A Radio Frequency Identification System for accurate indoor localization

In this paper we present a novel Radio Frequency Identification (RFID) system for accurate indoor localization. The system is composed of a standard Ultra High Frequency (UHF), ISO-18006C compliant RFID reader, a large set of standard passive RFID tags whose locations are known, and a newly developed tag-like RFID component that is attached to the items that need to be localized. The new semi-passive component, referred to as sensatag (sense-a-tag), has a dual functionality wherein it can sense the communication between the reader and standard tags which are in its proximity, and also communicate with the reader like standard tags using backscatter modulation. Based on the information conveyed by the sensatags to the reader, localization algorithms based on binary sensor principles can be developed. We present results from real measurements that show the accuracy of the proposed system.

Ultra Low Power FPGA-Based Architecture for Wake-up Radio in Wireless Sensor Networks

In this paper the capabilities of ultra low power FPGAs to implement Wake-up Radios (WuR) for ultra low energy Wireless Sensor Networks (WSNs) are analyzed. The main goal is to evaluate the utilization of very low power configurable devices to take advantage of their speed, flexibility and low power consumption instead of the more common approaches based on ASICs or microcontrollers. In this context, energy efficiency is a key aspect, considering that usually the instant power consumption is considered a figure of merit, more than the total energy consumed by the application.

Wake up Radio Architecture for Wireless Sensor Networks Using an Ultra Low Power FPGA

In this paper an implementation of a Wake up Radio(WuR) with addressing capabilities based on an ultra low power FPGA for ultra low energy Wireless Sensor Networks (WSNs) is proposed. The main goal is to evaluate the utilization of very low power configurable devices to take advantage of their speed, flexibility and low power consumption instead of the traditional approaches based on ASICs or microcontrollers, for communication frame decoding and communication data control.

Radiofrequency architectures and technologies for software defined radio

Six-port network is an interesting radiofrequency architecture with multiple possibilities. Since it was firstly introduced in the seventies as an alternative network analyzer, the six-port network has been used for many applications, such as homodyne receivers, radar systems, direction of arrival estimation, UWB (Ultra-Wide-Band), or MIMO (Multiple Input Multiple Output) systems. Currently, it is considered as a one of the best candidates to implement a Software Defined Radio (SDR). This thesis comprises an exhaustive study of this promising architecture, where its fundamentals and the state-of-the-art are also included. In addition, the design and development of a SDR 0.3-6 GHz six-port receiver prototype is presented in this thesis, which is implemented in conventional technology. The system is experimentally characterized and validated for RF signal demodulation with good performance. The analysis of the six-port architecture is complemented by a theoretical and experimental comparison with other radiofrequency architectures suitable for SDR. Some novel contributions are introduced in the present thesis. Such novelties are in the direction of the highly topical issues on six-port technique: development and optimization of real-time I-Q regeneration techniques for multiport networks; and search of new techniques and technologies to contribute to the miniaturization of the six-port architecture. In particular, the novel contributions of this thesis can be summarized as: - Introduction of a new real-time auto-calibration method for multiport receivers, particularly suitable for broadband designs and high data rate applications. - Introduction of a new direct baseband I-Q regeneration technique for five-port receivers. - Contribution to the miniaturization of six-port receivers by the use of the multilayer LTCC (Low Temperature Cofired Ceramic) technology. Implementation of a compact (30x30x1.25 mm) broadband (0.3-6 GHz) six-port receiver in LTTC technology. The results and conclusions derived from this thesis have been satisfactory, and quite fruitful in terms of publications. A total of fourteen works have been published, considering international journals and conferences, and national conferences. Aditionally, a paper has been submitted to an internationally recognized journal, which is currently under review.

Proyecto Investigador: Adaptación de tasa binaria y planificación de usuarios dependiente del canal radio en el estándar LTE (Long-Term Evolution)

Este Proyecto Investigador se presenta como parte de la documentación requerida para el Concurso de Acceso a plazas de cuerpos docentes universitarios. Centro: E.T.S.I. de Telecomunicación. Cuerpo: Profesores Titulares de Universidad. Departamento: Señales, Sistemas y Radiocomunicaciones (0935). Área de conocimiento: Teoría de la Señal y Comunicaciones (800). Perfil docente: Radiocomunicaciones; Comunicaciones Móviles. Perfil investigador: Tecnología de las Telecomunicaciones (3325). Dedicación: Completa

