Fernando Javier Álvarez

• BSc and MSc in Physics, PhD in Electronics
• Professor (Full) at University of Extremadura

This work establishes the theoretical foundations to optimally design Dual Linear Frequency Modulated (DLMF) Signals intended to measure range and speed. Expressions are derived to obtain the optimal DLFM signal bandwidth and sampling frequency to perform accurate estimations with a minimum computational load, for a given maximum signal frequency a...

For many industrial and medical applications, measuring sub-millimetre movements has become crucial, for instance, for the precise guidance of surgical robots. The literature shows the feasibility of millimetre-wave (mmWave) radars to deal with such micro-vibrations. However, the availability of reference devices to configure and test these systems...

Accurate object detection and location systems are essential for many robotic applications, including autonomous grasping and manipulation systems. In some cases, the target object may be obscured from view, in clutter, packaging, or debris. Millimetre wave radar is a potential alternative to visual sensing in such scenarios, owing to its ability t...

This paper proposes an indoor positioning system for mobile devices using visible light beacons. The device’s camera is used to acquire images in which the beacon appears. An algorithm processes these images to reconstruct the camera’s pose at the photo acquisition time. This reconstruction allows for estimating the camera position accurately. The...

Positioning systems have become increasingly popular in the last decade for location-based services such as navigation and asset tracking and management. As opposed to outdoor positioning, where the Global Navigation Satellite System became the standard technology, there is no consensus yet for indoor environments despite of the availability of dif...

Smartphones are powerful tools with extensive sensorization that can provide useful information in research or everyday life applications. This information can be obtained from the device’s built-in sensors or through other external sensors connected physically via USB or wirelessly via Bluetooth or WiFi. This paper presents the GetSensorData appli...

In the near future, as a consequence of the increasing percentage of elder people with respect to the total population, developed countries will face significant stress on their healthcare systems. The onset of some diseases associated with aging, such as dementia or cognitive decline, has been associated with a number of factors that can be detect...

Indoor positioning with smartphone-compatible technologies has fostered much research attention in recent years. In this context, Bluetooth Low Energy (BLE) reveals a good performance for this type of task. It offers more flexibility and better achievements when compared with similar systems based on IEEE 802.11 Wireless LAN (Wi-Fi) technology, esp...

Bluetooth Low Energy (BLE) fingerprinting has gained a lot of research effort in recent years due to flexibility in both beacons placement and configuration. Different works have addressed the effect of the configuration parameters, mainly the transmission power (Tx) and period (Ts), over positioning accuracy but not on the system lifespan and the...

In radio-frequency Indoor Positioning Systems, the fingerprinting technique, which involves a laborious database construction stage to achieve good positioning results, has become a standard solution. Several researchers have tried to find methods to reduce the number of reference points – which need to be manually collected – while maintaining the...

Currently, most acoustic positioning strategies are based on broadband coding and the pulse compression technique to obtain better accuracy and robustness against in-band noise. However, the accuracy and robustness of these systems is often seriously damaged in areas of low coverage and/or affected by multipath. This work proposes a High Availabili...

The detection and positioning of unmanned aerial vehicles has become essential for both automation and surveillance tasks, in recent years. The design of accurate drone localization systems is challenging, especially in cluttered environments, where the target may be partially or even completely obscured. This paper proposes a precise detection and...

El campo del posicionamiento en interiores es una de lasáreas con mayor crecimiento en losúltimos años. Dentro de estaárea, los sistemas diseñados para smartphones son de especial importancia dado lo extendido de su uso. Los sistemas más populares en este contexto están basados en redes inalámbricas como el Wi-Fi y el novedoso Bluetooth de Baja Ene...

Proximity-Based Indoor Positioning Systems (PIPSs) are a simple to install alternative in large facilities. Besides, these systems have a reduced computational cost on the mobile device of those users who do not continuously demand a high location accuracy. This work presents the design of an Acoustic Low Energy (ALE) beacon based on the emission o...

