specially designed to perform on-line measurements. Non-conventional PD methods operating in high frequency bands are usually used when this type of tests are carried out. In PD measurements the signal acquisition, the subsequent signal processing and the capability to obtain an accurate diagnosis are conditioned by the selection of a suitable detection technique and by the implementation of effective signal processing tools. This paper proposes an optimized electromagnetic detection method based on the combined use of wideband PD sensors for measurements performed in the HF and UHF frequency ranges, together with the implementation of powerful processing tools. The effectiveness of the measuring techniques proposed is demonstrated through an example, where several PD sources are measured simultaneously in a HV installation consisting of a cable system connected by a plug-in terminal to a gas insulated substation (GIS) compartment.

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.

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.

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.

Efficient Correlator for LS Codes Generated from Orthogonal CSS

This paper presents a novel method to correlate loosely synchronized (LS) codes generated from mutually orthogonal complementary sets of sequences (CSS). The proposed correlator significantly reduces the total number of multiplications and additions to be performed, in comparison with straightforward correlators. This fast correlator, together with the interference free window that LS codes exhibit, make them a good choice for next generation of Wireless communications.