Design and Test of a High QoS Radio Network for CBTC Systems in Subway Tunnels

Communications Based Train Control Systems require high quality radio data communications for train signaling and control. Actually most of these systems use 2.4GHz band with proprietary radio transceivers and leaky feeder as distribution system. All them demand a high QoS radio network to improve the efficiency of railway networks. We present narrow band, broad band and data correlated measurements taken in Madrid underground with a transmission system at 2.4 GHz in a test network of 2 km length in subway tunnels. The architecture proposed has a strong overlap in between cells to improve reliability and QoS. The radio planning of the network is carefully described and modeled with narrow band and broadband measurements and statistics. The result is a network with 99.7% of packets transmitted correctly and average propagation delay of 20ms. These results fulfill the specifications QoS of CBTC systems.

Radio-holografía de microondas para la optimización de la superficie de grandes antenas reflectoras

En el presente trabajo de tesis se afronta el problema de la optimización de la superficie de grandes antenas reflectoras. Es sabido que los grandes reflectores, formados por una superficie panelada, sufren deformaciones debidas al impacto del viento, a los cambios de temperatura y a los efectos gravitacionales derivados del gran peso de la estructura. Estos efectos hacen que los reflectores pierdan su forma ideal, generalmente de paraboloide, y se reduzca su eficiencia de apertura y, por tanto, se limite la máxima frecuencia de uso de los mismos. Es necesario, por tanto, disponer de técnicas que permitan medir el estado de la superficie de grandes reflectores, y derivar los ajustes necesarios a aplicar sobre los tornillos de soporte de cada uno de los paneles que conforman dicha superficie. De esta manera, se devolvería al reflector su forma óptima y aumentaría la eficiencia de apertura y el rango de frecuencias de uso. Hay que resaltar que el aumento de la eficiencia de un radiotelescopio supone una reducción en el tiempo de integración necesario para la detección de las debilísimas señales generadas por las radiofuentes naturales, ahorrando así valioso tiempo de observación. Además, el incremento en el rango de frecuencias permite la detección de nuevas líneas o especies moleculares en dichas radiofuentes. Tras un primer capítulo introductorio, se presenta, en el capítulo segundo, la geometría de estos grandes reflectores y la influencia de los distintos factores que afectan a la calidad de la superficie de los mismos, como la gravedad, el viento y la temperatura, particularizando para el caso del radiotelescopio de 40 metros del Centro Astronómico de Yebes. En el tercer capítulo, se presentan las diferentes técnicas metrológicas empleadas actualmente para abordar la determinación de estos ajustes, mostrándose las ventajas e inconvenientes de cada una de ellas. Actualmente, la técnica metrológica más precisa y rápida para llevar a cabo esta tarea de caracterización de la superficie de un gran reflector, es la radio-holografía de microondas presentada en el capítulo cuarto. A partir de las medidas proporcionadas por esta técnica, realizadas con la ayuda de un transmisor, y mediante transformaciones de campo, se calculan los errores de la superficie del reflector, respecto al paraboloide ideal, y se derivan los ajustes necesarios. En los capítulos quinto y sexto se presentan los resultados de la aplicación de esta técnica a dos radiotelescopios: el de 30 metros de IRAM en Pico de Veleta (Granada) y los prototipos de 12 metros de las antenas del proyecto ALMA. Por su parte, el capítulo séptimo contiene el núcleo fundamental de esta tesis y presenta el desarrollo de la técnica de radio-holografía de microondas para optimizar la superficie del radiotelescopio de 40 metros del Centro Astronómico de Yebes. Para ello, ha sido necesario diseñar, construir e instalar un receptor de doble canal en banda Ku en foco primario, y la instrumentación asociada para hacer las medidas de amplitud y fase del diagrama de radiación. Además, ha sido necesario desarrollar el software para llevar a cabo las transformaciones de campo y derivar los ajustes de los paneles. De las medidas holográficas iniciales resultó un error de la superficie del radiotelescopio de 485 μm WRMS, respecto al paraboloide ideal en dirección normal. Tras varias iteraciones del proceso de medida y ajuste, se consiguió reducir dicho error a 194 μm WRMS. Esta notable mejora de la calidad de la superficie ha supuesto aumentar la eficiencia de apertura desde 2,6% al 38,2% a 86 GHz, para un receptor a esta frecuencia situado en el foco primario que produjese la misma iluminación que el receptor de holografía. In this thesis the problem of large reflector antenna surface optimization is faced. It is well known that large reflectors, which are made of a panelled surface, suffer from deformations due to the impact of wind, temperature gradients and gravity loads coming from the high weigth of the structure. These effects distort the ideal reflector shape, which is a paraboloid in most cases, hence reducing the aperture efficiency of the reflector and limiting the maximum frequency of operation. Therefore, it is necessary to have some techniques to measure the status of large reflector surfaces and to derive the adjustment values to be applied to the screws that connect the surface panels to the reflector back-up structure. In this way, the reflector would recover its optimum shape and the aperture efficiency and frequency range would increase. It has to be stated that an increment in the radiotelescope aperture efficiency would imply a reduction in the integration time needed to detect such weak signals coming from natural radiosources in space and, hence, an important saving in observation time. In addition, the increase in the frequency range of operation would allow the detection of new molecular lines in those radiosources. After the introduction, the second chapter shows the geometry of large reflector antennas and the impact on its surface quality of different factors like gravity, wind and temperature, particularly for the case of the Centro Astronómico de Yebes 40 meter radiotelescope. The third chapter deals with the different metrology techniques used to determine the panel adjustments, including the advantages and drawbacks of each one Currently, the most accurate and fast metrologic technique to carry out the characterization of large reflector surfaces is microwave radio-holography2, which is shown in chapter four. From the measurements provided by microwave radio-holography, performed with the help of a transmitter, and with the use of field transformations, the reflector surface errors are computed and the panel adjustments are derived. Chapters five and six show the results of holographic measurements applied to two first class radiotelescopes: the IRAM 30 meter radiotelescope and the 12 meter prototype antennas for the ALMA project. Chapter seven contains the main work of this thesis. It presents the development of the microwave radio-holography technique for the optimization of the Centro Astronómico de Yebes 40m radiotelescope. The work implied the design, construction and instalation of a prime focus Ku-band dual channel receiver, together with the associated instrumentation to measure the amplitude and phase of the radiotelescope radiation pattern. In addition, the software to carry out field transformations and screw settings computations was developed too. Initial holography measurements came up with an surface error of 485 μmWRMS in normal direction with respect to the best-fit paraboloid. After a few iterations of the measurementadjustment cycle, the surface error was reduced to 194 μm WRMS. This remarkable improvement in surface quality means an increment in aperture efficiency from 2,6% to 38,2% at 86 GHz, assuming a receiver at this frequency in prime focus position which produces the same illumination as the holography receiver.