To estimate the user gait speed can be crucial in many topics, such as health care systems, since the presence of difficulties in walking is a core indicator of health and function in aging and disease. Methods for non-invasive and continuous assessment of the gait speed may be key to enable early detection of cognitive diseases such as dementia or...

Los sistemas de posicionamiento en interiores (del inglés, IPS) basados en Bluetooth Low Energy (BLE) que emplean como observable el indicador de la fuerza de la señal recibida (del inglés, RSSI), hacen uso del método fingerprinting que requiere de una algoritmia capaz de procesar este tipo de datos y obtener una estimación de la posición a partir...

En este trabajo se presenta un algoritmo de optimización de la posición de balizas Bluetooth de baja energía para ser usadas en un sistema de posicionamiento fingerpringting en entornos interiores. El método propuesto parte de un modelo virtual del entorno experimental y de un modelo de propagación de la señal que tiene en cuenta los diversos obstá...

The technologies and sensors embedded in smartphones have contributed to the spread of disruptive applications built on top of Location Based Services (LBSs). Among them, Bluetooth Low Energy (BLE) has been widely adopted for proximity and localization, as it is a simple but efficient positioning technology. This article presents a database of rece...

Current ultrasonic Local Positioning Systems (LPS) based on an infrastructure of beacons can provide centimeter-level accuracy employing the spread spectrum technique, which also adds robustness against noise. However, the strong attenuation of the acoustic waves at high frequencies, the high directionality of ultrasound transducers, and the Dopple...

The Doppler effect is a very useful phenomenon in both radar and sonar systems for measuring the speed of objects. Chirps have traditionally been used in these systems due to the good properties of their compressed pulse. However, these signals when emitted and/or received in motion can suffer from Range-Doppler Coupling (RDC) influencing the Time...

Nowadays the use of drones is rapidly growing, and the autonomous navigation capability depends on knowing their position at any time. The precision and robustness of a local positioning system for these devices is of particular importance in takeoff and landing maneuvers, especially in GPS-denied environments. The main contribution of this work li...

Accurate localization in indoor environments is crucial for the correct operation of location-aware and augmented reality applications, indoor navigation, and inventory management, among others. Magnetic, radiofrequency and inertial navigation systems typically provide room or meter-level accuracy. Despite being the most widely used, they are affec...

Self-calibrated Acoustic Local Positioning Systems (ALPS) generally require a high consumption of hardware and software resources to obtain the user’s position at an acceptable update rate. To address this limitation, this work proposes a self-calibrated ALPS based on a software/hardware co-design approach. This working architecture allows for effi...

This chapter is concerned with how digital technologies are changing habits, expectations and motivations in the use of public open spaces. These digital developments are a societal challenge with reflections on social practices and, on planning and design approaches to public spaces. This might also challenge the future development of information...

Information and Communication Technologies (ICTs) and mobile devices are deeply influencing all facets of life, directly affecting the way people experience space and time. ICTs are also tools for supporting urban development, and they have also been adopted as equipment for furnishing public spaces. Hence, ICTs have created a new paradigm of hybri...

Acoustic local positioning systems (ALPSs) are an interesting alternative for indoor positioning due to certain advantages over other approaches, including their relatively high accuracy, low cost, and room-level signal propagation. Centimeter-level or fine-grained indoor positioning can be an asset for robot navigation, guiding a person to, for in...

This paper proposes a multipath compensation algorithm (MCA) to enhance the performance of an ultrasonic local positioning system under adverse multipath conditions. The proposed algorithm is based on the accurate estimation of the environment impulse response from which the corresponding line of sight for each channel is obtained. Experimental res...

This work proposes the use of a hybrid acoustic and optical indoor positioning system for the accurate 3D positioning of Unmanned Aerial Vehicles (UAVs). The acoustic module of this system is based on a Time-Code Division Multiple Access (T-CDMA) scheme, where the sequential emission of five spread spectrum ultrasonic codes is performed to compute...

This paper presents a tag identification system based on the detection of high-frequency acoustic signals by means of a portable device. A binary frequency shift keying-modulated code is used to tag the different locations. This code is preceded by a synchronizing chirp waveform that allows noncoherent detection even under strong Doppler frequency...

This paper presents an Acoustic Local Positioning System (ALPS) suitable for indoor localization of mobile devices, based on the transmission of high frequency Code Division Multiple Access (CDMA) audio signals from a fixed beacon network to a tablet computer. The system permits positioning of the device (and the user carrying it) within a few cent...

The purpose of this work is to evaluate the impact of the imaging protocol as part of the optimization of patient doses in interventional cardiology. This paper reports the results of an initial study to refine the existing fluoroscopy and cine settings, evaluates a new imaging protocol by measuring the image quality and phantom entrance air kerma...

The internacionalization of european higher education is one of the guiding pillars of the Bologna Declaration, that aims to promote intra European student mobility and cooperation. Although different activities are needed to stimulate this mobility, Content and Language Integrated Learning (CLIL) has become one of most important ones, since studen...

Smart devices are attractive platforms for researchers to collect data coming from several sensors due to their small size, low cost, and the fact that they are already carried routinely by most people. The capability of smart devices to be used as the target of a positioning system has been already demonstrated in previous works. However, most of...

The chapter discusses how ICT can be used to enhance the understanding of the relationship between space, users and social practices. As an example of possible use of ICT for capturing and better understanding user’s needs, the new digital tool WAY Cyberparks is presented and discussed. A “cyberpark” is defined as a new type of urban landscape wher...

This paper presents an acoustic local positioning system (ALPS) suitable for indoor positioning of portable devices such as smartphones or tablets, based on the transmission of high frequency CDMA-coded signals from a fixed network of beacons. The main novelty of the proposed ALPS is its capability to mitigate the effects of multipath propagation b...

This paper proposes an algorithm to design band-limited Orthogonal Frequency Division Multiplexing (OFDM) pulses for accurate time-of-flight ranging in acoustic-based localization systems. The proposed algorithm is capable to generate OFDM pulses with higher energy when compared with other common pulse design approaches with similar characteristics...

This paper presents a characterization of an underwater positioning system based on surface nodes equipped with GPS and acoustic transducers. The positioning system calculates the coordinates of an underwater vehicle in one of the surface nodes or beacons, by the emission, detection, and reply of acoustic encoded signals. The characterization of th...

The aim of this study was to evaluate the occupational radiation dose in interventional cardiology by using a shielding drape on the patient. A random study with and without the protective material was conducted. The following control parameters were registered: demographic data, number of stents, contrast media volume, fluoroscopy time, number of...

A connectivist approach will be adopted to design and evaluate learning in technology-enhanced open spaces in Valletta city. Learning is considered as a process of creating connections between learner’s inner cognitive and affective systems with the external physical and social worlds. These interactions are organised within a model comprising dime...

In this work the performance of the Sucessive Interference Cancelation (SIC) architecture combined with Matching Pursuit (SIC/MP) and Least Squares (SIC/LS) algorithms is statistically analyzed when they are used to mitigate multipath effect in an Acoustic Local Positioning System (ALPS). The experiments are carried out with sets of two hundred rea...

This work proposes a novel method to estimate the Line-of-Sight Time-of-Flights (LOS-TOFs) in a broadband acoustic local positioning system (ALPS) with strong multipath interference. The proposed method is based on the Matching Pursuit channel estimation algorithm that provides a low complexity approximation to the Maximum Likelihood solution for s...

Time-of-Flight cameras deals with distance measurements in a matrix, pixel by pixel. Every pixel, called smart pixel, makes use of analog technology to calculate correlations, and in such a way, it computes the phase difference between the emitted signal and the received one, both modulated in RF-range. The main drawback of these systems is their s...

Ocean noise is a complex phenomenon in underwater environments. Different processes such as shipping traffic, wind, rain or animals contribute with a different signature to the background noise, which can worsen underwater systems performance. However, in the simulation of underwater systems the common approach is to consider an additive white Gaus...