Measurement of Distributed Antenna Systems at 2.4 GHz in a Realistic Subway Tunnel Environment.

Accurate characterization of the radio channel in tunnels is of great importance for new signaling and train control communications systems. To model this environment, measurements have been taken at 2.4 GHz in a real environment in Madrid subway. The measurements were carried out with four base station transmitters installed in a 2-km tunnel and using a mobile receiver installed on a standard train. First, with an optimum antenna configuration, all the propagation characteristics of a complex subway environment, including near shadowing, path loss,shadow fading, fast fading, level crossing rate (LCR), and average fade duration (AFD), have been measured and computed. Thereafter, comparisons of propagation characteristics in a double-track tunnel (9.8-m width) and a single-track tunnel (4.8-m width) have been made. Finally, all the measurement results have been shown in a complete table for accurate statistical modeling.

A Novel Method for Radio Propagation Simulation Based on Automatic 3D Environment Reconstruction

In this paper, a novel method to simulate radio propagation is presented. The method consists of two steps: automatic 3D scenario reconstruction and propagation modeling. For 3D reconstruction, a machine learning algorithm is adopted and improved to automatically recognize objects in pictures taken from target regions, and 3D models are generated based on the recognized objects. The propagation model employs a ray tracing algorithm to compute signal strength for each point on the constructed 3D map. Our proposition reduces, or even eliminates, infrastructure cost and human efforts during the construction of realistic 3D scenes used in radio propagation modeling. In addition, the results obtained from our propagation model proves to be both accurate and efficient

HF spectrum activity prediction model based on HMM for cognitive radio applications