Reducing occupational radiation dose in cardiac catheterisation laboratories is one of the objectives of the radiation protection system because the procedures performed involve high levels of radiation compared with others in health care. Recommendations on protection methods used are referred to different structural types and personal protection...

In this work the Near-Far problem is characterized in the context of an acoustic local positioning system (ALPS). First, a simple energy normalization algorithm is presented to identify the Near-Far situation and also to resolve the signal detection in the case of non-overlapping receptions. Then, an improved signal interference cancellation (ISIC)...

In those positioning systems based on the detection of acoustic signals, an accurate detection of the arrival times is crucial for a correct estimation of the distance between nodes, and therefore, for the precise estimation of the node that wants to be located. In order to obtain this arrival time more accurately, acoustic signals can be coded usi...

This paper describes a first prototype of an airborne ultrasonic array that combines pulse-compression techniques with localization algorithms in order to achieve accurate determination of the position of the reflectors placed in front of the array. The new sensory system is based on an array with four independently controlled emitters and a receiv...

Active sensing is a growing research field with long-standing open problems, whose applications range from CDMA communication systems, ultrasonic imaging or ranging systems to name a few. In those applications, spreading sequences are usually transmitted in a bursting manner, making their aperiodic correlation the most important feature to be consi...

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 distinguis...

This work benefits from the capability of the iPhone's or iPad's microphone to acquire high-frequency sound for accurate acoustic code identification. Although the maximum theoretical value for the frequency response of the built-in iOS device microphone is 20 kHz, emissions with frequencies close to 22 kHz have been experimentally detected. The fr...

The underwater channel is a highly variable medium due to the influence of several effects on the acoustic signal, and the physical variability of the environment. This behavior makes the underwater channel a very difficult one to model, and also a complex environment to work with. In acoustic-based positioning or sonar systems, where it is importa...

This paper presents the design of a novel receiver for a broadband ultrasonic Local Positioning System (LPS). As in other devices based on matched filtering of the transmitted encoded signals, this receiver features high robustness to noise and multiple access capability. Unlike previous solutions, the proposed receiver is capable of detecting beac...

The aim of this work is to propose an alternative way for wine classification and prediction based on an electronic nose (e-nose) combined with Independent Component Analysis (ICA) as a dimensionality reduction technique, Partial Least Squares (PLS) to predict sensorial descriptors and Artificial Neural Networks (ANNs) for classification purpose. A...

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 sy...

This paper presents a new architecture for the correlation of orthogonal complementary sets of sequences (OCSS) and their performance in an ultrasonic local posi-tioning system (U-LPS). OCSS are sets of sequences whose addition of correlation functions has ideal properties, that makes interference-free code-division multiple access (CDMA) possible....

In this work, an acoustic relative positioning system is presented, based on pseudorandom coded acoustic signals that are emitted underwater and detected by matched filtering processes. With this configuration the system is independent of GPS technology, being able to work even in low coverage regions. It is easier to deploy that LBL systems, and t...

A home-made and home-developed sensor network was proposed and developed in this paper for indoor air quality monitoring. The network consists of a base station connected to internet and several autonomous nodes equipped with different sensors to measure temperature, humidity, light and air quality. A specific program made with Labview is created t...

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 mo...

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 mul...

This work analyses the effect of the receiver movement on the detection by pulse compression of different families of codes characterizing the emissions of an ultrasonic local positioning system. Three families of codes have been compared: Kasami, Complementary Sets of Sequences and Loosely Synchronous, considering in all cases three different leng...

This work proposes the use of Genetic Algorithms (GAs) to search a Doppler resilient multilevel complementary pair of sequences. The fitness function deals with the desired ambiguity function to be fit, while it minimizes the crest factor of the resulting sequences. The simulated results show how the waveform obtained has a better performance than...

This work analyses the effect of the receiver move-ment on the pulse compression of the signals emitted by the beacons of an Ultrasonic Local Positioning System (ULPS). This analysis is first carried out by using a system model in order to obtain a set of results that are then experimentally validated with the help of an electric slider. The signal...