Although most of the research on Cognitive Radio is focused on communication bands above the HF upper limit (30 MHz), Cognitive Radio principles can also be applied to HF communications to make use of the extremely scarce spectrum more efficiently. In this work we consider legacy users as primary users since these users transmit without resorting to any smart procedure, and our stations using the HFDVL (HF Data+Voice Link) architecture as secondary users. Our goal is to enhance an efficient use of the HF band by detecting the presence of uncoordinated primary users and avoiding collisions with them while transmitting in different HF channels using our broad-band HF transceiver. A model of the primary user activity dynamics in the HF band is developed in this work to make short-term predictions of the sojourn time of a primary user in the band and avoid collisions. It is based on Hidden Markov Models (HMM) which are a powerful tool for modelling stochastic random processes and are trained with real measurements of the 14 MHz band. By using the proposed HMM based model, the prediction model achieves an average 10.3% prediction error rate with one minute-long channel knowledge but it can be reduced when this knowledge is extended: with the previous 8 min knowledge, an average 5.8% prediction error rate is achieved. These results suggest that the resulting activity model for the HF band could actually be used to predict primary users activity and included in a future HF cognitive radio based station.

Radio-echo sounding and ice volume estimates of western Nordenskiöld Land glaciers, Svalbard

As part of ongoing work to obtain a reliable estimate of the total ice volume of Svalbard glaciers and their potential contribution to sea-level rise, we present here volume calculations, with detailed error estimates, for ten glaciers on western Nordenskiöld Land, central Spitsbergen, Svalbard. The volume estimates are based upon a dense net of GPR-retrieved ice thickness data collected over several field campaigns spanning the period 1999-2012. On the basis of the pattern of scattering in theradargrams, we also analyse the hydrothermal structure of these glaciers.

Location-aided distributed primary user identification in a cognitive radio scenario

We address a cognitive radio scenario, where a number of secondary users performs identification of which primary user, if any, is trans- mitting, in a distributed way and using limited location information. We propose two fully distributed algorithms: the first is a direct iden- tification scheme, and in the other a distributed sub-optimal detection based on a simplified Neyman-Pearson energy detector precedes the identification scheme. Both algorithms are studied analytically in a realistic transmission scenario, and the advantage obtained by detec- tion pre-processing is also verified via simulation. Finally, we give details of their fully distributed implementation via consensus aver- aging algorithms.

Efficiency improvement of HF communications using cognitive radio principles

Cognitive Radio principles can be applied to HF communications to make a more efficient use of the extremely scarce spectrum. In this contribution we focus on analyzing the usage of the available channels done by the legacy users, which are regarded as primary users since they are allowed to transmit without resorting any smart procedure, and consider the possibilities for our stations -over the HFDVL (HF Data+Voice Link) architecture- to participate as secondary users. Our goal is to enhance an efficient use of the HF band by detecting the presence of uncoordinated primary users and avoiding collisions with them while transmitting in different HF channels using our broad-band HF transceiver. A model of the primary user activity dynamics in the HF band is developed in this work. It is based on Hidden Markov Models (HMM) which are a powerful tool for modelling stochastic random processes, and is trained with real measurements from the 14 MHz band.

High Efficiency Envelope Amplifier Using The Slow-Envelope Technique

High efficiency envelope amplifiers are demanded in EER technique for RF transmitters, which benefits low maintaining cost or long battery time. The conventional solution is a dc-dc switching converters. This dc-dc converter should operate at very high frequency to track an envelope in the MHz range to supply the power amplifier. One of the alternative circuits suitable for this application is a hybrid topology composed of a switched converter and a linear regulator in series that work together to adjust the output voltage to track the envelope with accuracy. This topology can take advantage of the reduced slew-rate technique (also called slow-envelope technique) where switching dc-dc converter provides the RF envelope with limited slew rate in order to avoid high switching frequency and high power losses, while the linear regulator performs fine adjustment in order to obtain the exact replica of the RF envelope. The combination of this control technique with this topology is proposed in this paper. Envelopes with different bandwidth will be considered to optimize the efficiency of the dc-dc converter.

An overview of fast DC-DC converters for envelope amplifier in RF transmitters

In the last years, RF power amplifiers are taking advantage of the switched dc-dc converters to use them in several architectures that may improve the efficiency of the amplifier, keeping a good linearity. The use of linearization techniques such as Envelope Elimination and Restoration (EER) and Envelope Tracking (ET) requires a very fast dc-dc power converter to provide variable voltage supply to the power amplifier but theoretically the efficiency can be much higher than using the classical amplifiers belonging to classes A, B or AB. The purpose of this paper is to analyze the state of the art of the power converters used as envelope amplifiers in this application where a fast output voltage variation is required. The power topologies will be explored and several important parameters such as efficiency, bandwidth and output voltage range will be discussed.