The development of positioning systems using underwater acoustic is a new research field. One of the main advantages of such a positioning system over absolute ones is that an external infraestructure is not needed, because only the distances between the buoys are used to obtain their positions. In this work, a relative positioning system using und...

A new spiking sonar based on the commercial 6500 module is presented in this work that, unlike the previous versions of this sensor, is capable to vary both the duration and the fre- quency of its emission. This feature is provided by a PIC18F452 device that also controls the module integrator to generate the se- quence of spikes whose density is p...

A portable electronic nose (see Fig.1) based on metal oxide semiconductor thin-film sensors has been developed to detect acetic acid present in four types of wines. The wines analyzed are from the same cellar but are made with different varieties of grapes. Data analysis was performed by two pattern recognition methods: principal component analysis...

Underwater acoustic channel modeling keeps being an active field of research, despite the fact that the physical effects are known since decades ago. The great variability that is found in this kind of channel makes modeling a difficult task, being highly dependent on a particular environment. For high frequencies, ray tracing is a simple and relia...

Sensor networks have experienced a fast development and extended their fields of application since their appearance for military uses. The monitoring of physical parameters in natural habitats is a typical application for assessing the risks of worsening the ecosystem. Among natural environments with scientific interest, there are the coastlines in...

This paper presents a new recursive algorithm to directly obtain the sum of the autocorrelation functions of the M sequences belonging to a Complementary Set of Sequences (M-CSS). The proposed algorithm allows a digital filter with only one stage to be obtained, what significantly reduces the total number of memory requirements, multiplications and...

This work presents the performance analysis of an Ultrasonic Local Positioning System (ULPS). The system is composed of four beacons, forming a square structure in the ceiling of a rectangular room, that emit orthogonal Kasami codes BPSK modulated with a carrier frequency of 50 kHz. These emissions are detected by the receiver by pulse compression,...

On current railway systems, it is becoming ever more necessary to install safety elements to avoid accidents. One of the causes that can provoke serious accidents is the existence of obstacles on the tracks, either fixed or mobile. In this paper, a multisensory system that can inform the monitoring system about the existence of obstacles is propose...

A new approach for the efficient correlation of loosely synchronised (LS) codes, when they are generated from Golay pairs, is presented. By employing this new approach, the total number of operations to be performed in the correlation is notably decreased, if compared with existing proposals based on classical efficient Golay correlators or straigh...

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...

The need for monitoring underwater sensors, communications between submarines or sonar, makes underwater acoustic communications an important field of research. Electromagnetic waves are quickly attenuated in this medium and thus acoustic waves are the best option for communications. When two buoys are present, one acting as the emitter and the oth...

This work presents an intelligent system which allows the detection of obstacles on railways. The sensory system is based on one barrier of infrared emitters and another of receivers, placed on opposing sides of the railway. Obstacle detection is achieved by a lack of reception in the detectors. The efficiency of the system is improved with the geo...

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...

En este artículo se describe la propagación de las señales acústicas en entornos subacuáticos, en los cuales las mismas cobran una importancia análoga a la radiofrecuencia en aire. En esta primera parte se abordará una breve revisión histórica, los parámetros fundamentales de los que depende la propagación acústica en el agua y diversos modelos exi...

A home-made and home-developed electronic nose based on a non-specific array of tin oxide sensors was built in order to discriminate among odors from wastewater treatment plants. The prototype uses headspace sampling system: The headspace of samples of water stored in 15 ml vials is carried out to the sensors cell using an integrated pump controlle...

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 po...

Loosely Synchronous (LS) codes improves the performance of Local Positioning Systems (LPS) in terms of noise immunity, capability of simultaneous measurements and precision in the location, provided that the multipath spread and the relative time offset between the codes are within the zero correlation zone (ZCZ) that they achieve in their correlat...

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....

A new spiking sonar based in the commercial 6500 module is presented in this work that, unlike the previous versions, is capable to vary both the duration and the frequency of its emission. This feature is provided by a PIC18F452 device that also controls the module integrator to generate the sequence of spikes whose density is proportional to the...